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Full text of "Annual report of the director of the Geophysical Laboratory"

CARNEGIE 
INSTITUTION 



Annual Report of the Director 
Geophysical Laboratory 

2801 UPTON STREET, NORTHWEST, WASHINGTON, D.C. 20008-3898 

1988-1989 



For the year July 1, 1988-June 30, 1989 

Issued December 1989 

Papers from the Geophysical Laboratory 

Carnegie Institution of Washington 

NO. 2150 



Digitized by the Internet Archive 

in 2012 with funding from 

LYRASIS Members and Sloan Foundation 



http://www.archive.org/details/annualreportofd198889carn 



Geophysical Laboratory 



Washington, District of Columbia 



Charles T. Prewitt 
Director 



Published by: Geophysical Laboratory 
2801 Upton St., N.W. 
Washington, D.C., 20008-3898 
USA 



ISSN 0576-792X 
December 1989 



When used in bibliographic citations, The Annual Report should be cited as follows: 

Author, Title, Annual Report of the Director of the Geophysical Laboratory, Carnegie Instn. Wash- 
ington, 1988-1989, Geophysical Laboratory, Washington, D.C., page range, 1989. 



GEOPHYSICAL LABORATORY 



Contents 



Introduction 1 

Igneous and Metamorphic Petrology - A. Field 
Studies 3 

Kaapvaal Spinel Peridotites: Evidence of Craton 
Origin. Francis R. Boyd 3 

Rare Earth Element Zoning in Pyrope-rich Gar- 
nets From Mantle Xenoliths. Donald D. 
Hickmott 6 

The Earth's Convection Framework: Its Behavior 
Since the Jurassic and Implications for the 
Geomagnetic Field. T. Neil Irvine 1 1 

Fracture-controlled Fluid Flow During Chlorite - 
grade Metamorphism at Waterville, Maine. 
Douglas Rumble, Nicholas H. S. Oliver, and 
Thomas C. Hoering 20 

The Reaction Progress Method: Quantitative Tests 
of Petrologic Models on a Microscopic Scale. 
Craig M. Schiffries 26 

Liquid- Absent Aqueous Inclusions. 

Craig M. Schiffries 30 

Igneous and Metamorphic Petrology - B. 
Experimental Studies 33 

Oxygen Fugacity and Evaporation Phase Rela- 
tions in the Solar Nebula. Bjorn O. My sen and 
Ikuo Kushiro 33 

Experimental Determination of Element Parti- 
tioning and Calculated Phase relations in the 
Mg-Fe-Si-O System at High Pressure and High 
Temperature. Yingwei Fei, Ho-kwang Mao, 
and Bjorn O. Mysen 37 

Partitioning of High Field Strength Elements 
Among Olivine, Pyroxenes, Garnet and Calc 
Alkaline Picrobasalt: Experimental Results and 
An Application. Peter Ulmer 42 

Relationships Between Composition, Pressure and 
Structure of Depolymerized, Peralkaline Alu- 
minosilicate Melts. Bjorn O. Mysen 47 

Igneous and Metamorphic Facies of Potassium- 
rich Rocks: Coexisting assemblages in 



Kalsilite-Forsterite-Larnite-Quartz at 950°C and 

2 kbar With and Without H 2 0. 

Hatten S. Yoder, Jr 54 

Techniques for Experimentally Loading and 

Analyzing Gases and Their Application to 

Synthetic Fluid Inclusions. John D. Frantz, Yi- 

gang Zhang, Donald D. Hickmott, and 

Thomas C. Hoering 59 

Investigations of Fluid Properties in the C0 2 -CH 4 - 

H 2 System using Synthetic Fluid Inclusions. 

Yi-gang Zhang and John D. Frantz 65 

A Laser-based Carbon Reduction Technique For 

Oxygen Isotope Analysis of Silicates and 

Oxides. Zachary D. Sharp and 

James R. O'Neil 72 

Crystallography - Mineral Physics 79 

Isotope Effects in Dense Solid Hydrogen: Phase 
Transition in Deuterium at 190 (±20) GPa. 
Russell J. Hemley and Ho-kwang Mao 79 

The Effect of Pressure, Temperature, and Compo- 
sition on the Lattice Parameters and Density of 
(Fe,Mg)Si0 3 - Perovskites to 30 GPa. Ho-kwang 
Mao, Russell J. Hemley, Jinfu Shu, Liang-chen 
Chen, Andrew P. Jephcoat, Yan Wu, and 
William A. Bassett 82 

Single Crystal X-ray Diffraction Study of A New 
Hydrous Silicate, Phase E. Yasuhiro Kudoh, 
Larry W. Finger, Robert M. Hazen, 
Charles T. Prewitt, and Masami Kanzaki...S9 

Spectroscopic Evidence for a new New High- 
pressure Magnesium Silicate Phase. 
James D. Kubicki and Russell J . Hemley... .91 

Compression and Polymorphism of CaSi0 3 at 
High Pressures and Temperatures. 
Liang-chen Chen, Ho-kwang Mao, and 
Russell J. Hemley 94 

The Polarized Raman Spectra of Tourmaline. 
Mingsheng Peng, Ho-kwang Mao, Liang-chen 
Chen, and Edward C. T. Chan 99 

New Optical Transitions in Type la Diamonds at 
Very High Stresses. Russell J. Hemley and 
Ho-kwang Mao 105 



CARNEGIE INSTITUTION 



Premonitory Twinning in the High-Pressure Phase 
Transition of ZrO r Yasuhiro Kudoh, 
Charles T. Prewitt, andHaruo Arashi 108 



BlOGEOCHEMISTRY Ill 

Nitrogen Isotope Tracers of Human Lactation in 
Modern and Archeological Populations. Mari- 
lyn L. Fogel, Noreen Tuross, 
and Douglas W. Owsley Ill 

Nitrogen Isotope Fractionation in the Uptake of 
Ammonium by a Marine Bacterium. 
Matthew P. Hoch, David L. Kirchman, 
and Marilyn L. Fogel 117 

Dissolved Nitrogen Isotopic Distribution in the 
Black Sea. David J. Velinsky, Marilyn L. Fogel, 
and Bradley M. Tebo 123 



Mineralogical and Oxygen Isotope Analyses of 
Manganese Oxides Precipitated by Spores of a 
Marine Bacterium. Kevin W. Mandernack, 
Marilyn L. Fogel, Bradley M. Tebo, 
and Jeffrey Post 130 

Separation and Purification of Phosphates for 
Oxygen Isotope Analysis. Ellen K. Wright 
and Thomas C. Hoering 137 



Scientific Highlights of the Geophysical 
Laboratory, 1905 - 1989 
Hatten S. Yoder, Jr 143 

Publications 199 

Personnel 204 



GEOPHYSICAL LABORATORY 



Introduction 



This is the second year in which the 
Annual Report of the Director is published 
by the Geophysical Laboratory using desk- 
top publishing techniques. I would like to 
thank the many people who wrote in re- 
sponse to last year's Report telling us that 
you were glad to see it revived after an 
absence of several years. We continue to 
feel that the Report is a very important part 
of our communication with the scientific 
community and take pleasure in preparing 
the scientific articles and sending the Re- 
port to those on our mailing list. I again 
emphasize that the articles in these issues 
are only progress reports and that you should 
expect to see the final results published in 
the refereed scientific literature. 

I am pleased to report that the Geo- 
physical Laboratory had a very successful 
year during 1988-1989, with a wide range 
of research activity by staff members, 
postdoctoral fellows, and visitors. Next 
year, 1990, will be one of great change for 
the Geophysical Laboratory staff and also 
for our colleagues at the Department of 
Terrestrial Magnetism. A new laboratory 
building is now under construction at the 
DTM site and we plan to move to this new 
building during the summer or early fall of 
1990. A resolution was passed by the 
Carnegie Institution of Washington Trus- 
tees in May 1986 to "Authorize the Presi- 
dent to commission the development of an 
architectural schematic plan for new con- 
struction and renovation of existing struc- 
tures on the Broad Branch Road site in 
Washington, DC, appropriate to co-loca- 



tion of the Geophysical Laboratory and the 
Department of Terrestrial Magnetism." 
Since that time, we have been involved in 
devising the general requirements for the 
building, working with the architectural 
firm of Peirce, Pierce & Kramer of Cambr- 
idge, Massachusetts, to produce a detailed 
design, and in planning for the actual trans- 
fer of equipment and personnel to the new 
facility. The New Research Building will 
have about 72,000 gross square feet of 
floor space, and the present main DTM 
building will be renovated to contain 
administrative, library, and auditorium 
facilities. The present Cyclotron Building 
will be expanded and refurbished, and will 
include clean laboratory facilities for use 
by the geochemists of the two departments. 
Many of us are sad at having to leave the 
Upton Street location that has served us so 
well for 85 years, but the prospect of having 
an increased amount of modem laboratory 
space and the great opportunity of expand- 
ing our horizons through collaboration with 
the DTM staff are very appealing. 

As this will be the last Annual Report 
published before the move to DTM takes 
place, I asked Director Emeritus Hatten S. 
Yoder, Jr. to write a section for this Report 
on the history of the Geophysical Labora- 
tory and he agreed to do so. As a relative 
newcomer to the Lab, I am always im- 
pressed when I read or hear about its his- 
tory and the people who have worked here 
during the 85 years of its existence. Rather 
small as research institutions go, the Lab 
usually has had about fifteen or sixteen 



CARNEGIE INSTITUTION 



research staff members at any one time 
along with ten to fifteen Post- and Predoc- 
toral Fellows and visitors. 

The Laboratory building itself was 
constructed for only $75,940 in 1905 and 
research budgets through the years have 
been relatively modest. However, the Lab's 
impact on geoscience has been enormous; 
I believe this is the result of the Carnegie 
Institution's policy of letting its scientists 
pursue their own goals with a minimum of 
interference. In a time when national re- 
search budgets are tight and industrial labo- 
ratory managements are requiring more 
applied research, I think the Carnegie ideal 
is a very important concept to maintain as 
an example of what can be done with lim- 
ited financial support coupled with flexi- 
bility and freedom in choosing research 
topics. 

A development of great interest to the 
Geophysical Laboratory is the recent es- 
tablishment of the Bayersiches 
Forschungsinstitut fur Experimentelle 
Geochemie und Geophysik at the Univer- 
sitat Bayreuth. The founding of this insti- 
tute was influenced greatly by the Geo- 
physical Laboratory experience and its 
Director, Friedrich Seifert, was a Postdoc- 



toral Fellow and Staff Member here in the 
1970s and early 1980s. This initiative has 
created worldwide interest among geos- 
cientists and is considered to be one of the 
more exciting developments in the basic 
earth sciences in recent years. It is interest- 
ing to note that when the Geophysical 
Laboratory was founded early in this cen- 
tury, it was based to a great extent on the 
experience of German laboratories and 
institutes. Now it appears that the circle has 
been completed. 

It is with regret that I report that re- 
search staff member Peter Bell decided to 
take early retirement at the end of June 
1989. During his 25 years at the Lab, Peter 
made many contributions in geophysics, 
mineral physics, and petrology. The col- 
laboration between Bell and Ho-kwang 
Mao was especially productive and they 
became known as the world's leading pro- 
ponents and users of the diamond-anvil cell 
for ultra-high-pressure research. Peter was 
a valuable member of our research staff and 
we will miss his involvement in day-to-day 
research activities. However, he will retain 
an official connection with the Lab and will 
continue to advise and consult with us in 
his areas of expertise and interest. 



GEOPHYSICAL LABORATORY 



Igneous and Metamorphic Petrology - 

A. Field Studies 



Kaapvaal Spinel Peridotites: Evidence 
of Craton Origin 

Francis R. Boyd 

Continental cratons have mantle roots 
that extend to depths of at least 200 km, 
giving cratonic lithosphere a thickness that 
is two or more times that of oceanic plates. 
Cratonic lithosphere differs from oceanic 
in composition as well as in thickness. The 
garnet peridotites that are the principal 
components of the Kaapvaal lithosphere, 
southern Africa, have markedly lower Mg/ 
Si, lower Ca/Al and higher Mg/Fe than do 
residual oceanic peridotites and their com- 
positional relations are believed to be rep- 
resentative of other cratons (Boyd, 1989). 
The origin of these differences in structure 
and composition between cratons and oce- 
anic plates is an important chapter in Earth 
history. 

There are few constraints on the origin 
of craton roots other than their Archaean 
age (Richardson et al., 1984). At least two 
scenarios seem possible. Cratonic nuclei 
might have developed at oceanic spreading 
centers and subsequently been underplated 
by peridotites having compositions similar 
to Kaapvaal garnet peridotites. If that ori- 
gin occurred, peridotites now forming the 
shallow portions of craton roots should 
have composition typical of oceanic peri- 
dotites. Alternatively, the cratonic litho- 



sphere in its entirety may be uniquely dif- 
ferent in composition and origin from 
oceanic lithosphere. In that event, perido- 
tites forming the top of a craton root would 
have compositions similar to the underly- 
ing garnet peridotites. 

Evidence required to distinguish be- 
tween these possible processes of craton 
development can be obtained by study of 
the compositional relations of the spinel- 
facies peridotites that occupy the upper 
portion of the craton lithosphere. Spinel 
peridotites are of widespread occurrence in 
xenolith suites of the Kaapvaal craton, 
having been collected at over a dozen lo- 
calities in South Africa and Lesotho. Their 
proportions in individual xenolith suites 
vary widely from small to amounts ap- 
proaching those of garnet peridotites. The 
relative abundance of spinel peridotites led 
Cars well et al. (1984) to propose that they 
form a continuous layer at the top of the 
craton lithosphere, overlying garnet peri- 
dotites that are the principal rock type at 
greater depth. 

The depth at which the assemblage Mg- 
rich garnet + olivine replaces aluminous 
pyroxene + spinel is the boundary dividing 
the spinel- and garnet-facies peridotites. 
This depth is difficult to estimate by ther- 
mobarometric methods because many of 
the peridotites that occur near the top of the 
lithosphere have failed to equilibrate at 
relatively low ambient temperatures and 



CARNEGIE INSTITUTION 



Table 1. Mineral and Bulk Analyses for Spinel Peridotite PHN 5254, Premier mine, R. S. A., wt%. 





Bulk* 


Olivine 


Enstatite 


Diopside 


Spinel 


Si0 2 


43.14 


40.6 


56.7 


54.8 


0.06 


Ti0 2 


0.05 


<0.03 


0.05 


0.12 


0.09 


MA 


1.36 


<0.03 


2.57 


3.34 


41.6 


Cr 2 3 


0.43 


<0.03 


0.41 


1.21 


26.8 


Fe 2 3 


2.78 


- 


- 


- 


- 


FeO 


4.21 


7.78 


5.11 


1.40 


12.0 


MnO 


0.12 


0.11 


0.14 


0.07 


0.16 


MgO 


42.47 


50.9 


35.6 


16.4 


18.4 


CaO 


1.53 


<0.03 


0.65 


22.4 


<0.03 


Na,0 


0.08 


n.d. 


0.06 


1.34 


n.d. 


K,0 


0.10 


n.d. 


n.d. 


n.d. 


n.d. 


PA 


0.00 


n.d. 


n.d. 


n.d. 


n.d. 


NiO 


0.27 


0.40 


0.09 


0.06 


0.18 


LOI 


4.53 


- 


- 


- 


- 


Totals 


101.07 


99.8 


101.4 


101.1 


99.3 


Mg/(Mg + Fe)** 


0.919 


0.921 


0.925 


0.954 


0.731 


Ca/(Ca + Mg)** 


- 


- 


0.013 


0.496 


- 








MODES 








Olivine 




66.6 








Enstatite 




25.2 


*S. A. Mertzman, 


analyst 




Diopside 




6.3 


**mole fractions 






Spinel 




1.3 







their pyroxenes are chemically inhomo- 
geneous. Nevertheless, the transition depth 
can be estimated to be near 50-55 km on the 
basis of experimental data (Wood and 
Holloway, 1984). If the base of the crust in 
the Kaapvaal craton is 40 km, the thickness 
of a spinel peridotite layer may then be 10- 
15 km. 

A chemical feature that effectively 
characterizes most Kaapvaal spinel peri- 
dotites (Table 1 ) is that the alumina content 
of the orthopyroxene is in the range 1 .5 - 4 



wt %, contrasting with values of 0.7 - 1 .0 wt 
% for the underlying garnet peridotites. 
Amphibole (pargasite)-bearing spinel peri- 
dotites form an exception to this generali- 
zation, however, because their alumina 
contents of orthopyroxene are low, 0.5 - 0.6 
wt % (e.g. Boyd, 1971). Spinels are more 
aluminous than the chromites in garnet 
facies rocks and there is a positive correla- 
tion for the concentration of A1 2 3 in coex- 
isting spinel and orthopyroxene (Carswell 
et al., 1984). Diopsides in the spinel peri- 



GEOPHYSICAL LABORATORY 



dotites contain somewhat less Cr 2 3 (aver- 
age 1.0 wt.%) than is commonly found in 
diopsides in garnet lherzolites. 

Distinctive textural characteristics of 
the spinel peridotites include an unusually 
coarse grain size, commonly 1-2 cm. The 
enstatite in almost all specimens have thin 
exsolution lamellae, presumed to be clino- 
pyroxene. The igneous age of the spinel 
peridotites, like that of the garnet perido- 
tites, may be Archaean, but the age of the 
exsolution is not known. The spinel charac- 
teristically forms symplectites (Dawson and 



SPINEL PERIDOTITES 

KAAPVAAL CRATON 



o> 

c 
*> 

*5 



94 r 
93- 
92- 
91- 
90- 
89- 




o 



J L 



J L 



100 90 80 70 60 50 

Modal olivine. wt% 



40 



Fig. 1. Compositional data for Kaapvaal spinel 
peridotites (solid circles) and transitional rocks 
(half solid circles) compared with data for low- 
temperature, Kaapvaal garnet peridotites (open 
circles), oceanic residues (open squares), and 
pyrolite (open diamond). Most of the spinel peri- 
dotites are from the Premier mine but samples 
from Kimberley, Frank Smith and Letseng are 
included. Sources of data for the oceanic residues 
and garnet peridotites are listed in Boyd (1989) 
and the pyrolite composition is from Ringwood 
(1979). Modes for the Kaapvaal rocks were cal- 
culated from the mineral and bulk analyses. Ana- 
lytical samples for the bulk analyses were ap- 
proximately 0.5 kg and were analyzed by S. A. 
Mertzman. 



Smith, 1975) with olivine and pyroxene as 
well as amphibole and mica; this habit 
contrasts markedly with the bleb-like tex- 
ture of primary spinels in peridotite xeno- 
liths in basaltic volcanics. Two specimens 
from the Premier mine have the textural 
characteristics of spinel peridotites but 
contain small amounts of fme-grained in- 
terstitial garnet; these are taken to be tran- 
sitional between the spinel and garnet fa- 
des. 

Insights to the origin of the spinel peri- 
dotites can be obtained by comparing their 
bulk compositions with those of cratonic 
garnet peridotites and oceanic peridotites. 
A plot of the modal abundance of olivine 
against mg number [mg number = Mg/(Mg 
+ Fe)] for either olivine or the whole rock 
does an excellent job of discriminating 
oceanic residues and craton-forming, low- 
temperature garnet peridotites (Fig. 1). The 
oceanic harzburgites represented by abys- 
sal peridotites and ophiolite tectonites have 
70-80% olivine and mg numbers predomi- 
nantly in the range 0.905-0.915. The cra- 
tonic peridotites from the Kaapvaal are 
enstatite-rich with 20-45 % modal enstatite, 
40-80% modal olivine and mg numbers of 
0.920 - 0.935. 

Points for the Kaapvaal spinel perido- 
tites superimposed on plots for low-tem- 
perature garnet peridotites and oceanic 
peridotites clearly overlap the garnet-fa- 
cies rocks (Fig. 1). These data suggest a 
common origin for the Kaapvaal perido- 
tites, whether of spinel or garnet facies. The 
compositional differences between these 
cratonic peridotites and oceanic residues 
make it appear unlikely that any large part 
of the Kaapvaal craton originated as an 



CARNEGIE INSTITUTION 



oceanic plate. Cratonic peridotites may have 
formed as bouyant residues of segregated 
ultramaf ic liquids at depths of 300-400 km 
(Boyd, 1989). The circumstances in which 
these residues floated in a denser, more 
fertile and largely crystalline mantle and 
coalesced to form proto-cratons are diffi- 
cult to clarify. Underplating may have 
played a role in this process, however, and 
the spinel peridotites at the top of the cra- 
tonic lithosphere might be the oldest rocks 
in these ancient tectonic blocks. 



References 

Boyd, F. R., Compositional distinction between 
oceanic and cratonic lithosphere, Earth Planet 
Sci. Lett., in press, 1989. 

Boyd, F. R., Pargasite - spinel peridotite xenolith 
from the Wesselton Mine, Carnegie Instn. 
Washington Year Book, 70, 138-142, 1971. 

Carswell, D. A., W. L. Griffin, and P. Kresten, 
Peridotite nodules from the Ngopetsoeu and 
Lipelaneng kimberlites, Lesotho: a crustal or 
mantle origin?, in Kimberlites - II: The Mantle 
and Crust-Mantle Relationships, J. Kornprobst, 
ed., Elsevier, New York, pp. 229-243, 1984. 

Dawson, J. B. and J. V. Smith, Chromite - silicate 
intergrowths in upper-mantle peridotites, Phys. 
Chem. Earth, 9, 339-350, 1975. 

Richardson, S. H., J. J. Gurney, A. J. Erlank, and 
J. W. Harris, Origin of diamonds in old enriched 
mantle, Nature, 310, 198-202, 1984. 

Ringwood, A. E., Origin of the Earth and the 
Moon, Springer- Verlag, New York, 1979. 

Wood, B. J., and J. R. Holloway, A thermody- 
namic model for subsolidus equilibria in the 
system CaO - MgO - A1 2 3 - Si0 2 , Geochim. 
Cosmochim.Acta,48, 159-176, 1984. 



Rare Earth Element Zoning in Pyrope- 
rich Garnets From Mantle Xenoliths 

Donald D. Hickmott 

Studies of mantle xenoliths in alkali 
basalts and kimberlites provide direct evi- 
dence concerning the chemical constitution 
and evolution of the sub-crustal lithosphere 
and upper asthenosphere. The abundances 
and isotopic compositions of the rare earth 
elements have been particularly important 
in determining the geochemical evolution 
of these rocks. 

Garnet peridotites from the Archeaen 
Kaapvaal craton can be divided into two 
texturally and chemically distinct classes, 
the granular lherzolites and the sheared 
lherzolites (Boyd and Nixon, 1973). Ther- 
mobarometric determinations suggest that 
the latter equilibrated at higher tempera- 
tures (> 1100°C vs. <1100°C) and pres- 
sures (> 55 kbar vs. < 55 kbar) than the 
former (Finnerty and Boyd, 1987). The 
major elements Na, Al, Ca and Ti are gen- 
erally enriched in the higher temperature 
peridotites (Nixon and Boyd, 1973; Boyd 
and Mertzman, 1 987), as are the heavy rare 
earth elements (HREE) (Shimizu, 1975). 
Sr and Sc may be enriched in the low-P-r 
suite lherzolites relative to those of the 
high-P-7 suite, based on reconstitution of 
bulk-rock abundances from element con- 
centrations in garnet and clinopyroxene 
(Shimizu and Allegre, 1978). Low-P-7 
nodules contain more modal enstatite and 
less olivine than those from the high-P-J 
suite (Boyd and Mertzman, 1987; Boyd, 
1989). 



GEOPHYSICAL LABORATORY 



100 



<D 

■C10 
"D 

C 

o 
O 

LU 
m 1 

tr 1 



0.1 



t — i — i — i — i — i — i — i — i — i — i — i — i — r 

FRB76 




J I L 



J I I I I I I I I L 



i — i — i — i — i — i — i — i — i — i — i — r 

FRB 450 




Ce Nd SmEu Dy Er 



J I I I I L 



J L 



Ce Nd SmEu Dy Er 



Fig. 2. Rare earth element abundances in two pyrope-rich garnets from the high-P-T suite. See Griffin 
etal. (1989) for a description of the petrography and chemistry of these samples. Open symbols - near- 
rim points; closed symbols - interior points. 



The mineral zoning observed in mantle 
nodules provides constraints on the nature 
and timing of processes that occurred within 
the upper mantle prior to eruption of the 
host magma of a nodule. Smith and co- 
workers have documented zoning of Ti, Cr, 
Fe, Na and P in garnets from selected 
xenoliths from the Kaapvaal craton, South 
Africa and The Thumb, Colorado Plateau 
(Smith and Ehrenburg, 1984; Smith and 
Boyd, 1987; Smith, 1988). Griffin et al. 
(1989) determined that garnets from two 
samples from Frank Smith kimberlite were 
characterized by Fe, Ti, Y, Zr and Ga en- 
richments in their rims relative to their 
cores. They suggested: 1) that the rim en- 
richments could be explained by infiltra- 
tion of an alkalic melt into the mantle 
rocks; 2) that the enrichments reflected re- 
equilibration of overgrowths on pre-exist- 



ing garnet rather than simple diffusional re- 
equilibration of such garnets; and 3) that 
the enrichments occurred within a few 
hundred years prior to eruption of the host 
kimberlite. 

Rare earth element abundances were 
measured in rims and cores of garnets from 
the two high-P-T suite samples (FRB 76 
and FRB 450) previously investigated by 
Griffin et al. (1989) and one low-P-7 suite 
garnet (PHN 2302A). The studied garnets 
from the high-P-T samples are from the 
same nodules, but are not the same crystals 
as those analyzed by Griffin et al. (1989). 
Analyses were made with a Cameca-IMS- 
3F ion microprobe with previously ana- 
lyzed pyrope-rich garnets as standards. 
Analytical techniques are similar to those 
described by Shimizu and Richardson 
(1987). Estimated accuracy of the REE 



8 



CARNEGIE INSTITUTION 



analyses is ±10%. Yb abundances are not 
presented due to GdO molecular ion inter- 
ferences on the Yb mass spectra. 

All of the REE investigated in the high- 
P-T samples are enriched in garnet rims 
relative to garnet cores (Fig. 2). Cerium 
rises by a small amount (less than 20%), 
whereas Er rises up to a factor of two; thus 
HREE/LREE ratios increase from core to 
rim. In contrast, garnets from lherzolite 
PHN 2302A from the low-P-7 suite are 
HREE enriched and LREE depleted in their 
rims relative to cores (Fig. 3). Cerium drops 
up to 70% from roughly 1.7 ppm to 0.4 
ppm, whereas Er rises up to a factor of three 
(0.3 ppm to 1.1 ppm). 

The trace element signature of the gar- 
net cores may provide constraints on the 
nature and evolution of the mantle in the 
source region of the kimberlites prior to 
final interaction with a metasomatizing 
agent, whereas that of the rim may help 
identify that metasomatic agent. The high 
LREE abundances of the cores of the high- 
P-T suite garnets relative to chondrites are 
incompatible with the hypothesis that the 
rocks are directly residual to magma gen- 
eration from a chondritic mantle. These 
samples may have experienced an earlier 
episode of fluid or melt infiltration prior to 
their most recent metasomatism. The low 
abundance of HREE in the core of the low- 
P-T suite garnet suggests that the granular 
nodules interacted with a LREE-enriched 
fluid or melt in the absence of garnet prior 
to subsolidus growth of the garnet cores 
(Shimizu, 1975). The relatively high mo- 
dal abundance of garnet in many low-P-T 
nodules may require an episode of meta- 
morphic differentiation subsequent to gar- 
net nucleation. 



100F 



CO 
CD 

-■£10 

"O 

c: 
o 

O 



LU 

cc 1 



0.1 



7— i — i — i — i — i — i — i — i — i — i — r 

PHN 2302A 




J I l I l l l l l l l I l L 



CeNdSmEuDy Er 



Fig. 3. Rare earth element abundances in a pyrope- 
rich garnet from the low P-T suite. See Boyd 
(1974), Shimizu (1975) and Shimizu and Allegre 
( 1 978) for petrographic and chemical data pertain- 
ing to this sample. Open symbols - near-rim points; 
closed symbols, interior points. 

Rare earth element patterns for hypo- 
thetical magmatic liquids calculated to be 
in equilibrium with the rims of the three 
samples are strongly LREE enriched rela- 
tive to chondrites (Fig. 4). Selection of 
alternate sets of partition coefficients for 
this calculation (i.e., Irving and Frey, 1978) 
leads to varying absolute REE abundances 
in calculated liquids, but yield roughly 
similar REE patterns to those shown. The 
calculated patterns for both the low-P-7 
and high-P-T suite samples are roughly 
similar in element abundance and slope to 
each other, although the low-P-7 garnet 
may have interacted with a fluid with lower 
HREE abundance and higher MREE/HREE 
and MREE/LREE ratios than the high-P-T 
samples. Absolute abundances of the REE 
in the hypothetical liquids are in approxi- 
mate agreement with REE abundances of 



GEOPHYSICAL LABORATORY 



1000 



CD 
•c100 

c 

O 

O 

LU 

LU 10 
DC 



t — i — i — i — ri — i — i — i — i — i — i — rr 



Calculated 
Liquids 




J I I I I I I I I I I I 1_L 



CeNdSmEu DyEr 



Fig. 4. Magmatic liquids calculated to be in equi- 
librium with select rim points of zoned, pyrope- 
rich garnets FRB 76, FRB 450 and PHN 2302A. 
Partition coefficients of Fujimaki et al. (1984) 
were used in the calculation. Diamond = PHN 
2302A; square = FRB 450; open square = FRB 76. 
Shaded area shows upper- and lower-bounds of 
kimberlite data reported by Kramers et al. ( 1 98 1 ). 
Solid symbols within shaded area is Kramers et al. 
(1981) "average kimberlite". 



South African kimberlites (Fig. 4), except 
for Ce and the HREE, which are depleted 
relative to most kimberlites. 

The simplest explanation for the major 
and trace element enrichments observed is 
that the nodules interacted with a melt with 
kimberlitic affinities. Alkali basalts gener- 
ally have higher HREE abundances than 
kimberlites (Menzies et al, 1987); thus, 
interaction with alkali basalt is unlikely. 
Hydrous fluid probably does not exist at the 
depth of origin of these nodules (Smith and 
Boyd, 1987) and mantle hydrous fluids are 
generally Ti-poor (Menzies et al, 1987); a 
hydrous fluid is an unlikely metasomatic 
agent for the high-P-r rocks. The discrep- 
ancies between the calculated REE pat- 



terns and those observed in kimberlites 
may be due to 1 ) inaccurate knowledge of 
partition coefficients between garnet and 
melt at the depth in the mantle where these 
nodules were derived (Kramers et al. , 1 98 1 ), 
or 2) interaction between the proto-kim- 
berlite and minerals in the mantle prior to 
interaction with the studied garnets. The 
large grain-size (> 5 mm diameter) and 
small diffusion coefficients (Cygan and 
Lasaga, 1986) of garnets enhance preser- 
vation of chemical gradients in this mineral 
relative to clinopyroxene, olivine and 
orthopyroxene. It is possible that other 
minerals in the studied nodules have also 
interacted with the melt that caused the 
garnet zoning, even though they are un- 
zoned (Griffin et al, 1989). 

Neodymium isotopic studies of lher- 
zolite nodules in kimberlites have been 
hampered by contamination problems 
(Richardson et al, 1985; Zindler and Ja- 
goutz, 1988). The most primitive mantle 
isotopic compositions are frequently deter- 
mined on the most painstakingly hand- 
picked and acid washed mineral separates 
(Richardson et al, 1985; Zindler and Ja- 
goutz, 1988). The present study of REE 
zoning in mantle garnets suggests that garnet 
isotopic compositions may also be sensi- 
tive to the relative percentages of rim- 
material and core-material in a given min- 
eral separate. The intermineral isotopic 
disequilibrium observed in some studies 
(Allegre et al, 1982) may reflect incom- 
plete infiltrative re-equilibration of the 
isotopic signatures of garnets relative to 
co-existing minerals (Smith and Boyd, 
1987). 

The presence of REE zoning in these 
garnets suggests that both the trace element 



10 



CARNEGIE INSTITUTION 



and isotopic signatures of the mantle de- 
rived from kimberlitic nodules must be 
interpreted cautiously. Even in cases where 
there is no evidence for modal metasomatic 
effects, recent cryptic metasomatism can 
be imprinted on older trace element and 
isotopic signatures. Accurate characteriza- 
tion of mantle chemistry by xenolith stud- 
ies requires an understanding of the proc- 
esses that produce element zoning in mantle 
minerals. 



References 

Allegre, C. J., Shimizu, N., and D. Rousseau, 
History of the continental lithosphere recorded 
by ultramafic xenoliths, Nature, 296, 732-735, 
1982. 

Boyd, F. R., Ultramafic nodules from the Frank 
Smith Kimberlite Pipe, South Africa, Carnegie 
Instn.Washington Year Book, 73, 285-294, 1974. 

Boyd, F. R., Compositional distinction between 
oceanic and cratonic lithosphere, Earth Planet. 
Sci. Lett., in press, 1989. 

Boyd, F. R., and S. A. Mertzman, Composition 
and structure of the Kaapvaal lithosphere, south- 
ern Africa, in Magmatic Processes: Physico- 
chemical Principles, B.O. Mysen, ed., Spec. 
Pub. No. 1, The Geochemical Society, Univer- 
sity Park, PA, pp. 13-24, 1987. 

Boyd, F. R., and P. H. Nixon, Structure of the 
upper mantle beneath Lesotho, Carnegie Instn. 
Washington Year Book, 72, 431-446, 1973. 

Cygan, R., and A. C. Lasaga, Self-diffusion of 
magnesium in garnet at 750° to 900°C, Am. J. 
Sci., 285, 328-350, 1985. 

Finnerty, A. A., and F. R. Boyd, Thermobarom- 
etry for garnet peridotites: basis for the determi- 
nation of thermal and compositional structure of 
the upper mantle, in Mantle Xenoliths, P. H. 
Nixon, ed., John Wiley & Sons, New York, pp. 
381-402, 1987. 

Fujimaki, H., M. Tatsumoto and K. Aoki, Partition 
coefficients of Hf, Zr, and REE between phe- 
nocrysts and groundmasses, in Proceedings of 



the 14th Lunar & Planetary Science Confer- 
ence, Part 2, J. Geophys. Res., 89 Supplement, 
pp. B662-B672, 1984. 

Griffin, W. L.,D. Smith, F. R. Boyd, D.R. Cousens, 
C. G. Ryan, S. S. Sie, and G. F. Suter, Trace 
element zoning in garnets from sheared mantle 
xenoliths, Geochim. Cosmochim. Acta, 53,561- 
569, 1989. 

Irving, A. J., and F. A. Frey, Distribution of trace 
elements between garnet megacrysts and host 
volcanic liquids of kimberlitic to rhyolitic 
composition, Geochim. Cosmochim. Acta, 42, 
771-787, 1978. 

Kramers, J. D., C. B. Smith, N. P. Lock, R. S. 
Harmon, and F. R. Boyd, Can kimberlites be 
generated from an ordinary mantle?, Nature, 
291, 53-65, 1981. 

Menzies, M., N. Rogers, A. Tindle, and C. Hawkes- 
worth, Metasomatic and enrichment processes 
in lithospheric peridotites, an effect of astheno- 
sphere - lithosphere interaction, in Mantle 
Metasomatism, M.A. Menzies & CJ. Hawkes- 
worth, eds., Academic Press, New York, pp. 
313-365, 1987. 

Richardson, S. H., A. J. Erlank, and S. R. Hart, 
Kimberlite-borne garnet peridotite xenoliths 
from old enriched subcontinental lithosphere, 
Earth Planet. Sci. Lett., 75, 116-128, 1985. 

Shimizu, N., Rare earth elements in garnets and 
clinopyroxenes from garnet lherzolite nodules 
in kimberlites, Earth Planet. Sci. Lett., 25, 26- 
32, 1975 

Shimizu, N., and C. J. Allegre, Geochemistry of 
transition elements in garnet lherzolite nodules 
in kimberlites, Contrib. Mineral. Petrol., 67,41- 
50, 1978. 

Shimizu, N., and S. H. Richardson, Trace element 
abundance patterns of garnet inclusions in peri- 
dotite - suite diamonds, Geochim. Cosmochim. 
Acta, 51, 755-758, 1987. 

Smith, D., Implications of zoned garnets for the 
evolution of sheared lherzolites: Examples from 
Northern Lesotho and the Colorado Plateau, /. 
Geophys. Res., 93, 4895-4905, 1988. 

Smith, D. and F. R. Boyd, Compositional hetero- 
geneities in a high-temperature lherzolite nod- 
ule and implications for mantle processes, in 
Mantle Xenoliths, P.H. Nixon, ed., John Wiley 
& Sons, New York, pp. 551-561, 1987. 

Smith, D., and S. N. Ehrenberg, Zoned minerals in 



GEOPHYSICAL LABORATORY 



11 



garnet peridotite nodules from the Colorado 
Plateau: implications for mantle metasomatism 
and kinetics, Contrib. Mineral. Petrol., 86, 274- 
285, 1984. 
Zindler, A., and Jagoutz, E., Mantle cryptology, 
Geochim. Cosmochim.Acta, 52, 319-333, 1988. 



The Earth's Convection Framework: 

Its Behavior Since the Jurassic and 

Implications for the Geomagnetic Field 

T. Neil Irvine 

In last year's Report, a "global convec- 
tion framework" was defined for the Earth, 
comprising six "convection centers" at the 
intersections of three mutually perpendicu- 
lar great circles. Four of the centers, distrib- 
uted at 90° -intervals on one great circle, 
appear to mark axes of upwelling in the 
Earth's convection system. Three of them 
are the major volcanic hotspots of Hawaii, 
Iceland, and the Balleny Islands (the last 
being affiliated with the McMurdo vol- 
canic province of Antarctica); and the fourth, 
located next to the Okavango Delta in 
Botswana, is a seismically active locality 
that effectively defines the southwest, 
"geophysical end" of the East African rift 
valley system. The other two centers are on 
either side of this circle of four, one in Peru, 
the second on the edge of Vietnam. Both 
these regions feature major subduction 
systems, so the two centers are presumed to 
represent axes of down- welling. The char- 
acteristics of the framework resemble 
considerably the tomography of the lower 
mantle, but the most intriguing correlations 
are with the geomagnetic field (Fig. 5), a 
matching that suggests that the framework 



reflects convection in the liquid part of the 
core as well as the mantle. 

When the framework was first con- 
ceived, it was thought that its position had 
probably been constant for some extended 
period of geological time because the three 
hotspots traditionally have been included 
in a global hotspot system that has been 
relatively stationary for millions of years. 
Further research has shown, however, that 
the Earth's magnetic history correlates 
closely with events of crustal rifting and 
continental flood basalt magmatism (Fig. 
6). In combination with observations that 
the convection framework appears to be 
linked to the geomagnetic field, that the 
Iceland and Balleny centers adjoin mid- 
ocean rift zones, and that the Okavango 
center is situated amidst the enormous 
Karoo basalt floods, this finding suggested 
that the framework might have moved with 
time in ways that can be defined by rifting 
events and flood basalt eruptions. This 
possibility has been explored, and results 
extending back to the Middle Jurassic are 
described below. Through them a convec- 
tion structure is suggested for the core that 
may be of interest to specialists in that field. 



Movement of the Convection Framework 
Since the Jurassic 

The process of locating the convection 
framework in the geological past involves 
two assumptions deriving from its present- 
day relationships. One is that the arrange- 
ment of the six convection centers was 
always orthogonal; the other is that the 
Peru and Vietnam centers were always on 



12 



CARNEGIE INSTITUTION 




,60E 

MAGNETIC \-" 
DECLINATION \ toe 
IN DEGREES 



Fig. 5. Map showing the global convection framework superimposed on the Earth's magnetic field 
(contoured data for 1980 from Fabiano et al., 1983). It is seen that the Peru and Vietnam centers (of down- 
welling) are almost coincident with the main intersections of the magnetic equator with the lines of zero 
declination extending from the North and South Magnetic Poles (NMP, SMP). Also, these two centers 
lie on the meridian (light dotted line) through the North and South Geomagnetic Poles (NGP, SGP; poles 
of the best-fit dipole field), and the great circle containing the four centers of upwelling (Hawaii, Iceland, 
Okavango, and Balleny) passes within a few degrees of all four magnetic poles. It might be noted that 
the large, double-hairpin loop of the line of zero declination extending across Asia is a transitory feature 
that has shifted widely in historic times because of secular magnetic field variations(see Courtillot and 
LeMouel, 1988, Fig. 35). Despite this shifting, the intersection of the line with the magnetic equator near 
Vietnam moved very little. 



the magnetic equator. At the present time, 
the magnetic equator is not coincident with 
the true equator, but such coincidence is 
generally assumed in paleomagnetic stud- 
ies, at least as a time-averaged condition. 
When it obtains, the combination of the 
above assumptions additionally implies that 



the four centers of upwelling are on the 
same meridian. 

Beyond these assumptions, the posi- 
tioning of the framework requires identifi- 
cation of the centers of upwelling based on 
events of rifting and volcanism. In this 
search, a valuable test or criterion derives 



GEOPHYSICAL LABORATORY 



13 



DATE 

MA 





iOO- 



120- 



140- 



160- 



180- 



200- 



220- 



240— 



260- 



280- 



300- 



AGE 
Pleistocene 



Late 
Cretaceous 



Early 
Cretaceous 



Middle 
Jurassic 



Early 
Jurassic 




Early 
Permian 



REVERSALS/ MA 
1 2 3 




VOLCANISM, RIFTING 
6 



Cretaceous 
normal 
superchron 






] 



-h 



Manicouagan 



Permian 
reverse 
superchron 



N<ursk, other? 



-Columbia River eruptions 
J-Main Ethiopian eruptions 

^Ethiopian start; Hawaii- Emperor bend 

East Greenland floods; N. Atlantic opens 

Brito-W. Greenland magmatism 

Main Deccan eruptions; Eurasian Basin 



India starts north 



opens 



•Benue rifting; Makarov Basin opens 



2 




Pacific Cretaceous hotspot track bend 
S.Atlantic opens; Rajmahal eruptions 
'-Karoo, Parana eruptions end; 
Canada Basin begins to open 

Parana eruptions begin-, minor Karoo 
Minor Karoo magmatism 

_^Minor Karoo; India leaves Africa 
-L-Central Atlantic opens, Ferrar magmas 
-^-Major Karoo eruptions; Rhine graben 



J-Major Karoo eruptions; Atlantic dikes 

Karoo magmatism begins (minor) 
-t Eastern U.S.A. volcanism 
Eastern U.S.A. rifting 

Gulf of Mexico opens 
J Scoresbyland rifting; Tethys opens 
>-Main Tunguskan eruptions 
-— -Tunguskan eruptions begin 



CRYPTOEXPLOSION 
OR IMPACT STRUCTURES 



Fig. 6. Correlation of the polarity reversal-frequency histogram for the Earth's magnetic field (Permian 
to present) with events of crustal rifting and flood basalt magmatism. The histogram is from Creer and 
Pal (1986); the other information is from many sources, but most notably Erlank (1984), MacDougall 
(1988), and Vogt and Tucholke (1986). It is seen that all the major changes in reversal frequency are 
matched by majorrifting events or continental flood basalt magmatism. Thus: ( 1 ) the episode of frequent 
reversals through the Triassic began with the eruption of the Tunguskan basalts in Siberia and continued 
with North American rifting events extending from East Greenland to the Gulf of Mexico; (2) the 
numerous reversals in the Jurassic and Early Cretaceous seem clearly related to the Karoo and Parana 
magmatism and the concurrent opening of the South Atlantic; and (3) the steplike increases of reversal 
frequency from Late Cretaceous through the Miocene successively match (a) the movements of India 
and the Deccan eruptions, (b) the opening of the North Atlantic and Arctic ocean basins and the related 
Brito- Arctic magmatism, (c) the rifting of central and eastern Africa and the Ethiopian basalt floods, and 
(d) the Columbia River basalt eruptions. A few major shock metamorphic (impact or crypto-explosion) 
structures are indicated for comparison (data from Grieve, 1 987) because some investigators believe that 
geomagnetic reversals are caused by meteorite impacts. 



from the orthogonal arrangement of these then the other three would be expected also 
centers. If one of them is properly located, to be within regions of rifting or volcanism. 



14 



CARNEGIE INSTITUTION 




110 MA 
LATE EARLY CRETACEOUS 



^sD> Convection center path ^Q Basaltic magma source sujpply 






GEOPHYSICAL LABORATORY 



15 



ICELAND 



Canada Basin continues 
to open 



West -dipping 
subduction 
\\ accompanies -? 
\\ Peru Center 




Makarov Basin opens 
mn ./ 




w-v^Abu Gabra rift 



80 MA 
_£^-^|MS LATE CRETACEOUS 




Bfito-Arctic 
magmatis'm 

60-54Ma^ h/( . 



\ Approximate 
Y* present-day 
\ framework 



galleys ;/ /y Basalt erupts 
S/ ^' when its supply 
/ /Center passes 
i / / south of the 
. />; w / / eruption site 

^South Sandwich arc / -y then moves rap 

M s _^^^ 65 Ma northward. 

CRETACEOUS- TERTIARY 
BOUNDARY 




PALEOCENE-EOCENE 
BOUNDARY 



Fig. 7. Paleo-reconstructions on which an attempt is made to position the convection framework with 
time over the past 175 Ma during the breakup of Gondawana and the opening of the Atlantic. Assump- 
tions are explained in the text. The reconstructions are slightly modified from Sclater et al. (1977), 
principally by the additions of India and Madagascar in maps F and G, and by slight shifting of the 
magnetic pole positions in maps G and H to bring them into better accord with more recent data from 
Irving and Irving (1982). Note how this latter change affects the configuration of the magnetic equator 
in the projection. Other control data are largely from the same sources as Fig. 6. Stars are hotspots. A 
feature of particular interest in the map sequence is that the convection framework was apparently 
aligned with the magnetic poles — and presumably, therefore, with the Earth ' s spin axis — during the time 
of the Cretaceous superchron (from about 115 to 90 Ma ; cf. Fig. 6) when there were no magnetic 
reversals. For further discussion, see text. 



16 



CARNEGIE INSTITUTION 



In the present documentation (Fig. 7), the 
use of this criterion is limited to a compari- 
son of Iceland and Okavango, because the 
maps cover only the half of the Earth on 
which the continents have been mostly 
concentrated since the Jurassic. A related 
effect is that the paths of the centers for any 
interval of time should be mutually com- 
patible within the restrictions of the above 
assumptions. This effect shows in Fig. 7 in 
the similarities of the Iceland and Okavango 
path segments on several maps. 

By the Jurassic, the structural bonds 
between North America and Africa had 
already been broken, as evidenced by the 
Late Triassic rift basins of the eastern U.S. A. 
The concern in Fig. 7, therefore, is primar- 
ily with events in the southern and extreme 
northern parts of the Atlantic. In map A, it 
is inferred that the Okavango center has 
just left Antarctica, where the Ferrar doler- 
ite and the large Dufek layered intrusion 
formed about 178-172 Ma ago. The center 
then moves westward around the tip of 
Africa, where Middle Karoo basalts erupted 
at 178 and 165 Ma, and past Patagonia, 
where volcanism was extensive between 
165 and 155 Ma. During the same period, 
the Iceland center moves northward from 
central Europe along the North Sea, where 
Jurassic volcanism has been reported, and 
then turns southwest past the Rockall 
Trough, which was the site of the earliest 
ocean-floor spreading in the North Atlan- 
tic. From there, the center loops back to the 
northwest past the tip of Greenland, where 
Jurassic basaltic sills and dikes are found. 

During the transition to the Cretaceous 
in map B, the Okavango center continues 
northward along the developing rift be- 



tween South America and Africa as the 
Parana volcanics formed in Brazil and the 
Late Karoo and Etendeka volcanics erupted 
in Africa. The Iceland center concurrently 
moves up the rift between Canada and 
Greenland, then hooks westward around 
Ellesmere Island. From there, it continues 
in map C past Axel Heiberg Island, where 
basalt was erupted in the Cretaceous, on to 
where the Canada basin was soon to open. 
Meanwhile, the Okavango center has moved 
north and west to the point where South 
America and Africa last were joined. A 
major implication of these paths, of course, 
is that the centers of upwelling were carv- 
ing out the future continental blocks. 

During the time period of maps D and E, 
the Iceland center is stationed at the North 
Pole, where it presumably controlled the 
opening of the Canada basin. The Okavango 
center accordingly is positioned on the 
equator, arbitrarily at a place where the 
Atlantic could broaden around it. It is no- 
table that the Canada basin has no magnetic 
stripes (Sweeney, 1983), which implies 
that it formed during the Cretaceous super- 
chron (see Fig. 6). We thus have an indica- 
tion that the core convection system was 
aligned with the Earth's spin axis during 
this extended period when the geomag- 
netic field did not reverse. Such a relation- 
ship would seem particularly significant to 
dynamo models for the origin of the geo- 
magnetic field. 

The opening of the Canada basin was 
completed by map F, and the Iceland center 
then moves successively to the neighbor- 
ing Makarov and Eurasian basins, which 
opened in that order — and which are both 
magnetically striped. To be in accord with 



GEOPHYSICAL LABORATORY 



17 



these movements, the Okavango center has 
to shift rapidly eastward across Africa at 
latitudes just below the equator. The Benue 
trough was developing in this region at that 
time (Browne and Fairhead, 1983). It re- 
ceived marine sediments from about 1 10 to 
65 Ma, and at about 85 Ma (during the 
Santonian), the existing deposits under- 
went relatively pronounced deformation. 
The Okavango center is presumed, there- 
fore, to have passed along the trough at 
about 85 Ma, ultimately inducing the for- 
mation of all three rift zones identified on 
mapF. 

Map F also shows the Okavango center 
turning southward at the East Africa rift 
valleys. This change of trend is obviously 
attractive, because it leads along the rift 
system to the present-day site of Okavango. 
It might, however, also be justified on other 
grounds. As the Okavango center reached 
the rift valleys, the Peru center, following 
behind 90° to the west, would just have 
reached South America. The proposition is 
that its progress was stopped by the conti- 
nent, hence the Okavango center (and the 
rest of the convection framework) had to 
change direction. By the illustrated inter- 
pretation, the Peru center was manifest as a 
west-dipping subduction zone that con- 
sumed ocean floor to its east as it moved 
across the Pacific. But the continent was 
too buoyant to subduct, hence when it was 
reached, the subduction system had to "flip" 
to its present east-dipping configuration, 
and the Peru center became locked to the 
continental margin. But if the flipping only 
occurred where the subduction encoun- 
tered continental blocks, then as illustrated 
in map G, two parts of the system that were 



exceptional could have continued on to the 
east to become the west-dipping Caribbean 
and South Sandwich Islands Benioff zones. 

In maps G and H, the Iceland and 
Okavango centers both move southward 
toward their present locations. Through 
this period, the Okavango upwelling had to 
yield, first the Deccan basalts, then the 
Ethiopian floods, and the Iceland center 
had to yield the Tertiary magmas of Britain 
and Greenland. The possibilities relating to 
these complex events cannot be discussed 
here, but it is interesting to note that the 
Deccan eruptions appear to have occurred 
just when the southward-moving Okavango 
center passed northward-moving India. 

If the analysis presented here has valid- 
ity, then it demonstrates that the convection 
framework is potentially a very useful 
device for relating tectonic and magmatic 
events in different parts of the world at 
various times in the geological past. But 
there obviously are many points on which 
the analysis might be challenged. Only one 
question can be addressed here, but it has 
been the most frequently asked: What about 
all the other hotspots? Two observations 
are noted. One is that, among the four 
centers of upwelling, only Hawaii has a 
hotspot track that is paralleled by other 
hotspot tracks. As discussed in last year's 
report, however, Hawaii apparently plays 
an extraordinary role in Earth convection 
in that it appears largely to control the 
motion of the Pacific Plate — which is where 
the parallel tracks occur. The other obser- 
vation is that many (if not all) of the other 
hotspots might have formed in consequence 
of the movements of the main centers of 
upwelling. Thus, for example, as the 



18 



CARNEGIE INSTITUTION 



VIETNAM 




PERU 



NORMAL/REVERSE 
0> SUPERCHRONS C5 



Fig. 8. A suggested convection structure for the Earth's core, based on the convection framework and 
a fluid dynamics model by Veronis (1959). See text for explanation and discussion. 



GEOPHYSICAL LABORATORY 



19 



Okavango center opened the South Atlan- 
tic (Fig. 7, A-D), it might also have initiated 
the volcanic centers at Bouvet, Tristan da 
Cunha, St. Helena, Ascension, and so on 
(see Fig. 7). 



Core Convection 

The suggested core structure (Fig. 8) 
combines the orthogonal axes of the con- 
vection framework with a fluid dynamics 
model by Veronis (1959) describing the 
effect of the Coriolis force on a fluid layer 
heated from below and cooled above. The 
key feature is that the liquid of the outer 
core rises and descends at the framework 
axes by way of spool-shaped vortex struc- 
tures in which it spirals inward with one 
sense of rotation to about mid-level in the 
layer, then switches and spirals outward 
with the opposite rotation as it completes 
its transit. When these structures are viewed 
individually from above, their directions of 
rotation appear opposite for upwelling and 
down-welling in the same (northern or 
southern) hemisphere, and they also appear 
opposed for either upwelling or down- 
welling structures in opposite hemispheres. 
But when the whole core structure is viewed 
from a single point, as in each diagram in 
Fig. 8, then the upper (or lower) parts of 
vortices on opposite sides of the solid inner 
core are seen actually to have the same 
rotation. A suggestion that arises here is 
that, if there were oscillations of the depth 
at which the flow spiraling reverses, then at 
any particular time (as illustrated sche- 
matically in a relatively extreme way in 
Fig. 8C), most of the liquid along axial 



lines through the whole core could be rotat- 
ing either one way or the other. The propo- 
sition is that such oscillatory flow reversals 
might underlie the polarity reversals of the 
geomagnetic field. 

A further feature of the proposed core 
structure, portrayed in Fig. 8C (c and d), is 
that the spiral vortex flow should not occur 
on convection axes lying in the plane of the 
equator where the Coriolis force vanishes. 
Thus, in the analysis of Fig. 7, there should 
not have been spiraling on the Peru-Viet- 
nam axis (at least until mid-Cenozoic times), 
nor should it have occurred on the 
Okavango-Hawaii axis during the Creta- 
ceous superchron. A possible implication 
of the latter condition is that it had the effect 
of damping the oscillatory flow reversals 
suggested above, thereby detering polarity 
reversals and causing the superchron. 

How these various processes might be 
tied to rifting and volcanism in terms of 
cause/effect relationships is debatable, but 
the physical connection is presumably 
plume activity in the mantle. It would seem 
also that, if the analysis in Fig. 7 is on the 
right track, then the inclination of the con- 
vection framework relative to the Earth's 
spin axis is especially critical, perhaps 
because it influences the planet's rotation 
characteristics. But this inclination in turn 
might be controlled by factors such as the 
interaction or coupling of the convection 
framework with the continents (as in the 
case postulated above for the Peru center), 
by the relative freedom of the lithospheric 
plates to move without interfering with one 
another, and by the ease with which the 
continental blocks can be rifted. A general 
implication is that the crystallization, cool- 



20 



CARNEGIE INSTITUTION 



ing, and convection of the core liquid is 
probably strongly linked to the major tec- 
tonic and magmatic events observed at the 
surface. 



References 



Browne, S. E, and J. D. Fairhead, Gravity study of 
the central African rift system: A model of 
continental disruption, Tectonophysics, 94, 1 87- 
203, 1983. 

Creer, K. M, and P. C. Pal, Geomagnetic reversal 
spurts and episodes of extraterrestrial 
catastrophism, Nature, 320, 148-150, 1986. 

Courtillot, V, and J. L. Le Mouel, Time variations 
of the Earth's magnetic field: from daily to 
secular, Ann. Rev. Earth Planet. Sci., 16, 389- 
476, 1988. 

Erlank, A. J, Pedogenesis of the Volcanic Rocks 
of the Karoo Province, Geol. Soc. S. Africa, 
Spec. Paper 13, 1984. 

Fabiano, E. B, N. W. Peddie, and A. K. Zunde, The 
magnetic field of the Earth, U. S. Geol. Surv., 
Misc. Invest. Series, Map 1-1457, 1983. 

Grieve, R. A. F., Terrestrial impact structures, 
Episodes, 10, 86, 1987. 

Irving, E., and G. A. Irving, Apparent polar wan- 
der paths, Carboniferous through Cenozoic , and 
the assembly of Gondwana, Geophys. Surveys, 
5, 141-188, 1982. 

MacDougall, J. D., Continental Flood Basalts, 
Kluwer, Dordrecht, Netherlands, 1988. 

Sweeney, J. F, Arctic seafloor structure and tec- 
tonic evolution, Am. Geophys Un., Geodynam- 
ics Series, 2, 55-64, 1981. 

Veronis, G, Cellular convection with finite ampli- 
tude in a rotating fluid, J. Fluid Mechanics, 5, 
311-324,1959. 

Vogt, P. R, and B. E. Tucholke, The western North 
Atlantic region, The Geology of North America, 
v. M, Geological Society of America, Boulder, 
Colorado, 696 p., 1986. 



Fracture-controlled Fluid Flow Dur- 
ing Chlorite-grade Metamorphism at 
Waterville, Maine 

Douglas Rumble, Nicholas H. S. Oliver,* 
and Thomas C. Hoering 

A current controversy in studies of 
metamorphic rocks concerns the nature 
and extent of fluid flow during metamor- 
phism. Some researchers have found fluid- 
rock ratios as high as 17.1 in bedded car- 
bonate metasediments (Hoisch, 1987). 
Other workers point out, however, that if 
large ratios are characteristic of an entire 
metamorphic complex rather than merely 
pertaining to specific acquifers, difficult 
questions arise about a feasible source for 
such vast amounts of fluid (Wood and 
Walther, 1986). Significant caveats have 
been issued regarding uncertainties in the 
magnitude of fluid-rock ratios measured 
with the reaction progress method (Wood 
and Graham, 1986). Resolving the contro- 
versy is important because of the ramifying 
effects the putative fluids would have on 
metamorphic belts. Among the effects that 
have been claimed are (1) regional alkali 
metasomatism (Ferry, 1982); (2) regional 
stable isotope metasomatism (Wickham and 
Taylor, 1985); (3) advective heat transfer 
(Chamberlain and Rumble, 1988); and (4) 
removal of fluid reaction products allow- 
ing devolatilization to proceed to comple- 
tion (Ferry, 1986a). 

We are addressing the controversy by 
testing the hypothesis of fluid flow in the 
Waterville-Augusta area, Maine. The re- 



* Monash University, Dept. of Earth Sciences, 
Clayton, 3168, Victoria, Australia 



GEOPHYSICAL LABORATORY 



21 



gion was chosen for study because it is here 
that the reaction progress method of esti- 
mating fluid-rock ratios was developed and 
widely applied (Ferry, 1980). The rocks of 
the area are the focus of a debate about the 
magnitude of fluid-rock ratios (Wood and 
Graham, 1986; Ferry, 1986). A practical 
advantage of the locality is that stratigra- 
phic units strike perpendicularly across 
metamorphic isograds from chlorite to sil- 
limanite zones (Osberg, 1968). Thus, it is 
possible to measure metasomatic changes 
caused by metamorphism with minimal 
ambiguity. 

The reaction progress method of esti- 
mating fluid flow developed by Ferry ( 1 980) 
is best suited to study of metasediments and 
meta-igneous rocks containing mineral 
assemblages with low phase rule variance. 
The method cannot be readily adapted to 
veins containing assemblages of one or two 
minerals (e.g. quartz-calcite), however. 
Ferry's (1980) mapping of fluid flow gives 
a detailed view of intergranular infiltration 
of H 2 0. But little is known of the role of 
fracture permeability during metamorphism 
as recorded by veins. This is a significant 
lack of knowledge in view of the likelihood 
that fluid flow through fractures may greatly 
exceed intergranular infiltration. We de- 
cided to investigate fracture permeability 
by measuring the stable isotope composi- 
tion of veins and their wall rocks from the 
Waterville limestone, a member of the Si- 
lurian Waterville Formation. 



Methodology 



Large specimens of 5 to 10 kg are col- 



lected showing structural relations of veins 
and their wall rocks. Hand specimens are 
slabbed with a rock saw, polished, and 
stained with Alizarin Red-S and Potassium 
Ferricyanide. Staining the polished slabs 
helps to locate and identify carbonate 
minerals, chiefly calcite and dolomite. 
Samples weighing 5 to 60 mg (larger 
amounts for rocks with lower abundances 
of carbonates) are drilled out with either a 
1 or 2 mm diameter, diamond tipped drill. 
Sample powders are loaded immediately 
into two-legged reaction vessels for reac- 
tion with 100% phosphoric acid at 25°C 
(McCrea, 1950). 

In many chlorite, biotite, and some 
garnet-grade wall rock samples, calcite and 
dolomite-ankerite solid solutions are so 
intimately intergrown that they cannot be 
physically separated. The simultaneous 
reaction of both carbonates with phospho- 
ric acid leads to cross-contamination of 
evolved C0 2 The problem of cross-con- 
tamination is usually dealt with by taking a 
first aliquot of C0 2 released early during 
reaction as representative of faster reacting 
calcite; a later aliquot samples slower re- 
acting dolomite (Epstein et al., 1964). 
Cross-contamination is not a major diffi- 
culty in the Waterville samples because the 
wall rocks are usually either predominantly 
calcite or dolomite. Samples with both 
carbonates equally abundant are uncom- 
mon. We have found that an aliquot taken at 
5 minutes into the reaction gives a reliable 
value for the # 8 of calcite from calcite 
rich rocks. Aliquots taken at 24 and 48 
hours give results for dolomite reproduc- 
ible to ±0. 1 %o for dolomite-rich rocks. We 
do not yet have accurate data on the iso- 



22 



CARNEGIE INSTITUTION 




" ■ r- 1 "■ i" -~i" ? "r -" i' r r 



topic compositions of co-existing ealcite 
and dolomite from the same powdered 
sample. The data presented below on both 
carbonates from the same hand specimen 
refers to ealcite and dolomite from separate 
lithologic layers. 



Results 

We have found evidence of fluid-rock 
interaction in the outcrops of the Waterville 
limestone along the east bank of the Ken- 
nebec River in Waterville, Maine. Analysis 
of ealcite and dolomite for # 8 and 5* 3 C 
shows that there are cryptic alteration halos 
around certain veins in which wall rock 
values have been depleted by 1-2 %o in 
S^O and by similar amounts in # 3 C. The 
halos are termed "cryptic" because no min- 
eralogical features have been recognized 
apart from proximity to veins. In what 
follows we demonstrate the pre-metamor- 
phic isotopic composition of the limestone 
and establish its range of isotopic heteroge- 
neity. An account is given of the relative 
chronology of vein emplacement and the 
evolution of isotopic values in the veins. 
These results are used to evaluate the sig- 
nificance of the isotopic alteration halos. 

The pre-metamorphic isotopic compo- 
sition of the Waterville limestone was 
measured by analyzing vein and wall rock 
samples taken from localities remote from 



Fig. 9. Sample locations and geologic sketch map 
at Waterville, Maine. Waterville limestone shown 
in blank with line sketches of refolded isoclinal 
folds. Graded bedded phyllite is stippled, SE cor- 
ner of map. Metamorphosed granitic dikes are 
heavily stippled at localities EE and PP. "WW" 
denotes Waterville- Winslow bridge. 



GEOPHYSICAL LABORATORY 



23 



-1 



o 

CO 

I/O 



-3 



-4 




B 



a 






□ 







WALLCC VEINCC WALL DO L VEINDOL 

■ D * A 



17 18 19 20 

5 18 

Fig. 10. Plot of ff^C vs. # 8 0. Box A shows compositions of pre-metamorphic limestone at localities H, 
I, J, and K (Fig. 9). Box B outlines limestone samples taken within 0.1 m of contact with granitic dikes 
at localities EE and PP. Box C gives analyses of limestone from 0.5 to 7 m from contact with graded 
bedded phyllite at GG and II. Area D denotes limestones inside alteration halo at localities AA and BB 
(Fig. 9). 



contacts with the metamorphosed granitic 
dikes and the graded bedded phyllite (Fig. 
9, samples H, I, J, K). The # 8 and # 3 C 
values are consistently higher than from 
any other samples analyzed but the &*0 
values are depleted by some 4.0 %o in 
relation to pristine marine limestones (Fig. 
10A). There is abundant evidence of fluid 
flow prior to metamorphism in the form of 
stylolites and the replacement of current- 
bedded, clastic calcite grains by fine-grained 
dolomite. Thus, it is possible that the initial 
depletion of the limestones in &*0 oc- 
curred during diagenesis. Analysis of indi- 
vidual beds 1-2 cm thick from single hand 
specimens shows variation of no more than 
0.3 %o in both # 8 and # 3 C from bed-to- 



bed. The effects of proximity to contacts 
with metamorphosed granitic dikes are 
depletion in ^ 8 by a maximum of 1.0 %o 
but little change in & 3 C (Fig. 10B, samples 
EE, PP). Samples collected within 1-5 
meters of the contact with the graded bed- 
ded phyllite are lower in ^ 8 by 1 .0 %obut 
unchanged in # 3 C (Fig. 10C, samples GG, 
II). It is concluded that pre-metamorphic 
values of the limestone ranged from 19.2 to 
20.0 %o in ^ 8 and from -0.9 to +0.3 %oin 
# 3 C. Isotopic exchange between limestone 
and dike rocks or phyllite led to depletion 
in # 8 by 1.0 %obut little change in # 3 C. 
The relative chronology of vein em- 
placement has been established by field 
observations of the structural relationships 



24 



CARNEGIE INSTITUTION 



between veins, re-folded isoclinal folds, 
and granite dikes. The oldest structures are 
bedding and stratigraphic contacts. These 
are followed in age by stylolites and dolo- 
mitized limestone beds. Beds, contacts, 
and diagenetic features were subsequently 
isoclinally folded and intruded by granitic 
dikes. Both the isoclinal folds and dikes are 
pre-metamorphic in age (Osberg, 1968). 
Finally, the area was metamorphosed un- 
der greenschist fades conditions and folded 
along NNE axes. 

The oldest (and rarest) vein (VI) dis- 
covered is composed of sigmoid black fibres 
of calcite extending perpendicular from the 
vein's wall. The vein is isoclinally folded 
and, therefore, is pre-metamorphic in age. 
The &*0 and # 3 C values for the pre-meta- 
morphic vein are 19.2%o, and +0.5, respec- 
tively. The next youngest group of veins 
(V2) consist of quartz and calcite. The V2 
veins are irregular in shape and size (up to 
20 cm in width) and contain isolated frag- 
ments of wall rock. Their &*0 and # 3 C 
values are typically in the range +19.2 to 
19.8 %o and -0.8 to +0.2 %o, respectively, 
and are closely similar to immediately 
adjacent wall rock (Fig. 10A). A third 
group of veins (V3) is made of fibrous 
calcite with a fringe of muscovite, quartz, 
and pyrite along the walls. The veins are 0. 1 
to 1.0 cm thick. They strike NNE and are 
parallel to the axial surfaces of the minor 
folds that refold the older, isoclinal folds. 
The V3 veins have values of 1 8. 1 to 1 8.5 %o 
in 9*0 and -0.5 to +0.2 %o in # 3 C (Fig. 
10C). Preliminary results of thin section 
study suggest that the growth of metamor- 
phic porphyroblasts began after the em- 
placement of VI and extended throughout 
the formation of V3. The youngest veins 



(V4) contain quartz, calcite, and rare ga- 
lena, and cross-cut the older veins. The 
isotopic values of V4 calcites range from 
+17.4 to 17.6 %o (# 8 0) and from -3.2 to - 
2.0%o(# 3 C)(Fig.lOD). 

There is a systematic trend of depletion 
in both 18 and 13 C from oldest to youngest 
veins. The values of the V4 veins are simi- 
lar to some of the wall rocks and veins of 
the Waterville limestone collected in the 
staurolite and sillimanite zones. Veins 
showing values characteristic of V4 have 
been found in the graded-bedded phyllite, 
as well. 

Cryptic alteration halos have been rec- 
ognized around V4 veins at the N end of the 
outcrop (sample locations A A and BB, Fig. 
9). The wall rocks consist of current-bed- 
ded clastic limestones that have been 
"dolomitized" parallel to bedding. Calcite- 
rich beds alternate with dolomitized layers 
on a scale of 1 to 2 cm. These rocks are 
indistinguishable in appearance from dolo- 
mitized limestones that preserve "pre- 
metamorphic" isotope values. Both wall 
rocks and older veins (V2 and V3) have 
been depleted in &*0 and # 3 C in halos 
surrounding V4 veins (Fig. 10D). Isotopic 
exchange between V4 and its wall rocks 
appears to be more complete in regard to 
&*0 than it is in # 3 C. The vein calcites at 
AA and BB (Fig. 9) with # 3 C values of -1.2 
to -0.5 %o belong to the V2 and V3 genera- 
tions (Fig. 10D). Wall rock calcite and 
dolomite have # 3 C values between -2.0 
and -1.2 %o. The calcite of V4, itself varies 
in # 3 C from -3.2 to -2.0 %o (Fig. 10D). 
Values of # 8 in veins and wall rocks, 
however, extend over a narrow interval 
from 17.4 to 18.1 %o. 

Calculation of single pass fluid/rock 



GEOPHYSICAL LABORATORY 



25 



ratios needed to convert pre-metamorphic 
wall rock # 8 and 5 13 C values to those 
observed in the alteration halos gives 2.4 
(molar ratio) for 18 and 2.9 (molar ratio) 
for 13 C. In these calculations the fluid 
composition is assumed to be H 2 0-C0 2 
[X(C0 2 ) = 0.07 Ferry, 1987] with # 8 (H 2 0) 
= 14.0 %o and & 3 C (C0 2 ) = -0.6 %o (e.g., 
fluid in equilibrium with most depleted V4 
vein calcite at 390°C). The initial and final 
values of # 8 for wall rocks are 19.5 and 
18.0, respectively, and for & 3 C these val- 
ues are -0.5 and -2.0 %o. The fractionation 
of 18 0/ 16 between calcite and H 2 is +3.5 
and that of 13 C/ 12 C between calcite and C0 2 
is -2.6 at 390°C (Friedman and O'Neil, 
1977). The calculations were made with 
the equations of Rye and Bradbury (1988, 
p. 214). 

Our results demonstrate that chlorite- 
grade limestones were penetrated by fluid- 
filled fractures during the peak-to-waning 
stages of metamorphism. Fluids infiltrated 
into wall rocks to a depth of at least 4 cm 
from vein walls. The fluid/rock ratios cal- 
culated from isotopic data for wall rock 
infiltration are approximately 3.0 by vol- 
ume, some 8 times greater than the largest 
ratios estimated by Ferry (1987, outcrop 7), 
for intergfanular infiltration at the same 
outcrop. 

References 

Chamberlain, C. P., and D. Rumble, Thermal 
anomalies in a regional metamorphic terrane: an 
isotopic study of the role of fluids, /. Petrol. , 29, 
1215-1232, 1988. 

Epstein, S., D. L. Graf, and E. T. Degens, Oxygen 
isotope studies on the origin of dolomite, in 
Isotopic and Cosmic Chemistry, H. Craig, S. L. 
Miller, and G. Wasserburg, eds., North-Hol- 



land, New York, pp. 169-180, 1963. 

Ferry, J. M., A case study of the amount and 
distribution of heat and fluid during 
metamorphism, Contrib. Mineral. Petrol., 71, 
373-385, 1980. 

Ferry, J. M., Mineral reactions and element migra- 
tion during metamorphism of calcareous sedi- 
ments from the Vassalboro Formation, south- 
central Maine, Am. Mineral. 68, 334-354, 1983. 

Ferry, J. M., Infiltration of aqueous fluid and high 
fluid-rock ratios during greenschist facies meta- 
morphism: a reply, J. Petrol., 27, 695-714, 
1986. 

Ferry, J. M., Metamorphic hydrology at 13-km 
depth and 400-550°C, Am Mineral. , 72, 39-58, 
1987. 

Friedman, I., and J. R. O'Neil, Compilation of 
stable isotope fractionation factors of geochemi- 
cal interest, U. S. Geol. Surv. Prof. Paper 440-K, 
12 pp., 1977. 

Hoisch, T. D., Heat transport by fluids during Late 
Cretaceous regional metamorphism in the Big 
Maria Mountains, southeastern California, Geol. 
Soc. Am. Bull. 98, 549-553, 1987. 

McCrea, J. M., On the isotopic chemistry of car- 
bonates and a paleo-temperature scale, /. Chem. 
Phys., 18, 849-857, 1950. 

Osberg, O. H., Stratigraphy, structural geology 
and metamorphism of the Waterville- Vassalboro 
area, Maine, Maine Geol. Surv. Bull., 20, 1968. 

Rye, D. M., and H. J. Bradbury, Fluid flow in the 
crust: an example from a Pyrenean thrust ramp, 
Am. J. Sci., 288, 197-235, 1988. 

Wickham, S. M., and H. P. Taylor, Jr., Stable 
isotope evidence for large scale seawater infil- 
tration in a regional metamorphic terrane: the 
Trois Seigneurs Massif, Pyrenees, France, 
Contrib. Mineral. Petrol., 91, 122-137, 1985. 

Wood, B. J., and C. M. Graham, Infiltration of 
aqueous fluid and high fluid: rock ratios during 
greenschist facies metamorphism,/. Petrol., 27, 
751-761, 1986. 

Wood, B. J., and J. V. Walther, Fluid flow during 
metamorphism and its implications for fluid- 
rock ratios, in Fluid Rock Interactions during 
Metamorphism, J. V. Walther and B. J. Wood, 
eds., Springer- Verlag, New York, pp. 89-108, 
1986. 



26 



CARNEGIE INSTITUTION 



The Reaction Progress Method: Quan- 
titative Tests of Petrologic Models on 
a Microscopic Scale 

Craig M. Schiffries 

A central problem in petrology is to 
understand the physical and chemical con- 
trols that govern the progress of mineral 
reactions. It is generally assumed that meta- 
morphic mineral reactions are driven by 
variations in temperature and pressure, and 
that metamorphism is nearly isochemical 
except for the loss or gain of volatiles. 
According to a growing school of thought, 
however, fluid infiltration commonly plays 
an essential role in driving metamorphic 
mineral reactions (Newton et al. 9 1980; 
Rumble et al., 1982; Ferry, 1986). In con- 
trast to the traditional view of metamor- 
phism, fluid infiltration can cause large- 
scale chemical mass transfer of non-vola- 
tile components. The dichotomy of opinion 
over the relative importance of the phys- 
icochemical variables that govern the prog- 
ress of metamorphic mineral reactions il- 
lustrates the need to develop quantitative 
tests that can distinguish between alterna- 
tive petrologic models. The principal pur- 
pose of this paper is to demonstrate that the 
reaction progress method (Thompson et 
a/., 1982; Thompson, 1982; Ferry, 1986) 
can be used to distinguish between iso- 
chemical and metasomatic models for the 
origin of myrmekite (Fig. 11). The iso- 
chemical model (Schwantke, 1909) is 
analogous to the traditional view of meta- 
morphism because the mineralogical 
changes occur in response to variations in 
temperature and pressure at constant bulk 




Fig. 1 1. BSE image of calcic myrmekite from the 
Bushveld Complex. The vermicular intergrowth 
consists of quartz (black) and calcic plagioclase 
(grey). 



composition. The metasomatic replacement 
model (Becke, 1908; Sederholm, 1916) is 
analogous to fluid infiltration models of 
metamorphism because the mineral reac- 
tions occur in response to fluid-rock inter- 
actions. 

Myrmekite has been studied by penolo- 
gists since the 19 th century (Michel-Levy, 
1874-75), and the extensive literature is 
reviewed by Ash worth (1972) and Phillips 
(1974). Myrmekite is commonly defined 
as a descriptive, nongenetic term that refers 
to vermicular intergrowths of quartz and 
plagioclase. The intergrowths discussed in 
this paper consist of quartz and plagio- 
clase, but they are referred to as * calcic 
myrmekite' because they are distinctly 
different from the type of myrmekite that 
has been widely discussed in the literature 
(Table 2). It appears that calcic myrmekite 



GEOPHYSICAL LABORATORY 

Table 2. Comparison between calcic myrmekite and typical myrmekite 



27 



Calcic Myrmekite 



Typical Myrmekite 



Occurrence 



Alkali Feldspar 

Plagioclase 
Composition 



anorthositic and 
gabbroic rocks 

generally absent 



An > An 

myr host 



granitic rocks and quartzo- 
feldspathic gneisses 

generally present 

An < An. 



myr 



host 



has been frequently overlooked and is a 
common accessory feature in anorthositic 
and gabbroic rocks (Schiffries and Dymek, 
1985; Dymek and Schiffries, 1987). Calcic 
myrmekite comprises minerals that are 
intergrown on a length-scale of approxi- 
mately 10 fim (Fig. 11), and precise meas- 
urements of modal composition cannot be 
obtained by standard point-counting tech- 
niques. Micro-modal data were obtained 
by inversion of broad-beam electron micro- 
probe analyses and by image processing of 
digitized BSE photomicrographs. Mineral 
compositions were determined by conven- 
tional electron microprobe techniques. 

The metasomatic model for the origin 
of calcic myrmekite involves an open sys- 
tem reaction in which the host plagioclase 
is replaced by an intergrowth of quartz and 
relatively calcic plagioclase. The replace- 
ment process can be represented by a single 
net-transfer reaction: 



2NaAlSi 3 8 +CaNa 2 



albite 



fluid 



=CaAl 2 Si 2 8 + 4Si0 2 . 



(1) 



anorthite 



qtz 



The endmember reaction (1 ) can be rewrit- 
ten in terms of arbitrary values for the 
initial and final plagioclase composition: 

(l^ajCa^SiJ), + (f-/)CaNa 2 = 
sodic plag fluid 

(l+/)Na,. / Ca / Al l4/ Si 3 . / 8 + A(f-i)S\O v (2) 
calcic plag qtz 

where i = [n r Kn r +n v )]. . . ., / = [n r I 

L Ca' x Ca Na'- 1 initial 7 •> L Ca' 

("c+nJkai' and / > *• An advantage of 
writing the net-transfer reaction in this form 
is that the stoichiometric reaction coeffi- 
cients are expressed in terms of the initial 
(host) and final (myrmekite) plagioclase 
composition. The production of quartz by 
reaction (2) is coupled with a progressive 
increase in the anorthite content of the 
plagioclase. 

The replacement model can be tested by 
comparing measurements of reaction prog- 
ress that monitor changes in mineral com- 
position and modal proportions. Reaction 
progress, ^, is defined for an arbitrary unit 
of rock as: 



I = An Iv 

^ XX 



(3) 



28 



CARNEGIE INSTITUTION 



1.0 
0.8 



£ 0.6 

CO 

i 
§? 0.4 



a Bushveld Complex 
St-Urbain anorthosite 
a Other anorthosites 




1.0 



n, 



Fig. 12. A 
model. 



qtz/( n qtz + n plag) 
test of the metasomatic replacement 



where An x is the change in the number of 
moles of species, x , per unit of rock that 
results from the progress of a given chemi- 
cal reaction, v is the stoichiometric reac- 
tion coefficient of species, jc, and the sign of 
v is positive for the reaction products and 
negative for the reactants. Two expressions 
for reaction progress of equation (2) are: 



S=AnJ4(f-i) 

S = AnJ(l+i) 



(3a) 
(3b) 



modal abundance). Fig. 12 shows there is 
excellent agreement between the empirical 
data and the relationship predicted by equa- 
tion (4), providing strong support for the 
replacement model for the origin of calcic 
myrmekite. 

The isochemical model is based on the 
assumption that myrmekite forms by exso- 
lution of quartz from the "Schwantke mole- 
cule" (Ca 05 □ 05 AlSi 3 O g ), which is essen- 
tially a feldspar that contains excess silica 
in solid solution. The isochemical model 
can be represented by the following end- 
member reaction: 

2Ca 05 q, 5 AlSi 3 O 8 = CaAl 2 Si 2 8 + 4Si0 2 ,(5) 
Schwantke anorthite qtz 

where myrmekite consists of a vermicular 
intergrowth of the product minerals. Reac- 
tion (5) can be rewritten for an arbitrary ini- 
tial composition: 

Na 1/ Ca / n / A 1+/ Si 3+y O g+gf 
Schwantke-albite solid solution 



= Na, / Ca / Al„ / Si 3 ,0, + (4/)SiO, 
plagioclase qtz 



(6) 



where n . refers to the number of moles of 

pi»g 

calcic plagioclase on the right hand side of 
reaction (2). The initial assemblage does 
not contain either quartz or calcic plagio- 
clase and therefore An = n and An . = 

qtz qtz plag 

n . . Rearrangement of equations (3a) and 
(3b) yields: 



nj(n a +nj = 4(f-i)/(4f-3i+l) (4) 



In contrast to the replacement model, the 
composition of plagioclase produced by 
the isochemical process is independent of 
the composition of plagioclase in the host 
rock. Two expressions for the progress of 
reaction (6) are: 



qtz 



9" 



plag 



I = «, • 

~ plag. 



(7a) 
(7b) 



Equation (4) provides a test of the replace- 
ment model that is based on two independ- 
ent sets of data (mineral composition and 



Combination of equations (7a) and (7b) 
yields: 



GEOPHYSICAL LABORATORY 



29 



100 
80 

? 60 

**— 

$ 40 
20 




* Q qbAB^*** 




n Bushveld Complex 
♦ St-Urbain anorthosite 
a Other anorthosites 



20 40 60 80 
n qtz/( n qtz + n plag) 



100 



Fig. 13. A test of the isochemical exsolution model 



nJ(n,+nJ = Afl{Af+l). 



qti « qtz plag 



(8) 



Equation (8) provides a test of the iso- 
chemical exsolution model and Fig. 13 
shows that the empirical data are inconsis- 
tent with this model. 

Alternative models for the origin of 
calcic myrmekite have been tested through 
the coordinated application of two micro- 
analytical techniques that monitor changes 
in mineral composition and modal abun- 
dance on a sub-millimeter scale. The data 
are in agreement with the metasomatic 
replacement model but are not consistent 
with the isochemical exsolution model. 
Similar applications of the reaction prog- 
ress method may provide a powerful tool 
for testing petrologic models on a micro- 
scopic scale. 



References 

Ash worth, J. R., Myrmekites of exsolution and 
replacement origins, Geol. Mag., 109, 45-62, 
1972. 

Becke, F., Uber Myrmekit, Tschermaks Mineral. 
Petrogr. Mitt., 27, 377-390, 1908. 

Dymek, R. F., and C. M. Schif fries, Calcic myrme- 
kite: Possible evidence for the involvement of 
water during the evolution of andesine anorthosite 
from St-Urbain, Quebec, Can. Mineral., 25, 
291-319, 1987. 

Ferry, J. M., Reaction progress: A monitor of 
fluid-rock interaction during metamorphic and 
hydrothermal events, in Fluid-Rock Inter actions 
During Metamorphism, J. V. Walther and B. J. 
Wood, eds., Springer- Verlag, New York, 89- 
108, 1986. 

Michel-Levy, A., De quelques characteres micro- 
scopiques des roches anciennes acides, consid- 
eres dans leurs relations avec l'age des eruptions, 
Soc. Geol. France Bull., 3rd series, 3, 199-236, 
1874-75. 

Newton, R. C, J. V. Smith, and B. F. Windley, 
Carbonic metasomatism, granulites, andcrustal 
growth, Nature, 288, 45-50, 1980. 

Phillips, E. R., Myrmekite — one hundred years 
later, Lithos, 7, 181-194, 1974. 

Rumble, D., J. M. Ferry, T. C. Hoering, and A. J. 
Boucot, Fluid flow during metamorphism at the 
Beaver Brook fossil locality, New Hampshire, 
Am. J. ScL, 282, 886-919, 1982. 

Schiffries, C. M., and R. F. Dymek, Calcic myrme- 
kite in gabbroic and anorthositic rocks, Geol. 
Soc. Am. Abstr. Program., 17, 709, 1985. 

Schwantke, A., Die Beimischung von Ca im 
Kalifeldspat und die Mymrekitbildung, Cen- 
tralbl. Mineral, 311-316, 1909. 

Sederholm, J. J., On synantectic minerals and 
related phenomena, Comm. Geol. FinlandeBull., 
153, 1-148, 1916. 

Thompson, J. B., Reaction space: An algebraic 
and geometric approach, Rev. Mineral., 10, 33- 
51,1982. 

Thompson, J. B., Jr., J. Laird, and A. B. Th- 
ompson, Reactions in amphibolite, greenschist, 
and blueschist, /. Petrol., 23, 1-27, 1982. 



30 



CARNEGIE INSTITUTION 



Liquid- Absent Aqueous 
Fluid Inclusions 

Craig M. Schiffries 

A wide variety of geological phenom- 
ena are governed by interactions between 
fluids and rocks at elevated temperatures 
and pressures. Studies of fluid inclusions 
provide important constraints on the chemi- 
cal composition of crustal fluids and the 
physical conditions of fluid-rock interac- 
tions. Raman spectra and microthermom- 
etric data are reported here for a new class 
of aqueous fluid inclusions that is charac- 
terized by the absence of a liquid phase at 
20°C. The inclusions hold special interest 
because they display the following proper- 
ties: (1) Although they do not contain a 
liquid phase at 20°C, the inclusions ho- 
mogenize to an aqueous liquid at elevated 
temperatures; (2) Initial melting occurs at a 
reaction point (+29°C), rather than a eutec- 
tic point as commonly assumed (T E = -52°C 
for the system CaCl,- NaCl - H 2 0); (3) Ice 
is absent in the subsolidus assemblage 
despite the high-H 2 contents of the inclu- 
sions. At room temperature, most of the 
water occurs as structurally bound H 2 in 
hydrate minerals and a relatively small 
amount occurs in a low-density vapor phase; 
(4) The most abundant daughter minerals 
in the subsolidus assemblage are antarc- 
ticite (CaCl 2 »6H 2 0) and a second hydrate 
that may be a new mineral; (5) The fluid 
compositions fall outside the compositional 
limits defined by previous studies of natu- 
ral fluid inclusions. The inclusions de- 
scribed here occur in quartz from a mafic 
pegmatoid in the Bushveld Complex. 



Similar inclusions probably occur in other 
geological environments, but they may be 
overlooked or misinterpreted because their 
solidus temperature is above 20°C. 

At room temperature, the liquid-absent 
aqueous inclusions consist of birefringent 
hydrates (-60 to 70 volume percent), halite 
(less than 10 volume percent), and a low 
density vapor (-20 to 30 volume percent). 
Raman spectroscopy was used to identify 
hydrate daughter minerals that are difficult 
to distinguish by optical microscopy 
(Dubessy et aL, 1982). Experimental con- 
ditions of the micro-Raman optical system 
are similar to those described by Hemley et 
al. (1987). The most abundant phase in the 
subsolidus assemblage has asymmetric 
Raman bands at 1660 and 3430 cm 1 that are 
indicative of the bending and stretching 
modes, respectively, of structural water in 
antarcticite. The presence of a second 
hydrate daughter mineral in the subsolidus 
assemblage is indicated by an additional 
peak at 1620 cm 1 (Fig. 14). The second 
hydrate has not been positively identified, 
but the most likely possibility is a poly- 
morph of CaCL/4H 2 0. A preliminary study 
of synthetic compounds indicates that at 
least one polymorph of CaCl^HjO has a 
Raman peak at approximately 1620 cm 1 . 
None of the CaCL^Hp polymorphs is 
currently recognized as a mineral species. 

Microthermometric measurements were 
performed with a USGS-type, gas-flow, 
heating-cooling stage (Fluid Inc.) mounted 
on a petrographic microscope. Initial melt- 
ing occurs at approximately +29°C and a 
large fraction of liquid (more than 25 vol- 
ume percent) is present at 30°C in some 
inclusions. It appears that antarcticite melts 



GEOPHYSICAL LABORATORY 



31 




Ice (H 2 0) 



Hydrohalite + L 



1300 1500 1700 1900 

A Wavenumber (cm 1 ) 

Fig. 14. Micro-Raman spectra (OH-bending mode 
region) of hydrate daughter minerals at 20°C. The 
position and shape of the Raman band at 1660 
cm 1 in the bottom spectrum are consistent with the 
spectrum of antarcticite. The presence of a second 
hydrate daughter mineral in the subsolidus assem- 
blage is suggested by an additional Raman band at 
1620 cm" 1 (top spectrum). The mineral responsible 
for the peak at 1620 cm 1 has not been positively 
identified, but the most likely possibility is a 
polymorph of CaCl 2 »4H 2 0. The Raman band at 
1660 cm 1 in the top spectrum may reflect contri- 
butions from both antarcticite and CaCl 2 »4H 2 0. 

incongruently at the initial melting tem- 
perature and the inclusions subsequently 
consist of CaCl^H/X?) and vapor. With 
increasing temperature, the final hydrate 
[CaCl 2 «4H 2 0(?)] rapidly diminishes in size 
and melts at +32° to +38°C. Halite is pres- 
ent in some inclusions [T m (halite) = 
199±26°C] and it is probably metastably 
absent in other inclusions. Further heating 
causes the vapor bubble to shrink and the 
inclusions homogenize to an aqueous liq- 
uid. 

The phase equilibria can be interpreted 
in terms of the vapor-saturated, liquidus 
diagram for the system CaClj- NaCl - H 2 
(Fig. 15; see also Brass, 1980; Crawford, 



Hydrohalite 
(NaCI-2H 2 0) 



Halite (NaCl) 




E~ 


-52°C 


Pf 


- -23°C 


P 2 " 


•+29°C 


P 3 - 


- +45°C 



Antarcticite + L 

ntarcticite (CaCl2-6Hs>0) 
' 4H 2 6 + L 
4H 2 . 

aCI,-2H,0 



CaCI, 



Fig. 15. Provisional vapor-saturated, liquidus 
diagram for the system CaCL-NaCl-Hp (after 
Brass, 1980; Crawford, 1981; Oakes etaU 1988; 
Vanko et al, 1988; Zhang and Frantz, 1989). 
Boundaries of the CaCl 2 # 4P^O liquidus are based 
on extrapolations that are consistent with the 
Alkemade theorem, Schreinemakers rules and the 
binary CaClj-I^O phase diagram. The liquidus 
fields for antarcticite and CaCl 2 *4H 2 have been 
enlarged for clarity. Subsolidus assemblages are 
indicated by dashed lines. The location of reaction 
point P 2 relative to the subsoludus join between 
antarcticite and hydrohalite is uncertain, but the 
point lies above the join between CaCl^HjO and 
hydrohalite. For the assemblage ice + hydrohalite 
+ antarcticite, the first equilibrium melt forms at 
-52°C at the ternary eutectic (E). For the assem- 
blage halite + hydrohalite + antarcticite, the first 
equilibrium melt forms at approximately -22°C at 
P x . For the assemblage halite + antarciticte + 
CaCl 2 *4H 2 0, the first equilibrium melt forms at 
approximately +29°C at P 2 . 



1981; Oaks etal., 1988; Vanko etai, 1988; 
Zhang and Frantz, 1989). For the subsoli- 
dus assemblage antarcticite + CaCL^F^O 
+ halite, the first equilibrium melt forms at 
approximately +29°C at reaction point P 2 . 
At P 2 antarcticite melts incongruently, to 
CaCl^HjO and an aqueous liquid. With 
increasing temperature, the composition of 
the liquid evolves along the cotectic bound- 
ary between halite and CaCl 2 «4H 2 until 
the latter phase melts completely at 32° to 
38°C. The composition of the liquid subse- 
quently migrates across the halite liquidus 
until 7 m (halite). Previous studies (e.g. 
Crawford, 1981; Vanko et al. y 1989) indi- 
cate that most fluid inclusions in the system 



32 



CARNEGIE INSTITUTION 



Ice (H 2 0) 



Hydrohalite + L 



Hydrohalite 
(NaCI-2H 2 0) 



Halite (NaCI) 




E ~ -52°C 

Pi - -23°C 

P 2 - +29°C 

P 3 ~ +45°C 



Antarcticite + L 

ntarcticite (CaCl2-6H20) 
"aCI 2 .4H 2 6 + L 
aCI 2 .4H 2 

aCI 2 -2H 2 



CaCI. 



Fig. 16. The bulk composition of the fluid lies at 
the intersection of the ^(halite) isotherm, and the 
tie-line between halite and the point on the halite- 
CaCl 2 *4H O cotectic that corresponds to 
r m (CaCl 2 4Hp). 

CaC^- NaCI - H 2 exhibit the following 
melting behavior: the subsolidus assem- 
blage consists of ice + hydrohalite + antarc- 
ticite; initial melting occurs at the eutectic 
point (£); and antarcticite is consumed at 
the eutectic temperature (-52°C). Given 
the topology of the phase diagram (Fig. 
15), small variations in bulk composition 
may result in large differences in the sub- 
solidus mineral assemblage, the initial 
melting temperature, the equilibrium melt- 
ing sequence, and the phase ratios at 20°C 
(Schiffries, in preparation). 

In theory, the bulk composition of the 
inclusions discussed here can be deter- 
mined from two measurements: (1) 
TJCaCl^HjO) in the presence of a cotec- 
tic liquid plus halite and vapor and (2) 
TJhalite) in the presence of liquid and 
vapor. By neglecting the mass of the vapor, 
the bulk composition lies at the intersection 
of the halite dissolution isotherm, and the 
tie-line between halite and the point on the 
halite - CaCl 2 *4H 2 cotectic correspond- 
ing to 7 m (CaCl 2 «4H 2 0) (Fig. 16). In prac- 
tice, the bulk composition cannot be deter- 
mined precisely by this technique because 
there are uncertainties in the location of the 



halite - CaCl 2 «4H 2 cotectic and the halite 
dissolution isotherms in the relevant part of 
the phase diagram. Despite uncertainties in 
the liquidus diagram, the subsolidus as- 
semblage indicates that the compositions 
of these inclusions fall outside the com- 
positional limits defined by previous stud- 
ies of natural fluid inclusions. The fluids 
are characterized by a high Ca/Na ratio and 
a very high concentration (greater than 52 
wt %) of total dissolved solids. 



References 



Brass, G. W., Stability of brines on Mars, Icarus, 
42, 20-28, 1980. 

Crawford, M. L., Phase equilibria in aqueous fluid 
inclusions, in Short Course in Fluid Inclusions: 
Applications to Petrology, L. S. Hollister, and 
M. L. Crawford, eds., Short Course Handbook 6, 
Mineral Assoc. Canada, Ottawa, pp. 75-100, 
1981. 

Dubessy, J. D., D. Audeoud, R. Wilkins, and C. 
Kosztilanyi, The use of the Raman micro-probe 
MOLE in the determination of the electrolytes 
dissolved in the aqueous phase of fluid inclusions, 
Chem. Geol, 37, 137-150, 1982. 

Hemley, R. J., P. M. Bell, and H. K. Mao, Laser 
techniques in high-pressure geophysics, Sci- 
ence, 237, 605-612, 1987. 

Oakes, C.S., RJ. Bodnar, and J. M. Simonson, 
Phase equilibria in the system NaCI - CaC^ - 
H 2 0: The ice liquidus, Geol. Soc. Am. Abstr. 
Progm., 20, A390, 1988. 

Vanko, D. A., R. J. Bodnar, and S. M. Sterner, 
Synthetic fluid inclusions: VIII. Vapor- satu- 
rated halite solubility in part of the system NaCl- 
CaCl 2 -H 2 0, with application to fluid inclusions 
from oceanic hydrothermal systems, Geochim. 
Cosmochim. Acta, 52, 2451-2456, 1988. 

Zhang, Y. G., and J. D. Frantz, Experimental 
determination of the compositional limits of 
immiscibility in the system CaC^-F^O-COj at 
high temperatures and pressures using synthetic 
fluid inclusions, Chem. Geol, 74,289-308, 1989. 



GEOPHYSICAL LABORATORY 



33 



Igneous and Metamorphic Petrology - 
B. Experimental Studies 



Oxygen Fugacity and Evaporation 
Phase Relations in the Solar Nebula 

Bjorn O. My sen and Ikuo Kushiro* 

Characterization of the pressure (P) - 
temperature (T) - oxygen fugacity \f(0 2 )] 
phase relations that govern evaporation, 
condensation and melting relations in the 
system CaO - MgO - A1 2 3 - Ti0 2 - Si0 2 is 
of interest because this system contains 
most of the refractory minerals (perovskite, 
corundum, spinel, hibonite and calcium 
dialuminate) expected to form at the high- 
est temperatures during rock-forming proc- 
esses in the early solar nebula. Principal 
evidence for this suggestion is the phase 
assemblages in Ca-, Al-rich inclusions 
(CAFs) in carbonaceous chondrites (see 
MacPherson et ai, 1988 for review). 

The suggested/(0 2 ) range during rock- 
forming processes in the early solar nebula 
is from about 5 orders of magnitude below 
to perhaps 2 orders of magnitude above 
that defined by the iron-wustite (IW) oxy- 
gen fugacity buffer (e.g., Fegley, 1985; 
Brett and Sato, 1984; KozuletaL, 1986). It 
is possible that partial or complete reduc- 
tion of metal cations (Si 4+ , Al 3+ , Ca 2+ , Ti 4+ , 
and Mg 2+ ) in the system may take place in 
the lowest portion of this/fO^ range. Thus, 
the phase relations in the early solar nebula 

* Address: Geological Institute, University of 
Tokyo, Hongo-Tokyo 113, Japan 



will be affected by the oxygen fugacity. Ex- 
perimental determination of phase rela- 
tions as a function of/(0 2 ) is reported here. 

The Knudsen Cell technique (Knudsen, 
1909) has been used to measure vapor 
pressures of the phase assemblages (with 
modifications and calibrations described 
by My sen and Kushiro, 1988). The samples 
were contained in Mo and C Knudsen cells. 
Through interaction between the sample 
containers (Mo and C) and the oxide start- 
ing materials, /(0 2 )- values at or near the 
Mo - Mo0 2 and C - CO - C0 2 buffers were 
defined This/(0 2 ) range covers that from 
near the highest oxygen fugacities recorded 
from intrinsic oxygen fugacity measure- 
ments of chondrites (1-2 orders of magni- 
tude above the IW buffer; Brett and Sato, 
1984; Kozul et al, 1986) to about two 
orders of magnitude above the /(0 2 ) sug- 
gested for the primordial solar nebula (5-6 
orders of magnitude below the IW buffer; 
Fegley, 1985). 

The melting and vaporous phase rela- 
tions of the high-temperature refractory 
aluminates and perovskite are distinctly 
dependent on the/(0 2 ) (Fig. 17). Not only 
do the P - T coordinates of the vaporous 
boundaries change as the/(0 2 ) is lowered, 
but in the case of the most important phases 
such as spinel (MgAl 2 4 ), hibonite 
(CaO6Al 2 3 ) and perovskite (CaTi0 3 ), the 
vaporous phase also changes as a function 
of /(Oj) at pressures below the triple point 



34 



CARNEGIE INSTITUTION 




Spinel 



1400 1600 1800 2000 

Temperature, °C 



£ 10 " 2 

CD 10 



-4 



3 10- 6 
8 io* 

qI 1400 




1600 1800 2000 

Temperature, °C 



Hibonite 



g10" 5 

^10" 7 
CO lu 

CD10" 9 



Mo - Mo0 2 
Hib+V 




_g 10"^C-CO-CO 2 



CD 10 



-5 . 



1400 1600 1800 2000 

Temperature, °C 



sho- 7 

W Q 

£ 10" 9 
CL 1400 



Cor+ 
L+V 




• Hib+V 



L+V - 



1600 1800 2000 

Temperature, °C 



Perovskite 




§ 10- 8 

CL 



1400 1600 1800 

Temperature, °C 



c5 1 0" 2 

13 10" 6 

co lu 

0) 1Q -8 
CL 1400 



c- 


CO- 


co 






.Rt 


,L- 












!+>- 


l+v 






Rt + 


V 




^ 




. Pv 


+ V 






V 







1600 1800 2000 

Temperature, °C 



Fig. 17. Pressure - temperature trajectories of phase relations in the systems MgAl 2 4 , CaO»6Al 2 3 and 
CaTiOj at the/(0 2 ) of the Mo - Mo0 2 and C - CO - C0 2 oxygen fugacity buffers. Abbreviations: Sp - 
spinel, Cor - corundum, Hib - hibonite, Pv - perovskite, Rt - rutile, L - liquid, V - Vapor. Closed symbols 
represent experimental points along a vaporous with congruent evaporation, grey symbols show the 
vaporous of liquid-bearing assemblages, and open symbols represent incongruent evaporation phase 
relations. 



(marked a in Fig. 17). Whereas spinel, 
hibonite and perovskite are the vaporous 
phases at the highftO,) (Mo - Mo0 2 ), at the 
lower/(0 2 ) (C - CO - C0 2 ), corundum (for 
the aluminates) or a Ti0 2 phase (for 
perovskite starting material, probably ru- 



tile) becomes the vaporous phase. 

These changes in vaporous phase rela- 
tions result from partial reduction of Ca 2+ 
and Mg 2+ in the vapor. From the slopes of 
the vapor pressure (In P v ) versus absolute 
temperature (1/T) for the CaO and MgO 



GEOPHYSICAL LABORATORY 



35 




«.60 5.00 5.40 

1/Tx10 4 (K" 1 ) 



5.80 



•c-co-co 2 


■ Mo - Mo0 2 


AH AS 


AH AS 


AIA 466 110 


405 80 


MgO 411 115 


332 67 


CaO 530 159 


349 54 







05 

> 

GL 




4.80 5.20 5.60 6.00 
1/Tx10 4 (K' 1 ) 



4.60 5.00 

l/TxKTOC 1 ) 



5.40 

4/lS-V 



5.80 



Fig. 18. Vapor pressure (natural logarithm, In P y ) versus temperature (1/T) for the systems AljOj, CaO 
and MgO at the/(0 2 ) of the Mo - Mo0 2 and C - CO - C0 2 oxygen fugacity buffers. Thermodynamic 
parameters pertinent to evaporation are also shown. 



system (Fig. 18) it is evident that both the 
entropy, AS, and enthalpy, AH, of evapora- 
tion increases with the reduced /(0 2 ). The 
effect of /(Oj) on the corundum vaporous 
relations is significantly less. 

The increased AH and AS values of 
evaporation of CaO and MgO with 
decreasing fiQ 2 ) (Fig. 18) can be rational- 
ized by suggesting increased dissociation 
in the vapor by lowering the^Oj) (e. g., Ca, 
Mg, 2 and O). At the /(0 2 ) of the Mo- 
Mo0 2 buffer, the evaporation reaction is: 



MgO(s) <=> MgO(v), 



(1) 



with a AH of evaporation of 331 KJ/mol 
(Fig 18). From the data of Do wart et al. 
(1964) about 50% of the MgO(v) will be in 
the elemental state at the log f{Q^) of the C- 
CO-C0 2 buffer. The resulting reduction of 
the activity of Mg 2+ most likely is the expla- 



nation of incongruent evaporation of spinel 
at the latter fiQ 2 ), whereas spinel evapo- 
rates congruently at the^OJ of the Mo - 
Mo0 2 buffer. 

Similar reasoning can be applied to 
evaporation of lime (CaO) at the two differ- 
ent oxygen fugacities. Analogous species 
(Ca, CaO, O and 2 ) exist in the vapor from 
this system as in the Mg-0 system . The AH 
for the reaction: 

CaO(v) + O(v) <=> Ca(v) + 2 (v), (2) 

is 117 KJ/mol (Dowart etai, 1964). From 
the data in Fig. 18, this enthalpy would 
imply essentially complete dissociation of 
CaO(v) to Ca(v) and 2 (v) as the oxygen 
fugacity is reduced from that of the Mo - 
Mo0 2 buffer to that of the C - CO - C0 2 
buffer. The consequent reduction in Ca 2+ 
activity in the vapor (probably can explain 



36 



CARNEGIE INSTITUTION 



~1450°C 

~1445°C 
~1375°C 
~1380°C 



Z 



MaO 



P tot = 10 3 bar 



mol % 



CaO 




C-CO-CO. 



MgO 



~1250°C 
~1200°C 

~1210°C 



P tot = 10* bar 



mol % 



CaO2AL0,\AI,0, CaO 



CaO6AI 2 3 




CaO-2AI 2 3 \AI 2 3 
CaO-6AI 2 3 



S: ~1 500°C 
i,: ~1475°C 

i 2 : ~1485°C 

l 3 : ~1485°C 



Z 



MaO 



CaO 



P tot =10- 3 bar 
mol % 




Mo-MoO, 



Hib 
Cor 



CaO-2AI 2 3 \AI 2 3 
CaO-6AI 2 3 



~1290°C 
~1275°C 

~1290°C 

~1295°C 

7ZZ 



MgO 



P tot = 10- 5 bar 



mol % 




Hib 
Cor 



CaO 



CaO-2AL0 3 \AI 2 



CaO-6AI 2 3 



Fig. 19. Vaporous surfaces in the system CaO - MgO - A^ - SiO, at 10 3 bar (A,C) and 10 5 bar (B, 
D) total pressure. S denotes solar CaO/MgO/Al 2 3 (from Anders and Ebihara, 1982). Si0 2 content is mat 
of the solar abundance. Temperatures of various invariant points and the vaporous surface temperatures 
of S are indicated in the inserts. The overall dilution in the gas is about l& (solar dilution). Abbrevia- 
tions: Cor - corundum, Sp spinel, Pe - periclase, CA2 - calcium dialuminate, Hib - hibonite, Fo - forsterite. 
Oxygen fugacity is at that of the C-CO-C0 2 (A,B) and Mo - Mo0 2 (C,D) buffer. 



the change from congruent to incongruent 
evaporation ofhibonite and perovskite (Ca- 
Ti0 3 ) as the^Oj) is lowered. 

From the evaporation data reported here 
and elsewhere (Mysen, 1988; Mysen and 



Kushiro, 1988), vaporous surfaces in the 
system CaO - MgO - Al^ - Si0 2 with Mg/ 
Si = 1 have been calculated (Fig. 19) under 
the assumption of ideal mixing in the gas 
phase and with the proportion of oxide 



GEOPHYSICAL LABORATORY 



37 



components relative to an inert gas diluent 
equal to that of the solar nebula (-10 4 ; 
Anders and Ebihara, 1982). The condensa- 
tion and evaporation sequences are strongly 
affected by /(0 2 ). For example, spinel is 
only stable at high pressure, or high/(0 2 ), 
orboth. The occurrence of spinel-rich CAI's 
may indicate that such conditions existed 
in the solar nebula. Corundum andhibonite- 
rich phase assemblages probably required 
either low total pressure (less than -10 5 
bar), or that the/(0 2 ) was at or below that of 
the C - CO - C0 2 oxygen buffer during their 
formation. For example, reheating and 
partial evaporation of materials rich in 
organic carbon will take place with/(0 2 ) 
near that of the C - CO - C0 2 buffer. With 
this low oxygen fugacity, the evaporation 
process yields a residue enriched in alumi- 
num relative to that of the starting material. 
In the early solar nebula where tempera- 
tures and pressures probably increased 
toward its center, the experimentally deter- 
mined phase relations lead to the sugges- 
tion of an overall increase in (Mg + Ca)/Al 
in the condensates with decreasing dis- 
tance to the Sun. This trend may be retained 
in the bulk composition of the planets to- 
day. 



References 

Anders, E., and M. Ebihara, Solar system abun- 
dances of the elements, Geochim.Cosmochim. 
Acta, 46, 2363-2380, 1982. 

Brett, R., and M. Sato, Intrinsic oxygen fugacity 
measurements on seven chondrites, a pallasite 
and a tektite and the redox state of meteorite 
parent bodies, Geochim. Cosmochim. Acta, 48, 
111-120,1984 

Dowart, J., G. Exsteen, and G. Verhaegen, Mass 



spectrometric determination of the dissociation 
energy of thermocouples MgO, CaO, SrO and 
Sr 2 0*, Trans, Faraday Soc, 60, 1920-1933, 
1964. 

Fegley, B., Oxidation state indicators of the solar 
nebula, Lunar Planet. Sci. XVI, 232-233, 1985. 

Kozul, J., G. C. Ulmer, and R. Hewins, Allende 
inclusions are oxidized!, EOS, 67, 300, 1986. 

Mysen, B. O., Rock - forming processes in the 
early solar nebula: Phase relations in the system 
CaO - MgO - Aip 3 - Si0 2 to 2000°C and 1 ■» bar, 
Annual Report of the Director of the Geophysi- 
cal Laboratory, Carnegie Instn. Washington, 
1987-1988, Geophysical Laboratory, Washing- 
ton, D. C. , 69-76, 1988. 

Mysen, B. O., and I. Kushiro, Condensation, 
evaporation, melting and crystallization in the 
primitive solar nebula: Experimental data in the 
system MgO - Si0 2 - H 2 to 10x1 a 9 bar and 
1870°C with variable oxygen fugacity, Am. 
Mineral., 73 1 1-19, 1988. 

Knudsen, M., Die Molekularstromung der Gase 
durch Offnungen und die Effusion, Ann. Phys., 
25,999-1016,1909. 

MacPherson, G. J., D. A. Wark, and J. T. Arm- 
strong, Primitive materials surviving in chon- 
drites: refractory inclusions, in Meteorites and 
the Early Solar System, J. F. Kerridge and M. S. 
Matthews, eds., The University of Arizona Press, 
Tucson, pp. 746-807, 1988. 



Experimental Determination of Ele- 
ment Partitioning and Calculated 
Phase relations in the Mg-Fe-Si-0 
System at High Pressure and High 
Temperature 

Yingwei Fei, Ho-kwang Mao, and 
Bjorn O. Mysen 

The principal components of the Earth's 
mantle are MgO, FeO and Si(\ Phase rela- 
tions in this system are of great interest to 
geochemists and geophysicists because both 
the 400 km and the 670 km seismic discon- 



38 



CARNEGIE INSTITUTION 



tinuities may reflect the phase transforma- 
tions of olivine (a) to p-phase and of spinel 
(y) to perovskite plus magnesiowiistite, 
respectively. 

The phase relations can be established 
in two ways. One is to determine phase 
boundaries in P-T-X space (e.g. Akimoto, 
1987; Katsura and Ito, 1989; Ito and Taka- 
hashi, 1989). The other is to determine 
precisely the phase boundaries of pure 
phases and the mixing properties of each 
solid solution. The phase relations in bi- 
nary or multi-component systems can then 
be calculated. Solid solutions in the Mg- 
Fe-Si-0 system include (Mg,Fe)0 (mag- 
nesiowiistite), (Mg,Fe) 2 Si0 4 (olivine, p- 
phase, spinel) and (Mg,Fe)Si0 3 (pyroxene, 
ilmenite, perovskite). These solid solutions 
form four pairs of coexisting phases with 
magnesiowiistite (Mw), Mw-olivine, Mw- 
p, Mw-spinel and Mw-perovskite. The 
solution properties of the individual phase 
may be derived from the element distribu- 
tion data by considering the distribution of 
an element between two solid solutions as 
an exchangeable reaction (Fei and Saxena, 
1986). The purpose of this study is to derive 
the mixing properties of each solution by 
determining experimentally the distribu- 
tion of Mg and Fe between coexisting solid 
solutions at various pressure and tempera- 
ture conditions and to establish phase rela- 
tions in the system. 

The experiments are conducted with the 
piston-cylinder apparatus (up to 50 kbar) 
(Boyd and England, 1960, 1963), the multi- 
anvil device (up to 300 kbar) (Liebermann 
et al. , 1 986 and Remsberg et al. , 1 988), and 
the diamond-anvil cell device (Mao and 
Bell, 1978). Chemical and structural ana- 



lytical techniques such as x-ray diffraction, 
microprobe or SEM and Raman spectros- 
copy were used to characterize the struc- 
ture and chemical composition of the 
samples. 

Synthetic olivine and magnesiowiistite 
solid solutions with different iron contents 
were used as starting materials. Magne- 
siowiistite solid solutions were those syn- 
thesized by Rosenhauer et al. (1976). Oli- 
vine solid solutions were synthesized in the 
piston-cylinder apparatus, with oxide mix- 
tures as starting material, for 48 hours at 
1273K and 15 kbar. The synthetic olivines 
were examined optically and with x-ray 
diffraction; no oxide remainder was pres- 
ent. The compositions were checked by 
electron microprobe. 

For the Mg-Fe partition experiments 
with magnesiowiistite and olivine, magne- 
siowiistite and olivine of suitable composi- 
tions were mixed in appropriate proportions 
(e.g., 2 magnesiowiistite to 3 olivine in 
most cases). The mixtures were ground to 
a grain size of less than 3 jim and well ho- 
mogenized. Two different types of cap- 
sules, platinum capsule sealed inside with 
graphite capsule and molybdenum cap- 
sule, were used to test if there was iron loss 
in the runs. No evidence for iron-loss was 
found. 

The piston-cylinder apparatus was used 
for experiments below 50 kbar. The multi- 
anvil device was used for determining dis- 
tribution coefficients between magne- 
siowiistite and olivine at 90 kbar and 1 723K, 
between magnesiowiistite and p-phase and 
between magnesiowiistite and spinel at 1 50 
kbar and 1773K. The multi-cell sample 
chambers described by Mao et al. (1989) 
were used in the experiments. 



GEOPHYSICAL LABORATORY 



39 



1.0 



0.8 



1 £ 0.6 [ 



X 



0.4 - 
0.2 - 



0.0 




a 20 kb, 1473 K 
. 20 kb, 1723 K 



0.0 0.2 0.4 0.6 0.8 1.0 



X 



oi 

Fe 



Fig. 20. Distribution of Mg and Fe between coex- 
isting magnesiowiistite (Mw) and olivine (Ol) at a 
pressure of 20 kbar and at temperatures of 1473K 
(upper curve) and 1723K (lower curve). Curves 
are calculated results and symbols represent the 
experimental data. 

Figs. 20 and 21 show the temperature 
and pressure dependences of the Mg-Fe 
distribution coefficients between magne- 
siowiistite and olivine. The experimental 
results show systematic variations of the 
distribution data with temperature and 
pressure. 



I.U 


• i ' 


~i — • — i — ■—J'-'- ** 






^*~*~ 




f 


0.8 


/ 


- 




■ / 


■ 


<: 0.6 




- 


5 © 






2 u. 


f 


• 


X 0.4 


J 


P = 150kb ' 


0.2 




T=1773K - 




C- *. i i 


-i — i i l,..i i 



0.0 0.2 0.4 0.6 0.8 1.0 



X 



P 

Fe 



Fig. 22. Distribution of Mg and Fe between coex- 
isting magnesiowiistite (Mw) and P-phase (p) at a 
pressure of 150 kbar and at a temperature of 
1773K. Curves are calculated results and symbols 
represent the experimental data. 




+ 90kb, 1723K. 
a 40 kb, 1723K 
■ 20 kb, 1723 K 



0.0 0.2 



0.4 0.6 
-Ol 
Fe 



0.8 1.0 



X 



Fig.21. Distribution of Mg and Fe between coex- 
isting magnesiowiistite (Mw) and olivine (Ol) at a 
temperature of 1723K and at pressures of 20 kbar 
(lower curve), 40 kbar (middle curve) and 90 kbar. 



The Mg-Fe distribution coefficients 
between magnesiowiistite and p-phase or 
spinel are shown in Figs. 22 and 23. The 
results by Ito et al. (1984) and Yagi et al. 
(1979) are also shown for comparison. 



1.0 



0.8" 



| 0) 

X 



0.6" 



0.4 
0.2 



0.0 





I » ! ' I ' ■—rjpii^' 


— 


&y A 


- 


kw* 


- 


JTa This work 




/ + Yagiefa/, 1979 


"tr 


a Ito, 1984 
i i i i i i * j 



0.0 0.2 0.4 0.6 0.8 1.0 



X 



Sp 
Fe 



Fig. 23. Distribution of Mg and Fe between coex- 
isting magnesiowiistite (Mw) and spinel (Sp) at a 
temperature of 1773K and pressures of 150 kbar 
(lower curve), and at temperature of 1873K and 
pressure of 200 kbar (upper curve). Curves are 
calculated results and symbols represent the ex- 
perimental data. 



40 CARNEGIE INSTITUTION 

Table 3. Nonideal mixing parameters of solid solutions in the Mg-Fe-Si-O system 



Solid solutions 



Wr (J/mol) 



MgFe 



Wr (J/mol) 



Magnesiowiistite 
Olivine (a) 
p-phase 
Spinel (y) 
Perovskite 



16100 

4500 + 0.013P 

1000 

3900-1. 107 

4130- 1.377 + 0.01 IP 



26300 - 5.567 

6500 + 0.013/> 

2000 

3900 

-4050- 2.457 + 0.015P 



To determine the distribution of Mg and 
Fe between magnesiowiistite and 
perovskite, olivines (Fo 85 , Fo 80 and Fo 73 ) 
were used as starting materials in the dia- 
mond-anvil cell. Olivine with small ruby 
grains was imbedded in a 250 jim hole 
drilled in a gasket. The sample was pressur- 
ized in the diamond-anvil cell and heated 
by YAG laser beam. The pressure was 
measured with the fluorescence technique. 
The products were examined optically and 
by x-ray diffraction. The composition of 




■ This work 

a Yagi etal, 1979 



+ Ito, 1984 



J • L 



0.0 0.2 0.4 0.6 0.8 1.0 



X 



Pv 
Fe 



Fig. 24. Distribution of Mg and Fe between coex- 
isting magnesiowiistite (Mw) and perovskite (Pv) 
at a temperature of 1873K and pressures of 260 
kbar (lower curve), and 300 kbar (upper curve). 
Curves are calculated results and symbols repre- 
sent the experimental data. 



each phase in the assemblage was deter- 
mined both by x-ray diffraction (the rela- 
tion between volume and composition us- 
ing the calibrations of Yagi et ah, 1979; 
Rosenhauer et al. 9 1976) and by electron 
microprobe. The lattice parameters of each 
phase were determined by x-ray diffrac- 
tion, with gold as internal standard for 
calibration. The results accord with those 
determined with the electron microprobe. 
The results on the Mg-Fe partitioning be- 
tween magnesiowiistite and perovskite are 
shown in Fig. 24. These are in agreement 
with those obtained by Ito etal. (1984) and 
Yagi et al. (1979). 

Solution parameters (W.) for five solid 
solutions have been obtained by fitting the 
experimental data simultaneously using the 
Margules formulation (Table 3). Various 
calculated Roozeboom diagrams for the 
exchange of Mg 2+ and Fe 2+ between coexist- 
ing solid solutions are shown in Figs. 20 - 
24. 

The solution parameters listed in Table 
3 with an internally consistent thermody- 
namic data set on phases in the system (Fei, 
1989) can be used to compute phase rela- 
tions. Fig. 25 shows computed isothermal 
phase relations in the binary system Mg 2 Si0 4 
- Fe 2 Si0 4 at temperatures of 1473K and 



GEOPHYSICAL LABORATORY 



41 



300 




0.0 0.2 0.4 0.6 0.8 1.0 

Mg 2 Si0 4 X Fe Fe 2 Si0 4 

Fig. 25. Calculated isothermal phase relations in 
the binary system Mg 2 Si0 4 and Fe 2 Si0 4 at tem- 
peratures of 1473K (the heavy lines) and 1873K 
(the light lines) and pressures to 300 kbar. 

1873K and pressures to 300 kbar. 

The calculated diagram is in good agree- 
ment with those determined by Katsura and 
Ito (1989) and Ito and Takahashi (1989) in 
the Mg-rich region and by Akimoto (1987) 
in the Fe-rich region. The thermodynamic 
data base evaluated from experimental data 
can be used not only for reproducing the 
existing experimental results, but also for 
interpolation and even extrapolation with 
caution. It allows us to explore phase rela- 
tions in the system in various ways. For in- 
stance, one may construct phase relations 
in pressure-temperature space or in pres- 
sure-composition space. In the mantle 
model of peridotitic composition where 
olivine (Mg 088 Fe 012 ) 2 SiO 4 is the major 
component, the phase diagram of this oli- 
vine indicates that the depth and width of 
the phase transformations of olivine to p- 
phase and of spinel to perovskite plus 
magnesiowiistite are compatible with the 
seismic observation of the 400 km and the 



670 km discontinuity, respectively. The 
density profile of the mantle can be simu- 
lated by varying chemical composition 
along the assumed geotherm. However, to 
make the comparison between the calcu- 
lated and observed profiles, at least Ca and 
Al should be included in the system. Ex- 
perimental determination and computer 
simulation of phase relations in the ex- 
tended system can provide critical con- 
straints for models of the Earth's mantle. 



References 



Akimoto, S., High-pressure research in geophys- 
ics: past, present and future, in High Pressure 
Research in Mineral Physics, M. H. Manghnani 
and Y. Syono, eds., Terra Scientific Publishing 
Company (TERRAPUB), Tokyo/American 
Geophysical Union, Washington, D. C, pp. 1- 
13, 1987. 

Boyd, F. R., and J. L. England, Apparatus for 
phase-equilibrium measurements at pressures 
up to 50kilobars and temperatures up to 1750°C, 
/. Geophys. Res., 65, 741-748, 1960. 

Boyd, F. R., and J. L. England, Effect of pressure 
on the melting of diopside, CaMgS^Og, and 
albite, NaAlSi 3 O g , in the range up to 50 kilobars, 
/. Geophys. Res., 68, 311-323, 1963. 

Fei, Y., Thermochemical - thermophysical data on 
phases in the Mg-Fe-Si-O system: a synthesis of 
theory and experimental data and computation 
of phase equilibrium, Ph.D. dissertation, City 
University of New York, 1989. 

Fei, Y., and S. K. Saxena, A thermochemical data 
base for phase equilibria in the system Fe-Mg- 
Si-0 at high pressure and temperature, Phys. 
Chem. Minerals, 13, 311-324, 1986. 

Ito, E., and E. Takahashi, Post- spinel transforma- 
tions in the system Mg 2 Si0 4 -Fe 2 Si0 4 and some 
geophysical implications, /. Geophys. Res., in 
press, 1989. 

Ito, E., E. Takahashi, and Y. Matsui, The mineral- 
ogy and chemistry of the lower mantle: an impli- 
cation of the ultrahigh-pressure phase relations 



42 



CARNEGIE INSTITUTION 



in the system MgO - FeO - Si0 2 , Earth Planet. 
Sci. Lett., 67, 238-248, 1984. 

Katsura, T., and E. Ito, The system Mg 2 Si0 4 - 
Fe 2 Si0 4 at high pressures and temperatures: 
precise determination of stabilities of olivine, 
modified spinel and spinel, /. Geophys. Res., in 
press, 1989. 

Liebermann, R. C, H. Watanabe, T. Gasparik, C. 
T. Prewitt, and D. J. Weidner, High pressure 
mineral synthesis in USSA-2000, EOS, 67, 361, 
1986. 

Mao, H. K., and P. M. Bell, Design and varieties 
of the megabar cell, Carnegie Inst. Washington 
Year Book, 77,904-908, 1978. 

Mao, H. K., Y. Fei, and T. Gasparik, Multi-cell 
sample chamber in multi-anvil apparatus - a tool 
for high-resolution and high-efficiency experi- 
mental studies, EOS, 70, 471, 1989. 

Remsberg, A. R., J. N. Boland, T. Gasparik, and R. 
C. Liebermann, Mechanism of the olivine-spi- 
nel transformation in Co 2 Si0 4 , Phys. Chem. 
Minerals, 15, 498-506, 1988. 

Rosenhauer, M., H. K. Mao, and E. Woermann, 
Compressibility of (Fe 04 Mg 06 )O magne- 
siowiistite to 264 kbar, Carnegie 
Instn.Washington Year Book, 75, 5 1 3-5 1 5, 1 976. 

Yagi, T., P. M. Bell, and H. K. Mao, Phase rela- 
tions in the system MgO - FeO - Si0 2 between 
150 and 700 kbar at 1000°C, Carnegie Instn. of 
Washington Year Book, 78, 614-618, 1979. 



Partitioning of High Field Strength 

Elements Among Olivine, Pyroxenes, 

Garnet and Calc Alkaline Picroba- 

salt: Experimental Results and An 

Application 

Peter Ulmer 

On chondrite- and MORB -normalized 
trace element plots, the calc-alkaline mag- 
mas of convergent plate margins character- 
istically show depletion of high field 
strength elements (HFSE) such as Ta, Nb, 
Zr, Ti, Hf, and Y relative to the alkaline 



earth and rare earth (REE) elements. This 
characteristic is widely interpreted as an 
imprint of a depleted MORB -type source, 
a possibility that is also consistent with Sr, 
Nd, and Hf isotopic relationships (e.g., 
Morris and Hart, 1 983; White and Patchett, 
1984). On the other hand, the magmas 
show relatively strong enrichments of 
highly incompatible elements (notably Ba, 
K, Rb, Sr, Th) and REE, and these charac- 
teristics are frequently attributed to metaso- 
matism of the mantle source by fluids re- 
leased through dehydration or low-percent- 
age melting of subducting oceanic crustal 
slabs (Green and Ringwood, 1968; Lam- 
bert and Wyllie, 1970; Arculus and Curran, 
1972; Green, 1980). The need for metaso- 
matism is perhaps most strongly suggested 
by modelling results (e.g., Lopez-Escobar 
et ai, 1977) indicating that, for a primor- 
dial or chondritic mantle source, simple 
batch or fractional melting can only yield 
the observed incompatible element con- 
centrations at degrees of melting too low 
(2-5%) to be consistent with major element 
constraints established by experimental 
studies (e.g., Green, 1973). 

The basis of this concept requiring first 
depletion, then metasomatism of the mantle 
source is weak, however, in that reliable 
HFSE partition coefficients have not been 
available for minerals and liquids of appro- 
priate compositions at appropriate pres- 
sure-temperature conditions. In the study 
described here, the crystal/liquid partition 
coefficients of Nb, Ta, P, Zr, Hf , Ti, Y, Sc, 
and V have been determined experimen- 
tally for olivine, clinopyroxene (cpx), 
orthopyroxene (opx), and garnet in equilib- 
rium with a calc-alkaline picrobasaltic melt. 



GEOPHYSICAL LABORATORY 



43 



Table 4. Summary of the Experimentally Determined Crystal/Liquid Partition Coefficients for High 
Field Strength Elements. 



Element 


Garnet 


Cpx 


Opx 


Olivine 


Nb 


0.07 


0.02 


<0.01 


<0.01 


Ta 


0.04 


0.02 


<0.01 


<0.01 


P 


0.10 


0.03 


0.03 


<0.01 


Zr 


0.32 


0.03 


0.03 


0.01 


Hf 


0.44 


0.22 


0.14 


<0.01 


Ti 


0.28 


0.18 


0.10 


0.02 


Y 


2.11 


0.20 


<0.01 


<0.01 


Sc 


2.27 


0.51 


0.33 


0.16 


V 


1.57 


1.31 


0.90 


0.06 



Partition coefficients were determined experimentally using powders of picrobasalt sample RC158c 
(Ulmer, 1988) doped with 1 wt % of oxide of the element. The melting experiments for garnet, cpx, and 
opx were run at 1330°-1340°C at 28 kbar; those for olivine, at 1330°-1350°C at 1 atm with oxygen 
fugacity close to the NNO buffer. 



The picrobasalt (sample RC158c) comes 
from late dikes in the Tertiary calc-alkaline 
Adamello batholith of northern Italy. Pre- 
vious phase-equilibria work showed that 
the rock probably represents primary 
magma because its melt is in equilibrium 
with garnet lherzolite at an upper mantle 
pressure of 28 kbar (Ulmer, 1988). 



Experimental Study 

For garnet and the pyroxenes, the HFSE 
partition coefficients were determined at 
28 kbar and 1330°C, conditions approxi- 
mating the liquidus of the picrobasalt in the 
upper mantle. Doped powders of the rock 
were melted in graphite containers sealed 
in Pt capsules in solid-media, high-pres- 
sure apparatus at the Geophysical Labora- 
tory and ETH-Zurich. Standard 12.5 mm 
and 14 mm talc-.Pyrejc™ assemblies were 



used. Run products typically consisted of 
60-70% melt, as represented by glass and 
quench products, plus stable, unzoned 
crystals of cpx, opx, and garnet. 

For olivine, the HFSE partitioning had 
to be determined from 1-atm experiments, 
because the mineral is not readily stabi- 
lized at liquidus conditions at high pres- 
sures owing to Fe losses from the melt to 
the Pt capsules by way of cracks in graphite 
container and to gains of C0 2 through reac- 
tion of the melt with the graphite. The 1- 
atm experiments were done by the Pt wire 
loop technique at oxygen fugacities close 
to the NNO buffer at 1330°C. 

Run products from all experiments were 
analyzed by electron microprobe for major 
elements and HFSE. No reversals were 
made, but the approach of the HFSE parti- 
tioning to equilibrium was tested by com- 
paring results for runs of 6 and 12 hours. 
For Zr, P, and Ti, test runs of 5 1 hours were 



44 



CARNEGIE INSTITUTION 



100 



c/) 

c 

o 

o 
o 

c 
tr 

0$ 
Q. 



1 F 



2 .1 



.01 



.001 



Zr-Partitioning 

JT* 



\ 



Garnet/Liquid 
Cpx/Liquid 



10 20 30 40 50 

Run duration, hours 



60 



Fig. 26. Variation of the crystal/liquid partition 
coefficients of Zr for garnet and cpx in picrobasal- 
tic liquid as a function of run duration. The error 
bars indicate uncertainties for single runs. 

also made. With the possible exception of 
Zr, the partition coefficients were stable in 
runs longer than 6 hours. The coefficient 
for Zr showed a slight increase from 6 to 1 2 
hours but was the same after 51 hours as at 
12 (Fig. 26). 

The determined partition coefficients 
are summarized in Table 4 and illustrated in 
Fig. 27. Garnet has the highest partition 
coefficients, followed by cpx and opx in 
that order. Solubilities of the HFSE in oli- 
vine were barely detectable by the electron 
microprobe analytical method, so its coef- 
ficients are all low; in fact, only those for Sc 



10 



1 1 



x 

Q .1 



.01 



1 1 r 

-•— Garnet 
-*— Cpx 
-■-- Opx 
—•• Olivine 



T 1 1 I 1 — 3 




Nb Ta 



Sc V 



Fig. 27. Experimentally measured coefficients 
describing the crystal/liquid partitioning of HFSE 
for garnet, cpx, opx, and olivine in picrobasalt 
melt. 




Nb Ta 



Zr Hf 



Fig. 28. (A) Variation diagram for natural HFSE 
abundances in picrobasalt RC158c. Concentra- 
tions are chondrite normalized for all elements 
except Sc and V. Primitive mantle values are from 
Sun and Nesbitt (1977), Sun (1982), Thompson et 
al. (1982). (B) Crystal/liquid partition coefficients 
for the HFSE for garnet in picrobasaltic melt. 

and V are significant. It is evident that, in 
the melting of garnet lherzolite, garnet will 
be the dominant control for all HFSE, but 
cpx could have a substantial subordinate 
influence, especially for Hf, Ti, Sc, and V. 
The opx coefficients are almost as large as 
the cpx coefficients for P, Zr, Hf , Ti , Sc and 
V, but the opx value for Y is lower by an 
order of magnitude. 

The partition coefficients for garnet are 
compared with the chondrite-normalized 
natural HFSE concentrations of the picro- 
basalt in Fig. 28. An inverse relationship is 
revealed, implying strongly that garnet 
largely controlled the HFSE composition 
of the picrobasalt magma during partial 
melting of a garnet lherzolite source. 



GEOPHYSICAL LABORATORY 



45 




100 



wjlj jlj ni m w w. u c_ *— -J h— 

COCC *Z I- _lO CO 2 Q. (ON UJ I 



>££3<8: 



Fig. 29 . The natural trace element pattern of 
picrobasalt RC158c compared with patterns cal- 
culated for melts of a garnet lherzolite source 
using the simple batch-melting equation of Shaw 
(1970) and experimental partition coefficients 
(including those obtained in the present study). 

Application 



Trace element patterns have been calcu- 
lated for partial melts of a garnet lherzolite 
source using the measured HFSE coeffi- 
cients in combination with published coef- 
ficients for other elements (Harrison, 1981; 
Shimizu and Kushiro, 1974; Irving, 1978; 
Hanson, 1980;TerakodaandMasuda, 1979; 
Irving, 1 978). Two sets of calculations were 
made, as illustrated in Figs. 29 and 30. 

For Fig. 29, the following conditions 
were assumed: (1) the source rock was a 
fertile garnet lherzolite composed of 57% 
(by weight) olivine, 19% opx, 12% cpx, 
and 12% garnet; (2) the melting equation 
was that derived in the experimental study 
by Ulmer (1988): 0.582 cpx + 0.388 garnet 
+ 0.031 opx <=> 0.075 olivine + 0.925 
liquid; and (3) after extraction of the melt, 
0.2% liquid remained trapped in the source. 
The simple, non-modal batch melting 
equation of Shaw (1970) was used, and 
partial melting percentages of 5, 10, and 
20% were investigated. The cpx content of 



10 r 





— •- PicriteRC158c 


. 


— ♦-•- 20% batch melting \ 


J> 


— •— 1 6% batch melting ■ 


^^W^V, i 


*Vi 


** 


» ' » I -1 1 1 1 1 i- 1 1 1 1 1 11 11 1 1 1 1 



0) 

*c 

c 
o 

o 

^» 

c 

E 
o 

lli 


O 
CO 



C0.O -O (0 (0 ® ,_ -Q Ei_=Jh-"D._.q E.O 3 O 

CO0C *Z I--JO CO Z O.CONUJIO \-\->\-> -J CO > 

Fig. 30. The natural trace element pattern of picro- 
basalt RC158c compared with patterns calculated 
for aggregated liquid from a garnet lherzolite 
mantle plume using the batch plume melting 
equation of O'Hara (1985). The curve labeled 
20% melting represents a maximum of 20% melt- 
ing in the center of a plume composed of the same 
fertile peridotite assumed in the calculations in 
Fig. 29. The pattern for 16% melting pertains 
similarly to a plume of less fertile peridotite. For 
both calculated patterns, the melting maximum 
represents the stage at which the cpx-content of the 
source rock was exhausted. 



the source is just exhausted at 20% melting. 
The model patterns show that the picroba- 
salt composition can be approximated by 
the simple batch melting equation only if 
the percentage of melting is low, of the 
order of 5% or less. The heavy REE con- 
centrations derived by this equation are too 
low, and the depletion of the HFSE is also 
poorly reproduced. This type of melting 
would indeed require metasomatism of .the 
source to account for the enrichment of the 
highly incompatible elements and REE. 

It is unlikely, however, that the simple 
batch partial melting equation is appropri- 
ate. The mantle source was probably a 
plumelike structure in which temperature 
varied both horizontally and vertically; 
hence the amount of melting probably was 
not constant. O'Hara (1985) has derived al- 
ternative partial melting equations that 



46 



CARNEGIE INSTITUTION 



describe trace element abundances for 
aggregated melt from such a regime. The 
equations are denoted CAPEPM and 
CAPFPM, acronyms for Complex Aggre- 
gated Perfect Equilibrium (or Fractional) 
Partial Melting. They were modified for 
present purposes in such a way that melt 
percentages varied with temperature in 
accordance with 30 kbar experiments on 
the picrobasalt (Ulmer, 1988). The melt 
distribution was approximated by a simple 
analytical function, and the equation was 
integrated numerically from the edge of the 
melting region to its center. The important 
consequence is that, in the aggregated liq- 
uid, the melt from the high-percent-melt- 
ing central part of the plume mostly con- 
trols major element abundances, whereas 
that from the low-percent-melting fringe 
mainly controls the trace elements. 

Trace element patterns from the O ' Hara- 
type equilibrium (batch) calculations are 
compared with the natural picrobasalt pat- 
tern in Fig. 30. The dotted-line pattern 
derives from the same parameters used in 
Fig. 29 for 20% melting at the center of the 
plume. The broken-line pattern represents 
a less fertile source containing only 11% 
cpx and 7% garnet. With it, cpx and garnet 
are both consumed at approximately 16% 
melting. The two calculated patterns both 
match the natural pattern reasonably well, 
but Zr and, to a lesser extent, Hf, Nb, and 
Ta, are not closely reproduced. Possible 
explanations of the discrepancies are: 
(1) The measured distribution coefficients 
for Zr, Hf, Nb, and Ta are too low in 
consequence of the charge doping. The 
doped concentrations are 2-4 orders of 
magnitude larger than the natural abun- 



dances of the picrobasalt; thus the distribu- 
tion coefficients could be outside the range 
of Henry's law (cf. Mysen, 1978; Harrison; 
1981). The reported D-values should be 
regarded as minimum values. 
(2) Some additional mineral might retain 
these elements in the melting range of the 
picrobasalt (cf. Sauders etal., 1980; Green, 
1981). For example, rutile was observed in 
picrobasalt charges melted at 35 - 40 kbar 
at temperatures up to 1150°C. 

The O'Hara model does, however, re- 
produce most of the trace element pattern 
of the natural calc-alkaline picrobasalt from 
a chondritic to primitive mantle source 
without requiring that it be metasomatized. 
Most particularly, it reproduces the enrich- 
ment of LLLE and REE and the depletion of 
the HFSE. The possibility of metasoma- 
tism is not ruled out, but much less is 
necessary than has commonly been con- 
tended. 



References 



Arculus, R. J., and E. B. Curran, The genesis of the 
calc-alkaline rock suite, Earth Planet. Sci. Lett., 
75,255-262,1972. 

Green, D. H., Experimental testing of "equilib- 
rium" partial melting of peridotite under water 
saturated, high-pressure conditions, Can. Min- 
eral., 14, 255-268, 1976. 

Green, T. H. , Experimental evidence for the role of 
accessory phases in magma genesis, J. Vol- 
canol. Geotherm. Res., 10, 405-422, 1981. 

Green, T. H., and A. E. Ringwood, Genesis of the 
calc-alkaline igneous rock suite, Contrib. Min- 
eral. Petrol, 18, 269-385, 1968. 

Green, T. H., Island arc and continent-building 
magmatism - A review of petrogenic models 
based on experimental petrology and 
geochemistry, Tectonophysics, 63, 367-385, 
1980. 



GEOPHYSICAL LABORATORY 



47 



Irving, A. J., A review of experimental studies of 
crystal/liquid trace element partitioning, Geo- 
chim. Cosmochim. Acta, 42, 743-770, 1978. 

Hanson, G. N., Rare earth elements in petrogen- 
etic studies of igneous systems, Ann. Rev. Earth 
Planet. Sci. Lett., 8, 371-406, 1980. 

Harrison, W. J., and B. J. Wood, An experimental 
investigation of the partitioning of REE between 
garnet and liquid with reference to the role of 
defect equilibria, Contrib. Mineral. Petrol., 72, 
145-155,1980. 

Harrison, W. J., Partition coefficients for REE 
between garnets and liquids: implications of 
non-Henry's law behavior for models of basalt 
origin and evolution, Geochim. Cosmochim. 
Acta, 45, 1529-1544, 1981. 

Lambert, J. B., and P. J. Wyllie, Melting in the 
deep crust and upper mantle and the nature of 
low- velocity layer, Phys. Earth Planet. Inter., 3, 
316-322. 

Leeman, W. P., The influence of crustal structures 
on compositions of subduction-related magmas, 
J. Volcanol. Geotherm.Res., 18, 561-598, 1983. 

Lopez-Escobar, L. L., A. F. Frey, and M. Vergara, 
Andesites and High-Alumina basalts from the 
central-south Chile high Andes: Geochemical 
evidence bearing on their pedogenesis, Contrib. 
Mineral. Petrol., 63, 199-228, 1977. 

Morris, J. D., and S. R. Hart, Isotopic and incom- 
patible element constraints on the genesis of 
island arc volcanics from Cold Bay and Amak 
Island, Aleutians, and implications for mantle 
structure, Geochim. Cosmochim. Acta, 47, 2015- 
2033, 1983. 

Mysen, B. O., Experimental determination of nickel 
partition coefficients between liquid, pargasite, 
and garnet peridotite minerals and concentration 
limits of behavior according to Henry's law at 
high pressure and temperature, Am. J. Sci., 278, 
217-243, 1978. 

O'Hara, M. J., Importance of the 'shape' of the 
melting regime during partial melting of the 
mantle, Nature, 314, 58-62, 1985. 

Shaw, D. M., Trace element fractionation during 
anatexis, Geochim. Cosmochim. Acta, 34, 237- 
243, 1970. 

Shimizu, N., and I. Kushiro, The partitioning of 
REE between garnet and liquid at high pres- 
sures: Preliminary experiments, Geophys. Res. 
Lett., 2, 413-416, 1974. 



Sun, S. S., and R. W. Nesbitt, Chemical heteroge- 
neity of the Archean mantle, composition of the 
Earth and mantle evolution. Earth Planet. Sci. 
Lett., 35, 429-448, 1977. 

Sun, S. S., Chemical composition and origin of the 
Earth's primitive mantle, Geochim. Cosmochim. 
Acta, 46, 179-192, 1982. 

Terakoda, Y. and A. Masuda, Experimental study 
of REE partitioning between diopside and melt 
under athmospheric pressure, Geochem. J,, 13, 
121-129, 1979. 

Thompson, R. N., A. P. Dickin, L. L. Gibson, and 
M. A. Morrison, Elemental fingerprints of iso- 
topic contamination of Hebridean Palaeocene 
mantle-derived magmas by Archean Sial, Con- 
trib. Mineral. Petrol, 79, 159-168, 1982. 

Ulmer, P., High pressure phase equilibria of a 
calc-alkaline picro-basalt: Implication for the 
genesis of calc-alkaline magmas, Annual Report 
of the Director of the Geophysical Laboratory, 
Carnegie Instn. Washington, 1987-1988, Geo- 
physical Laboratory, Washington, D. C, 28-35, 
1988. 

White, W. M., and J. Patchett, Hf-Nd-Sr isotopes 
and incompatible element abundances in island 
arcs: implications for magma origins and crust- 
mantle evolution, Earth Planet. Sci. Lett., 67, 
167-185, 1984. 



Relationships Between Composition, 

Pressure and Structure of Depolymer- 

ized, Peralkaline Aluminosilicate 

Melts 

Bjorn O. Mysen 

The structure of silicate liquids at high 
temperature and high pressure, and rela- 
tionships between structure and properties 
are important to characterize natural mag- 
matic processes. Bulk compositions be- 
tween depolymerized (nonbridging oxy- 
gen per silicon; NBO/Si > 0) alka&or alka- 
line earth silicates and fully polymerized 
(NBO/Si = 0) silica - aluminates represent 



48 



CARNEGIE INSTITUTION 



mol % 




rhyolitic 
andesitic J°, 

basaltic ^ 2 9 
30 



40 
komatiitic 



Fig. 36. Approximate fields of major groups natu- 
ral magmatic liquids in in the system MO - A1 2 3 
- Si0 2 (M = K + Na + Ca + Mg + Fe 2+ ) (data from 
Mysen, 1988). 

the structural environment of natural mag- 
matic liquids (see Fig. 36). Their A1/(A1 + 
Si) typically is between 0.2 and 0.3. Alkali 
metals are the principal cations for charge- 
balance of tetrahedrally-coordinated Al 3+ at 
1 atmosphere (Mysen, 1988).The excep- 
tions are picrite andkomatiite. These melts 
are less polymerized and often have lower 
A1/(A1 + Si) than other major groups of 
magmatic melts. 

Silicate melts in this composition range 
(Fig. 36) consist of coexisting structural 
units characterized by their average num- 
ber of nonbridging oxygen per tetrahe- 
drally-coordinated cations (NBO/T) equal 
to (T0 2 , or (^-species), 1( T 2 5 , or Q 3 - 
species), and 2 (T0 3 , or (^-species; see, for 
example, Virgo et al., 1980). The equilib- 
rium in such melts is described with the 
equation (Virgo et al., 1980); 

T 2 5 (Q 3 )^T0 3 (Q 2 ) + T0 2 (Q<), (1) 

where T = Al + Si. The Q 4 , Q 3 and Q 2 
notations are sometimes used in place of 
the stoichiometric designations. The su- 



perscript in the Q-notation denotes the 
number of bridging oxygen in the unit. 

Physical and chemical properties of 
natural magmas depend on the properties, 
detailed structure, and proportions of these 
individual structural units. The relative 
abundance of the different structural units 
is likely to depend on melt polymerization, 
the ionization potential of charge-balanc- 
ing and network-modifying cations, A1/(A1 
+ Si), pressure, and temperature (e.g., 
Mysen et al., 1985; Brandriss and Steb- 
bins, 1988). In order to provide a structural 
framework for quantitative characteriza- 
tion of the properties of natural magma, it 
is necessary to characterize the relation- 
ships between pressure, temperature, and 
the compositional variables. In view of the 
fact that most magmatic processes take 
place at pressures above 1 atmosphere, it is 
particularly important to determine these 
relationships at high pressure. 

Raman spectroscopy (Fig. 37) has been 
used to determine the abundances of indi- 
vidual structural units in the quenched melts. 
All compositions in this study are on the 
join M 2 Si 4 9 - M 2 (MA1) 4 9 (M = K, Na and 
Li; denoted KS4 - KA4, NS4 - NA4 and 
LS4 - LA4), with, therefore, NBO/T = 0.5 
(see Fig. 36). The unit distributions in 
quenched melts probably reflect those near 
the glass transition temperature (T ). One- 
bar samples were formed by quenching at 
~500°C/s in vertical quench-furnaces, 
whereas high-pressure samples (to 30kbar) 
were quenched at ~100°C/s in the solid- 
media, high-pressure apparatus. The abun- 
dances have been determined from calibra- 
tion of area ratios of (Si,Al) - O stretch 
bands in the high-frequency envelopes of 



GEOPHYSICAL LABORATORY 



49 



1 bar 

0.80 - 



T3 °- 60 

g 0.40 t- 



0.30 




0.00 



0.10 0.20 

AI/(AI+Si) 



0.30 




0.00 0.10 0.20 

AI/(AI+Si) 



0.30 



1UU 




/\ AI/(AI+Si)=0.15 


^ 
o^ 




/ \ NBO/T=0.5 


>* „,. 






■t= 75 






co 






c 






CD 


A4+A5 




■- 50 






T5 






CD 






N 






| 25 


A 2 J 


/ U 3 


o 


A 1 ->V 


■ ••^' >/\ 


2 


mrf^ V ' " 


'■\''0->. v 




850 975 1100 1225 1350 

Wavenumber, cm' 1 



Fig. 37. Relationship between area ratios (as indicated) from Raman spectra of quenched melts on the 
join KjS^O, - K 2 (KA1) 4 9 at 1 bar, 12 and 30 kbar. The relevant portion of the high-frequency envelope 
of a typical Raman spectrum with compositional variables as indicated is also shown. 



the spectra (Fig. 37). In order to obtain the 
exact frequencies and areas of individual 
Raman bands, the spectra were fitted statis- 
tically with the method described by My sen 
et al. (1982). The A l is the area of the (Si,Al) 
- O antisymmetric stretch band from T0 3 
units and A 3 from T 2 5 units. The remaining 
bands, against which these areas are nor- 
malized, are from bridging oxygen bonds. 



The relative errors (from the fitting proce- 
dure) in these determinations are between 
10 and 20%. 

The 1-bar relationship between unit 
abundances and A1/(A1 + Si) is shown in 
Fig. 38. Substitution of charge-balanced 
Al 3 * for Si 4 * results in a systematic lowering 
of the abundance of T 2 5 units together 
with a concomitant increase in the more po- 



50 



CARNEGIE INSTITUTION 



0.8 



2 0.6 TOiJQl 




T 2 5 (Q 3 ) 1 A; LS4-LA4 

T0 3 (Q 2 ) 




0.1 0.2 

AI/(AI+Si) 



0.8 

.2 0.6 

+- • 
o 
0$ 0.4 



O 0.2 



0,0 



TO- (Q 4 ) 


i — 

(Q 3 ) 


i 




B 
NS4-NA4 • 


'TOajQfL-^ 







0.1 0.2 0.3 0.4 

AI/(AI+Si) 



0.5 




0.1 0.2 

AI/(AI+Si) 



0.3 



Fig. 38. Mol fraction of structural units in 1-bar, 
temperature-quenched melts as a function of Al/ 
(Al + Si). A - The join LLSi 4 9 - LL(LiAl) 4 9 (LS4 

- LA4), B - The join Na 2 Si 4 9 - Na^aAlJA (NS4 

- NA4), C - The join ICSi 4 9 - IC(KA1) 4 9 (KS4 - 
KA4). 



lymerized tinit, T0 2 and the less polymer- 
ized one, T0 3 . The overall degree of po- 
lymerization of the melts remains constant 
(NBO/T = 0.5) in this process. Thus, quali- 
tatively, increasing A1/(A1 + Si) shifts equa- 
tion (1) to the right. It is notable, however, 
that even in the absence of Al 3+ the larger 
the ionization potential of the network- 
modifying cation (Li > Na > K), the mol 
fractions, X(T0 2 ) and X(T0 3 ), are greater, 
and the X(T 2 5 ) is smaller. This observa- 





50 




40 


CD 




O 








CD 
Q. 


30 


c 




o 




CO 


20 


CD 




Q. 




CO 




b 


io n 



T0 2 ;Q4 




0.0 0.1 0.2 0.3 0.4 0.5 

AI/(AI+Si) 



20 r 



T 2 5 ;Q3 











8 -20 








w. 








CD 
CL 


x\ \ 






- -40 








c 








o 






Li 


o - 60 


\ 






CL 








CO 

Q -80 




N. Na 




-mn 


I ■ 




— i 



0.0 0.1 0.2 0.3 

AI/(AI+Si) 



0.4 




-200 



0.0 0.1 



0.2 0.3 0.4 

AI/(AI+Si) 



0.5 



Fig. 39. Dispersion of structural units (as indicated 
on the panels) as a function of A1/(A1 + Si) and the 
type of network-modifying and charge-balancing 
cation. 



GEOPHYSICAL LABORATORY 



51 



0.80 r 



O 0.60- 




10.0 r 



n^^s 



AI/(AI+Si) 



0.80 r 



g 0.60 

"«£■? 

o 
£: 0.40 r 



0.20 - 



12kbar 



T0 2 (Q 4 ) 



TCb(tf) 



0.00 
0.0 



0.80 



§ 0.60 

cO « , A 
£: 0.40 - 



0.20 - 



0.00 




0.1 0.2 

AI/(AI+Si) 



0.3 



30 kbar 



T0 2 (Q 4 ) 

T0 3 (Q 2 ) 
T 2 5 (OP) 



o.o 



0.1 0.2 

AI/(AI+Si) 



0.3 



Fig. 40. Mol fraction of structural units in K^S^O, 
- K^KAl^melts as a function of A1/(A1 +Si) at 
the pressures indicated. 

tion accords with results from 29 Si NMR 
spectroscopy of analogous melt composi- 
tions (Stebbins, 1987). 

For the compositions studied here, the 
alkali metals also serve to charge-balance 
Al 3+ in tetrahedral coordination. It is evi- 




-40.0 



0.00 



0.10 0.20 

AI/(AI+Si) 



0.30 



10.0r 




-40.0 



0.00 0.10 0.20 0.30 

AI/(AI+Si) 

Fig. 41 . Free energy (AG) for equilibrium ( 1) at the 
glass transition temperature (AG Tg ) and at 273K 
{AG™) for melts on the join K^O, - K^KAl)^ 
as a function of pressure as indicated. 

dent that the influence of Al/Al + Si) on 
equation (1) at 1 bar also depends on the 
charge-balancing cation (Fig. 39). The 
increase (or decrease) in mol fractions of 
the coexisting structural units, relative to 
the abundance in the Al-free end-member 
silicate melts is termed dispersion. The dis- 
persion is more pronounced (K > Na > Li) 
the smaller the ionization potential of the 
cation. 

The distribution of structural units as a 
function of A1/(A1 + Si) follows the same 
general trends at high pressure (Fig. 40) as 



52 



CARNEGIE INSTITUTION 



at 1 bar (Fig. 38) at least for the potassium 
tetra-aluminosilicate quenched melts. 
Qualitatively, from the abundance infor- 
mation in Fig. 40, at a given A1/(A1 + Si), 
the X(T 2 5 ) tends to be lower at higher 
pressure, thus indicating a shift of equation 
(1) to the right. Such a trend has also been 
suggested for Al-free KS4 quenched melts 
reported by Dickinson et al. (1985). 

Under the assumption of ideal mixing 
of the structural units, the free energy of 
reaction (1) can be calculated (Fig. 41). 
Although the viscosity of these melts proba- 
bly decreases with increasing pressure 
(Kushiro, 1976), and, therefore, the glass 
transition temperature probably also de- 
creases (e.g., Rosenhauer et al., 1979). 
This effect has not been taken into account 
as the exact relationship between pressure 
and T is not known for these melts. Also 
shown in Fig. 41 are the free energy data at 
273K calculated with the AS-value (5 J/mol 
K) suggested by Stebbins (1989). In light 
of available high-temperature calorimetric 
data (see Richet and Bottinga, 1986, for 
summary), temperature-dependence of ACp 
for equation (1) is not considered. 

It is clear (Fig. 41) that not only does the 
AG decrease with increasing A1/(A1 + Si) at 
constant pressure, but increasing pressure 
generally results in a further decrease in AG 
for all aluminum contents studied. The 
pressure effect on AG for reaction (1) is 
further enhanced as a function of increas- 
ing aluminum content. Thus, as suggested 
from density measurements on fully po- 
lymerized (NBO/T = 0) alkali aluminosili- 
cate melts (e.g., Kushiro, 1980), depolym- 
erized (NBO/T > 0) aluminosilicate melts 
become increasingly compressible as Al 



20 r 





10 


o 




F 




c^ 





E 




o 


-10 


> 




< 


-20 



-30 




30 kbar 



J i I i L 



J i I 



0.0 



0.1 



0.2 



3+ 



AI/(AI+Si) 

Fig. 42. Volume change, AV, for equilibrium (1) at 
30 kbar as a function of A1/(A1 + Si) for melts on 
the join K^i fi 9 - ^(KAl^O,. 



is substituted for Si 4+ (Fig. 42) at least for 
the potassium tetra-aluminosilicate com- 
positions. 

The shift of reaction (1) to the right with 
increasing ionization potential of the net- 
work-modifying cation probably is a result 
of local electric charge constraints. That is, 
geometric constraints increasingly tend to 
prevent neutralization of the negative charge 
in the anionic network the smaller the net- 
work-modifying metal cation. This prob- 
lem compounds as theNBO/Si of a particu- 
lar structural unit decreases. Notably, among 
crystalline alkali silicates, only potassium 
forms a stable tetrasilicate. Potassium and 
sodium form stable disilicate crystalline 
materials, whereas no lithium disilicate is 
known. In melts where more than one de- 
polymerized structural unit is present, the 
smaller cations will prefer the least polym- 
erized unit, and, thus, drive, reactions such 
as (1) to the right. 

The aluminum distribution between the 
structural units is governed by the differ- 
ences in intertetrahedral angles (a) be- 



GEOPHYSICAL LABORATORY 



53 



tween the various units, and will favor the 
unit with the smallest intertetrahedral angle 
(Mysen et al., 1985). As a(T0 2 ) < a(T 2 5 ) 
< a(T0 3 ) (Furukawaef a/., 1981),Al 3+ will 
then substitute preferentially for Si 4+ in the 
T0 2 units, thus driving equation (1) to the 
right. 

Finally, because the intertetrahedral 
angle in fully polymerized structural units 
depends on pressure (Seifertet al., 1983), it 
is suggested that the compressibility of the 
individual coexisting units in melts govern 
the influence of pressure on reaction (1). 
Among the coexisting units in tetrasilicate 
and tetra-alumino silicate melts, the T0 2 
structure is much more compressible than 
either the T 2 5 or the T0 3 (Bockris and 
Kojonen, 1960). These compressibility 
relations have two consequences. First, 
because (dV/dP) T < even for Al-free sili- 
cate melts, equation (1) shifts to the right. 
Second, by substituting charge-balanced 
Al 3+ for Si 4+ , the X(T0 2 ) increases, thus 
increasing the bulk compressibility. Fur- 
thermore, the A1/(A1 + Si) in the T0 2 units 
increases. This increase lengthens the 
(Si,Al)-0 bridging bonds, and the oc(T0 2 ) 
becomes smaller. This angle is expected to 
be more compressible. All these factors 
serve to enhance the bulk melt compressi- 
bility. Thus, the observed enhancement of 
bulk melt compressibility with increasing 
A1/(A1 + Si) would be expected. 

The pressure-composition relationships 
provides a rationale to understand the be- 
havior of natural magmatic liquids under 
pressure, (i) As indicated in Fig. 36, mag- 
matic liquids become more polymerized 
with increasing silica, or alumina, or both. 
Thus, the relative abundance of T0 2 units 



in the melts increases. As a result, the molar 
volume and the melt compressibility of 
magmatic liquids increase in the order 
komatiite < basalt < andesite < rhyolite. (ii) 
For basaltic melts, high-aluminum basalt is 
more compressible than tholeiite even 
though their NBOITdst practically the same 
(Mysen, 1988). This behavior is the result 
of the higher A1/(A1 + Si) in the high- 
alumina basalt as compared with tholeiite. 
This higher A1/(A1 + Si) shifts reaction (1) 
to the right thus enhancing the melt com- 
pressibility, (iii) The bulk composition of 
alkali basalt and tholeiite differs princi- 
pally in the values of the average ionization 
potential (Z/r) of the charge-balancing metal 
cations. The (Z/r) a]kalibasalt < (Z/r\ olciisc with the 
result that AG of reaction (1) for alkali 
basalt is smaller (more negative) resulting 
in greater compressibility. Relationships 
similar to (i-iii) would also be expected for 
all other melt properties that depend on the 
abundance and character of bridging oxy- 
gen bonds in T0 2 units in the magmatic 
liquids. 



References 



Bockris, J. O., and F. Kojonen, The compressibil- 
ity of certain molten alkali silicates and borates, 
/. Am. Chem. Soc., 82, 4493-4497, 1960. 

Brandriss, M. E., and J. F. Stebbins, Effects of 
temperature on the structures of silicate liquids: 
29 Si NMR results, Geochim. Cosmochim. Acta, 
52, 2659-2669, 1988. 

Dickinson, J. E., and C. M. Scarfe, Pressure- 
induced structural changes in K^S^O, silicate 
melt, EOS, 66, 395, 1985. 

Furukawa, T., K. E. Fox, and W. B. White, Raman 
spectroscopic investigation of the structure of 



54 



CARNEGIE INSTITUTION 



silicate glasses. IE. Raman intensities and struc- 
tural units in sodium silicate glasses, /. Chem. 
Phys., 153, 3226-3237, 1981. 

Kushiro, I., Changes in viscosity and structure of 
melt of NaAlS^Og composition at high pressures, 
/. Geophys. Res., 81, 6347-6350, 1976. 

Kushiro, I., Viscosity, density, and structure of 
silicate melts at high pressures, and their petrol- 
ogical implications, in Physics of Magmatic 
Processes, R. B. Hargraves, ed., Princeton Uni- 
versity Press, Princeton, Ch. 3, 1980. 

Mysen, B. O., Structure and Properties of Silicate 
Melts, Elsevier, Amsterdam, 354 pp., 1988. 

Mysen, B. O., L. W. Finger, F. A. Seifert, and D. 
Virgo, Curve-fitting of Raman spectra of amor- 
phous materials, Am. Mineral., 67, 686-696, 
1982. 

Mysen, B. O., D. Virgo, and F. A. Seifert, Rela- 
tionships between properties and structure of 
aluminosilicate melts, Am. Mineral, 70, 834- 
847, 1985. 

Richet, P., and Y. Bottinga, Thermochemical 
properties of silicate glasses and liquids: A 
review, Rev. Geophys., 24, 1-26, 1986. 

Rosenhauer, M., C. M. Scarfe, and D. Virgo, 
Pressure dependence of the glass transition 
temperature in glasses of diopside, albite and 
sodium trisilicate composition, Carnegie Instn. 
Washington, Year Book, 78, 556-559, 1979. 



950°C 
2kbar 




En 
Mol Percent 



Fo 



Fig. 31. Potassium analogue of the extended nor- 
mative, basalt tetrahedron Ks - La - Fo - Qz 
exhibiting stable joins determined experimentally 
at 950°C and 2 kbar. 



Ak 


akermanite 


Lc 


leucite 


Di 


diopside 


Mer 


merwinite 


En 


enstatite 


Mo 


monticellite 


Fo 


forsterite 


Ra 


rankinite 


K-mel 


potassium melilite 


Sa 


sanidine 


Ks 


kalsilite 


Qz 


quartz 


La 


larnite 


Wo 


wollastonite 



Igneous and Metamorphic Facies of 
Potassium-rich Rocks: Coexisting as- 
semblages in Kalsilite-Forsterite- 
Larnite-Quartz at 950°C and 2 kbar 
With and Without H 2 0. 

Hatten S. Yoder, Jr. 

The wide variety of potassium-rich 
igneous and metamorphic rocks appears to 
result primarily from the great diversity of 
bulk composition and from the large num- 
ber of reactions between phases (Yoder, 
1986). The mineralogical complexity of 
the final products probably results from 



incomplete or failed reactions as the mag- 
mas cool. For this reason an effort was 
made to establish experimentally a stable 
array of assemblages with which observed 
and alternative assemblages could be 
compared. 

The principal minerals involved in an- 
hydrous potassium-rich rocks are displayed 
in Fig. 3 1 . The tetrahedron is the potassium 
analogue of the extended basalt tetrahe- 
dron (Schairer and Yoder, 1964) wherein 
kalsilite replaces nepheline. The joins 
connecting coexisting phases were estab- 
lished by experiments at 950°C and P=2 
kbar of 5 days duration. Stable assem- 
blages were determined by reacting natural 



GEOPHYSICAL LABORATORY 



55 



minerals close to endmember composition, 
synthetic endmembers, or both, in compat- 
ible and incompatible combinations. The 
experiments were carried out in an inter- 
nally-heated, gas-media, high-pressure 
apparatus (Yoder, 1950). Over 60 mixtures 
of compatible and incompatible phases were 
reacted to establish the stable joins for both 
the anhydrous and hydrous tetrahedrons at 
isothermal, isobaric conditions. The condi- 
tions 950°C and 2 kbar were chosen so that 
there was adequate pressure to stabilize the 
appropriate hydrous minerals, and at a 
sufficiently high temperature to be at or 
near the beginning of melting, yet above 
the stability of the amphiboles. 

To illustrate the strategy in determining 
these joins under anhydrous and hydrous 
conditions, the join Di (CaMgSi 2 6 ) - Ks 
(KAlSi0 4 ) will be used as an example. 
(Abbreviations are defined in the caption 
of Fig. 31). 

The reactions investigated that prove 
that Di-Ks is the stable join are: 



Fo + 3Lc + 2Ak -> 4Di + 3Ks 



(1) 



H 2 



Fo + 3Lc + 2Ak -> 4Di + 3Ks (2) 



Ph + 3Ak + 4Lc -> 6Di + 5Ks + HX)(3) 



Mo + Lc -> Di + Ks 



2Mo + Sa -> 2Di + Ks 



h 2 o 
2Mo + Sa -> 2Di + Ks 



(4) 



(5) 



(6) 



12Di + 5Y-ALP3 + 5[K 2 02Si0 2 ] 

-> 12Di + lOKs ' (7) 



Dol + Sa -> Di + Ks + 2C0 2 . (8) 



The Di-Ks join is critical because it pene- 
trates the common assemblage Mel+Fo+Lc 
of the katungites. Note that the join is stable 
under both hydrous and anhydrous condi- 
tions. (The hydrous tetrahedron is presented 
below.) Reactions 4-6 show that monticel- 
lite is not stable with either Lc or Sa at these 
conditions - it is cut by the planes Ak - Ks 
- Fo and Di-Ks - Fo. Reaction 7 was a test 
of the alkali-loss problem experienced in 
the past. To avoid alkali loss, it was usually 
necessary to use natural minerals close to 
the end members or well characterized 
synthetic phases. The last reaction is the 
well known metamorphic reaction observed 
at Brome Mt., Quebec, and Hendrickspla- 
ats, RSA. 

In order to appreciate the value of the 
tetrahedron and clarify the relationships, 
the various subtetrahedra are presented in 
an exploded view in Fig. 32. The subtetra- 
hedral volumes are labelled with the appro- 
priate rock names underlined. The faces 
and joins have also been labelled where 
rock names have been assigned. (Alkali- 
rich rock enthusiasts have, fortunately, 
missed naming a few of the joins). Begin- 
ning at the left, the kalsilite-rich end, the 
principal mineral assemblage for the me- 
lilite mafurites, Mel + Ks + Cpx + Fo, is 
found. Passing through the mafurites, Ks + 
Cpx + Fo, one comes to the leucite mafu- 



56 



CARNEGIE INSTITUTION 



Wo Wo Wo 




r"y Hy 



Fo Fo Fo 



Fig. 32. Exploded view of generalized subtetrahedra in Fig.3 1 with names of closely related rock types 
inscribed. Names for four-phase volumes are underlined. 



Cpx 


clinopyroxene 


Mel 


melilite 


Hy 


hypersthene 


Ol 


olivine 


Kf 


potassium feldspar 







rites. Then, through the ugandites, Lc + 
Cpx + Fo, the absarokite assemblage is 
next encountered. The adjoining assem- 
blages are the cancalites and finally the 
chamockites. Illustrated in the subtetrahe- 
dra on the top row of Fig. 32 are those 
assemblages of monticellite -bearing rocks 
related to the kimberlites to be discussed 
below. Potassium melilite (K-Mel) did not 
form on the join Ks-Wo under either anhy- 
drous or hydrous conditions at this pressure 
and temperature. The vesbites, common in 
the Roman region of Italy, are next exhib- 
ited. The two upper subtetrahedra on the 
right are very rare metamorphic assem- 
blages. 

The point to be emphasized is that all of 
these rock types may be stable at the same 
pressure and temperature under anhydrous 
conditions. Thermodynamically, all com- 



950°C 
P H 2 o = 2kbar 




En 
Mol Percent 



Fo 



Fig. 33. Potassium analogue of the extended nor- 
mative basalt tetrahedron Ks - La - Fo - Qz exhib- 
iting stable joins determined experimentally at 
950°C with PiUfi) = 2 kbar. 

Mg-Cel magnesium celadonite 
Ph phlogopite 

Tr tremolite 

See Fig. 31 for definition of abbreviations of 
anhydrous phases. 



GEOPHYSICAL LABORATORY 



57 




Hy Hy 



Fig. 34. Exploded view of generalized subtetrahedra by Fig. 33 with names of closely related rock types 
inscribed. Abbreviations given in Figs. 32 and 33. 



positional space must be represented by a 
stable or metastable assemblage at every 
pressure and temperature. Displayed is the 
entire array of stable assemblages, which 
describe a consistent set of rock types and 
show their compositional relationships. 

The hydrous tetrahedron at the same 
pressure and temperature is displayed in 
Fig. 33. The anhydrous phases are the same. 
Phlogopite is the key hydrous phase and 
joins radiate out to all the principal phases 
except Qz, Wo, and, contrary to natural 
occurrences, Mo. Phlogopite is the phase 
that appears to provide liquid lines of de- 
scent through many of the thermal barriers 
in the flow sheet developed for the anhy- 
drous potassium-rich lavas (Yoder, 1986). 
The theoretical mica, magnesium celadonite 
(Mg-Cel), lies on the join Sa - En, but it did 
not form under the applied conditions. The 
amphibole tremolite (Tr) lies on the face Di 
- En - Qz. It is stable only up to 890°C at 2 



kbar, and was, therefore, not encountered. 
On the other hand, tremolite was a useful 
starting material because joins with other 
phases penetrated a large number of other 
planes. 

The significance of these stable assem- 
blages, all proven experimentally, can be 
appreciated in an exploded view of the 
individual subtetrahedra in the hydrous 
tetrahedron in Fig. 34. Only six of the 
previous subtetrahedra in the anhydrous 
tetrahedron persist. Note again that Mo is 
cut off from Lc and Sa, whereas Ak is stable 
with Lc, but not Sa, as observed in natural 
rocks. The principal mineral assemblages 
are assigned the names of the most repre- 
sentative rock types. The Italian and Afri- 
can provinces are represented in the upper 
left two subtetrahedra. One may begin a 
review of the array of assemblages with the 
okaites and katungites. These adjoin the 
alnoites, a major member of the lampro- 



58 



CARNEGIE INSTITUTION 



phyres. After passing through the verites, 
one comes to the mica peridotites. These 
rocks are contiguous with the lamproites, 
represented by the jumillites and orendites. 
The lamproites in turn adjoin sequentially 
the basic and acid charnockites. The in- 
credible array of rock types may be stable 
at the same pressure and temperature. It is 
not necessary, therefore, to assign special, 
exotic pressure and temperature conditions 
to explain the assemblages represented by 
kimberlite, lamprophyres, lamproites or 
charnockites. The critical question to be 
resolved is how the large range of bulk 
composition was generated. 

Special note should be made of the 
absence of the join Mo - Phi so critical to 
the Group I variety of kimberlite. The planes 
Ak-Ks-XandAk-Fo-XcuttheMo-Phl 
join. The X represents a K - Mg-rich fluid, 
not yet adequately characterized, that is 
required to account for mass balance. The 
composition X is of exceptional impor- 
tance because there appears to be a fluid 
available for metasomatism that is comple- 
mentary to phlogopite. In other words, 
phlogopite is an indicator that a metasoma- 
tizing solution was produced and is not 
itself a product of that solution. From this 
viewpoint, phlogopite may form at the same 
time the metasomatizing fluid is generated; 
for example, by reaction of Fo+Ks with 
H 2 0. It will be illuminating to reexamine 
the textural relations of phlogopite in kim- 
berlites with this concept in mind. 

These results are for exactly one pres- 
sure, 2 kbar, and one temperature, 950°C. If 
the temperature is raised or lowered 100°C, 
another ensemble of assemblages will be 
generated. In addition, a modest pressure 



Ks 



950°C 
P H20 =2kbar 




Fo 



En 
Weight Percent 



Fig. 35. The system Ks - Fo - Qz at 950°C and 
PQlfi) = 1 kbar. Abbreviations as in Figs. 32 and 
33. L = liquid. 



increase of 5-10 kbar will eliminate me- 
lilite, monticellite, and leucite — some of 
the principal phases in these assemblages. 
Melting was not observed in the anhy- 
drous tetrahedron, but melting was ob- 
served in the charnockite subtetrahedra 
under hydrous conditions (Fig. 35). Only 
the base plane of the tetrahedron is dis- 
played to reduce the complexity. Melting 
begins near the alaskite join previously 
investigated by Shaw (1963). All of the 
major phases except Fo and Ks are on the 
liquidus. The significance of these obser- 
vations is that the charnockites and related 
migmatites may be partially melted while 
all the other rock types will be in a crystal- 
line state. These results suggest that mig- 
matites, formed in several ways, do not 
necessarily imply a hot spot — difficult to 
explain thermally — but may indicate a 
regional temperature rise where all the 
surrounding related rock types may remain 
stable in the solid state. For this reason it 



GEOPHYSICAL LABORATORY 



59 



will be necessary in the future to relate 
igneous facies with ultrametamorphic fa- 
des for the entire array of compositions in 
order to characterize the pressure and 
temperature. 

The results provide a consistent en- 
semble of assemblages from which com- 
patible and incompatible mineral assem- 
blages in K-rich rocks can be determined. 
The complexity of the alkaline rocks ap- 
pears to result primarily from variations in 
bulk composition, however the large num- 
ber of potential reactions between phases 
(Yoder, 1986) contribute to further com- 
plexity when the successive reactions are 
incomplete. Because of the large number of 
phases in alkaline rocks, the textural rela- 
tions (e.g., rimming, morphology, and 
zoning) may be of great importance in 
revealing the sequence of reactions. 

References 



Schairer, J. F., and H. S. Yoder, Jr., Crystal and 
liquid trends in simplified alkali basalts, Carne- 
gie Instn. Washington Year Book, 63, 65-74, 
1964. 

Shaw, H. R., The four-phase curve sanidine - 
quartz -1 iquid - gas between 500 and 4000 bars, 
Am. Mineral., 48, 883-896, 1963. 

Yoder, H. S., Jr., High-low quartz inversion up to 
10,000 bars, Trans. Am. Geophys. Union, 31, 
827-835, 1950. 

Yoder, H. S., Jr., Potassium-rich rocks: Phase 
analyses and heteromorphic relations, J. Petrol., 
27, 1215-1228, 1986. 



Techniques for Experimentally Loading 
and Analyzing Gases and Their Appli- 
cation to Synthetic Fluid Inclusions 

John D. Frantz, Yi-gang Zhang, 

Donald D. Hickmott, and 

Thomas C. Hoering 

Experimental studies of equilibria be- 
tween minerals and mixed-volatiles under 
hydrothermal conditions have long been a 
research focus for many experimentalists. 
One of the principal difficulties in experi- 
mentally investigating reactions between 
minerals and mixed volatiles under hy- 
drothermal conditions is loading the ex- 
perimental charges with gas mixtures of 
known composition. In the past, gas load- 
ing was accomplished primarily by the 
addition of solid compounds that produced 
volatiles in the experimental charge. For 
example, silver oxalate was used as a source 
of carbon dioxide (Holloway etal., 1968); 
iridium carbonyl, to produce carbon mon- 
oxide (Eggler et al., 1979); oxalic acid, as 
a source of carbon dioxide, water, and 
hydrogen (Holloway and Reese, 1974); 
chromium nitride, to produce nitrogen or 
ammonia if used in conjunction with an 
external oxygen buffer (Hallam and Eug- 
ster, 1976); acetic acid, as a source 6f 
carbon dioxide and methane (Seitz et al, 
1987; Palmer and Drummond, 1986); and 
graphite to produce carbon dioxide, carbon 
monoxide, and methane when used in 
conjunction with an external oxygen buffer 
(French, 1966; Eugster and Skippen, 1967). 
The applications of these procedures have 
been instrumental in many studies impor- 
tant to our understanding of equilibria be- 



60 



CARNEGIE INSTITUTION 



K 




VACUUM 



Details of I 




Fig. 43. Gas pipette apparatus. See text for details. 



tween metamorphic mineral assemblages 
and mixed volatiles (Skippen, 1971; Jacobs 
and Kerrick, 1981). 

The use of these compounds, however, 
has limitations. For example, at tempera- 
tures below 700°C, graphite reacts slowly 
with C-O-H gases (Ziegenbein and Johan- 
nes, 1980). Below 600°C, the breakdown 
of acetic acid is sluggish (Palmer and 
Drummond, 1986). Chromium nitride does 
not decompose completely under hydroth- 
ermal conditions and thus cannot be used 
quantitatively to add fixed amounts of gas 
to an experimental charge. Compounds such 
as oxalic acid, ammonium oxalate, and 
ammonium nitrate decompose to yield 
unwanted gas species such as hydrogen or 
oxygen (Holloway and Reese, 1974). 
Continuously variable gas compositions in 



ternary and quaternary gas mixtures such 
as the C-O-H and C-O-H-N systems are 
difficult to achieve by the addition of stoi- 
chiometric compounds. For research in- 
volving mixed volatiles in synthetic fluid 
inclusions, a relatively fixed ( and known) 
distribution of gas species must be achieved 
shortly after the experimental temperature 
and pressure is reached because inclusions 
form rapidly, trapping the current fluid 
compositions. Seitz et al. (1987) demon- 
strated a large variability in the carbon 
dioxide-methane ratio for different inclu- 
sions in the same sample. The synthetic 
fluid inclusion sample contained carbon 
dioxide, methane, and water generated by 
the addition of acetic acid and water to the 
charge. Due to these limitations, develop- 
ment of a new technique for loading mixed 



GEOPHYSICAL LABORATORY 



61 



volatiles in hydrothermal experiments was 
desirable. 

In order to load volatiles quantitatively 
in experimental hydrothermal charges, a 
gas pipetting apparatus was constructed of 
Pyrex glass shown in Fig. 43. The system 
consists of a gas storage section (separated 
from the rest of the system by valves A, D, 
and F), a measured gas aliquot section 
(between valves F and //), a vacuum 
manifold K with a vacuum gauge, and the 
sample holder/. Gas is first introduced into 
the gas storage section that consists of a 
2000 ml flask C, a 100 ml flask £, and a 
mercury manometer E. The small flask can 
be used to purify gases, such as C0 2 , which 
have relatively high condensation tempera- 
tures of gas impurities with lower conden- 
sation temperatures such as methane, nitro- 
gen, and oxygen. This is accomplished by 
immersing the small flask in liquid nitro- 
gen and evacuating the system by opening 
valve D and exposing the storage section to 
the vacuum manifold. In the case of load- 
ing gases with low condensation tempera- 
tures, gas impurities having high conden- 
sation temperatures can be condensed into 
the cold finger G by immersing it in liquid 
nitrogen bath with valve F open. Valve F is 
then closed, the liquid nitrogen bath is 
removed, and the gas impurities in the gas 
aliquot section are evacuated. With valves 
A, D, and H closed and F opened, a small 
quantity of gas can be introduced into the 
gas aliquot section. By having previously 
evacuated this section (using valves H and 
7), the pressure of gas introduced into this 
section can be determined with the second 
manometer and a cathetometer. After evacu- 
ating the sample holder section, the gas 



aliquot section can then be opened to the 
sample holder section by opening valve H 
(valve / closed). The sample holder con- 
sists of a 1/2" Swagelock™ 1 union (L) with 
Teflon ferrules (to connect the holder to the 
1/2" glass tubing used in the pipette appa- 
ratus), a valve (M), a 1/4" Swagelock™ 
union with Teflon ferrules (N), and a noble- 
metal capsule with the bottom end welded 
(0). Electronic pressure transducers could 
be used to replace the above-mentioned 
mercury manometers. 

The volume of the gas aliquot section 
was calibrated by connecting a glass bulb 
fitted with a stopcock. The volume of the 
bulb has been determined accurately by 
weighing it when filled with mercury and 
subtracting the weight of the empty volu- 
metric. Then, carbon dioxide gas is al- 
lowed to enter both the gas aliquot and 
sample holder sections with the valve on 
the calibration volumetric open. After the 
pressure is measured, the valve on the cali- 
bration bulb is closed and both sections are 
evacuated through the vacuum manifold. 
Next, the valve on the calibrated volumet- 
ric is opened and all the carbon dioxide is 
transferred into the gas aliquot section by 
immersing the cold finger (G) into liquid 
nitrogen. After closing valve H and allow- 
ing the carbon dioxide to warm to room 
temperature, the pressure on the manome- 
ter is again measured. Because we know 
the volume and the gas pressure that ex- 
isted in the calibrated volume and we know 
the final gas pressure of the same quantity 
of gas in the gas pipette section alone, the 
volume and the number of moles of gas 
contained in the gas pipette section can be 
computed for that particular pressure using 



62 



CARNEGIE INSTITUTION 



D) 

X 

E 
E. 

Z3 

</) 



o 

Q. 
(0 

> 



Moles (x10" 4 ) 



ono _ 


2 

i 


4 6 8 

i i < 


10 

i 


^uu 












Ny 


(a) 


100 - 




/ CH 4 .N 2 






"*"^*^'^7 


^ CH 4 


COo 






r • 



10 20 30 40 

Total Pressure (mm Hg) 



Moles (x10" 4 ) 




o 

Q_ 

05 20 40 60 80 10 

Total Pressure (mm Hg) 

Fig. 44. (a), (b) Vapor pressure of nitrogen, meth- 
ane, carbon dioxide, and 50-50 mole% methane- 
carbon dioxide mixture above 38 mg silica gel as 
a function of the pressure and number of moles of 
the gases in the measured gas aliquot section of the 
gas loading apparatus. 

the ideal gas law. This calibration was done 
at a series of pressures because the volume 
of the manometer contributes to the vol- 
ume of the gas pipette section. 

A quantity of gas in the gas aliquot 
section is transferred to the experimental 
capsule by opening valve H to the evacu- 
ated sample holder section and drawing the 
gas into the capsule by immersing it in 
liquid nitrogen. In the case of carbon diox- 
ide, the resultant vapor pressure above the 



frozen gas is less than lxlO" 4 mm mercury 
at -195.8°C and the transfer is complete. In 
the case of other gases, there may be sig- 
nificant vaporpressure above the condensed 
gas at liquid nitrogen temperatures. It is 
well known that solid compounds with 
pore structures absorb gases strongly at 
low (liquid nitrogen) temperatures. When 
dealing with gases having significant va- 
por pressures at liquid nitrogen tempera- 
tures, the adsorbtion by porous solids is 
advantageous since substantial vapor pres- 
sures above the condensed gases at liquid 
nitrogen temperatures introduce appre- 
ciable error. A gel, zeolite, or some other 
compound that adsorbs gases at cryogenic 
temperatures is placed in the capsule with 
the charge. Due to the properties of adsorp- 
tion of these compounds, the resultant vapor 
pressures are quite reduced. In Fig. 44a, the 
vapor pressures above 38 mg of silica gel 
for nitrogen, methane, carbon dioxide, and 
methane -nitrogen mixtures are plotted as a 
function of both the total pressure and the 
number of moles of the gas or gas mixture 
contained in the measured gas aliquot sec- 
tion of our apparatus (Fig. 43). In the case 
of nitrogen, for example, the vapor pres- 
sure of liquid nitrogen is 760 mm mercury 
and quantitative transfer without the use of 
a gas adsorbing compound is not possible. 
When nitrogen is adsorbed, however, the 
vapor pressure is only 6 mm Hg (using 38 
mg gel) for 0.0001 mol of the gas (Fig. 
44b). In the case of methane, the vapor 
pressure is even lower. A vaporpressure of 
less than 1 mm Hg occurs for 0.001 mol of 
methane, allowing the addition of precisely 
known quantities of the gas. Addition of 
more gel will result in lower vapor pres- 



GEOPHYSICAL LABORATORY 



63 



f~\ 




Au 
Capsule 

Silica 
Gel 

Quartz 
Prism 

Pt Capsule 
Water 



Fig. 45. Experimental capsule detail. 

sures and the possibility of adding a larger 
quantity of gas. This technique can be used 
for any mixture such as carbon dioxide + 
methane or carbon dioxide + methane + 
nitrogen containing a non-condensed gas. 
The use of an adsorbing compound is vital 
in this case because significant partitioning 
between the condensed and solidified gases 
and the coexisting vapor would occur with 
mixtures comprised of gases with varying 
vapor pressures at liquid nitrogen tempera- 
ture. With respect to C0 2 - CH 4 mixtures, 
best results were obtained by first loading 
pure carbon dioxide into the capsule. By 
keeping the capsule at liquid nitrogen 
temperature, pure methane can then be 
added. Carbon dioxide appears to freeze 
before being adsorbed by the gel and thus 
the capacity of the gel for methane is not 
reduced by the presence of carbon dioxide. 
In fact, the resultant vapor pressure is even 
somewhat less than in the case of pure 
methane possibly indicating adsorption of 
methane on solid carbon dioxide. 



Water, however, cannot be directly added 
to the capsule as it may saturate the porous 
solid. To overcome this problem, a length 
of 2 or 3 mm platinum tubing is completely 
filled with water and a section correspond- 
ing to the length containing the desired 
quantity of water is cut and cold welded on 
both ends using a pinch-off device 
(Komarneni et ai, 1979). This inner cap- 
sule is placed in the larger capsule. After 
the loading procedure is complete, the 
portion of the capsule containing the ex- 
perimental charge is cut and cold welded 
using the pinch-off device and, while the 
capsule remains in the liquid nitrogen, is 
electrically welded. A vacuum-tight cold 
weld is essential as a large amount of air 
can be drawn into the capsule by the ab- 
sorbing solid before the capsule is electri- 
cally welded. The capsule is then removed 
from the nitrogen, checked for leaks in 
water, and placed in the hydrothermal pres- 
sure vessel. Such a welded capsule can 
safely hold 100 bar of pressure. Upon 
heating, the absorbing solid releases the 
gases and the inner platinum capsule con- 
taining water ruptures, releasing water, 
producing a mixed volatile fluid of known 
composition. 

A major application of this technique 
lies in the experimental study of the prop- 
erties of hydrothermal fluids containing 
mixed volatiles using synthetic fluid inclu- 
sions. In an effort to both test the loading 
technique described above and to initiate a 
thorough study of the C-O-H system (dis- 
cussed in Zhang and Frantz, this Report), 
synthetic fluid inclusions with fluids con- 
taining mixtures of carbon dioxide, meth- 
ane, and water were grown. Fractured quartz 



64 



CARNEGIE INSTITUTION 



Table 5. Analyses by gas chromatography 



Initial Gas Composition 

Wt% Mol Mol Mol Mol Ratio 

CH 4 CH 4 CQ 2 Hp CH 4 /CQ 2 



Measured Gas Composition 

Mol Mol Mol Mol Ratio 

CH 4 CQ 2 Hp CiyC0 2 



5 0.000098 

10 0.000143 

15 0.000145 

20 0.000169 

25 0.000152 



0.000175 0.001221 0.560 

0.000124 0.000843 1.153 

0.000083 0.000537 1.747 

0.000068 0.000442 2.485 

0.000047 0.000298 3.234 



0.000086 0.000169 -na- 0.509 

0.000131 0.000122 0.0008995 1.074 

0.000129 0.000079 0.0005386 1.633 

0.000176 0.000066 -na- 2.667 

0.000155 0.000047 0.0002778 3.298 



prisms, cold welded platinum capsules 
containing water, and approximately 75 
mg silica gel were placed in thick-walled 
gold capsules (4.75 mm O.D.; 4.0 mm I.D.) 
(Fig. 45). The gas pipette was used to load 
the methane and carbon dioxide. Five dif- 
ferent bulk compositions containing 5,10, 
15, 20, and 25 wt% methane were chosen 
with wt% ratios for CO JYL£> of 0.357. The 
experiments were placed in standard hy- 
drothermal pressure vessels for four days at 
600°C and 2000 bar. In order to assure 
thorough mixing of water and the gases in 
the tiny cracks of the quartz prism, the 
pressure vessel was heated at 1000 bar. 
After reaching the experimental tempera- 
ture, the vessel was cycled four or five 
times between 500 and 3000 bar. Further 
discussion of the synthetic fluid inclusion 
techniques and the hydrothermal proce- 
dures employed in this study are described 
in Bodnar and Sterner (1987) and Zhang 
and Frantz (1987, 1989). An Accuspec™ 
Compac II gas chromatograph was modi- 
fied to accept gases released from the gold 
hydrothermal capsules. The results of these 
measurements are tabulated in Table 5 . The 



measured number of moles of methane and 
carbon dioxide are computed based on the 
measured area as referenced to the least- 
squares fit of all the data and thus only 
reflect the internal consistency of the 
measurements. The mole ratios, however, 
depend only on the ratio of the measured 
areas and the instrument calibration using 
the above mentioned gas standards. The 
measured values for water were determined 
by weighing the capsule before puncturing, 
drying it in a vacuum oven (120°C) after 
puncturing, re weighing the capsule, and 
computing the number of moles of H 2 
after subtracting the measured weight of 
the carbon dioxide and methane. The close 
agreement of these mole ratios between the 
initial composition and the measured 
composition demonstrates the precision of 
both our gas loading and the gas chroma- 
tography techniques. 

A new gas loading technique has been 
described by which gases that are non- 
condensible at room temperature and pres- 
sure can be loaded into experimental 
charges. The method has been successfully 
demonstrated by growing synthetic fluid 



GEOPHYSICAL LABORATORY 



65 



inclusions in C-O-H fluids at high tempera- 
tures and pressures analyzing the gases in 
the capsule by gas chromatography. Ex- 
perimental studies of mineral-fluid equili- 
bria and other studies involving mixed 
volatiles at hydrothermal temperatures and 
pressures should benefit from the develop- 
ment of the gas pipette loading technique. 



References 



Bodnar, R. J., and S. M. Sterner, Synthetic fluid 
inclusions, in Hydrothermal ExperimentalTech- 
niques, G. C. Ulmer and H. L. Barnes, eds., John 
Wiley & Son, New York, pp. 423-458, 1987. 

Eggler, D. H., B. O. Mysen, T. C. Hoering, and J. 
R. Holloway, The solubility of carbon monox- 
ide in silicate melts at high pressures and its 
effect on silicate phase relations, Earth and 
Planetary Sci. Lett., 43, 321-330, 1979. 

Eugster, H. P., and G. B. Skippen, Igneous and 
metamorphic reactions involving gas equilibria, 
in Researches in Geochemistry, 2, P. H. Abel- 
son, ed., John Wiley and Sons, New York, pp. 
492-520, 1967. 

French, B. M., Some geological implications of 
equilibrium between graphite and a C-H-O gas 
phase at high temperatures and pressures, Rev. 
Geophys., 4, 223-253, 1966. 

Hallam, M., and H. P. Eugster, Ammonium sili- 
cate stability relations, Contrib. Mineral. Pet- 
rol, 57, 227-244, 1976. 

Holloway, J. R., C. W. Burnham, and G. L. Mill- 
hollen, Generation of I^O-CX^ mixtures for use 
in hydrothermal experimentation, /. Geophys. 
Res., 73, 6598-6600, 1968. 

Holloway, J. R., and R. L. Reese, The generation 
of N^CX^-Hp fluids for use in hydrothermal 
experimentation I. Experimental method and 
equilibrium calculations in the C-O-H-N system, 
Am. Mineral., 59, 587-597, 1974. 

Jacobs, G. K., and D. M. Kerrick, Devolatilization 
equilibria in H 2 - C0 2 and H^O - C0 2 - NaCl 
fluids: An experimental and thermodynamic 
evaluation at elevated pressures and 
temperatures, Am. Mineral., 66, 1135-1153, 



1981. 

Komarneni, S., W. P. Freeborn, and C. A. Smith, 
Simple cold- weld sealing of noble-metal tubes, 
Am. Mineral., 64, 650-651, 1979. 

Palmer, D. A., and S. E. Drummond, Thermal 
decarboxylation of acetate. Part I. The kinetics 
and mechanism of reaction in aqueous solution, 
Geochim. Cosmochim.Acta,50, 813-823, 1986. 

Seitz, J. C, J. D. Pasteris, and B. Wopenka, Char- 
acterization of C0 2 - CH 4 - I^O fluid inclusions 
by microthermometry and laser Raman micro- 
probe spectroscopy: Inferences for clathrate and 
fluid equilibria, Geochim. Cosmochim. Acta, 
51, 1651-1663, 1987. 

Skippen, G. B., Experimental data for reactions in 
siliceous marbles, /. Geol., 70, 457-481, 1971. 

Zhang, Y. G., and J. D. Frantz, Determination of 
the homogenization temperatures and densities 
of supercritical fluids in the system NaCl - KC1 
- CaC^ - H^O using synthetic fluid inclusions, 
Chem. Geol, 64, 335-350, 1987. 

Zhang, Y. G., and J. D. Frantz, Experimental 
determination of the compositional limits of 
immiscibility in the system CaC^ - C0 2 - Hfi at 
high temperatures and pressures using synthetic 
fluidinclusions,C/^m.Geo/.,74,289-308,1989. 

Ziegenbein, D., and W. Johannes, Graphite in C- 
O-H fluids: an unsuitable compound to buffer 
fluid composition at temperatures up to 700°C, 
N. 3b. Miner. Abh., 7, 289-305, 1980. 



Investigations of Fluid Properties in 
the CO,-CH -H,0 System using syn- 

2 4 2 

THETIC FLUID INCLUSIONS 



Yi-gang Zhang and John D. Frantz 

High-temperature, high-pressure inter- 
granular fluids in the Earth's mantle and 
crust have had a profound influence on the 
evolution and resulting mineral pedogene- 
sis of igneous and metamorphic rock suites. 
These fluids, mixtures of gases, water, and 
dissolved electrolytes, exist either as a 



66 



CARNEGIE INSTITUTION 



supercritical phase or possibly as a mixture 
of two immiscible phases (Zhang and 
Frantz, 1989). Of particular importance is 
the ubiquitous C-O-H system. Its presence 
has a major influence on the genesis of 
primary magma in the mantle and subse- 
quent metasomatism resulting from ele- 
ment partitioning between the melt and the 
fluid (Green etal, 1987). Calculation of the 
oxidation state of the mantle involves 
multicomponent equilibria between the 
mineral phases and C-O-H fluids (Saxena, 
1989). In the Earth's crust, element parti- 
tioning and material transport within C-O- 
H fluids containing dissolved electrolytes 
have resulted in the metasomatism of meta- 
morphic mineral assemblages and the for- 
mation of ore deposits (Hollister and Burrus, 
1976; Wintsche et. al. 1981; Ramboz et. 
al. y 1985). Vestiges of ancient C-O-H fluids 
are commonly found in the incorporation 
of these components in minerals and in 
their presence in natural fluid inclusions. 
The latter represent a unique opportunity to 
1) detect the composition of the fugitive 
volatile phase; 2) to determine the tempera- 
ture-pressure conditions of the formation 
of the surrounding mineral; and 3) to un- 
derstand the evolution of the associated 
rock suites. Petrologists routinely measure 
properties of fluid inclusions such as the 
homogenization temperature along the liq- 
uid-vapor curve and, assuming that the 
volume of the inclusion remains constant 
with increasing temperature and pressure, 
use these measurements to delineate the 
possible temperature-pressure conditions 
of formation. Measurements such as these 
require knowledge of both the composi- 
tions of the inclusions and the PVT proper- 



ties of the fluids corresponding to those 
particular compositions. 

Due to its obvious importance, the C-O- 
H has received considerable attention in 
both experimental and theoretical investi- 
gations. For the most part, the studies have 
been concerned with one of the three bina- 
ries: C0 2 - Hp, CH 4 - H 2 0, and C0 2 - CH 4 . 
In the case of the C0 2 - H 2 system, experi- 
mental work at high temperatures and pres- 
sures has been performed by Franck and 
Todheide (1959), Todheide and Franck 
(1963), Takenouchi and Kennedy (1964), 
Greenwood (1969, 1973), and Schmulov- 
ich (1980). The CH 4 - H 2 binary has 
received less attention with the work of 
Welsch (1973) being the principle high- 
temperature, high-pressure study. The C0 2 
- CH 4 binary system, important to the chemi- 
cal industry, has attracted geologists ' atten- 
tion as fluids of this composition have been 
discovered in natural fluid inclusions 
(S wanenberg, 1 979). The system along with 
previous experimental work is discussed in 
Swanenberg (1979), Burrus (1981), and 
H&ycnetal., (1982). No experimental work 
has been done at high temperatures and 
pressures for the ternary C0 2 - CH 4 - H 2 
system. 

With the development of accurate gas- 
loading techniques (Frantz et al., this 
Report) combined with synthetic fluid 
inclusion techniques (Bodnar and Sterner, 
1985; Zhang and Frantz, 1987), experi- 
mental studies of the C-O-H system are 
now possible. Experiments producing 
synthetic fluid inclusions containing wa- 
ter-rich CH 4 - H 2 binary and C0 2 - CH 4 - 
1^0 ternary fluids were performed at tem- 
peratures from 400 to 600'C and at pres- 



GEOPHYSICAL LABORATORY 



67 



^ 3000 

CO 

O 2000 

O 1000 A 



(a) 



v>v 



/ 



:x> 



yy 




/ 

/////s'sos' 

■••' y ?' s s S-' s *s y ** a" 



/' *» 



. MO 



250 350 450 550 650 

Temperature (°C) 



cd 3000 




250 350 450 550 



650 



Temperature (°C) 



-^3000- 

co 

0) 2000- 

to 

to 

0) 1000- 

CL 



(c) /*3 / y& 

s s s y 

19» >• /\l*y ,•''15.1 ,s 

< •' S S S «•■* «■*" ,-* T-*"* 



Liquid 
Vapor 



250 



350 



450 550 



Temperature (°C) 



650 



CO 

© 

Ik. 
13 
CO 
CO 
CD 







* '• i» 


3000- 


(d) 


20-3 .- X jSxi*** 

y y y » 






20.9 /^/^ ,. 


2000- 






< ^ ,y i7,V X "^''' J«5^ ^^''(13.7) m 








1000- 


Liquid + \^-~"'^' "" 




Vapor 


1 1 1 1 1 



250 



350 



450 



550 



650 



Temperature (°C) 



Fig. 46. Plot of the measured clathrate melting temperatures as a function of experimental temperature 
and pressure for a) Hp, b) 5.5 mol% CH 4 -H 2 0, c) 1 1.0 mol% CH^Hp, and d) 16.5 mol% CH 4 -H 2 0. 
The shaded lines represent lines of constant clathrate melting temperature (isochores). The non-italicized 
numbers refer to the measured clathrate melting temperatures and the italicized numbers refer to the 
clathrate melting temperatures represented by these lines. The curved lines represent the liquid- vapor 
curve for that compositional section. 



sures from 1000 to 3000 bar. These experi- 
ments have resulted in the determination of 
1) isochores; 2) liquid-vapor curves; and 3) 
the melting relations of clathrate as a func- 
tion of composition. 



CH 4 -H 2 binary compositions 

Lines of constant homogenization tem- 
perature and isochores have been extremely 
useful in natural fluid inclusion studies for 
the determination of the temperature-pres- 
sure history of the host minerals. Zhang 



and Frantz (1987) determined constant 
homogenization temperature lines and 
isochores for fluids in the NaCl - KC1 - 
CaCl 2 - H 2 system and found that they 
could be represented in temperature-pres- 
sure space by a series of straight lines 
described by a simple function of the form; 



/ ? (bar)=A 1 +A 2 r(°C) 



(1) 



The coefficients A t and A 2 were functions 
of the homogenization temperature (T h ) y 
the solute type, and the solute concentra- 
tion. Using the regression parameters of 



68 



CARNEGIE INSTITUTION 



Table 6. Isochore regression parameters 



System 



Mol% 
CO, 



Mol% 
CR 



a. 



a. 



a, 



CH 4 -H 2 


— 


5.5 


3.274x10* 


-9.974 x 10 2 


4.317 x W 


-7.073 x 10° 







11.0 


3.528 x 10 3 


-6.123 x 10 2 


1.760 xlO 1 


-2.661 x 10° 




— 


16.5 


1.482x10* 


-1.919 xlO 3 


5.634 x 10 


-3.500 x 10 1 


C0 2 -CH 4 -H 2 


5.5 


5.5 


6.011 xlO 3 


-1.311 xlO 3 


5.135 x 10 


-7.779 x 10° 




11.0 


5.5 


-4.771 x 10* 


6.277 x 10 3 


-2.096 x 10 2 


1.097 x 10 2 




5.5 


11.0 


-6.906 x 10 3 


9.524 x 10 2 


-3.725 x 10 1 


2.027 x W 



Zhang and Frantz ( 1 987) isochores for pure 
water for the unary H 2 system are pre- 
sented as a function of temperature and 
pressure in Fig. 46a. 

Clathrate melting temperatures ranging 
from 7° to almost 2 1°C were measured with 
temperature-cycling techniques and are 
plotted as a function of the experimental 
temperature and pressure in Figs. 46b, 46c, 
and 46d for 5.5, 11.0, and 16.5 mol% CH 4 
respectively. The italicized numbers repre- 
sent experiments in which the inclusions 
homogenized to vapor rather than liquid. 
Since the melting temperature of clathrate 
in the pure CH 4 -H 2 system depends only 
on composition and total inclusion density, 
they can be used in much the same way as 
homogenization temperatures were in the 
salt - H20 system to determine isochores. 
The data were fit to the following function: 



P = (a, + a 7 T +aj 2 ) 

v 1 2 mc 3 mc ' 

+ (a A + a,T +al 2 )7, 

v 4 5 mc 6 mc ' ' 



(2) 



in which T m is the clathrate melting tem- 
perature. The regression constants of these 
fits are given in Table 6. Lines of constant 



clathrate melting temperature or isochores 
are shown as shaded lines in Figs. 46b, 46c 
and 46d. The italicized numbers represent 
the clathrate melting temperatures corre- 
sponding to the lines. The slopes of the 
isochores generally become shallower with 
increasing concentration of the volatile, 
but the major change in slope occurs below 
5.5 mol%. The liquid-vapor curve for each 
concentration was computed by solving 
equation (1) for homogenization pressures 
using the experimental homogenization 
temperatures (letting T=T h ) and clathrate 
melting temperatures. The results are shown 
as diamonds in Figs. 46b, 46c, and 46d. The 
homogenization pressures are high, with 
some high density inclusions being greater 
than 2000 bar. In Fig. 47, our CH 4 - H 2 
liquid vapor curve results plotted as solid 
squares are compared to those of Welsch 
(1973) shown as shaded curves. The agree- 
ment is remarkable considering the differ- 
ent techniques used in the two studies. 

The volumetric properties of the CH 4 - 
C0 2 isochores can be computed using the 
clathrate melting temperatures in conjunc- 
tion with the bulk compositions. Bonham 



GEOPHYSICAL LABORATORY 



69 



2500 




2500 



2000 



CO 

£, 1500 • 

3 
W 

a> 1000 h 

0. 



500 • 



250 300 350 400 

Temperature (C) 



11.0 Mol% 






* 

V 



2500 



2000 - 



CO 

* 1500 -| 

fl> 

k. 

3 
CO 
CO 

2 1000 . 

Q. 



500 - 



250 300 350 400 

Temperature (C) 



16.5 Mol%. 



f 

t 



350 



250 300 350 

Temperature (C) 



Fig. 47. Comparison of the liquid-vapor curve data of this study (solid squares) with those of Welsh 
(1973) for 5.5 mol% , 11.0 mol%, and 16.5 mol% CH^Kp. 



(1978) demonstrates that the solubility of 
methane in water at ambient temperatures 
and pressures to 100 bar is less than 0.2 
mol% . The ice melting point measurements 
made on our methane-water experiments 
were within 0. 1 or 0.2 of 0°C indicating low 
methane solubility in the liquidphase. Based 
on this, the vapor phase can be assumed to 
be composed entirely of methane and the 
liquid phase, of water and 

V** =V(H 2 0)/(l+l/X) +V(CH 4 )/(1 +X),(3) 

where V toul is the molar volume of the entire 
inclusion, V(CH 4 ) is the molar volume of 
the vapor phase, V(H 2 0) is the molar vol- 
ume of the liquid phase, andX is the ratio of 
the number of moles of CH A over the number 
of moles of H 2 0. Values for X can be 
computed from the relative amounts of 
methane and water introduced into the 
experimental charge. The clathrate melting 
temperature can be used to compute the 
internal pressure of the inclusion at the 
clathrate melting temperature using the data 
of Deaton and Frost (1946). Their data 



appear to be linear when the logarithm of 
the pressure is plotted against the melting 
temperature and the computed pressures 
ranged from 70 to over 200 bar. These 
values of the internal pressure were used in 
conjunction with the molar volume data for 
methane (Angus etal., 1978) and the molar 
volume data for pure water to compute the 
total inclusion molar volumes correspond- 
ing to our experiments. These are shown as 
functions of the clathrate melting tempera- 
ture for 5.5, 11.0, and 16.5 mol% CH 4 in 
Fig. 48. 



o 

E 

CO 

E 

<D 

E 

3 

O 
> 
hi 
« 

O 

S 

10 20 30 

Clathrate Melting Temperature ( °C) 

Fig. 48. Plot of the molarvolume of 5.5, 1 1.0, and 
16.5 mol% CF^-t^O as a function of the clathrate 
melting temperature. 




70 



CARNEGIE INSTITUTION 



00 

O 

3 
CO 
(0 

o 







» '« is 


3000 - 


(a) 








/' y" X / 

y ' y y y 

/Ha y y*.9 y ^tt.s 

.y ■ y .y • s y ■ it 


2000 - 








y y y y y y 
y y y y' y' y ^ " 

y y y S s' **" 
s ..' y y y^ *■* 


1000 - 




y y y y y y 

y y y *y y ■ 
y y y y y 


. 


Liquid + 


• y v .y •' 

Y/'y>" 




Vapor 


^t y.-*' 


0- 




— i ' 1 ■ 1 ' 



250 



350 



450 



550 



650 



Temperature (°C) 



3000 - 



(b) 



CO 






s y** 


.a 


2000 - 




y y 

y 1S.3 -•• t4 5 

y ■ .y ■ 


a> 






* y 


i_ 








3 
CO 






y y 
>•' y' 


2> 


1000 - 




\ y^ m y* 


Q. 






V" .y 






Liquid 


+ \ y^ 






Vapor 


\*y 



:tr 



.***' 



old 



250 350 450 550 650 

Temperature ( ° C) 



3000 - 



CO 

5. 2000 - 
CO 



3 
(/> 
CO 
0) 



1000 



(c) 



Liquid + 
Vapor 




250 350 450 550 650 

Temperature (°C) 



Fig. 49 Plot of the measured clathrate melting 
temperatures as a function of experimental tem- 
perature and pressure for a) 5.5 mol% CO : 5.5 
mol% CH 4 , b) 11.0 mol% C(X : 5.5 mol% CH 4 , 
and c) 5.5 mol% C0 2 :1 1 mol% CH The shaded 
lines represent lines of constant clathrate melting 
temperature (isochores). The non-italicized num- 
bers refer to the measured clathrate melting tem- 
peratures and the italicized numbers refer to the 
clathrate melting temperatures represented by these 
lines. The curved lines represent the liquid- vapor 
curve for that compositional section. 



C0 2 -CH 4 -H 2 ternary compositions 

As in the case of the binary CH 4 -H 2 
system, the clathrate melting temperatures 
for ternary C0 2 -CH 4 -H 2 compositions 
were plotted as a function of the experi- 
mental temperature and pressure in an ef- 
fort to determine the location of lines of 
constant T me or isochores (Fig. 49a shows 
the results for 5.5 mol% C0 2 : 5.5 mol% 
CH 4 ; Fig. 49b, for 11.0 mol% C0 2 : 5.5 
mol% CH 4 ; Fig. 49c, for 5.5 mol%C0 2 : 
1 1 .0 mol% CH 4 ). The numbers in parenthe- 
ses indicate experiments in which the in- 
clusions homogenized to vapor. These data 
were fit with equation (2) yielding regres- 
sion coefficients listed in Table 6. Lines of 
constant clathrate melting temperature 
calculated from these regressions are shown 
in Figs. 49a, 49b, and 49c as shaded lines 
labeled with italicized values of T . De- 

mc 

spite the limited number of data points for 
the ternary compositions, it is clear that the 
slopes of the isochores in Fig. 49a for the 
5.5 mol% C0 2 : 11.0 mol% CH 4 are quite 
similar to those of the 5.5 mol% methane- 
water binary (Fig. 46b). The 5.5 mol% C0 2 
: 11.0 mol% CH 4 (Fig. 49c) has isochores 
with slopes similar to those of the 11.0 
mol% CH 4 - H 2 binary (Fig. 46c). It ap- 
pears from these observations that the slopes 
of the isochores as determined from 
clathrate melting temperatures tend to fol- 
low the trends of the CH 4 - H 2 0. The loca- 
tions of the liquid-vapor curves were 
computed in the same manner as in the case 
of the CH 4 -H 2 binary using the measure- 
ments of both the clathrate melting tem- 
peratures and the homogenization tempera- 
tures in conjunction with equation (2). The 



GEOPHYSICAL LABORATORY 



71 



results, plotted as diamonds, are shown on 
Figs. 49a, 49b, and 49c. Liquid-vapor curves 
for the 5.5 mol% C0 2 : 5.5 mol% CH 4 and 
the 1 1 .0 mol% C0 2 : 5.5 mol% decompo- 
sitions are both almost identical to that of 
the 5.5 CH 4 - H 2 binary. The liquid- vapor 
curve for the 5.5 mol% C0 2 : 11.0 mol% 
CH 4 is very similar to that of the 1 1 .0 mol% 
CH 4 binary. Even more than in the case of 
the slopes of the isochores, the positions of 
the liquid-vapor curves in the portion of the 
C0 2 - CH 4 - H 2 ternary studied in this 
investigation closely follow the locations 
of the CH 4 - F^O liquid-vapor curves hav- 
ing the same mol% methane. 

The synthetic fluid inclusion method 
combined with the gas-loading techniques 
of Frantz et al. (this Report) have proven 
quite effective in the determination of the 
molar volumes, liquid-vapor curves, iso- 
chores, and low-temperature phase rela- 
tions of C-O-H gas mixtures. The fluids 
produced using these techniques yielded 
inclusions of extremely homogeneous 
composition as evidenced by the low stan- 
dard deviations of the microthermometric 
measurements for clathrate melting tem- 
perature (approximately ±0.1 °C). Regres- 
sions considering measurements of the 
clathrate melting temperature or the ho- 
mogenization temperature as a function of 
the experimental temperature and pressure 
yielded sets of isochores which systemati- 
cally varied as a function of concentration. 
As the gas concentration increases, the 
slopes of the sets of isochores tend to be- 
come shallower. Molar volumes consid- 
erably larger than those of pure water were 
computed for the isochores using measure- 
ments of the clathrate melting temperature 



The quality of the data permitted the calcu- 
lation of liquid-vapor curves for the CH 4 - 
Hf> binaries which are in reasonable agree- 
ment with data obtained using large-vol- 
ume hydrothermal pressure vessels. The 
presence of methane appears to dominate 
both the slopes of the isochores and the 
position of the liquid-vapor curve in the 
ternary compositions considered in this 
study. 



References 

Angus, S., B. Armstrong, and K. M. deReuck, 
InternationalThermodynamicTables of the Fluid 
State-5. Methane. IUPAC chemical data series 
16, Pergamon Press, New York 251pp, 1978. 

Bodnar, R. J., and S. M. Sterner, Synthetic fluid 
inclusions in natural quartz, n. Application to 
PVT studies, Geochim. Cosmochim. Acta, 49, 
1855-1859, 1985. 

Burrus, R. C, Analysis of fluid inclusions: phase 
equilibria at constant volume, Am. J. ScL, 281, 
1104-1126,1981. 

Deaton, W. M., and E. M. Frost, Gas hydrates and 
theirrelation to the operation of natural pipelines, 
U. S. Bur. Mines Monogr., 8, 103p, 1946. 

Franck, E. U., and K. Todheide, ThermischeEigen- 
schaften uberkritischer Mischungen von 
Kohlendioxyd und Wasser bis zu 750 °C und 
2000 atm, Chem. Neue. Folge., 22, 232-245, 
1959. 

Green, D. H., T. J. Falloon, and W. R. Taylor, 
Mantle-derived magma-roles of variable source 
peridotite and variable C-H-O fluid composi- 
tions, in Magmatic Processes: Physicochemical 
Principles, B. Mysen, ed., Spec. Pub. No. 1, The 
Geochemical Society, University Park, Penn- 
sylvania, pp. 139-154,1987. 

Greenwood, H. J., The compressibility of gaseous 
mixtures of carbon dioxide and water between 
and 500 bars pressure and 4500 and 800°C, Am. 
J. ScL, 267 A, 191-208, 1969. 

Greenwood, H. J., Thermodynamic properties of 
gaseous mixtures of H 2 and C0 2 between 



71 



CARNEGIE INSTITUTION 



450°and 800°C and to 500 bars, Am. J. Sci., 
273,561-571,1973. 

Heyen, G., C. Ramboz, and J. Dubessy, Simula- 
tion des equilibres des phases dans le system 
C0 2 -CH 4 en-dessous de 50°C et de 100 bars, C. 
R. Acad. Sci. Paris, 294, 203-206, 1982. 

Hollister, L., and R. C. Burrus, Phase equilibria in 
fluid inclusions from the Khtada Lake metamor- 
phic complex, Geochim. Cosmochim. Acta , 40, 
163-176, 1976. 

Ramboz, C, D. Schnapper, and J. Dubessy, The P- 
V-T-X-f(0 2 ) evolution of Ufl - CO, - CH 4 - 
bearing fluid in a wolframite vein: Reconstruc- 
tion from fluid inclusion studies, Geochim. 
Cosmochim. Acta, 49, 205-219, 1985. 

Saxena, S. K., Oxidation state of the mantle, 
Geochim. Cosmochim. Acta, 53, 89-95, 1989. 

S wanenberg, H. E. C, Phase equilibria in carbonic 
system, and their application to freezing studies 
of fluid inclusions, Contr. Mineral. Petrol., 68, 
303-306, 1979. 

Takenouchi, S., and G. C. Kennedy, The binary 
system Hfl - C0 2 at high temperatures and 
pressures, Am. J. Sci., 262, 1055-1074, 1964. 

Welsch, H., Die Systems Xenon-Wasser und 
Methan-Wasser bei lohen Drucken und tem- 
perature, Ph. D. dissertation, Inst, for Physical 
Chem., Karlsruhe, 1973. 

Wintsche, R. P., A. F. O'Connell, L. Ransom, and 
M. J. Wiechmann, Evidence for the influence of 
f(CH 4 ) on the crystallinity of disseminated car- 
bon in greenschist facies rocks, Rhode Island, 
USA,Contr.Mineral.Petrol., 77,207-213, 1981. 

Zhang, Y. G., and J. D. Frantz, Determination of 
the homogenization temperatures and densities 
of supercritical fluids in the system NaCl - KC1 
- CaCl 2 - I^O using synthetic fluid inclusions, 
Chem. Geol., 64, 335-350, 1987. 

Zhang, Y. G., and J. D. Frantz, Experimental 
determination of the compositional limits of 
immiscibility in the system CaCl 2 - C0 2 - H 2 at 
high temperatures and pressures using synthetic 
fluid inclusions, Chem. Geol., 74,289-308, 1989. 



A Laser-based Carbon Reduction Tech- 
nique For Oxygen Isotope Analysis of 
Silicates and Oxides 

Zachary D. Sharp and James R. O'Neil 

Stable isotope analysis is one of the 
most valuable geochemical techniques 
available for constraining the conditions of 
formation and alteration in most rock types. 
However, the methods for extracting oxy- 
gen from silicates and oxides have remained 
relatively unchanged over the past 25 years. 
As a result, large sample sizes are required 
for analysis and nearly all spatial resolution 
is lost. Fine-scale variations in the # 8 of 
oxides and silicates cannot normally be 
determined. In comparison, other geo- 
chemical techniques have been used suc- 
cessfully to determine major, minor and 
trace element concentrations, crystal struc- 
tures, and isotopic compositions (i.e., U- 
Th-Pb, ^ArrAr, # 4 S) on a Jim scale. This 
report outlines a microanalytical method 
for &*0 determinations of selected sili- 
cates and oxides using a laser-heated car- 
bon reduction technique. 

The natural variations in the 5 18 of 
minerals is so small that analytical tech- 
niques of very high precision are required 
to distinguish them. Two analytical meth- 
ods have been developed that are capable 
of analyzing the S l 8 of oxides and sili- 
cates at the high level of precision neces- 
sary to discern these small isotopic differ- 
ences: 1) fluorination and 2) carbon reduc- 
tion. 

Fluorination of minerals at moderate 
temperatures (200-650° C) liberates 2 



* Dept. of Geological Sciences, University of 
Michigan, Ann Arbor, Ml 48109-1063 



GEOPHYSICAL LABORATORY 



73 



Stabilities of Common Oxides 



h0 
o 



-20 



-40 



•60 



i i 


Mln. temp. 

of system 


£.'»»■ 


1 


CO 

, so 2 

A1 2 3 

MgO 

CaO 

FeO 

t^O 



1000 1500 2000 2500 

Temperature (K) 



3000 



Fig. 50. T-f(0) 2 diagram showing the stability of 
common oxides relative to the elements. The C - 
CO buffer (thick solid line) crosses below the 
stability field of all common oxides above 2450K. 
In the presence of graphite, all oxides will reduce 
to the elements and carbon monoxide above this 
temperature. The minimum temperature of the 
present system (shaded area) is 2890K (melting 
point of molybdenum). Thermodynamic data are 
from Chase etal (1985). 



which is converted to C0 2 and subsequently 
analyzed by conventional isotope ratio mass 
spectrometry. The fluorinati on method (e.g. , 
Baertschi and Silverman, 1951; Clayton 
and Mayeda, 1963) is applicable to all but 
the most refractory minerals, but relatively 
large sample sizes of 5-30 mg are generally 
required to obtain accurate and reproduc- 
ible results. Samples as small as 1 mg can 
be analyzed only with extreme care and 
assigning a somewhat arbitrary blank cor- 
rection (Lee et al., 1980). 

The carbon reduction method involves 
the high temperature (1000-2400°C) re- 
duction of minerals to carbides or native 
elements and CO with varying amounts of 
C0 2 . The evolved CO is converted to C0 2 
and analyzed. This technique has met with 
partial success (e. g., Schwander, 1953; 
Clayton and Epstein, 1958), but has been 
limited, in part, by the difficulty of attain- 
ing the high temperatures required for reac- 



tion. The traditional carbon reduction tech- 
nique also requires large sample sizes, a 
time consuming degassing procedure and 
is claimed to be unsatisfactory for alkali- 
bearing minerals (Clayton and Epstein, 
1958). This is a result of the volatile alkali 
metals being oxidized by the evolved CO, 
which involves a large isotopic fractiona- 
tion. The laser-based carbon reduction 
technique allows for reduced sample sizes 
of 1-3 mg or less, and because the heating 
is so rapid, analyses can be made much 
more quickly and cleanly than with either 
the conventional fluorination or carbon 
reduction method. 

The carbon reduction method is based 
on the fact that all common oxides and 
silicates will be reduced in the presence of 
carbon, if sufficient temperatures are 
reached. For example, quartz and mag- 
netite are reduced by the following reac- 
tions, respectively (Clayton and Epstein, 
1958): 



Si0 2 + 3C = SiC + 2 CO, 



(1) 



Fe 3 4 + 4 C = 3 Fe + 4 CO. (2) 



The stabilities of selected common oxides 
relative to the C - CO - C0 2 buffer are 
shown as a function of temperature at 1 bar 
in Fig. 50. Above 2400°C, all common 
oxides in the presence of graphite should be 
reduced to either elements or carbides. 
Temperatures of 2617°C (melting point of 
molybdenum) are easily achieved with the 
Nd- YAG laser equipment at the Geophysi- 
cal Laboratory. 

In the present system, samples are pre- 
pared by grinding the weighed mineral 



74 



CARNEGIE INSTITUTION 



7\ 






EXTRACTION SYSTEM 



m 



%K 



V 



LASER 



c 



n^O 1 ^ 



SAMPLE 
CRUCIBLE 



REACTION CHAMBER T 



1 ZEOLITE 

Itrap 



CO-C0 2 
CONVERTER 




Sample 
Bulb 



Manometer 



w 



Fig. 51. Laser extraction system. The system consists of a Nd-YAG laser, a sample crucible, a reaction 
chamber with zeolite trap and a CO - C0 2 converter. During reaction, the CO is collected on the zeolite 
trap, which is removed from the reaction chamber and placed onto the vacuum line. The CO is then 



desorbed and converted to C0 2 on the CO 



C0 2 converter. 



with excess graphite (15-50% over stoi- 
chiometric). The mixture is pressed into a 
pellet 3 mm in diameter to insure intimate 
contact between the two phases. During 
laser heating, the graphite absorbs the ra- 
diation, heating the entire pellet to ex- 
tremely high temperatures. To prevent 
reaction with the sample chamber, the pel- 
let is nested in a 5 mm O.D. graphite 
crucible which in turn is placed in a plati- 
num crucible holder. The platinum cup is 
used to prevent direct contact between the 
hot graphite crucible and the walls of the 
sample chamber. 

The extraction system comprises a la- 
ser, a sample crucible, a reaction chamber 
and a CO - C0 2 converter (Fig. 51). A 
variable power, 18 watt maximum Nd- 
YAG laser (A = 1.064 ^m) with a 6X air- 



objective is used as a heating source. The 
focal length of this lens is 20 mm with a 
focused spot of -10 jum. Although most 
minerals are transparent to radiation of this 
wavelength, graphite strongly absorbs the 
radiation and heats up. The admixed min- 
eral is heated by conduction from the graph- 
ite powder. The sample chamber consists 
of a 20 mm O.D. quartz sample tube with a 
ground glass joint to admit the sample and 
a removable zeolite trap (cold finger) 
equipped with a stopcock (Fig. 51). The 
reaction chamber containing the sample 
pellet is evacuated and degassed at 600°C 
for 1 hour. The sample is gently rastered 
under the focused laser beam until the 
sample pellet is entirely reacted. The 
evolved CO is collected on the cold finger 
as the reaction proceeds. Thus a high vac- 



GEOPHYSICAL LABORATORY 



75 



uum is maintained in the reaction chamber 
at all times. By keeping the CO fugacity 
extremely low, there is less chance for the 
CO to react with reactive alkali metals that 
may vaporize and plate out on the chamber 
walls during reaction. The zeolite trap is 
isolated from the reaction chamber and 
heated to 300°C to desorb the CO. The CO 
is then converted to C0 2 with a high volt- 
age electric discharge between two parallel 
platinum plates (Aggetera/., 1965; Rafter, 
1967) by the reaction 



2 CO = C0 2 + C. 



(3) 



The C0 2 yield is measured manometri- 
cally, and the gas is fed to a sample tube. 
Isotopic data obtained with the laser- 
based carbon reduction method are pre- 
sented in Table 7 and Fig. 52. Analyses of 
all oxides and some of the silicate minerals 
examined are in agreement with analyses 
made with conventional fluorination meth- 
ods. Refractory minerals such as olivine 
and kyanite give erratic results and are not 
amenable to the present carbon reduction 
technique. Analyses of feldspars are con- 
sistently low by 3.3 ± 0.3 %o. During laser 
heating, tiny particles of unreacted mate- 
rial are blown out of the graphite crucible 
along with the evolving CO and conse- 
quently yields are generally low, typically 
40-60 per cent. Because magnetite reacts at 
very low temperatures, yields of 100% are 
achieved. The low yields obtained for the 
other minerals do not affect the isotopic 
results. There is no correlation between the 
% yield of a mineral and the difference 
between the measured and true isotopic 
composition of that mineral, as long as 



feldspar is not included in the correlation. 
If the isotopic analyses of feldspars are 
always low by a constant amount, a correc- 
tion can be applied to the data in order to 
bring them into accord with the actual 
values as is done for carbonates analyzed 
by the H 3 P0 4 technique (McCrea, 1950). It 
is not clear why the # 8 values are lower 
than their accepted values. Clayton and 
Epstein (1958) first reported a problem 
with carbon reduction of feldspar. They 
observed the formation of a metallic mirror 
on the walls of the glass chamber as the 
samples were heated. Such mirrors are 
probably the result of the vaporization of 
alkalis from the mineral and condensation 
on the glass walls as metals. As their reac- 
tions proceeded, the mirrors lost their 
metallic finish presumably due to the oxi- 
dation of the highly reactive metal by either 
CO or C0 2 . Because the oxidation of the 



c 
o 

o 

=J 

ID 

rr 

c 
o 

-Q 

t_ 

03 

o 



30.0 
25.0 
20.0 
«M5.0 
10.0 
5.0 



0.0 



¥' 



* ♦ 



ft' \k i v i i i i i 



,-tj 



,- A Monticellite a 

Quartz a 

Magnetite A 

MnC>2 O 

BiP0 4 + 

Garnet x 

Diopside a 

Orthopyroxene ■ 

Wollastonite • 

Olivine y 

i F.eldjjpar, + 



0.0 5.0 10.0 15.0 20.0 25.0 30.0 

5 18 
Fluorination 



Fig. 52. Comparison between &*0 values deter- 
mined with the carbon reduction method and those 
from the fluorination method. The diagonal line 
represents perfect agreement between the two 
methods. The # 8 values of feldspar determined 
with the carbon reduction method are consistently 
3.3 %o light. Olivine and garnet may give erratic 
results. 



76 



CARNEGIE INSTITUTION 



Table 7. Isotopic composition, sample size and % recovery of various minerals determined with the 
carbon reduction technique. The # 8 actual represents either accepted values of isotopic standards or 
newly measured values using the fluorination method. All data are reported in the %o notation relative 
to SMOW. 



Mineral 


(TO 


# 8 o 


Sample Size 


/zmole C0 2 


% 




actual 


measured 


(mg) 


recovered 


recovery 


Quartz 


7.2 


7.2 


3.6 


n.d. 


n.d. 




7.2 


7.1 


3.0 


12 


23 




7.2 


7.1 


3.9 


25 


38 




16.2 


15.9 


3.2 


24 


45 




16.2 


15.7 


2.8 


20 


42 




16.2 


16.5 


3.0 


7 


13 




16.2 


16.5 


3.3 


35 


63 




25.3 


24.4 


2.3 


23 


59 




25.3 


25.4 


1.5 


n.d. 


n.d. 


Magnetite 


0.6 


0.6 


1.9 


16 


100 




0.6 


0.8 


2.3 


20 


100 


MnO z 


3.1 


3.1 


2.9 


14 


34 




3.1 


3.5 


2.9 


18 


56 


BiP0 4 


11.7 


11.5 


3.6 


13 


55 




11.7 


11.7 


2.7 


8 


42 


Orthopyroxene 


6.8 


6.8 


3.9 


34 


77 




6.8 


6.4 


2.4 


16 


60 


Diopside 


19.0 


18.0 


2.7 


18 


49 




19.0 


19.4 


6.6 


41 


45 




19.0 


19.5 


4.1 


32 


56 


Wollastonite 


9.3 


9.1 


5.3 


18 


26 




9.3 


9.6 


2.4 


12 


39 




9.3 


9.3 


4.1 


20 


38 


Garnet 


6.4 


5.7 


4.1 


23 


46 




6.4 


5.8 


2.7 


14 


44 




6.4 


6.3 


3.0 


16 


44 


Forsterite 


5.7 


6.0 


3.0 


n.d. 


n.d. 




5.7 


7.2 


3.2 


n.d. 


n.d. 




5.7 


1.0 


1.9 


4 


13 




5.7 


6.4 


1.2 


4 


25 



GEOPHYSICAL LABORATORY 
Table 7. Continued 



77 



Mineral 


#*o 


# 8 o 


Sample Size 


/miole C0 2 


% 




actual 


measured 


(mg) 


recovered 


recovery 


Monticellite 


22.0 


21.5 


4.8 


20 


33 




22.0 


21.6 


4.5 


18 


31 




22.0 


21.4 


4.8 


19 


31 


Feldspar 


12.5 


9.1 


2.7 


16 


42 




12.5 


9.5 


2.5 


16 


46 




3.4 


0.3 


3.2 


13 


29 




3.4 


-0.2 


3.7 


17 


32 


Kyanite 


n.d. 


7.5 


3.6 


19 


34 




n.d. 


8.6 


4.0 


24 


39 


CaO 


n.d. 


25.6 


3.3 


11 


37 




n.d. 


25.4 


4.9 


20 


46 


A1 2 3 


n.d. 


14.4 


4.7 


24 


35 




n.d. 


14.2 


3.8 


23 


41 


MgO 


n.d. 


n.d. 


3.1 


15 


39 




n.d. 


n.d. 


3.4 


20 


47 



metallic mirror is a kinetic rather than 
equilibrium reaction, carbon oxides con- 
taining the light isotope of oxygen should 
react preferentially. As a result, the residual 
CO would have a &*0 value that is higher 
than the actual value of the alkali-bearing 
silicate. This expected elevation of the & % 
values of feldspars was observed by Clay- 
ton and Epstein (1 958), but with the present 
carbon reduction technique, the measured 
& % of the feldspars is lower than the actual 
value (Table 7). One explanation for the 
low isotopic values is that the oxygen in the 
Si-O-Al bonds reacts preferentially to the 
oxygen in Si-O-Si bonds in the laser-based 



carbon reduction procedure. The sign and 
magnitude of this effect is consistent with 
previous estimates based on relative bond 
strength (Taylor and Epstein, 1962). 

Isotopic analyses of the refractory min- 
erals forsterite, kyanite, and to a lesser 
extent, garnet are more erratic than those of 
other minerals, and in the case of olivine, 
the yields are substantially lower. The ox- 
ides that comprise olivine and kyanite 
(MgO, Si0 2 and A^Og) all react to a uni- 
form extent with reproducible isotopic 
analyses. The calculated /(0 2 ) required to 
reduce forsterite to its elements is higher 
than for the oxide components, so thermo- 



78 



CARNEGIE INSTITUTION 



dynamics favors the reduction of olivine 
over the oxides. Furthermore, olivine melts 
when radiated by the Nd-YAG laser be- 
cause the iron linkages absorb radiation at 
1 .063 Jim. The reaction involves a thermo- 
dynamically favorable reduction of a melt 
with graphite, but very little takes place. 
The erratic # 8 observed for forsterite, but 
not monticellite (CaMgSi0 4 ), cannot be 
explained by preferential reaction of differ- 
ently bound oxygen. All of the oxygen in 
olivine is shared between a silicon and M 2 * 
cation. There is no isotopic distinction 
between sites, and therefore, no possible 
reaction of one site relative to another. 

The safety, rapidity and small sample 
sizes are the primary benefits of the laser- 
based carbon reduction technique over 
conventional fluorination. Microvariations 
in the &*0 of quartz veins, porphyroblasts 
and phenocrysts can be measured with this 
new method. Unfortunately, not all miner- 
als are amenable to the carbon reduction 
method at this time, but further investiga- 
tions of the isotopic systematics involving 
the laser-based carbon reduction technique 
may lead to a better understanding of high- 
temperature, rapid kinetic processes that 
occur during laser heating. 



Baertschi, P., and S. R. Silverman, The determina- 
tion of relative abundances of the oxygen iso- 
topes in silicate rocks, Geochim. Cosmochim. 
Acta, 7,317-328, 1951. 

Chase, M. W. Jr., C. A. Davis, J. R. Downey, Jr., 
D. J. Frurip, R. A. McDonald, and A. N. Syverud, 
JANAF Thermochemical Tables, 3rd ed., J. 
Phys. Chem. Ref. Data, 14, 1986. 

Clayton, R. N., and S. Epstein, The relationship 
between 18 /0 16 ratios in coexisting quartz, 
carbonate and iron oxides from various geologi- 
cal deposits, /. Geol., 66, 352-371, 1958. 

Clayton, R. N., and T. K. Mayeda, The use of 
bromine pentafluoride in the extraction of oxy- 
gen from oxides and silicates for isotopic analysis, 
Geochim. Cosmochim. Acta, 27, 43-52, 1963. 

Lee, T., T. K. Mayeda, and R. N. Clayton, Oxygen 
isotopic anomalies in Allende inclusion HAL, 
Geophys. Res. Lett., 7, 493-496, 1980. 

McCrea, J. M., On the isotopic chemistry of car- 
bonates and a paleotemperature scale, /. Chem. 
Phys., 18, 849-857, 1950. 

Rafter, T. A., Oxygen isotopic compositions of 
sulphates - 1: A method for extraction of oxygen 
and its quantitative conversion to carbon diox- 
ide for isotope ratio measurements, N. Zealand 
J.ScL, 70,493-510, 1967. 

Schwander, H., Bestimmung des relativen Sauer- 
stoffisotopen-Verhaltnisses in Silikatgesteinen 
und -Mineralien, Geochim. Cosmochim. Acta, 
4, 261-291, 1953. 

Taylor, H. P., Jr., and S. Epstein, Relationship 
between 18 /0 16 ratios in coexisting minerals of 
igneous and metamorphic rocks, Geol. Soc. Am. 
Bull., 73, 675-694, 1962. 



References 



Aggett, J., C. A. Burton, T. A. Lewis, D. R. 
Llewellyn, C. O'Connor, and A. L. Odell, The 
isotopic analysis of oxygen in organic com- 
pounds and in coordination compounds contain- 
ing organic hazards, /. Appl. Radiat. I sot., 16, 
165-170, 1965. 



GEOPHYSICAL LABORATORY 



79 



Crystallography - Mineral Physics 



Isotope Effects in Dense Solid 

Hydrogen: Phase Transition in 

Deuterium at 190 (±20) GPa 

Russell J. Hemley and Ho-kwang Mao 

Once the exclusive domain of theory, 
the behavior of hydrogen at ultrahigh pres- 
sures is now amenable to direct experimen- 
tal investigation using ultrahigh-pressure, 
diamond-anvil techniques (Hemley and 
Mao, 1988; Mao and Hemley, 1989). The 
goal of this effort has been the characteriza- 
tion of hydrogen above 100 GPa and test- 
ing of theoretical predictions of the insula- 
tor-metal transition pressure in this mate- 
rial, currently predicted to occur between 
150 and 300 GPa. Recently, we demon- 
strated that solid hydrogen undergoes a 
phase transition at 145 GPa and 77K 
(Hemley and Mao, 1988). Changes in the 
Raman spectra indicate that the transition 
may be a structural one between insulating 
molecular phases, possibly associated with 
orientational ordering. Recently, we have 
shown that on further increase in pressure 
the optical properties of the high-pressure 
phase change dramatically. Above 200 GPa 
there is evidence for ground-state elec- 
tronic excitations at visible wavelengths, 
and at pressures in the 250 GPa range 
hydrogen samples are opaque (Mao and 
Hemley, 1989). These observations have 
led to the possibility that the transition at 
145 GPa may be associated with band 
overlap. If so, the character of the optical 



spectra indicate that the gap may be indi- 
rect at closure. This interpretation is con- 
sistent with theoretical predictions that band 
overlap may occur below 200 GPa (Friedli 
andAshcroft, 1977; MmetaL, 1986;Barbee 
et al, 1989). 

An important constraint on the nature of 
phase transitions in solid hydrogen is pro- 
vided by the study of isotope effects, which 
produce a well-known effect on the orien- 
tational ordering transformation at low 
densities (Silvera, 1988). The ordering 
transformation occurs at significantly lower 
pressures in D 2 than in H 2 because of the 
lower rotational constant of the heavier 
isotope. There is a pronounced isotope effect 
on the Raman-active vibron. In both hydro- 
gen and deuterium, the frequency of the 
vibron increases with pressure but then 
decreases above a critical pressure. In H 2 
the critical pressure is 30 GPa whereas in 
D 2 it is shifted to 50 GPa (Sharma et al. 
1980). The weaker negative pressure shift 
of the D 2 vibron is magnified at higher 
pressures: at 125 GPa, for example, the 
vibron frequency is 40 cm * above and 40 
cm 1 below the zero-pressure values for D 2 
and H 2 , respectively (Mao et al, 1985). 
Although these results suggest that the 
equations of state for the two solids are 
significantly different at these very high 
densities, direct measurements at low pres- 
sures indicate that the compressibility of 
the two solids are similar (Mao et al., 
1988). 

In the present study we have pressur- 



80 



CARNEGIE INSTITUTION 



ized deuterium to pressures above 250 GPa 
to examine its vibron shift above the previ- 
ous limit of 125 GPa (Mao et ai, 1985). In 
particular, we wished to examine possible 
phase transitions in the region of the transi- 
tion observed in hydrogen. The experi- 
ments were performed using techniques 
described previously (Hemley and Mao, 
1 988). The Raman active vibron was meas- 
ured as a function of pressure, with pres- 
sure determined using the ruby fluores- 
cence technique. Because of the use of low- 
fluorescence diamonds and the high sensi- 
tivity of the optical system, time-resolved 
techniques were not needed to measure the 
ruby fluorescence spectra. The ruby spec- 
tra were measured to pressures of about 
240 GPa on the quasihydrostatic pressure 
scale. 

The pressure shift of the Raman-active 
vibron of molecular deuterium to pressures 
above 200 GPa is shown in Fig. 53. A 
single, well-resolved band which decreases 
in frequency above 50 GPa was observed 
initially, as in previous studies (Sharma et 
al, 1980; Mao et ai, 1985). Above 100 
GPa, the negative pressure shift of the 
vibron, measured here at 77 K, converged 
with that measured previously at room 
temperature to 125 GPa, and continued 
smoothly to higher pressures. At 190 (±20) 
GPa, however, a second, broader peak 
appeared 130 (±5) cm * below that of the 
first. The two peaks coexisted over a small 
pressure interval with the intensity of the 
new peak growing at the expense of the 
first with increasing pressure. With further 
increase in pressure, the higher frequency 
peak completely disappeared. The second 
peak continued to decrease in frequency 



3200 



§3100 



_§3000 

E 

§2900 
CD 

03 2800 



2700 



i I I 
Vibron 

Pressure Shift 




Deuterium 
77 K 




50 100 150 200 250 300 

Pressure, GPa 

Fig. 53. Pressure shift of the Raman-active 
vibron of molecular deuterium to ultra-high 
pressures. The second, lower frequency vibron 
first appeared at a ruby pressure of 190 (± 20) 
GPa. The two peaks coexisted over a pressure 
interval of approximately 20 GPa, with an aver- 
age separation of 130 cm 1 between them. The 
width of the mixed phase region is likely to 
reflect the magnitude of pressure gradients in 
the sample across the laser spot (~5 mm in 
diameter). Similar effects were observed in 
hydrogen.The error bars for the higher pressure 
points include the uncertain-ties arising from 
the broadness of the ruby Rj peaks and from 
pressure calibration (hydrostatic versus qua- 
sihydrostatic). The pressure could not be meas- 
ured directly for the two highest pressure spec- 
tra. At these pressures, the sample had com- 
pletely transformed to the high pressure phase, 
as evidenced by the single peak present in the 
measured spectra. 



with increasing pressure; at the highest 
pressures attained, the frequency of the 
peak was 2793 cm 1 . The pressures could 
not be determined reliably above 240 GPa 
as a result of the decrease in the ruby 
fluorescence intensity. We estimate that 
the maximum pressure reached on the 
deuterium was 240-280 GPa (see Mao and 
Hemley, 1989). 

The appearance of the second, broader 
vibron, and coexistence of the two peaks 
over a small pressure interval, strongly 
resembles that recently observed in hydro- 



GEOPHYSICAL LABORATORY 



81 



gen. However, there are some notable dif- 
ferences in the two isotopes that bear fur- 
ther analysis. First, despite the uncertain- 
ties in pressure, the data clearly indicate 
that the transition in deuterium occurs at a 
higher pressure than that in hydrogen (190 
versus 145 GPa). Second, the vibron dis- 
continuity is larger (130 versus 105 cm 1 for 
hydrogen). The weaker pressure depend- 
ence of the vibron in deuterium has been 
noted previously (Mao et al. 1985). The 
transition in deuterium occurred when the 
vibron reached a value of 2990 cm 1 , which 
is close to its zero-pressure value; in con- 
trast the transition in hydrogen occurred 
when the vibron was approximately 100 
cm 1 below its zero-pressure value. 

The more pronounced pressure depend- 
ence of the vibron frequency for hydrogen 
indicates that the molecules in this solid are 
significantly more anharmonic than in 
deuterium at a given pressure (density). 
Ashcroft (1988) has argued that the differ- 
ent pressure dependencies of the vibron 
frequencies may arise from large differ- 
ences in zero-point energy for the two iso- 
topes. If the phase transitions in the two 
isotopes involve the same crystal struc- 
tures, it is possible that the differences in 
zero-point energy may also be responsible 
for the higher phase transition pressures for 
the heavier isotope. Moreover, since the 
difference in zero-point energy for the two 
isotopes is expected to be comparable to 
the energy differences between different 
structures, it is also possible that the two 
isotopes crystallize in different structures 
at high pressures and have a different series 
of phase transitions in the molecular solid 
prior to metallization. Finally, recent theo- 



retical calculations indicate that band over- 
lap should occur in the molecular phase as 
low as 150 GPa (see Mao and Hemley, 
1989). At the point of band overlap, elec- 
tron density will be removed from the 
molecular bonds to conduction states, 
causing a decrease in the frequency of the 
molecular vibron. The magnitude of this 
frequency shift could therefore provide 
useful constraints on possible band overlap 
in the molecular phase. 



References 

Ashcroft, N. W., Quantum liquid metals: the 
physics of dense hydrogen, Z. Phys. Chemie, 
756,41-51,1988. 

Barbee, T. W., A. Garcia, M. L. Cohen, and J. L. 
Martins, Theory of high-pressure phases of 
hydrogen,Phys.Rev.Lett.,62, 1150-1153, 1989. 

Friedli, C, and N. W. Ashcroft, Combined repre- 
sentation method for use in band structure calcu- 
lations: application to highly compressed 
hydrogen, Phys. Rev. B, 16, 662-672, 1977. 

Hemley, R. J., and H. K. Mao, Phase transition in 
solid molecular hydrogen at ultra-high pressure, 
Phys. Rev. Lett. 61, 857-860, 1988. 

Mao, H. K., and R. J. Hemley, Optical studies of 
hydrogen above 200 gigapascals: evidence for 
metallization by band overlap, Science, 244, 
1462-1465, 1989. 

Mao, H. K., P. M. Bell, and R. J. Hemley, Ultra- 
high pressures: optical observations and Raman 
measurements of hydrogen and deuterium to 
1.47 Mbar, Phys. Rev. Lett., 55, 99-102, 1985. 

Mao, H. K., A. P. Jephcoat, R. J. Hemley, L. W. 
Finger, C. S. Zha, R. M. Hazen, and D. E. Cox, 
Synchrotron x-ray diffraction measurements of 
single-crystal hydrogen to 26.5 gigapascals, 
Science, 239, 1131-1134, 1988. 

Min, B. I., H. J. F. Jansen, and A. J. Freeman, 
Pressure-induced electronic and structural phase 
transitions in solid hydrogen, Phys. Rev. B, 33, 



82 



CARNEGIE INSTITUTION 



6383-6390, 1986. 

Sharma, S. K., H. K. Mao, and P. M. Bell, Raman 
measurements of deuterium in the pressure range 
of 8-537 kbar at room temperature, Carnegie 
Instn. Washington Year Book, 79, 358-364, 1980. 

Silvera, I. F., The phase diagram and excitations in 
solid hydrogen: prospects for metallization, in 
Simple Molecular Systems at Very High 
Densities, A. Polian, P. Loubeyre, and N. Boc- 
cara, eds., Plenum, New York, pp. 33-46, 1988. 



The Effect of Pressure, Temperature, 
and Composition on the Lattice Para- 
meters and Density of (Fe,Mg)Si0 3 - 
Perovskites to 30 GPa 

Ho-kwang Mao, Russell J. Hemley, Jinfu 

Shu, Liang-chen Chen, 

Andrew P. Jephcoat, Yan Wu, and 

William A. Bassett* 

Information on the physical properties 
(density, bulk modulus, and lattice parame- 
ters) of the MgSi0 3 -perovskite as a func- 
tion of pressure, temperature and Fe-Mg 
composition is of fundamental importance 
for a realistic model of the lower mantle. 
Although there is a growing body of data 
on these properties from high pressure 
single-crystal and polycrystalline x-ray 
diffraction (Yagi etal., 1982; Kudoh etal., 
1987; Knittle and Jeanloz, 1987; Ross and 
Hazen, 1989), from Brillouin scattering 
measurements (Yeganeh-Haeri and Weid- 
ner, 1989) and from theoretical calcula- 
tions (Hemley etal. , 1 987; Wolf and Buko w- 
inski, 1987), little is known about the prop- 
erties of perovskite at higher pressures. 

* Department of Geological Sciences, 
Cornell University, Ithaca, NY 14853 



Indeed, the equation of state of the orthor- 
hombic perovskite has not been studied 
above 1 3 GPa under hydrostatic pressure 
conditions; hydrostatic pressure is neces- 
sary for distinguishing the compressibility 
of individual lattice parameters. Previous 
quasihydrostatic measurements on the elas- 
ticity of the perovskite were made at ambi- 
ent conditions or at pressures far below the 
stability field of the perovskite, which could 
cause samples to behave abnormally. Ther- 
mal expansion data for (Fe,Mg)Si0 3 - 
perovskite were collected at ambient pres- 
sure by Knittle et al. (1986). No measure- 
ments have yet been carried out at simulta- 
neous high-pressure and high-temperature 
conditions. The effects of Fe/Mg ratio on 
the equation of state or the perovskite, 
which is crucial for the determination of the 
iron content in the mantle, has also not been 
studied experimentally nor theoretically. 

Polycrystalline x-ray diffraction in the 
megabar diamond-anvil cell with an exter- 
nal resistance heater can reach the stability 
field of the perovskite and cover the pres- 
sure range of the lower mantle. A high 
degree of hydrostaticity and high resolu- 
tion in the diffraction measurements are 
necessary for observing changes in orthor- 
hombic distortion and for determining a 
precise equation of state for the perovskites. 
The present paper reports the development 
of a new technique for such experiments . 

The silicate perovskite samples were 
synthesized from synthetic pyroxenes by 
laser-heating at 40 GPa in diamond-anvil 
cells (Mao et al., 1977). The perovskite 
sample formed a disc-shaped polycrys- 
talline aggregate, 150 mm diameter and 20 
to 50 mm thick and gold was used as a high- 



GEOPHYSICAL LABORATORY 



83 



Belleville Springs 




TC1 



III Lever 




Diamond Anvil 




Fig. 54. (a) The diamond-anvil cell with external 
heater; (b) Sample configuration 



temperature high-pressure calibrant 
(Jamieson et al., 1982; Ming et al., 1983). 
Several ruby grains, 2-5 mm size, were 
placed on top of the perovskite sample as 
an ambient-temperature high-pressure cali- 
brant (Mao etal. y 1986). The sample cham- 
ber was then filled with neon gas at 200 
MPa and ambient temperature in a high- 
pressure gas-loading device (Jephcoat et 
al., 1987). In the present experiment, a 
sleeve-shaped platinum-wire heater with a 
shell of ceramic insulator was fit around the 
extruded portion of piston-cylinder (Fig. 
54). Temperatures were measured with two 
chromel - alumel thermocouples, mounted 
on the diamond anvils. The temperature 



difference between the two thermocouples 
was normally less than the uncertainty of 
the thermocouple (~2 K) at 900K. 

One of the major difficulties in studying 
the (Fe,Mg)Si0 3 -perovskite by polycrys- 
talline x-ray diffraction techniques arises 
from the fact that the diffraction pattern 
consists primarily of many groups of multi- 
plets (Yagi et al., 1977). The separation of 
the peaks within each multiplet is typically 
only ~ 1%. In order to obtain accurate 
measurement of the lattice parameters, it is 
necessary to resolve these multiplets by 
high-resolution techniques. Monochro- 
matic synchrotron x-ray radiation currently 
provides the highest possible resolution for 
polycrystalline diffraction. In the present 
study, we used a wiggler beamline at Cor- 
nell High Energy Synchrotron Source 
(CHESS); a sagittal single-crystal mono- 
chromator was used to provide focused 
16.1 keV x-ray radiation. The diffraction 
patterns were recorded using film tech- 
niques. In order to increase the angular 
resolution, we replaced the commonly used 
50-mm radius film cassette for diamond 
cell with a newly designed 100-mm radius 
cassette. Example of diffraction patterns 
are shown in Fig. 55. 

The orthorhombic distortion of the 
(Fe,Mg)Si0 3 -perovskites is clearly revealed 
by the splitting of single diffraction lines of 
the cubic structure into doublets or triplets 
in the orthorhombic structure. The most 
intense triplet consists of the 020, 112, and 
200 diffraction lines (Fig. 55), which are 
equivalent to the 110 diffraction peaks of 
the cubic perovskite. By monitoring the 
splitting of these triplets at high pressure 
and temperatures, the change of orthor- 



84 



CARNEGIE INSTITUTION 



CO 



— Perovskite 
9.7 GPa, 298 K 




30 31 



32 33 

29 (°) 



34 35 



— i 1 1 r~ 

F< b.i M 9o.9 Si< % Au 
— Perovskite 
4.2 GPa, 877 K 




30 31 



32 33 
20 (°) 



34 35 



Fig. 55. (a,b) Diffraction patterns of (Fe,Mg)Si0 3 - 
perovskite at 9.7 GPa and 298 K and at 4.2 GPa 
and 877 K. 



hombic distortion can be obtained directly. 
The lattice parameters and unit cell vol- 
umes of the (Fe,Mg)Si0 3 -perovskites de- 
termined at high pressures and 298 K in this 
manner are listed in Table 8. 

Pressures measured on the gold and 



ruby scales were in good agreement, and 
were averaged (standard deviation, 0.2 GPa) 
to yield the reported pressures in Table 8. 
Pressures were also determined by the 
volume compression and P-V equation of 
state of neon (Hemley et al., 1989). 

The compressibilities of the three 
Fe x Mg 1 x Si0 3 perovskites with 
x = 0, 0.1, and 0.2 determined from the 
present study are indistinguishable (Table 
8). The three sets of data were combined for 
a least-squares fit of a second-order Mur- 
naghan equation of state (Murnaghan, 
1944); 



V/V o = /7 + (K'P/KJ]^ 



(1) 



K = - (dP/dlnV) T = K o + K o 'P, (2) 

where V, K, and K' are molar volume, bulk 
modulus, and pressure derivative of the 
bulk modulus; the subscript zero denotes 
the parameters at zero pressure. Two-pa- 
rameter, least-squares fitting yielded K o = 
275(±8) GPa and K ' = 3.7 (±0.8). How- 



300 



280- 



*°260 



220 
220 



(Fe,Mg)Si0 3 
Perovskite 




4 6 
K ' 



8 10 



Fig. 56. Dependence of K o on fixed K\ for the 
298 K isotherm of (Fe,Mg)Si0 3 perovskites. 



GEOPHYSICAL LABORATORY 



85 



Table 8. Lattice Parameters and Unit-Cell Volume of Fe x Mg 1 . i Si0 3 -Perovskite up to 30 
GPa (298 K). 



/>,GPa 


a> A 


b, A 


c, A 


V,A 3 


a/a 

o 


bib 




clc 

o 


V/V 

o 


x=0.0 


















3.86 


4.753 


4.911 


6.875 


160.46 


0.9947 


0.9962 


0.9966 


0.9876 


6.29 


4.736 


4.895 


6.852 


158.84 


0.9911 


0.9931 


0.9932 


0.9776 


13.3 


4.707 


4.869 


6.793 


155.69 


0.9851 


0.9877 


0.9847 


0.9582 


x=0.1 


















2.50 


4.768 


4.916 


6.881 


161.30 


0.9972 


0.9971 


0.9965 


0.9908 


9.69 


4.726 


4.883 


6.819 


157.37 


0.9885 


0.9903 


0.9875 


0.9667 


13.5 


4.707 


4.867 


6.796 


155.70 


0.9844 


0.9871 


0.9842 


0.9564 


18.6 


4.683 


4.848 


6.761 


153.51 


0.9795 


0.9832 


0.9792 


0.9430 


27.2 


4.648 


4.815 


6.690 


149.73 


0.9721 


0.9765 


0.9689 


0.9197 


x=0.2 


















5.13 


4.770 


4.905 


6.857 


160.41 


0.9944 


0.9940 


0.9925 


0.9810 


13.3 


4.713 


4.868 


6.795 


155.87 


0.9826 


0.9864 


0.9835 


0.9532 


20.3 


4.689 


4.846 


6.750 


153.37 


0.9776 


0.9820 


0.9769 


0.9379 


29.6 


4.642 


4.807 


6.688 


149.24 


0.9679 


0.9740 


0.9680 


0.9126 



ever, since the total range of volume com- 
pression in the present study was only 9%, 
the data were better used to constrain only 



1.02 
1.00 
0.98 



I 


1 X r- 1 *,J „l J 

Mg ) . x Fe x Si0 3 — Perovskite 

877 K — 298KIK _ 
X- 0.0 + 


- 


V -820K «" 

N. •773 K 01 * Hi * ,Twn P 


- 


>s^ • 658 K 


- 


548KV544 K 


I 


382 KN» - 
1 1 1 1 1 1 



>° 

^ 0.96 

0.94 

0.92 

0.90 

5 10 15 20 25 30 

Pressure, GPa 

Fig. 57. P-V-T relations for Fe x Mg 1]5 Si0 3 
perovskites. Open squares (x=0.2), open circles 
(x=0.1) and crosses (x=0) are measurements at 
298 K. Solid circles (x=0.1) are high-pressure data 
at high temperatures as marked next to the data 
points. The solid curve is the 298 K isotherm. 



one parameter by fixing K\ The depend- 
ence of K q on the fixed K o is shown in Fig. 
56. The preferred value is K o = 272.5(±2.4) 
GPa when K = 4 is assumed. The curve and 

o 

data are plotted in Fig. 57. When a second- 
order Birch equation of state (Birch, 1952) 
is used instead of the Murnaghan equation 
to fit the data, we obtained K o = 273.4(±2.4) 
GPa with fixed K o = 4. Within the present 
range of compression, the Murnaghan and 
Birch equations are indistinguishable. 

A similar least-squares fit for the iso- 
thermal compression data of the three lat- 
tice parameters yields: 

b ao = L291(0.02)GPa 7 , K'a o = 11.4; 

b bo = 1. 053(0.011 )GPa - 1 , K'b = 13.9; 



86 CARNEGIE INSTITUTION 

Table 9. Lattice Parameters and Unit-Cell Volume of Fe^M^SiC^-Perovskite at High 
Pressures and Temperatures. 



/>,GPa 


t,k 


a> A 


b, A 


c, A 


v,A 3 


ala o 


bib. 


clc m 


v/v # 


7.2 


298 


4.648 


4.815 


6.690 


149.73 


0.9721 


0.9765 


0.9689 


0.9197 


26.8 


382 


4.661 


4.802 


6.696 


150.46 


0.9749 


0.9777 


0.9698 


0.9243 


23.9 


544 


4.665 


4.830 


6.730 


151.63 


0.9757 


0.9795 


0.9746 


0.9315 


22.5 


548 


4.668 


4.829 


6.735 


151.81 


0.9762 


0.9793 


0.9755 


0.9325 


15.1 


658 


4.737 


4.872 


6.790 


156.72 


0.9908 


0.9881 


0.9834 


0.9627 


11.4 


773 


4.745 


4.894 


6.829 


158.56 


0.9923 


0.9925 


0.9890 


0.9740 


8.38 


820 


4.770 


4.908 


6.863 


160.66 


0.9975 


0.9954 


0.9939 


0.9869 


4.19 


877 


4.794 


4.937 


6.916 


163.72 


1.0027 


1.0014 


1.0016 


1.0057 



Table 10. Zero-Pressure Bulk Modulus and Linear Compressibilities of Fe^Mg^SiC^ 
Perovskite at 298 K. 



o 


FT 

o 


b„ 


K 


b a 


P 

max 


rneda 


Sample 


X 


GPa 






TPa» 


TPa-» 


TPa 1 


GPa 






246 1 




1.31 


1.20 


1.56 







single xl. 





247 2 


4 


1.41 


1.07 


1.57 


10 


M-E-W 


single xl. 





254 3 


4 


1.30 


1.04 


1.24 


13 


M-E, Ne 


single xl. 





258* 


4 


1.58 


1.19 


1.10 


7 


M-E 


powder 





266 5 


3.9 


— 


— 


— 


112 


none 


powder 


0.12 


272« 


4 


1.29 


1.05 


1.33 


30 


Ne 


powder 


0,0.1,0.2 



(1) Adiabatic bulk modulus and compressibilities measured with Brillouin scattering tech- 
nique, 

(2)-(6) Isothermal moduli and compressibilities determined by fitting P-V-a-b-c data meas- 
ured with x-ray diffraction techniques. 

M-E: methanol ethanol mixture; -H: -water. 

Reference 

(1) Yeganeh-Haeri et al. (1989) 
(2)Kudohefa/.(1987) 
(3) Ross and Hazen (1989) 
(4)Yagiera/.(1982) 

(5) Knittle and Jeanloz (1987) 

(6) Present study 



GEOPHYSICAL LABORATORY 



87 





1.01 


1.00 
o 




0.94 




0.97 



I 




1 A J 

Mg^Fe 


x Si °3- 


— Perovskite 





• 


877 K 

• 820 k ;•; 

^V . 773 K oi 
+ \~ * 658 K 


— 298 K fit 

D 

o _ 

•High Temp 


- 




o\ 




548 K 
v. .544 K 
XsV o 382j* 


I 


a 


I I I 


1 


i r 



5 10 15 20 25 30 

Pressure, GPa 



1.01 
1.00 
,Q O 0.99 - 
0.94 - 

0.97 - 

1 



1.01 

1.00 

o°0.99 
o 

0.94 
0.97 



Mg^^ejjSiOg — Perovskite 



• 877K 



— 298 K fit 
X- 0.0 + 
02 O 
.820K 0.1 O 

•770 1/ °- 1 • HighTsmp 




658 K 

544 K _ 
\.382K 



J L 



5 10 15 20 25 30 

Pressure, GPa 



i i I i i r 

Mg^xFexSiOj — Perovskite 
• 877 K x. oo + 

2 o 
\ + ,820 K , . High Temp 




548 K X V 544 K 



382 K^^> 
L _t 



5 10 15 20 25 30 

Pressure, GPa 



Fig. 58. Compression of lattice parameters, (a) 
a. (b) b. (c) c. See Fig. 57 for notation. 



1.026 

1.020 
oo 

8 1.015 
^ 1.010 



>°- 



1.005 r- 
1.000 



MaJoFeJ SiO| — Perovskite 
- 09 af ^ 4.19 GPa % 


8.38 GPa /6 _ 


15.1 GPa° X° 


26.8 GPa ^ 
° ^^° 23.9 GPa 

r-^""" ° 22.5 GPa 
27.2 GPa 

I I I I I I 



0.995 

280 380 480 580 680 780 880 

Temperature, K 

Fig. 59. Thermal expansion, V ^V m , as a func- 
tion of temperature at various pressures. The 
value of P is marked at each data point. 



b co = 1.330(0. 0l8)GPa ■' K'c = 11.0; 

b x = -(dlnx/dlP) T 

The three compression curves and data 
points are plotted in Fig. 58A-C. 

A study for simultaneous high P-T dif- 
fraction measurements was also conducted 
for Fe 01 Mg 09 SiO 3 perovskite. At tempera- 
tures above 500K, however, the gold stan- 
dard tended to anneal to larger crystals. The 
effect can be seen in Fig. 55, in which the 
298 K diffraction peak of gold is broad due 
to the small grain size, and the 877K peak 
of gold is sharpened. The results of lattice 
parameters and volume as a function of 
pressure and temperature were listed in 
Table 9 and plotted in Fig. 58. The thermal 
expansion as a function of temperature at 
various pressures is plotted in Fig. 59. 

The orthorhombic (Fe,Mg)Si0 3 
perovskite has the axial ratio a:b:c = 
0.97: 1 : 1 .4 1 , which differs from the equiva- 
lent ratio of the ideal cubic perovskite, 



88 



CARNEGIE INSTITUTION 



1:1:1.41, mainly in that the a axis is 3 % 
smaller. The present results clearly show 
that the orthorhombic (Fe,Mg)Si0 3 
perovskite is elastically anisotropic with 
the b axis being the least compressible, ~ 25 
% less compressible than a or c. The com- 
pressibilities of a and c are similar, with c 
slightly more compressible. With such 
differential compressibilities, the differ- 
ence between a and b becomes even larger 
and the structure becomes more distorted at 
higher pressures. Results from other stud- 
ies of linear compressibilities of lattice 
parameters of (Fe,Mg)Si0 3 perovskite are 
listed in Table 10 for comparison. 

Nonhydro static pressure has major ef- 
fect on the relative compressibilities of the 
lattice parameters. Pressure conditions in 
the diffraction measurements of Yagi etal. 
(1982) became clearly nonhydrostatic be- 
tween 7.5 and 9 GPa, and thus only data 
below 7.5 GPa were used for the calcula- 
tions of the compressibility. The pressure 
conditions in the measurements of Knittle 
and Jeanloz (1987) were nonhydrostatic. 
The relative axial compressibility would 
be different from the hydrostatic one. In 
addition, without the resolution to separate 
the orthorhombic splitting of the equiva- 
lent cubic diffraction peaks, relative com- 
pressibilities of lattice parameters could 
not be accurately determined. 

In summary, the differences in K o among 
various studies are larger than the claimed 
uncertainty in each study, but are much 
smaller than those typically observed in 
other materials when compared with meas- 
urements from different laboratories. It is 
also important to emphasize that although 



the extrapolated zero-pressure parameters 
are useful for comparisons with low-pres- 
sure data, they do not carry any specific 
significance in high-pressure experiments. 
Since the purpose of studying the 
(Fe,Mg)Si0 3 perovskite for solid-earth 
geophysics is to assess its role in the lower 
mantle, the more important parameters are 
the density and bulk modulus of perovskite 
with the appropriate composition above 20 
GPa. These parameters were measured 
directly in the present study. 



References 

Birch, R, Elasticity and constitution of the Earth's 
interior, /. Geophys. Res., 57, 227-286, 1952. 

Hemley, R. J., M. D. Jackson, and R. G. Gordon, 
Theoretical study of the structure, lattice dy- 
namics, and equations of state of perovskite- 
type MgSi0 3 and CaSi0 3 , Phys. Chem. Miner- 
als, 74,2-12, 1987. 

Hemley, R. J., C. S. Zha, A. P. Jephcoat, H. K. 
Mao, L. W. Finger, and D. E. Cox, X-ray dif- 
fraction and equation of state of solid neon to 
U0GPsL,Phys.Rev.B,39, 11820-11827, 1989. 

Ito, E., and D. J. Weidner, Crystal growth of 
MgSi0 3 perovskite, Geophys. Res. Lett., 11, 
464-466, 1986. 

Jamieson, J. C, J. N. Fritz, and M. H. Manghnani, 
Pressure measurement at high temperature in x- 
ray diffraction studies: Gold as a primary stan- 
dard, in High-Pressure Research in Geophys- 
ics, S. Akimoto, and M. H. Manghnani, eds., 
Reidel Publ., Boston, pp. 27-48, 1982. 

Jephcoat, A. P., H. K. Mao, and P. M. Bell, 
Operation of the megabar diamond- anvil cell, in 
Hydrothermal Experimental Techniques, G. C. 
Ulmer and H. L. Barnes, eds., Wiley-Inter- 
science, New York, Chapter 1 1 , pp. 469-506, 
1987. 

Knittle, E., and R. Jeanloz, Synthesis and equation 
of state of (Mg,Fe)Si0 3 perovskite to over 100 
gigapascals, Science, 235, 668-670, 1987. 



GEOPHYSICAL LABORATORY 



89 



Knittle, E., R. Jeanloz, and G. L. Smith, The 
thermal expansion of silicate perovskite and 
stratification of the Earth's mantle, Nature, 319, 
214-216, 1986. 

Kudoh, Y., E. Ito, and H. Takeda, Effect of pres- 
sure on the crystal structure of perovskite-type 
MgSi0 3 . Phys. Chem. Minerals, 14, 1987. 

Mao, H. K., T. Yagi, and P. M. Bell, Mineralogy 
of the Earth's deep mantle: quenching experi- 
ments on mineral compositions at high pres- 
sures and temperature, Carnegie Instn. Wash- 
ington Year Book, 76, 502-504, 1977. 

Mao, H. K., J. Xu, and P. M. Bell, Calibration of 
the ruby pressure gauge to 800 kbar under qua- 
sihydrostatic conditions, /. Geophys. Res., 91, 
4673-4676, 1986. 

Ming, L. C, M. H. Manghnani, S. B. Qadri, E. F. 
Skelton, J. C. Jamieson, and J. Balogh, Gold as 
a reliable internal pressure calibrant at high 
temperatures, J. Appl. Phys., 54, 4390-4397, 
1983. 

Murnaghan, F. D., The compressibility of media 
under extreme pressures, Proc. Nat. Acad. Sci. 
USA, 30,244-241, 1944. 

Ross, N. L., and R. M. Hazen, High-pressure 
crystal chemistry of MgSi0 3 perovskite, Phys. 
Chem. Minerals, 16, 415-420, 1989. 

Wolf, G., and M. Bukowinski, Theoretical study 
of the structural properties and equations of 
state of MgSi0 3 and CaSi0 3 perovskites: impli- 
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Manghnani and Y. Syono, eds., Terra Scientific 
Publishing Company (TERRAPUB), Tokyo/ 
American Geophysical Union, Washington, D. 
C, pp. 313-331, 1987. 

Yagi, T., H. K. Mao, and P. M. Bell, Crystal 
structure of MgSi0 3 perovskite, Carnegie Instn. 
Washington Year Book, 76, 516-519, 1977. 

Yagi, T., H. K. Mao, and P. M. Bell, Hydrostatic 
compression of perovskite-type MgSi0 3 , in Ad- 
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Single Crystal X-ray Diffraction 

Study of A New Hydrous Silicate, 

Phase E 

Yasuhiro Kudoh, Larry W. Finger, Robert 

M. Hazen, Charles T. Prewitt, 

and Masami Kanzakv 

Ringwood and Major (1967) investi- 
gated the system MgO - Si0 2 - H 2 at 
pressures between 10 and 18 GPa and at 
temperatures from 600 to 1100°C. They 
discovered three new phases denoted A, B 
and C and suggested phase B as a probable 
host mineral for H 2 in the deep mantle. 
Subsequently, Yamamoto and Akimoto 
(1974) reported the discovery of phase D 
with chemical composition close to that of 
chondrodite Mg(F,OH) 2 2Mg 2 Si0 4 Among 
these, phase B is known to have a tempera- 
ture-pressure stability field higher than the 
others (Akimoto and Akaogi, 1980) but its 
Mg/Si ratio is 3.0 (Finger et ai, 1989). 
More recently Kanzaki ( 1 989) investigated 
phase relations in the system MgO - Si0 2 - 
H 2 up to 15 GPa and 1500°C using a 
uniaxial split-sphere multi-anvil apparatus 
and discovered a new phase that was syn- 
thesized at 1000°C pressures higher than 
13 GPa, which he denoted phase E. This 
hydrous silicate phase has an Mg/Si ratio 
less than 2, close to that of the mantle. 

In this paper we report the crystal struc- 
tural and crystal chemical aspects of phase 
E, which is a potential host for H 2 in the 
mantle transition zone. 



* University of Alberta, Edmonton, Alberta, 
Canada 



90 



CARNEGIE INSTITUTION 



Experimental Results 

Phase E (Kanzaki, 1989) was synthe- 
sized at 15 GPa and 1000°C using a uniax- 
ial split-sphere multi-anvil apparatus. The 
starting material was a stoichiometric 
mixture of high-purity Si0 2 and 2Mg(OH) 2 . 
A single crystal with approximate dimen- 
sions 160x110x40 jiim was used for x-ray 
diffraction, x-ray photographs indicated 
systematic absences of reflections with 
-h+k+1 = 3n for hkl, which is consistent 
with a rhombohedral space group, indicat- 
ing that the space group of phase E is either 
R3m, R3 orR5m. Intensity statistics did not 
indicate a definite conclusion as to whether 
the crystal has center of symmetry or not. 
The cell constants determined by means of 
a four-circle diffractometer, using 14 re- 
flections of with 20 from 26-36°, with a 
wavelength of 0.7093 A were a = 2.959(1) 
A, c=\ 3.844(2) A, V = 104.98(6) A 3 . They 
are close to those refined from powder 
diffraction data [a=2.9701(l) A, 
c=13.842(l) A, V = 106.05(4) A 3 ]. Electron 
microprobe analysis of the specimen at 12 
sampling points showed homogeneous 
chemical composition with MgO 48 .4 wt. % , 
Si0 2 40.1 wt.% (no other element was 
detected), yielding a total of 88.6. When 
closest-packing of oxygen atoms is as- 
sumed, the short axis allows only one 
oxygen atom per layer in the (2 r a 2 plane and 
the length of the c axis allows six oxygen 
layers; therefore, there are six oxygen atoms 
per unit cell. If the difference of the total 
weight is ascribed to H 2 0, the formula is 
calculated to be Mg 227 Si L26 H 240 O 6 . Crystal 
structure analysis is now in progress. 

Since phase E was observed co-existing 



with stishovite in run products of a silica- 
rich starting material (Kanzaki, 1989), phase 
E is considered to have a stability field 
corresponding to the mantle transition zone. 
Phase E has geophysical importance be- 
cause it is a hydrous phase with a chemical 
composition close to that of the mantle. Its 
density, 2.89 g/cm 3 , is rather low, however. 
The composition of phase E can be 
derived from a brucite starting point with a 
cell content of Mg 3 (OH) 6 . If a magnesium 
atom is removed, silicon atoms in tetrahe- 
dral coordination can be placed over this 
vacancy. The two possible reactions are: 



Mg(OH) 2 +Si 4+ «=> 

Si0 2 + Mg 2+ + 2H + , 



(1) 



which corresponds to a single Si per Mg 
removed, or 

2Mg(OH) 2 + 2Si 4+ <=» 

MgSi 2 4 2+ + Mg 2+ + 4H + , (2) 

which results when two Si are involved. 
The measured composition corresponds to 
1.73 Si atoms added for each Mg removed 
from the hypothesized starting position, 
which indicates that both mechanisms 
apply; however, the second one is more 
important. From the diffraction data, it is 
obvious that these substitutions result in 
short-range order. Although clusters of 
defects are expected, the size of the cluster 
does not result in diffuse scattering with 
appreciable intensity. Long-term x-ray 
photographs indicate the existence of dif- 
fuse maxima with the a axis seven times 
longer and the c axis doubled, as compared 
to the subcell. 



GEOPHYSICAL LABORATORY 



91 



References 

Akimoto, S., and M. Akaogi, The system Mg 2 Si0 4 

- MgO - H 2 at high pressures and temperatures- 
possible hydrous magnesian silicates in the 
mantle transition zone, Phys. Earth Planet. In- 
ter., 23, 268-275, 1980. 

Finger, L. W., J. Ko, R. M. Hazen, T. Gasparik, R. 
J. Hemley, C. T. Prewitt, and D. J. Weidner, 
Water in the upper mantle: crystal chemistry of 
phase B and a new anhydrous magnesium silicate, 
Nature, in review. 

Kanzaki, M., High pressure phase relations in the 
system MgO - Si0 2 - H 2 0, EOS, 70, 508, 1989. 

Ringwood, A. E., and A. Major, High-pressure 
reconnaissance investigations in the system 
Mg 2 Si0 4 - MgO - H 2 0, Earth Planet. Sci. Lett., 
2, 130-133, 1967. 

Yamamoto, K., and S. Akimoto, The system MgO 

- Si0 2 - H z O at high pressures and temperatures- 
stability field for hydroxyl-chondrodite, hy- 
droxyl-clinohumite and 10 A -phase, Am. /. Sci., 
277,288-312,1977. 



Spectroscopic Evidence for a new 

New High-pressure Magnesium Silicate 

Phase 

James D. Kubicki and Russell J. Hemley 

Experimental constraints on the miner- 
alogy of the lower mantle have mainly been 
obtained from high-pressure phases that 
are quenchable to ambient pressure and 
temperature (Yagi etai, 1979). A series of 
experiments have been started using the 
laser-heated, diamond-anvil cell and mi- 
cro-Raman spectroscopy to investigate the 
possible existence of non-quenchable 
phases under lower mantle conditions. 
Micro-Raman spectroscopy was employed 
to probe the sample after melting and 
quenching at high pressure. With micro- 



Raman spectroscopy, it is possible to study 
any heterogeneities in the sample that may 
be induced by laser-heating. The in situ 
nature and spatial resolution of the tech- 
nique are ideally suited for identification of 
small amounts of non-quenchable high- 
pressure phases. 

Approximately 1 weight percent plati- 
num black was mixed and ground with 
MgSi0 3 glass to absorb Nd-YAG laser- 
radiation (1.06 mm line). The sample was 
compressed to 35 GPa at room temperature 
and the Raman spectra measured (Fig. 60). 
The platinum fluoresces under the argon 
laser (514.5 nm line) thereby reducing the 
signal-to-noise ratio, and obscuring the 
broad band between 800 and 1100 cm" 1 
observed in previous spectra (Kubicki et 
ai, 1987). The sample was then heated 
with a Nd-YAG laser. Regions exposed to 
the highest temperatures (estimated to be 
above 2000K) formed rounded spots more 
transparent than the surrounding unheated 

MgSiO} 35 GPa Raman spectra 



After heating 764 
626 




i Before heating 



50 250 450 650 850 10501250 

Frequency (cm" 1 ) 

Fig. 60. Raman spectrum of MgSi0 3 glass mixed 
with Pt black at 35 GPa before laser-heating and 
after heating with Nd/Y AG laser and m^/m quench- 
ing. A linear, sloping baseline due to platinum 
fluorescence has been subtracted from both spec- 
tra. 



92 



CARNEGIE INSTITUTION 



regions. Platinum was also concentrated 
around the inner boundary between the 
heated and unheated region. From these 
observations we conclude that melting has 
occurred at the most intensely heated re- 
gions. Heating to lower temperatures was 
also performed to drive subsolidus trans- 
formations such as the crystallization of 
MgSi0 3 -perovskite. In this case, the heated 
region was visibly darker than either the 
starting material or melted regions and the 
Raman spectra are identifiable as MgSi0 3 - 
perovskite (Hemley et ah, 1989). 

The Raman spectrum of the melted and 
quenched sample (Fig. 60) is significantly 
different from the unheated sample. Five 
major peaks (193, 375, 626, 764, and 926 
cm appear in the spectrum. These were 
not present before laser-heating. These 
peaks also became sharper and more in- 
tense with time under the argon-laser radia- 
tion used to measure the Raman spectrum. 
Spectra were also measured upon decom- 
pression. Broad bands centered at 631 and 
997 cm" 1 from MgSi0 3 glass (Kubicki et 
ai, 1987) and peaks of MgSi0 3 -perovskite 
were observed. No unassigned peaks exist 
in the spectrum of the heated region after 
decompression that could be attributed to 
the high-pressure, laser-heated spectrum. 

There are several possible explanations 
for the spectrum induced by laser-heating. 
The unidentified spectrum may be of a 
glass quenched from the high-pressure melt. 
In this case, the spectrum of the glass melted 
at high-pressure would be very different 
from the glass compressed at room tem- 
perature (Kubicki etal. y 1987). The sharp- 
ness of the Raman peaks, however, indicate 
some degree of crystalline order. Crystal- 



lites may have formed under the very rapid 
heating and quenching conditions of the 
experiment. Very fine-grained crystals (i.e., 
less than 1 mm) and poorly crystalline ma- 
terials exhibit peak-broadening effects 
associated with the breakdown of crystal- 
line selection rules (Hemley et aL, 1986). 
The fact that the new peaks become more 
intense and sharper with time under the 
argon laser suggests that annealing or re- 
crystallization has taken place resulting 
from a small degree of heating of the sample 
by the argon laser. Under these high- 
temperature and rapid quench conditions, 
the possibility of crystallizing a metastable 
phase also exists. Another possibility is 
that the high-temperature and pressure 
conditions of the experiment caused a reac- 
tion between the MgSi0 3 glass and the Pt 
black. Formation of a platinum-magne- 
sium silicate under the experimental condi- 
tions can not be ruled out. 

Raman frequencies of silicates at high- 
pressure are compared with this new spec- 
trum in Table 11. Although certain peaks 
may be correlated with known phases, no 
combination of Raman peaks for phases 
previously measured will explain the entire 
spectrum. For example, the peaks at 193 
and 626 cm 1 may be correlated with the 
high-pressure Raman spectra of stishovite 
and MgSi0 3 -perovskite, respectively (Table 
11); but the other peaks of stishovite and 
MgSi0 3 -perovskite at 35 GPa are not pres- 
ent in this spectrum. The intensity pattern 
of the spectrum is also broadly similar to 
that of stishovite. The structure of the phase 
may have features in common with other 
high-pressure silicates, such as octahedral 
Si, which gives rise to these similar Raman 



GEOPHYSICAL LABORATORY 



93 



Table 11. Comparison of Raman frequencies for stishovite, MgSi0 3 -perovskite, orthoenstatite, and the 
spectrum of this study all at 35 GPa (s, strong; m, moderate;w, weak; vw, very weak; b, broad). 



MgSiO, Orthoenstatite* Stishovite b MgSiO -Perovskite 



This Study 



— 


195 m 


— 


193 w 


265 w 


— 


342 w 


— 


360 w 


— 


353 w 


375 b 


— 


— 


454 w 


— 


525 m 


— 


464 s 


— 


— 


647 m 


646 s 


626 b 


— 


— 


648 vw 


— 


770 s 


855 s 


— 


764 s 


1140 m 


969 w 


1040 vw 


926 m 



"Kubicki (unpublished data) 
b Hemley (1987) 
c Hemley etal (1989) 



features. The overall crystal structure, 
however, must be different to account for 
all the peaks observed. It is not known if the 
MgSi0 3 -phases melt congruently at high 
pressures so the new phase may be en- 
riched in either Mg or Si relative to MgSi0 3 . 
In addition, high temperature gradients 
present during laser-heating could have 
altered the composition of the sample lo- 
cally due to the Soret effect (Heinz and 
Jeanloz, 1987). The heterogeneity of the 
sample in this laser-heated region also al- 
lows the possibility of a combination of 
phases giving rise to this Raman spectrum. 
The spectrum most probably arises from 
a previously unidentified phase that ap- 
pears to be non-quenchable from high pres- 
sures. Also, it has been demonstrated that 
micro-Raman spectroscopy, used in com- 
bination with the laser-heated, diamond- 



anvil cell, is a useful technique for probing 
the possible existence of non-quenchable, 
high-pressure phases. Future work to ana- 
lyze the structure of newly identified phases 
should be carried out with in situ, high- 
pressure X-ray diffraction and TEM tech- 
niques. 



References 



Hemley, R. J., H. K. Mao, and E. C. T. Chao, 
Raman spectrum of natural and synthetic 
stishovhe,Phys.Chem.Min., 73,285-290, 1986. 

Hemley, R. J., Pressure dependence of Raman 
spectra of Si0 2 polymorphs: Quartz, coesite, 
and stishovite, in High-Pressure Research in 
Mineral Physics, M. H. Manghnani and Y. Syono, 
eds., Terra Scientific Publishing Co. (TER- 
RAPUB), Tokyo/American Geophysical Un- 
ion, Washington, D. C, 1987. 

Hemley, R. J., R. E. Cohen, A. Yeganeh-Haeri, H. 



94 



K. Mao, D. J. Weidner, and E. Ito, Raman 
spectroscopy and lattice dynamics of MgSi0 3 - 
perovskite at high pressure, in Perovskite: A 
Structure of Great Interest to Geophysics and 
Materials Science, A. Navrotsky and D. A. 
Weidner, eds., Am. Geophys. Union, Washing- 
ton, D. C, pp. 35-53, 1989. 

Heinz, D. L. and R. Jeanloz, Measurement of the 
melting curve of Mg 9 Fe ^iC^ at lower mantle 
conditions and its geophysical implications, /. 
Geophys. Res., 92, 11437-11444, 1987. 

Kubicki, J. D., R. J. Hemley, and H. K. Mao, In 
situ, high-pressure Raman spectroscopy of 
MgSi0 3 , CaSi0 3 , and CaMgSi 2 6 glasses, 
(abstract) EOS, Trans. Am. Geophys. Union, 68, 
1456, 1987. 

Yagi, T., P. M. Bell, and H. K. Mao, Phase rela- 
tions in the system MgO - FeO - Si0 2 between 
150 and 700 kbar at 1000°C, Carnegie Instn. 
Washington Year Book, 78, 614-618, 1979. 



Compression and Polymorphism of 

CaSi0 3 at High Pressures 

and Temperatures 



Liang-chen Chen, Ho-kwang Mao, and 
Russell J. Hemley 



CARNEGIE INSTITUTION 

CaSi0 3 at about 16 GPa and obtained a 
diffraction pattern consistent with the cu- 
bic perovskite. Further, they showed that 
the phase reverted to a glass on release 
from high pressure; this observation was 
confirmed in later diamond-anvil studies 
(Mao et al., 1977). Further information on 
the properties of CaSi0 3 at high pressure 
has been obtained from theoretical calcula- 
tions in which only the perovskite-type 
phase has been examined (Hemley et al., 
1 987 ). The present study was undertaken to 
investigate phase transitions and pressure- 
volume equation of state of CaSi0 3 up to 
conditions equivalent to those at the core- 
mantle boundary. We have also studied the 
phase transitions at low pressure (< 1 5 GPa) 
and examined the range of stability of the 
low-pressure polymorphs. A new phase 
named CaSi0 3 (III) has been identified. In 
addition, we have investigated the onset of 
vitrification of CaSi0 3 -perovskite decom- 
pression below its stability field. 



Experimental Methods and Results 



Introduction 

Numerous experimental studies have 
determined high pressure properties of 
magnesium and iron-magnesium silicates, 
but much less information is available on 
those of CaSi0 3 at under upper and lower 
mantle conditions. Ringwood and Major 
(1967) found a high pressure modification 
of CaSi0 3 (I) (wollastonite) at about 3 GPa. 
The structure was analyzed by Trojer (1 969) 
and found to be related to walstromite. 
Later, Liu and Ringwood (1975) measured 
in situ x-ray diffraction from laser heated 



In the first set of experiments, natural 
CaSi0 3 (I) (Wollastonite) ground and mixed 
with 1% platinum black was used as a 
starting material. The samples were loaded 
in the diamond-anvil cell, and were heated 
with the Nd- YAG laser (A = 1 .06/xm) after 
each pressure increment. Powder x-ray 
diffraction data were collected using a sealed 
tube MoK a source and film techniques with 
a camera radius of about 50 mm. Pressures 
were measured with the ruby fluorescence 
technique. 

The diffraction data demonstrate that 
following increasing pressure and heating, 



GEOPHYSICAL LABORATORY 



95 



1 1 

(a) GPa, CaSi0 3 (l) (Wollastonite) 






1 


i 
(c) 8.5 GPa, 


I 

CaSi0 3 (lll) 




2.753 






g 


ft 


1.982 


1.608 

1 830 


CO 

r 


2507 o. 


2.063 i 1-936 R 1 569 
8.1361 All il 1.761 II. 


CD 


\ il 2241,.! e5 A 1 T. 


J \jJl 1680 | \k 


L_ 


f. 


I 


V 1 ! " V 1 484 

Ul 1.448 
i\A1 402 

1 



15 



20 25 

29 (°) 



30 




20 25 

29 (°) 



30 





I I 
(b) 6.8 GPa, 


CaSiO 


I 

3 (ll) (Walstromite) 




2.922 








3* 




1.810 






(O 


12 819 2256 20 13 197<M 


1.716 






1 k 2158 1955 J \ 
I l 2.490 Alil? 072 JF~ J " 




\?** 1.516 


■♦— < 










_c 


' I I 






1 



15 



20 25 

29 (°) 



30 



CO 

c 



(d) 10.4 GPa, CaSi0 3 (III) 



1.813 1601 




20 25 

29 (°) 



30 



CO 

c 

(D 
•♦— » 

c 




1 1 

(f) GPa, CaSi0 3 (ll) (Walstromite) 



2 194 1 - 97 « , 

2.112 I 1 893/ 
2308? 




15 



20 25 

29 (°) 



30 



fig. 61. Examples of x-ray diffraction patterns of CaSi0 3 as a function of pressure. The patterns were 
digitized from film with an automated densitometer. 



walstromite-type CaSi0 3 (II) is stable up to 
about 7 GPa at 300K. Above 8 GPa 
CaSi0 3 (II) was observed to convert to a 
new non-quenchable phase named 
CaSi0 3 (III) which is stable to 1 1 GPa. This 
phase converts to walstromite-type 



CaSi0 3 (II) when quenched to ambient 
conditions. A list of the x-ray diffraction 
lines observed at 8.3 GPa and at ambient 
conditions is shown in Table 1 2. The simple 
cubic perovskite phase of CaSi0 3 appeared 
above 11 GPa. When the pressure was 



96 



CARNEGIE INSTITUTION 



Table 12. The d-spacings and relative intensities for CaSi0 3 (III) 



CaSi0 3 (ni) 


CaSi0 3 (n) (Walstromite) 


at 


8.3 GPa 


; 


atO.lMPa 


/ 


d(k) 


/ 


d(A) 


2 


3.050 






10 


2.916 


10 


3.002 


9 


2.750 


5 


2.889 


1 


2.692 


1 


2.762 


5 


2.560 


3 


2.608 


5 


2.478 






5 


2.393 


2 


2.448 


7 


2.240 


1 


2.256 


4 


2.122 


3 


2.194 


5 


2.062 


1 


2.112 


5 


1.980 


1 


2.038 


5 


1.919 


1 


1.974 






1 


1.893 


7 


1.831 


4 


1.823 


7 


1.606 


4 


1.644 


2 


1.571 


4 


1.597 



released at room temperature, the perovskite 
structure remained at 0.8 GPa and disap- 
peared at zero pressure. X-ray diffraction 
patterns of CaSi0 3 (I), CaSi0 3 (H), 
CaSi0 3 (]H) and CaSi0 3 -perovskite formed 
at different pressures are compared in Fig. 
61. Changes in the measured d-spacings 
for CaSi0 3 with increasing pressure are 
shown in Fig. 62. 

In a second set of experiments, the 
perovskite phase was synthesized at about 
17 GPa, the sample was examined by x-ray 
diffraction up to 40 GPa and on pressure 
release to ambient conditions. Pressure was 
again measured from ruby fluorescence. 
The sample was heated with the Nd-YAG 
laser after each pressure change in order to 
accelerate transformations in the material 



to reduce pressure inhomogeneity. Four 
diffraction lines of CaSi0 3 -perovskite (110, 
111, 200, and 211) were measured for each 
film. Because of the incompressibility of 
the perovskite phase, additional measure- 
ments at higher pressure were required to 
constrain the equation of state of this phase. 
These measurements also permitted us to 
examine possible polymorphic transfor- 
mations in CaSi0 3 under lower mantle 
pressure and temperature. 

A third set of experiments was therefore 
performed; these were similar to the first 
set except that 3% platinum black was 
added to the sample. Two x-ray diffraction 
lines from the platinum (111 and 200) were 
observed in addition to the four diffraction 
lines from CaSi0 3 -perovskite. The plati- 



GEOPHYSICAL LABORATORY 



97 



3.00 



2.75 



co 2.50 

D) 

I 2.25 

Q. 
CO 

~6 2.00 



1.75 h 
1.50 



CaSi0 3 (ll) 



(III) 



Perov. 



0.0 2.5 5.0 7.5 10.0 12.5 

Pressure, GPa 

fig. 62. Observed d- spacings of CaSi0 3 as a func- 
tion pressure. 



45.0 


_ SL 




CaSiO 3 — Perovskite - 






•V 


281 (+4)GPa, KqS4 


o< 42.5 






V Q = 45.37 (±0.08) A 3 


• 






- B-M fit 


CD 

i 40.0 






D LP data 


_ 




o HP data 


3 








O 








> 








37.5 








35.0 


I 


I 


i i i i®*^. 



25 50 75 100 125 150 

Pressure, GPa 



Fig. 63. Pressure-volume data for CaSi0 3 - 
perovskite at 300K. Squares (LP): low and moder- 
ate pressure data. Circles (H): high-pressure data. 
Curve: Third-order Birch-Murnghan equation fit. 



num diffraction served as an internal pres- 
sure standard; the new ultrahigh-pressure 
equation of state of platinum, recently 
developed by Lawrence Livermore Labo- 
ratory was used to calculate the pressure 
(Holmes, et al., 1989). Again, the sample 
was laser-heated after each pressure change 
in order to drive possible high-pressure 
transformations. The maximum pressure 
reached in this set of experiments is 134 
GPa, the pressure of the core -mantle bound- 
ary. The diffraction data indicate that Ca- 
Si0 3 is stable in the cubic perovskite over 
this entire pressure range. 

The pressure -volume data from the low- 
and high-pressure x-ray diffraction meas- 
urements for the perovskite phase are plot- 
ted in Fig. 63. All data points were fitted 
with a third-order Birch-Murnaghan equa- 
tion of state. The zero-pressure parameters 
are: V o = 45.31 (±0.08) A 3 , K o = 281 (±4) 
GPa, and /T = 4.3 (±0.2), density p o = 4.258 
(±0.008) g/cm 3 . 



Discussion 

The pressure range of stability of the 
CaSi0 3 polymorphs identified in this study 
are indicated in Fig. 62. Above 8 GPa, 
walstromite-type CaSi0 3 (II) converts to a 
new non-quenchable phase CaSi0 3 (III) 
which is stable to 1 1 GPa. Tamai and Yagi 
(1988) have also obtained evidence for 
CaSi0 3 (III), although they report its range 
of stability at 10 to 13.8 GPa. The diffrac- 
tion patterns measured at high pressure 
indicate that the structure is complex and 
cannot be determined from the. available 
powder diffraction data. Experimental 
determination of the density, structure, and 
elastic properties of this phase is essential 
in order to assess the possible role of this 
phase in the upper mantle. It is useful to 
note that recent single-crystal diffraction 
studies suggest that numerous upper mantle 
minerals may indeed have complex struc- 
tures (Finger et ai, in preparation). 



98 



CARNEGIE INSTITUTION 



The perovskite-type of CaSi0 3 remains 
in the simple cubic structure up to at least 
134 GPa. During pressure release, the 
perovskite remains metastable at pressures 
close to 0.1 MPa. It is also of interest to 
compare the densities of the mixed oxide 
assemblage of CaO + Si0 2 (stishovite) with 
that of CaSi0 3 (Richet etal, 1988; Bass et 
ai, 1981). At -80 GPa the density of the 
oxide assemblage exceeds that of CaSi0 3 - 
perovskite. This result may indicate that 
the extrapolated equation of state of 
stishovite overestimates the densities at 
high pressure. Alternatively, the compari- 
son may indicate that CaSi0 3 -perovskite 
may disproportionate at pressures above 
134 GPa (outside the range of the lower 
mantle). 

Our results strongly suggest that cubic 
CaSi0 3 -perovskite is a stable phase through- 
out the entire lower mantle. Under stable 
conditions, the CaSi0 3 -perovskite exists in 
the lower mantle as a major separate phase 
with abundance only next to ferromagne- 
sian silicate perovskite and probably to 
magnesiowustite, depending on the chemi- 
cal composition model (Anderson, 1989). 
Further, the cubic CaSi0 3 -perovskite phase 
may also be significant as a reservoir for 
rare earth elements in the lower mantle 
(Mao et al., this Report). The 300K equa- 
tion of state of CaSi0 3 -perovskite is close 
to that of (Mg 090 Fe 010 ) Si0 3 -perovskite (Mao 
et al.y this Report). We also note that the p o 
of CaSi0 3 -perovskite, 4.26 g/cm 3 , is in 
excellent agreement with the inferred 300K, 
zero-pressure density of the lower mantle. 
Hence, CaSi0 3 -perovskite must be consid- 
ered an "invisible" component, in terms of 
density and bulk modulus constraints, in 
the lower mantle. 



References 

Anderson, D. L., Composition of the Earth, Sci- 
ence, 245,367-370, 1989. 

Bass, J. D., R. C. Liebermann, D. J. Weidner, and 
S. J. Finch, Elastic properties from acoustic and 
volume compression experiments, Phys. Earth 
Planet. Inter., 25, 140-158, 1981. 

Hemley, R. J., M. D. Jackson, and R. G. Gordon, 
Theoretical study of the structure, lattice dy- 
namics, and equations of state of perovskite- 
type MgSi0 3 and CaSi0 3 , Phys. Chem. Miner- 
als, 14,2-12, mi. 

Holmes, N. C, J. A. Moriarty, G. R. Gathers, and 
W. J. Nellis, The equation of state of platinum to 
660 GPa (6.6 Mbar), /. Appl. Phys., in press, 
1989. 

Liu, L. and A. E. Ringwood, Synthesis of a 
perovskite-type polymorph of CaSi0 3 , Earth 
Planet. Sci. Lett., 28, 209-211, 1975. 

Mao, H. K., T. Yagi, and P. M. Bell, Mineralogy 
of the Earth's deep mantle: quenching experi- 
ments on mineral compositions at high pres- 
sures and temperature, Carnegie Instn. Wash- 
ington Year Book, 76, 502-504, 1977. 

Mao, H. K., P. M. Bell, J. W. Shaner, and D. J. 
Steinberg, Specific volume measurements of 
Cu, Mo, Pd, and Ag and calibration of the ruby 
R, fluorescence pressure gauge from 0.06 to 1 
Mbar, /. Appl. Phys., 49, 3276-3283, 1978. 

Richet, P., H. K. Mao, and P. M. Bell, Static 
compression and equation of state of CaO to 
1.35 Mbar,/. Geophys.Res., 75,279-288, 1988. 

Ringwood, A. E., and A. Major, Some high- 
pressure transformations of geophysical 
significance, Earth Planet. Sci. Lett., 2, 106- 
110,1967. 

Tamai, H., and T. Yagi, High-pressure and high- 
temperature phase relations in CaSi0 3 and 
CaMgSi206 and elasticity of perovskite-type 
CaSi03, Phys. Earth Planet. Inter., 54, 370- 
377, 1989. 

Trojer, F. J., The crystal structure of a high- 
pressure polymorph of CaSi0 3 , Z. Kristallogr., 
130, 185-206, 1969. 



GEOPHYSICAL LABORATORY 



99 



The Polarized Raman Spectra of 
Tourmaline 

Mingsheng Peng, Ho-kwang Mao, 

Liang-chen Chen, 

and Edward C. T. Chao 

Polarized Raman spectroscopy (PRS) 
has been used extensively for structural 
and compositional characterization of 
minerals, (White, 1975, Mao etal, 1987, 
Hemley, 1988). The Raman spectra of 
minerals are generally analyzed in terms of 
factor group analysis (McMillan, 1985). 
For tourmaline with several structural 
groupings, a general assumption is that its 
Raman spectra are made of internal modes 
of each of the individual structural units in 
the crystal (Si 6 18 , B0 3 OH), plus lattice 
modes characteristic of the entire unit cell. 
Each structural unit, [Si 6 18 ] 12 \ [B0 3 ] 3 - and 
(OH) 1 ", has its distinctive vibrational spec- 
trum. 

In this paper we present results of PRS 
of samples of tourmaline from three differ- 
ent geological occurrences in China, namely 
granite pegmatites, hydrothermal veins, and 
metamorphic skarns. Our interest is fo- 
cussed on the correlation of the PRS to the 
compositional and structural differences 
among tourmalines, and the nature of or- 
der-disorder of the OH ions in the tourma- 
line structure in regards to the specific 
geological occurrences. 



Crystal Structure of Tourmaline and 
Description of Samples 

Tourmaline is a complex borosilicate of 
aluminum varying considerably in compo- 
sition with a general formula: 

WX 3 Y 6 (B0 3 ) 3 Si 6 18 (OH,F,Cl) 4 . 

where W= Na and Ca; X= Mg, Fe 2+ , Mn, 
Al, andFe 3+ ; and 

Y=Al,Fe 3+ ,Cr,andV. 

As shown by Buerger et al. (1962), 
tourmaline has rhombohedral symmetry, 
and is in the space group R3m - C 3 V . The 
crystal structure is characterized by a layer 
of six nearly regular Si0 4 tetrahedra in 
hexagonal arrangement similar to that of a 
phyllosilicate sheet. The octahedral layer 
consists of three larger central octahedra 
containing X cations, six smaller periph- 
eral octahedra containing Y cations, and 
three boron atoms. The three octahedra of 
X cations (mainly Mg) shares edges and 
forms a trigonal unit similar to a brucite 
[Mg(OH) 2 ]-like layer. The trigonal X octa- 
hedra unit also share edges with the six Y 
cations. Each of the boron atoms is in a 3- 
fold coordination of oxygens at the vertices 
of octahedra of this layer. The W cation and 
OH are located along the 3 -fold axis of 
symmetry in the middle of the unit cell. The 
(OH) hydroxyl groups are confined to three 
Mg(OH) 2 4 octahedra lying in the same 
layer as the three pairs of Al(OH)0 5 octa- 
hedra. 



*U.S. Geological Survey, Mail Stop 929, Reston, 
VA 22920 



100 



CARNEGIE INSTITUTION 



Table 13. Microprobe analysis of tourmaline of three different types 



Types 


Pegmatitic 


Hydrothermal 


Metamorphic 


Sample No 


T05 


T04 


T09 


T06 


T08 


Color 


Red 


Lt. Green 


Green 


Blue 


Deep Blue 


Si0 2 


37.60 


37.05 


35.33 


34.37 


35.1 


fi0 2 


0.22 


0.50 


0.61 


0.32 


0.21 


A1 2 3 


33.30 


31.63 


33.09 


29.83 


32.89 


FeO 


2.19 


4.89 


4.79 


5.43 


6.43 


MnO 


3.30 


0.23 


0.37 


0.18 


0.4i 


MgO 


3.65 


3.95 


8.76 


10.05 


7.03 


CaO 


2.37 


2.58 


0.29 


3.36 


4.11 


K 2 


0.11 


0.20 


0.30 


0.64 


0.29 


Na 2 


2.86 


2.18 


1.66 


1.48 


1.68 


Total 


85.6 


83.21 


85.20 


85.66 


88.17 



The pegmatitic tourmaline samples are 
from Xinjiang Province in northwest China 
(samples no. T05 and T04). The associ- 
ated minerals are beryl, columbite, and 
pollucite. The tourmaline crystals are al- 
most of gem quality. Their color changes 
from rose-red to green and blue along the c- 
axis. Normal to the c-axis, color rings of the 
same color occurs. The tourmaline from 
the hydrothermal vein (T09) came from 
Hunan province of China. It is associated 
with quartz and beryl. The tourmaline crys- 
tals exhibit prismatic habit.The color ranges 
from light green to dark green. The tourma- 
lines from metamorphic skarn (T06 and 
T08) came from the tin deposit of Yunnan 
province of China. The tourmalines have 
the highest iron content among the three 
types of samples. The associated minerals 
are cassiterite, calcite, scapolite and diop- 
side. Chemical compositions of tourmaline 
samples are listed in Table 13. 



Characteristics ofPRS of Tourmalines 
and Assignment of Spectral Peaks 

Polarized Raman spectra of tourmaline 
samples are presented in Table 2. Raman 
peaks are observed in the regions of 0-1200 
cm' 1 and 3400-3600 cm 1 . Representative 
spectra are shown in Figs. 64 and 65. 

The major peaks of the PRS in the 0- 
1200 cm 1 region are related to the [Si 6 18 ] 12 " 
hexagonal rings (Table 14). Peak assign- 
ments are based on the analysis of Raman 
spectra of a powdered tourmaline sample 
by Griffith (1969). In the present study, 
intense Si-0 stretching vibration peaks are 
observed at 1000-1200 cm 1 . Two symmet- 
rical ring stretching peaks lie between 400 
and 570 cm 1 . Two asymmetrical ring 
stretching peaks lie at 962-999 cm 1 and at 
600-700 cm 1 . Two ring deformation stretch- 
ing peaks are located between 220 - 380 
cm 1 . These two ring deformation stretch- 



GEOPHYSICAL LABORATORY 



101 






if) 

c 

Q) 



C/) 

c 

CD 




200 400 600 800 1000 1200 

Wavenumbers, cm" 1 



200 400 600 800 1000 1200 

Wavenumbers, cm" 1 



Fig. 64. Polarized Raman spectra of different types of tourmaline in N direction and in N o direction,. The 
ring deformation stretching peaks of [Si 6 Oj J are very strong at 220-3 §0 cm 1 . The PRS peak correspond- 
ing to the stretching of the B-O bond in BO lies between 700-800 cm 1 . 



ing peaks are very intense. At different po- 
larization directions, the number of Raman 
peaks are the same, but the positions of the 
peaks shift, and the intensities of the peaks 
vary. The PRS in the N e direction is much 
more intense than that of the N direction. 

o 

In addition, as the iron content in the tour- 
maline increases, the spectral peak splits or 
distorts, so that the PRS from the granite 
pegmatite (Fig. 64; T05) are clearly differ- 
ent from the PRS from the skarn metamor- 
phic tourmaline (Fig. 64; T08) along the N o 
direction. 

The PRS peak corresponding to the B- 



O bond in [B0 3 ] 3 - lies between 700 and 800 
cm 1 . Brethous etal. (1981) studied Raman 
spectra of the synthetic system of B 2 3 - 
Si0 2 - Li 2 0. By holding the Li 2 content 
constant but varying B 2 3 and Si0 2 con- 
tent, they found that the intensity of the 760 
cm" 1 peak increased with increasing B 2 3 
content, and that the intensity of the peaks 
at 1040, 950, and 600 cm 1 increased with 
increasing Si0 2 content. Our finding re- 
garding the ring vibrational peaks assigned 
to Si-0 and B-0 vibrational peaks is gener- 
ally consistent with that of Brethous et al. 
(1981). However, the B-0 vibration peaks 



102 



CARNEGIE INSTITUTION 



Table 14. Frequencies (cm 1 ) of polarized Raman spectra of tourmaline in the N e direction 



Types 


Pegmatitic 


Hydrothermal 


Metamorphic 


Powdered 














Samples 














(Griffith, 1969) 


Sample No. 


T05 


T04 


T09 


T06 


T08 




[Si 6 o 18 ] 12 " 








1049 


1048 




V s (Si-O) 


1114 


1115 


1082(s) 


1016(s) 


1016(s) 


1040(6) 


Ring Stretches* 
















543 


540 
563 


510 


527 


526 


569(5) 




437 


436 


403 


484 


487 


464(10) 




404(s) 


404(s) 










Ring Stretches** 
















999 


998 


971 


965 


962 


929(1) 




671 


685 


638 


672 
633 


669 
634 


682 


Ring deformation 
















304 


342(s) 


372(s) 


363(s) 


363(s) 


353(5) 








314 


306 


306 


340(l/ 2 ) 


[B0 3 ] 3 - 
















253(s) 


255(s) 


220(s) 


228(s) 


228(s) 






744 


775 


746 


764 


764 






734(s) 


737(s) 


703(s) 


693(s) 


692(s) 




[OH] 1 " 














V 2 


3635 


3636 


3648 


3629 


3630 




V l 


3573(s) 


355 l(s) 
3577 


3589(s) 


3562(s) 


3555(s) 




V 3 


3460 


3472 


3482 


no 


no 





* = symmetrical stretching vibration 
** = asymmetrical stretching vibration 



GEOPHYSICAL LABORATORY 



103 



in tourmaline often split into two peaks. 
The main splitting is probably due to the 
variation of bond lengths between boron 
and adjacent oxygen (B-0 2 bond length is 
1.375 , B-0 8 bond length is 1.358 A). The 
C 3 symmetry of the boron atom is reduced 
to C 2v , and thus the peak splits into two. 

Raman peaks in the region between 
3400 and 3600 cm 1 are assigned to OH 
stretching. The peak positions and multi- 
plicities in this region are complicated due 
to the combined influence of octahedral 
site occupancies, in- and out-of-phase ef- 
fects, Al/Si ordering, OH/OH 2 ordering, 
alkali cations (K, Na, Li), and the extent of 
Al substitution in octahedral and/or tetra- 
hedral sites. The PRS in tourmaline struc- 
ture peaks assigned to (OH) show clear 
differences parallel to N o as compared to 
N e . The intensities of the main (OH) band 
(v 2 ) in tourmalines are particularly sensi- 
tive to the orientation of the sample. 

The blue (Fig. 65; T06) and deep blue 
(Fig. 65; T08) tourmalines from metamor- 
phic skarn have two (OH) 1 " stretching vi- 
brational peaks. The most prominent fea- 
ture in the spectrum of tourmaline is a 
sharp, intense peak v x at 3550-3590 cm 1 
and a weak peak v 2 at 3630 cm 1 . For the 
blue tourmaline, the two (OH) peaks are 
located at 3562 (Vj), and 3629 (v 2 ) cm 1 ). 
For the deep blue tourmaline, the two (OH) 
peaks are located at 3555 (v^, and 3630 
(v 2 ) cm 1 . 

Based on the crystal structure of tour- 
maline, we know that the (OH) site is at the 
center of the hexagonal silicon tetrahedra 
and below the Na ion. The Na-OH bond is 
3.285 A long. The (OH) ion is surrounded 
by 3 Mg ions which form three octahedra of 



C/) 

c 

CD 




TOc 



*-'V/\/^-,/ , v 



Na T °4 



a T0 6 

^AjunAsyW-\^rvVV\A« 



TOs 



3200 3333 3466 3600 3733 3866 4000 

Wavenumbers, cm -1 

Fig. 65. PRS of [OH] 1 * groups in different types of 
tourmaline in N e direction at 3400-3650 cm 1 . 
Spectra of tourmalines from metamorphic skarn 
(T06 and T08) and from pegmatite and hydroth- 
ermal vein (T04 and T05) are plotted. 

Mg (OH) 2 4 . The Mg-OH bond length is 
2.063A. Thus the tourmaline structure 
contains brucite type (OH) groups. 

The vibration peak assigned to (OH) in 
brucite is shown in Fig. 66 (brucite from 
U.S. National Museum No. 14390, cour- 
tesy of the Division of Mineralogy, U. S. 
National Museum). A very sharp single 
peak is observed at 3648 cm 1 . The singular 
peak is due to its high degree of symmetry 
of (OH) in the brucite structure. The OH 
group is surrounded by one type of cation 
(Mg) only. In tourmaline, although the (OH) 
ion has symmetry similar to that of brucite, 
the surrounding atoms varies. Thus its 
symmetry is reduced and the Raman peak 
splits into two. The deep blue and blue 
tourmaline of metamorphic skarn origin is 
high in Fe 2+ content (Table 13). The Fe 2+ 



104 



CARNEGIE INSTITUTION 



C 



, , J 


L 



3200 3333 3466 3600 3733 3866 4000 

Wavenumbers, cm* 1 
Fig. 66. Raman spectra of brucite [Mg (OH)J. 

replacement of Mg 2+ in the (Mg,Fe) (OH) 2 4 
octahedra causes distortion of octahedra 
and splitting of the OH peak. 

The PRS of tourmalines from the granitic 
pegmatite and from the hydrothermal vein 
have an additional OH peaks. There are 
three peaks attributed to (OH) stretching. 
The rose red Mn-bearing tourmaline has 
three (OH) peaks at 3460 (v 3 ), 3570 (v x ) 
and 3635 (v 2 ) (Fig. 65; T05). The three 
peaks may be accounted for if (OH) occupy 
two different sites. In addition to the one at 
the center of the unit all in the middle of the 
ring as mentioned earlier, (OH) may also 
substitute an oxygen which surrounds bo- 
ron atoms, and form an (OHB0 2 ) ion group. 
The location of this peak is similar to that of 
B-0 stretching vibrational peak of HOB0 2 2 " 
ion (Grice etal., 1986). The light green Fe- 
bearing tourmaline (Fig. 65; T04) from the 
granite pegmatite has 4 peaks where the v x 
peak splits into two. These four peaks are 
located at 3472 (v 3 ), 3551 and 3577 (v,), 
and 3636 (v 2 ). 



Conclusion 



Based on the PRS of single crystals of 



tourmaline, we are able to assign the vibra- 
tional spectra to [Si 6 18 ] 12 \ [B0 3 ] 3 \ and 
[OH] 1 ". The general feature of the polarized 
Raman spectra (PRS) of tourmaline in the 
ranges of 200-1200 and 3400-3600 cm 1 
are presented. Strong peaks of tourmaline 
were observed at 1000-1200 and 200-400 
cm 1 . They belong to Si-0 stretching vibra- 
tion and ring deformation vibration of 
[Si 6 18 ] 12 \ Strong peaks of [B0 3 ] 3 - vibra- 
tion were measured at 700-800 cm* 1 . PRS 
peaks of [B0 3 ] 3 " shift to higher frequencies 
in the N direction. 

o 

Strong peak of (OH) 1 " vibration occurs 
at 3550-3565 (v^ in the N c direction. The 
(OH) vibration is strongly polarized. PRS 
of (OH) can only be detected in the N e 
direction. The (OH) group in the metamor- 
phic skarn tourmaline occupies a single 
site. The site occupancy is ordered. In 
hydrothermal and granitic pegmatite tour- 
malines, (OH) occupies two sites with dis- 
ordered distribution. The (OH) vibrational 
can be used to characterize site occupancy, 
and are potentially indicative of the mode 
of geological occurrences of tourmaline. 



References 



Brethous, J. C, A. Levasseur, G. Villeneuve, P. 
Echegut, and P. Hagenmueller, S tudies by spec- 
troscopic Raman and by RMN of the glasses of 
the system B 2 3 - Si0 2 - Li 2 0, J. Solid State 
Chem.,39, 199-208, 1981. 

Buerger, M. H., C. W. Burnham., and D. R. 
Peacor, Assessment of the several structures 
proposed for tourmaline, Acta Crystallogr., 15, 
583-590, 1962. 

Grice, D. J., and J. V. Velthuigen, Moydite (Y. 
REE) [B(OH) 3 (C0 3 )], a new mineral species 
from the evans-lou pegmatite, Quebec Can. 



GEOPHYSICAL LABORATORY 



105 



Min. y 24, 665-673, 1986. 

Griffith, W. P., Raman studies on rock-forming 
minerals, Part I orthosilicates and cyclosilicates, 
/. Chem. Soc. (A), 1372-1377, 1969. 

Hemley, R. J., H. K. Mao, and E. C. T. Chao, 
Raman spectrum of natural and synthetic 
stishovite, Phys. Chem. Minerals, 13, 285-290, 
1986. 

Mao, H. K., R. J. Hemley, and E. C. T. Chao, The 
application of micro-Raman spectroscopy to 
analysis and identification of minerals in thin 
section, Scanning Microscopy, 7,495-501, 1987. 

McMillan, P., Vibration spectroscopy in the min- 
eral sciences, Rev. Mineral., 14, Miner. Soc. 
Am., 9-63, 1985. 

White, B. W., Structural interpretation of lunar 
and terrestrial minerals by Raman spectros- 
copy, in Infrared and Raman Spectroscopy of 
Lunar and Terrestrial Minerals, C. Karr, Jr., 
ed., Academic Press, New York, Chap. 13, pp. 
325-356, 1975. 



New Optical Transitions in Type Ia 

Diamonds 

at Very High Stresses 

Russell J. Hemley and Ho-kwang Mao 

The generation of ultrahigh pressures in 
the megabar range is now routine with the 
diamond-anvil high-pressure cell (Mao, 
1988). One of the important features of the 
diamond-cell arises from the transparency 
of the diamond anvils to large regions of the 
electromagnetic spectrum, permitting spec- 
troscopic characterization of materials at 
high pressures using ultraviolet, visible, 
and infrared radiation (Hemley etal, 1987). 
Type Ia diamonds are used in ultrahigh 
pressure studies owing to the presence of 
nitrogen platelets which may enhance their 
strength (Mao et aL, 1979). The nitrogen 



impurities in these diamonds give rise to a 
variety of absorption and luminescence 
systems in the visible and ultraviolet at 
ambient pressures (Walker, 1979). In opti- 
cal studies using the diamond-anvil cell, 
the absorption system at 3 eV in type Ia 
diamonds serves as an effective absorption 
edge, precluding most optical measure- 
ments at higher energies. Laser excitation 
in this region gives rise to a broad back- 
ground fluorescence that can complicate 
optical measurements of samples within 
the cell. Further, the enhancement of this 
luminescence at very high pressure (above 
200 GPa) can interfere with measurements 
of ruby fluorescence used for pressure de- 
termination (Mao et al. 9 1978). 

Recently, we performed a series of op- 
tical studies of hydrogen and a variety of 
materials compressed at pressures in the 
200 GPa range (Mao and Hemley, 1989; 
Hemley and Mao, this Report). During the 
course of this work we discovered dramatic 
changes in the optical characteristics of the 
diamonds in the high stress regions (tips) of 
the anvils. Documenting these effects is 
essential for further optical studies of ma- 
terials at pressures above 200 GPa. In par- 
ticular, this work is a prerequisite for opti- 
cal characterization of the pressure-induced 
insulator-metal transition in hydrogen and 
other systems. 

In the present work optical measure- 
ments were performed on anvils with 25- 
50 mm diameter tips, 300-500 mm culets, 
and bevel angles of 8-10° (see Mao, 1988). 
As a result of their small tips, at a given load 
these diamonds generate higher stresses 
within the anvils than those used in previ- 
ous spectroscopic studies. The spatial de- 



106 



CARNEGIE INSTITUTION 



0) 



2.41 eV 
Excitation 



?\ 




J \ Diamond 
\ Fluorescence 



V. 



X 



2.0 1.9 1.8 

Energy, eV 



1.7 



Fig. 67. Fluorescence spectrum of a type la 
diamond anvil at ultra-high pressure excited with 
514.5 nm (2.41eV) Ar + laser line. The sample 
consisted of hydrogen and ruby at a peak pres- 
sure of 250 to 300 GPa. 



pendencies of luminescence and Raman 
spectra within the anvils were measured 
using a -135° scattering configuration 
with a 2 x 2 mm aperture and an argon-ion 
laser beam focused to 2-4 mm at the im- 
aged spot within the diamond (Hemley et 
al., 1987). An example of this fluorescence 
is shown in Fig. 67. With increasing stress 
(corresponding to sample pressures above 
200 GPa) a fluorescence peak appears at 2 
eV. At very high pressures the signal dra- 
matically increases. The peak tends to shift 
toward lower energies with higher energy 
excitation. Absorption extending through- 
out the visible region of the spectrum, with 
a broad peak at 2.4 eV, is also observed. 

These changes in the fluorescence and 
absorption spectra of the diamonds are 
accompanied by new Raman bands (Fig. 
68). Changes in the Raman spectra have 
been documented with samples consisting 
of hydrogen, neon, ruby, NaCl, and Si0 2 . 
Peak pressures were estimated from both 
the pressure profile determined from ruby 
fluorescence and from x-ray diffraction 
measurements on metal pressure standards. 
Fig. 68 shows the dependence of the Raman 




400 800 1200 1600 2000 

Wavenumbers, cm' 1 

Fig. 68. Raman spectrum of a type la diamond 
anvil as a function of distance from a sample at 
ultrahigh pressure: (a) 30mm. (b) 20mm. (c) 
10mm. (d) sample-diamond interface. The sample 
consisted of NaCl and ruby at a peak pressure of 
-250 GPa. 

spectrum on distance from the sample- 
anvil interface for a sample containing NaCl 
with 10-20% ruby. At the top of the dia- 
mond anvil the zone-center, Raman-active 
T. mode of the diamond at 1333 cm 1 is 

2g 

clearly visible, with no bands apparent at 
lower frequencies. The stress dependence 
of this band has been measured previously 
in diamond anvils under load (Sharma et 
al, 1985; Hanfland and Syassen, 1985). As 
the tip of the diamond is approached a new 
feature at 590 cm* 1 with a broad shoulder at 
-350 cm 1 appears. In some runs, a sharper 
band at -900 cm 1 was also observed. At the 
sample-anvil interface the intensity of the 
band overwhelms the diamond T band. 



GEOPHYSICAL LABORATORY 



107 



Although the relative wavenumbers of the 
bands are independent of laser excitation 
wavelength (indicative of Raman transi- 
tions), they are superimposed on a struc- 
tured fluorescent background, which is 
especially strong with 488.0 and 514.5 nm 
excitation. In addition, the intensities of the 
Raman bands showed a large degree of 
resonance enhancement with decreasing 
wavelength (e.g., 647.1 to 476.5 nm). The 
bands were found to be reversible on re- 
leasing the stress, although the 590 cm 1 
peak can remain at low sample pressures (~ 
30 GPa) before disappearing. The tips of 
the diamonds have been found to exhibit 
higher luminescence intensity upon un- 
loading. 

The present experiments demonstrate 
that significant changes in the electronic 
properties of type la diamonds occur at 
stresses in the 200 GPa range. The lumines- 
cence may be due to pressure-induced elec- 
tronic changes in deep level impurity cen- 
ters (Walker, 1980). If so, the Raman bands 
may be associated with localized vibra- 
tional modes at these centers. In this regard, 
we note that the N-V (nitrogen-vacancy) 
defects have an absorption band in this 
region (zero-phonon line at 1 .95 eV at zero 
stress) with a fundamental vibrational in- 
terval in this range (n = 525 cm 1 , also at zero 
stress) (Davies andHamer, 1978). Alterna- 
tively, the new bands may be associated 
with actual changes in the diamond struc- 
ture. There is a close similarity between the 
new Raman features and the one-phonon 
density of states of diamonds which has a 
broad peak centered at 600 cm 1 (Dolling 
and Cowley, 1966). Such a correlation 
would imply a breakdown in crystalline 



selection rules, resulting perhaps from 
growth of defects at the anvil tips or macro- 
scopic flow of the diamond (Mao et al., 
1979). Although a structural transforma- 
tion in the diamond itself induced by non- 
hydrostatic stress also cannot be ruled out 
(Nielsen, 1986), our results indicate that 
such a transition must be reversible. Simi- 
lar measurements carried out on different 
diamond types (type II, lb, including syn- 
thetics) can be used to determine the extent 
to which the optical effects are associated 
with impurities or are intrinsic to diamond. 

References 



Davies, G., and M. F. Hamer, Optical studies of 
the 1.945 eV vibronic band in diamond, Proc. 
Roy. Soc. London A, 348, 285-298, 1978. 

Dolling, G., and R. A. Cowley, The thermody- 
namic and optical properties of germanium, 
silicon, diamond, and gallium arsenide, Proc. 
Phys. Soc. (London), 88, 463-494, 1966. 

Hanfland, M., and K. Syassen, A Raman study of 
diamond anvils under stress, /. Appl. Phys., 57, 
2752-2756, 1985. 

Hemley, R. J., P. M. Bell, and H. K. Mao, Laser 
techniques in high-pressure geophysics, Sci- 
ence, 237, 605-612, 1987. 

Mao, H. K., Static compression of simple molecu- 
lar systems in the megabar range, in Simple 
Molecular Systems at Very High Densities, P. 
Loubeyre, A. Polian, and N. Boccara, eds., Ple- 
num, New York, pp. 221-236, 1988. 

Mao, H. K., and R. J. Hemley, Optical studies of 
hydrogen above 200 gigapascals: evidence for 
metallization by band overlap, Science, 244, 
1462-1465, 1989. 

Mao, H. K., P. M. Bell, J. W. Shaner, and D. J. 
Steinberg, Specific volume measurements of 
Cu, Mo, Pd, and Ag and calibration of the ruby 
R, fluorescence pressure gauge from 0.06 to 1 
Mbar, J. Appl. Phys., 49, 3276-3283, 1978. 

Mao, H. K., P. M. Bell, K. J. Dunn, R. M. Chrenko, 
and R. C. Devries, Absolute pressure measure- 



108 



CARNEGIE INSTITUTION 



ments and analysis of diamonds subjected to 

maximum pressures of 1.3-1.7 Mbar, /. Appl. 

Phys., 50, 1002-1009, 1979. 
Nielsen, 0. H., Optical phonons and elasticity of 

diamond at megabar stresses, Phys. Rev. B, 34, 

5808-5819, 1986. 
Sharma, S. K., H. K. Mao, P. M. Bell, and J. A Xu, 

Measurement of stress in diamond anvils with 

micro-Raman spectroscopy, /. Raman Spectros., 

16, 350-352, 1985. 
Walker, J., Optical absorption and luminescence 

in diamond, Rep. Prog Phys, 42, 1605-1659, 

1979. 



Premonitory Twinning in the High- 
Pressure Phase 
Transition of Zr0 2 

Yasuhiro Kudoh, Charles T. Prewitt, and 
Haruo Arashi* 

At room temperature, a single crystal of 
the monoclinic phase of Zr0 2 with space 
group P2Jc transforms to a single crystal of 
the orthorhombic phase at 35 kbar (Fig. 
69). At pressures higher than 130 kbar, a 
further phase transition to a different 
orthorhombic phase with the cotunnite- 
type structure is known. In this paper we 
report two observations of stress-induced 
twinning: the formation of 90° twin do- 
mains about the c axis in single crystal Zr0 2 
of the orthorhombic phase, and formation 
of ( 1 1 1 ) twinning in a single crystal Zr0 2 of 
the tetragonal phase under the application 
of stress in a diamond-anvil cell at 298K. 
These observations provide direct evi- 
dence of ferroelastic behavior in Zr0 2 and 
further corroborate predictions of the oc- 



*Tohoku University, Research Institute for 
Scientific Measurements, Sendai, Japan 



Tetro. 




2 3 4 5 6 7 
PRESSURE (GPo) 



Fig. 69. In situ phase diagram for Zr0 2 deduced 
from diffraction measurements at high tempera- 
tures and pressures (after Arashi et al., 1988). 



currence of a displacive phase transition to 
a higher symmetry phase in this material at 
high temperatures and pressures. 



Twinning in the orthorhombic phase 
with a tetragonal symmetry operation 

A single crystal of Zr0 2 was pressurized 
up to 45 kbar with cedar oil as the fluid- 
pressure medium using a modified Merrill- 
Bassett type diamond-anvil pressure cell. 
After loading in the diamond-anvil cell, the 
pressure on the crystal was gradually in- 
creased up to 45 kbar at room temperature, 
exceeding the hydrostatic limit of cedar oil. 
The pressure was then reduced slowly back 
to ambient pressure and the sample re- 
moved from the cell. X-ray precession pho- 
tographs were made on the crystal, both 
before and after pressure loading and at 45 
kbar, using Mo#a radiation. Fig. 70 shows 
an x-ray precession photograph taken of 



GEOPHYSICAL LABORATORY 



109 



a£ b* b* 

t 




h* 

b L' 



Fig. 70. X-ray precession photograph of Zr0 2 after pressure loading to 45 kbar. Twinning by a mirror 
plane parallel to the b-c plane [(100) twinning] is indicated by L. Twinning resulting from fourfold 
rotation about the c axis of the orthorhombic phase is indicated by L'. 






the pressure-released specimen at ambient 
conditions. An analysis of the precession 
photograph indicates the presence of two 
types of twinning: 

(1 ) Twinning by mirror plane parallel to 
the b-c plane [(100) twinning]. Reciprocal 
lattice axes resulting from these twin op- 
erations are indicated by L in Fig. 70. This 
type of twinning is known to occur in the 
monoclinic phase prior to transition to the 
orthorhombic phase (Kudoh et aL, 1986). 
The mechanism of this twinning can read- 
ily be interpreted by the slip system 
(100)<001>. In monoclinic Zr0 2 this slip 
system results in a 1 80° rotation of the axes 
about the c axis, such that the b axis in some 
domains lies parallel to the -b axis in others. 



(2) Twinning by fourfold rotation about 
the c axis of the orthorhombic phase (U in 
Fig. 70). This twinning is consistent with a 
unit cell rotation of exactly 90° about the c 
axis, such that the a axis in some domains 
lies parallel to the b axis in others. Because 
the pressure of 45 kbar exceeds the hydro- 
static limit of the cedar oil, this twinning is 
thought to have occurred under a non- 
hydrostatic condition. Since the fourfold 
symmetry operation is included in the 
tetragonal or cubic class, this twinning is 
considered to be a premonitory phenome- 
non, suggesting the possible existence of a 
phase transition of the orthorhombic phase 
to tetragonal symmetry, which was con- 
firmed by the experiment described below. 



110 



CARNEGIE INSTITUTION 



Twinning in the tetragonal phase with a 
cubic symmetry operation 

Another single crystal of Zr0 2 was pres- 
surized up to 550kbarat room temperature. 
Pressure was generated using a lever-type 
diamond-anvil cell and measured by using 
the ruby fluorescence method. Distilled 
water was employed as the pressure trans- 
mitting medium. Details of the experimen- 
tal procedure have been reported previ- 
ously (Arashi et al., 1989). The high pres- 
sure phase is quenchable to atmospheric 
pressure when the diamond anvil pressure 
cell is unloaded rapidly (Arashi etal., 1 989). 
After reducing the pressure to room pres- 
sure, the recovered crystal was examined 
by x-ray precession photography. 

An analysis of the precession photo- 
graph indicates the presence of two crystal- 
lographically distinct orientations for the 
tetragonal Zr0 2 crystal, indicating the pres- 
ence of twinning on (111). Because the 
pressure of 550 kbar exceeded the hydro- 



static limit of distilled water, this twinning 
also occurred under a non-hydrostatic 
condition. Because the (111) mirror plane 
is not included in the tetragonal class, but is 
included in the cubic class, this twinning is 
probably a premonitory phenomenon, sug- 
gesting the possible existence of a transi- 
tion of the tetragonal phase to cubic sym- 
metry. 



References 



Arashi, H., O. Shimomura, T. Yagi, S. Akimoto, 
and Y. Kudoh, P-T Phase diagram of Zr0 2 
determined by in-situ x-ray diffraction measure- 
ments at high pressures and high temperatures, 
in Advances in Ceramics, Vol. 24, Science and 
Technology of Zirconia III, The American 
Ceramic Society, Inc., Westerville, Ohio, 493- 
500, 1988. 

Kudoh, Y. and H. Takeda, In situ determination of 
the crystal structure for high pressure phase of 
Zr0 2 using a diamond anvil and single crystal x- 
ray diffraction method, Phys. Chem. Minerals, 
13, 233-237, 1986. 



GEOPHYSICAL LABORATORY 



111 



BlOGEOCHEMISTRY 



Nitrogen Isotope Tracers of Human 

Lactation in Modern and Archeologi- 

cal Populations 

Marilyn L. Fogel, Noreen Tuross/and 
Douglas W. Owsley' 

Variations in the stable isotope ratios of 
carbon (& 3 C)** and nitrogen (# 5 N)** are 
useful for paleodietary analysis of archae- 
ologically-derived skeletal material (e.g., 
van der Merve, 1982; Schoeninger and 
DeNiro, 1984; DeNiro, 1986). Because 
plants and animals have distinctive iso- 
topic signatures, the isotopic composition 
of humans can therefore be correlated with 
diets. For example, the C isotopic compo- 
sition of com is distinct from other crop 
plants, such as beans or squash. The differ- 
ence in the # 3 C value is due to the operation 
of a different photosynthetic pathway (C-4 
photosynthesis) that occurs in corn relative 
to that which is operational in most other 
higher terrestrial plants (C-3 photosynthe- 
sis). Accordingly, the introduction of com 
(maize) into the diet of prehistoric North 
American Indians has been traced with 
stable C isotope ratios of the protein colla- 

' * = <fi-J* M - D 103 . wh ere X refers to »C or 
,5 N, and R refers the ratio of the heavy to light 
isotope of either C (* 3 C/ 12 C) or N ( ,S N/ ,4 N) in the 
sample or the standard. 

* Conservation Analytical Laboratory, Smithsonian 
Institution, Washington, D.C., 20550 

# Department of Anthropology, Smithsonian Insti- 
tution, Washington, D.C., 20550 



gen preserved infossil bones (van der Merve 
and Vogel 1977; Boutton et aU 1983). 

Nitrogen isotopes are useful tracers of 
an animal's diet primarily because isotopic 
fractionation occurs during the metabo- 
lism of dietary nitrogen and its incorpora- 
tion into animal biomass. The protein in the 
tissue of an animal is enriched in 15 N rela- 
tive to the diet of the animal by about +3 %o 
(Minigawa and Wada, 1983). The enrich- 
ment in the 15 N in the animal relative to the 
diet has been used to determine a variety of 
important features concerning prehistoric 
human diets such as the importance of 
marine-derived food sources, legumes, and 
meat (e.g., Schoeninger and DeNiro, 1984). 

One of the major questions in anthro- 
pology is what effect did the introduction 
of horticulture have on weaning and birth 
intervals in prehistoric peoples? Some have 
hypothesized that, before agriculture, 
humans nursed their infants longer and 
concomitantly, birth intervals were longer 
(e.g., Buikstra et al. y 1986). They assume 
that with the introduction of agriculture, 
mothers weaned their babies onto alterna- 
tive food sources at a younger age, and 
were thus able to give birth again in a 
shorter time interval. These hypotheses are 
difficult to test in modem populations, and 
seemingly would be impossible to test in 
prehistoric ones. In this paper, we investi- 
gate whether breast milk has a unique iso- 
topic signature that can be used to trace 
lactation in humans. Infant nutrition in both 
modem and fossil populations was studied 



112 



CARNEGIE INSTITUTION 



Longitudinal Study 



o 



in 

to 



14 



13 - 



12 - 



11 - 



10 - 



9 - 



8 



I 


I I I 
□ 


I I 

■ 
□ □ n 




I I 


I 


I 


— 




□ 


□ 


□ 

□ 
□ 


D 





~~ • 















K 


□ 

m 


K 




• 




D [] 

M 





M 


* 




K 


K 


__U 


I 


I I I 


I I 




I I 


I 


I 



1 



2 3 4 5 6 7 8 9 10 11 12 
Age (months) 



Fig. 71. Longitudinal study of the variation in # 5 N in the fingernail cuttings of a single mother (*) and 
infant pair (□). The time (months after birth) indicates when the fingernails were sampled. The infant's 
hair (■) and the father's fingernails (•) were also measured. The infant was exclusively breast fed until 
5 months of age, when a bovine milk-based formula was introduced (100 ml/ day). Formula amounts 
increased with time to 500 ml/ day at 1 1 months. Dairy products were introduced at 7 months (100 g/ 
day). Fingernails (1-3 mg) were combusted at900°C, as in Tuross etai, (1988). The error of the analysis 
for^NwasztO^oo. 



with carbon and nitrogen isotopic tracers. 
The hypothesis that nursing infants exist 
one trophic level up on the food chain from 
their lactating mothers, and thus protein 
from infant tissue should be enriched in 15 N 
relative to the mother's protein, was tested. 



In our study of contemporary mothers 
and infants, fingernails were sampled and 
analyzed. Fingernails are a rapidly synthe- 
sized tissue easily obtainable from both 
infants and their mothers. Numerous stud- 
ies on nail growth have documented that in 



GEOPHYSICAL LABORATORY 



113 



Cross-sectional Nursing Study 



o 






14 



13 



12 - 



11 



10 - 



9 - 



8 








6 8 10 
Age (months) 



12 14 



Fig. 72. Cross-sectional study of isotope variation in fingernail samples collected from 16 mother (*) and 
infant pairs (D). Several children were sampled at different times afterbirth. All infants were fully breast 
fed for at least three months. At approximately 3 months after birth a variety of substitute foods were 
introduced to their diets. Children who were totally weaned to milk or milk-formula are indicated with 
(•). 



healthy, growing infants, fingernails re- 
quire 2-3 months time to grow from cuticle 
to finger tip. We sampled one infant and her 
mother from birth to 15 months in a longi- 
tudinal study (Fig. 71), in addition to 16 
separate mothers and their infants in a 
cross-sectional study (Fig. 72). In all cases, 
the isotopic composition of the nursing 



infants' fingernails was enriched in 15 N as 
compared to that of the mothers' over the 
age range from three months until several 
months after alternate food sources were 
introduced. A decrease in the infant & 5 N 
values toward those of their mothers corre- 
lates with the introduction of alternative 
nitrogen sources: infant formula, milk, dairy 



114 



CARNEGIE INSTITUTION 



products, and meat. Carbon isotopic com- 
positions of infant fingernails (-17.5 %o) 
were nearly identical to those of their mother 
and were not useful for tracing a human 
milk source. 

Fingernails cut in the first three months 
of life were synthesized in utero. The in- 
crease in the 15 N content in the nursing 
infants' fingernails after 3 months corre- 
sponds to the introduction of breast milk at 
birth (# 5 N = +8.0; n=4). After three months 
of age, each infant was enriched in 15 N by an 
average +2.4 %o, when compared to the 
mother. Four babies who were totally 
weaned at 4-8 months of age to bovine 
milk-based formula (# 5 N = +4) (n=3) or 
whole bovine milk (n=l) showed a de- 
crease in the # 5 N of their fingernails 3-5 
months after the dietary change. The other 
infants who were not given a milk substi- 
tute, or provided formula in limited 
amounts, maintained the enrichment of 15 N 
in their fingernails for the duration of the 
study. Thus, the natural abundance of stable 
nitrogen isotopes provides a measure of the 
nitrogen sources, especially breast milk, 
being utilized by a growing infant. 

No attempt was made to control for the 
diet of the mothers, yet 14 females had an 
average # 5 N of +10 ±0.6 (la). In the lon- 
gitudinal study, the woman had an average 
# 5 N of +10.2 ±0.3. The isotopic composi- 
tion of three individual nails from different 
fingers sampled at one time from this mother 
and her baby had a standard deviation of 
±0.4 %o, which is larger than the mean of 
the adult isotopic signal. In a study of nine 
subjects from Chicago, Schoeller et al. 
(1986) reported an average # 5 N of +9.4. 
Given the diversity of nitrogen sources in 



current diets, and the range of # 5 N in these 
sources, the lack of variation is surprising. 
The difference in # 5 N between infants and 
their mothers (+2.4 %6) is thus eight stan- 
dard deviations away from the adult iso- 
topic mean and provides a distinct tracer of 
lactation. 

Whereas fingernails have a more clearly 
defined and straightforward turnover time 
in infants, collagen synthesis in bone and 
its relation to diet are more complex. Gen- 
erally, the stable isotopic values obtained 
from fossil bone collagen are thought to 
reflect the dietary input over a long period 
of time, because the turnover time of colla- 
gen in adult bone is on the order of 10-20 
years. In the modern American society, 
infants triple their birth weight by one year 
(Ryan and Martinez, 1 987). Therefore, even 
without any resorption of the bone collagen 
present at birth, the one year old infant 
would be expected to have synthesized a 
minimum of two-thirds of its bone mass 
after birth. 

To determine whether a nursing signal 
could be detected in skeletal remains, bone 
samples from infants, small children and 
adults were analyzed for age differences in 
# 5 N values of bone collagen. The samples 
are from archaeological contexts and rep- 
resent pre- and post-horticultural popula- 
tions. This contrast in subsistence patterns 
provides a test of the hypothesis that the 
time of weaning changed after agriculture 
became established. The pre-horticultural 
population sample (13 adults, 34 children) 
was comprised of skeletal remains from 
three Tennessee Valley Middle and Late 
Archaic period sites located in Benton 
County, TN: Cherry (40Bn74), Eva 



GEOPHYSICAL LABORATORY 



115 



Tennesee Valley - Pre-Agricultural 

i — i — i — r* 




Sully — Agricultural 
1 1 I--T-* 



3 4 5 
Age (years) 



'Adult 



Fig. 73. Nitrogen Isotopic composition of bone 
collagen from the Tennessee Valley as a function 
of the age at the time of death of the individual. 
Horticulture was not practiced at this site. 

(40Bnl2), and Ledbetter (40Bn25) (Hig- 
gins, 1982; Magennis, 1977; Lewis and 
Kneberg, 1959; Lewis and Lewis, 1961). 
The subsistence pattern was based on 
hunting and gathering. There is no evi- 
dence for maize horticulture during this 
period, which dates from about 5500 B.C. 
until 2000 B.C. Permission to use the 
samples was granted by J. Chapman and 
M.O. Smith of the Frank H. McClung 
Museum of the University of Tennessee. 

Rib bones from the Sully site (39S14), 
Sully Co., South Dakota, were obtained 
primarily from the Smithsonian collection 
and represent a population dependent on 
horticulture. This protohistoric North Plains 
Coalescent Tradition site dates to A.D. 1 650- 
1700 (Owsley and Jantz, 1978). This popu- 
lation relied on a mixed subsistence econ- 
omy, involving the hunting and collecting 
of wild foods, as well as horticulture with 
principal crops being com, squash, beans, 



CO 




1 2 3 4 5 6 Adult 
Age (years) 

Fig. 74. Nitrogen isotopic composition of bone 
collagen from the Sully site, South Dakota, as a 
function of the age of the individual at the time of 
death. The Sully site is representative of a Plains 
Indian population that practiced maize agricul- 
ture. 

and sunflowers (e.g., Holder, 1970). A total 
of 12 adult and 27 children specimens were 
analyzed. 

Age determination of infants and chil- 
dren in both populations were based on the 
dental calcification standards of Moorrees 
<?fa/.(1963),asmodifiedbyHyman(1987), 
and characteristic lengths of the long bones 
(Merchant and Ubelaker, 1977). Bone 
samples, usually rib fragments (1-2 g), 
were decalcified in either EDTA solution 
or 1 N HC1 (Tuross et ai, 1988), and the 
isotopic ratio was determined as described 
therein. 

An enrichment in 15 N of total collagen 
was measured in almost all of the bones 
tested from one year old infants (Figs. 73 
and 74). Age determination of the humans 
at the time of death is a critical component 
of the study. If the infant age were off by 6 
months to a year, the isotopic ratios would 



116 



CARNEGIE INSTITUTION 



be random. In the Tennessee samples, the 
difference between the babies and the adults 
at 1 year was +4 %o, whereas at Sully it was 
+2.5 %o. Both differences are similar to that 
measured between the isotopic ratio of 
modem infant and maternal fingernails. 
The # 5 N of bones from both archeological 
sites declined sharply at 1 8-20 months. The 
initial enrichment and subsequent deple- 
tion of the isotopic ratio of collagen is 
consistent with the establishment and pres- 
ervation of a nursing signature in the 
younger group and a weaning pattern in the 
older group. The 5 15 N of the newborns was 
variable but, on average, was almost iden- 
tical with that of the adults. These children 
were probably too young to have expressed 
the extra utero nursing pattern, as was the 
case with the isotopic ratios in modem 
infants under 3 months of age. 

From the modem data presented here, 
we conclude that a clear tracer of lactation 
is established in the protein of fingernails. 
In every sample tested, the isotopic ratio of 
a nursing infant was always more enriched 
in 15 N than that of its mother. The results 
from the analysis of prehistoric human 
populations demonstrate that when a suite 
of individuals with known ages are ana- 
lyzed, then the # 5 N of collagen preserved 
in bone can be used as a tracer of infant 
nutrition: breast feeding, weaning, and the 
introduction of alternate food sources. 
Nursing and weaning practices in the pre- 
and post-horticultural Indian populations 
studied were not significantly different from 
one another. In both populations alternate 
food sources were introduced at 18-20 
months, and breast milk became less im- 
portant in the diet. Full realization of the 



application of this technique will require 
the analysis of well-characterized collagen 
from large skeletal populations. 



References 



Boutton T. W. , P. D. Klein, M. J. Lynott, J. E. Price, 
and L. L. Tieszen, Stable carbon isotope ratios as 
indicators of prehistoric human diet, in Stable 
Isotopes in Nutrition, ACS Symposium Series 
258, J. R. Turnland, P. E. Johnson, eds., Ameri- 
can Chemical Society, Washington, D. C. pp. 
191-204. , 1984 

Buikstra, J. E., L. W. Konigsburg, and J. Bulling- 
ton, Fertility and the development of agriculture 
in the prehistoric midwest, Amer. Antiquity, 51 , 
528-546, 1986. 

DeNiro, M. J., Stable isotopy and archaeology, 
Am.ScL, 75, 182-191, 1986. 

Higgins, Katherine F., The Ledbetter Site: A Study 
of Late Archaic Mortuary Patterning. Unpub- 
lished Master's thesis. Dept. of Anthropology, 
The University of Tennessee, Knoxville, Ten- 
nessee, 1982. 

Holder, P., The Hoe and the Horse on the Plains, 
University of Nebraska Press, Lincoln, 1970. 

Hyman, Suzanne A., The Relationship Between 
Dental Age and Long Bone Growth in Arikara 
Infants, Unpublished Master's thesis, The Uni- 
versity of Tennessee, Knoxville, 1987. 

Lewis, Thomas M. N. and Madeline Kneberg, The 
archaic culture in the middle South, Am. Antiq., 
25(2), 161-183, 1959. 

Lewis, Thomas M. N., and M. K. Lewis, Eva, An 
Archaic Site, University of Tennessee Study in 
Anthropology, Knoxville, Tennessee, 1961. 

Magennis, Ann L., Middle and Late Archaic 
Mortuary Patterning: An Example from the 
Western Tennessee Valley, Unpublished Mas- 
ter's Thesis, Dept. of Anthropology, The Uni- 
versity of Tennessee, Knoxville, 1977. 

Merchant, Virginia L. and Douglas H. Ubelaker, 
Skeletal growth of the protohistoric Arikara, 
Am. J. Phys. Anthropoid 46(1), 61-72. 

Minagawa, M. and E. Wada, Step-wise enrich- 
ment of 15 N along food chains, Further evidence 



GEOPHYSICAL LABORATORY 



117 



and the relationship between # S N and animal 
age, Geochim. Cosmochim.Acta,48, 1 135-1 140, 
1984. 

Moorrees, Coenraad F. A., Elizabeth A. Fanning, 
and Edward E. Hunt, Jr., Formation and resorp- 
tion of three deciduous teeth in children, Am. J. 
Phys.Anthropol.,21, 205-213, 1963a. 

Owsley, D. W. and R. L. Jantz, Intracemetary 
morphological variation in Ankara crania from 
the Sully site (39SL4), Sully County, South 
Dakota, Plains AnthropoL, 23, 139-147, 1978. 

Schoeller, D. A., M. Minagawa, R. Slater, and I. R. 
Kaplan, Stable isotopes of carbon, nitrogen and 
hydrogen in the contemporary North American 
food web, Ecol. Food Nutrition , 18, 159-170, 
1986. 

Schoeninger, M. J., and M. J. DeNiro, Nitrogen 
and carbon isotopic composition of bone colla- 
gen from marine and terrestrial animals, Geo- 
chim. Cosmochim. Acta, 48, 625-639, 1984. 

Ryan, A.S. and G.A. Martinez, Physical growth of 
infants 7 to 13 months of age, results from a 
national survey, Amer. J. Physical AnthropoL, 
73, 449-457, 1987. 

Tuross, N., M. L. Fogel, and P. E. Hare, Variability 
in the preservation of the isotopic composition 
of collagen from fossil bones, Geochim. Cosmo- 
chim. Acta, 52, 929-935, 1988. 

van der Merve, N. J., Carbon isotopes, photosyn- 
thesis and archeology, Amer. Sci.,70, 596-606, 
1982. 

van der Merve, N.J., Isotopic evidence for early 
maize cultivation in New York State, Amer. 
Antiquity, 42, 238-242, 1977. 



Nitrogen Isotope Fractionation in the 
Uptake of Ammonium by a Marine Bac- 
terium 

Matthew P. Hoch, David L. Kirchman* 
and Marilyn L. Fogel 

Heterotrophic bacteria can contribute 
substantially to total biomass and biomass 

* College of Marine Studies, University of 
Delaware, Lewes, DE 19958 



production in marine environments. On the 
order of 50% of primary production, in the 
form of dissolved organic matter (DOM), 
can be processed by heterotrophic bacteria 
in marine and freshwater environments 
(Ducklow, 1983). In marine nitrogen cy- 
cling, bacteria have traditionally been 
viewed as consumers of dissolved organic 
nitrogen (Fuhrman, 1987) and regenera- 
tors of ammonium (HoUibaugh, 1980). 
Contrary to this, recent studies have shown 
that ammonium is a significant source of 
nitrogen required for bacterial biomass 
production, and a large fraction of total 
ammonium uptake can be attributed to 
bacteria (Wheeler and Kirchman, 1986). 
For example, in the Delaware Estuary 4 - 
30% of the total ammonium uptake can be 
attributed to bacteria (Hoch and Kirchman, 
in preparation). 

The influence of heterotrophic bacteria 
in changing the isotopic composition of 
organic and inorganic pools of nitrogen in 
the water column has not been considered 
extensively (Altabet, 1988; Sigleo and 
Macko, 1985). In situ microbial processes 
can greatly influence the isotopic signature 
of nitrogen that enters the sedimentary 
records. Large isotope fractionation asso- 
ciated with microbial processes such as 
denitrif ication and nitrification (Mariotti et 
al., 1981) can alter the isotopic composi- 
tion of N0 3 , N0 2 , and NH 4 + , and therefore, 
particulate organic matter when this nitro- 
gen is fixed. A large isotope fractionation 
associated with the assimilation of ammo- 
nium by heterotrophic bacteria would af- 
fect the 15 N abundance of the ammonium 
pool in addition to bacteria and phyto- 
plankton. 



118 



CARNEGIE INSTITUTION 



40 



F 


30 






^ 




X 


20 


CO 






O 


10 








8 12 16 
Time (hrs) 



20 







i 

-4 


b 


o 


IS 




8 15 N 

° "ammonium 


ID 


-8 
-12 


_e = 


-15.0 ±0.76% 

" ^bacteria 




-16 


-i i 


* A A » 
1 1 1* 1 1 1 1 1 1 1 1 1 1 



4 8 12 16 20 
Time (hrs) 



Fig. 75. Growth of Vibrio harveyi on 20 mM ammonium and 10 mM glucose; 

a) bacterial cell numbers over time, b) # 5 N of bacterial nitrogen and residual ammonium in the medium 

for replicate cultures (a, +, ▲ ;b, □,♦). 



In this study, the isotope fractionation 
between NH 4 + and bacterial nitrogen has 
been determined for a common marine 
isolate, Vibrio harveyi, grown on ammo- 
nium as its sole nitrogen source. Bacteria 
have been shown to have two enzymatic 
pathways for NH 4 + assimilation, which are 
regulated by the concentrations of this N 
source in the growth media. The hypothesis 
that the isotopic fractionation would corre- 
late with a switch in the enzymatic pathway 
for the assimilation, from glutamate dehy- 
drogenase to glutamine synthetase as 
ammonium concentration decreased, was 
tested. 

Batch cultures of Vibrio harveyi were 
grown on a minimum nutrient media with 
ammonium and glucose as the sole source 
of nitrogen and carbon, respectively. Addi- 
tions of glucose, to 10 mM, and ammo- 
nium, to either 20, 10, 5, 2, or 0.5 mM, were 
first filter sterilized through 0.22 fm\ Mil- 
lipore™ membrane. Cell growth was fol- 
lowed by monitoring the absorbance at 660 
nm and by cell abundance epifluorescent 



microscopy. Cultures were incubated at 
25 °C until stationary phase of the growth 
curve was reached. 

Cultures were sampled for the measure- 
ment of their ammonium concentration and 
bacterial nitrogen content, and for isotopic 
analysis of ammonium and bacterial nitro- 
gen. Bacterial biomass was collected on 
pre-combusted 25mm Whatmann™ GF/F 
glass fiber filters for analysis of nitrogen 
content with a Hewlett Packard™ 185B 
CHN Analyzer. Ammonium concentration 
of the medium was determined by the indo- 
phenol blue method (Solorzano, 1969). 
Bacteria for isotopic analysis were concen- 
trated by centrifugation, washed with dis- 
tilled water, freeze dried, and stored in 
vacuo. Filtrate collected for ammonium 
isotope analysis was frozen at -80°C until 
distillation. A Labconco™ Rapid Kjeldahl 
System, Rapid Still HI was used for alka- 
line distillation of ammonium (Velinsky et 
al., 1989). Bacterial biomass and zeolite 
with ammonium were converted to N 2 for 
mass spectral analysis by combustion 



GEOPHYSICAL LABORATORY 



119 



(Macko,eftf/., 1987). 

Specific activities for the bacterial en- 
zymes glutamate dehydrogenase (GDH) 
and glutamine synthetase (GS) were meas- 
ured in cultures of V. harveyi grown on 20, 
10, 5, 2, or 0.5 mM ammonium and har- 
vested at mid-exponential growth. Total 
GS activity was assayed using the g-glu- 
tamyltransferase assay of Bender et al. 
(1977). Activity of GDH was assayed by 
following the oxidation of NADH (Sanwal 
and Lata, 1961). 

At high concentrations (20 and 5 mM) 
only a small fraction of ammonium 
(<0.05%) was assimilated by cultures that 
had grown to stationary phase (Fig. 75a). 
These conditions are characteristic of an 
open system, so the isotope enrichment (e) 
approximates the difference between the 
& 5 N of the bacteria and that of ammonium: 

e ~ & 5 N bacteria - # 5 N ammonium. (1) 

For the 20mM NH 4 + cultures, e equaled 
-15 %o (± 0.78 %o) (Fig. 75b). 




-3.2 



-2.8 -2.4 



-2.0 -1.6 



log [NHJ ] (M) 

Fig. 76. Composite plots of the nitrogen isotope 
fractionations for Vibrio harveyi grown on 20, 5, 
2, and 0.5 mM ammonium, plotted as the log of the 
molar ammonium concentration. One error bar 
equals one standard deviation. 



All the ammonium was assimilated by 
the stationary phase in cultures with 2 and 
0.5 mM NH 4 + at the start of growth. The 
isotope ratio of NH 4 + was determined at 
intervals before it was totally assimilated. 
In this case e was calculated with equations 
described by Mariotti et al. (1981): 



£=1000 log (R/RJ/ log f, 



(2) 



where / is the fraction of ammonium 
remaining, R is the ratio of 15 N/ 14 N in the 
initial NH 4 + and R o is the ratio in the sample 
at time (t o ). There is an inverse relationship 
between the ammonium concentration of 
the culture medium and the isotope frac- 
tionation (Fig. 76). V. harveyi grown on 5 
and 20 mM NH/ fractionated ammonium 
nitrogen by ca. -15 %o. At the lowest con- 
centration (0.5 mM) the isotope fractiona- 
tion was the greatest, -22 %o. In order to 
explain the change, the activity of the pri- 
mary ammonium assimilatory enzymes 



100 



:g 80 

o 

< 

.9 60 

o 

8.40 
CO 



I I I I I I I 1 I I I I I I I I 
Glutamine Synthetase 

:\(gs) 

Glutamate 

Dehydrogenase 

(GDH). 



20 - 




» » ' » 



-3.2 



-2.8 



-2.4 



-2.0 



-1.6 



log [NHJ ] (M) 



Fig. 77. Composite plot of percent specific activ- 
ity of glutamine synthetase and glutamate dehy- 
drogenase for V. harveyi grown on 20, 10, 5, 2, 
and 0.5 mM ammonium, plotted as the log of the 
molar ammonium concentration. 



120 



CARNEGIE INSTITUTION 



were assayed. 

The highest specific activities for V. 
harveyi GDH and GS were in the cultures 
with 20 mM and 0.5 mM ammonium, re- 
spectively (Fig. 77). This relationship sug- 
gests that isotope fractionation is depend- 
ent on the enzymatic pathway for ammo- 
nium assimilation. At high ammonium 
concentrations, GDH is the dominant as- 
similatory enzyme for bacteria, and is re- 
sponsible for catalyzing the reaction: 

2-oxoglutarate + NHj + NAD(P)H 
<=» L-glutamate + NAD(P)+ + Hfi. (3) 

At lower concentrations of ammonium, GS 
becomes dominant, and catalyzes the reac- 
tion: 



L-glutamate + NH3 + ATP 
<=> L-glutamine + ADP + P.. 



(4) 



Nitrogen isotope fractionation associ- 
ated with ammonium assimilation by other 
cultured organisms is about the same as 
that for V. harveyi (Table 15). When both 
algal and bacterial species were grown on 
millimolar concentrations of ammonium 
(3.5 to 70 mM), the nitrogen isotope frac- 
tionation ranges from -13.5 to -15 %o. 
Pennock et al. (in preparation) measured 
fractionations within the range of -19 to 
-27 %o for a marine diatom, Skeletonema 
costatum, grown on 50 /xM NH 4 + . These 
values for this diatom are similar to those 
for V. harveyi grown at 0.5 mM NH 4 + . 
Apparently, nitrogen isotope fractionation 



Table 15. Isotope fractionation (c) between NH 4 * and organic matter for various organisms studied. 
Ammonium concentration of growth media are given in parentheses. 



Organism 



e(%o) £(%©) 

High [NH 4 + ] Low [NH 4 + ] 

(mM) (//M) 



Vibrio harveyi 
(marine bacterium) 


-15.0 
(5,20) 


-22.0 
(500) 


(present study) 


Azotobacter vinelandii 
(soil bacterium) 


-14.8 
(70) 




Delwiche and Steyn (1970) 


Anabaena sp 
(cyanobacterium) 


-13.6 
(18) 




Mzcko etal. (1987) 


Skeletonema costatum 
(marine diatom) 




-19 to -27 
(100) 


Pennock et al. (unpublished) 


Phaeodactylum tricornutum 
(marine diatom) 


-13.6- 
(3.5) 




Wada and Hattori (1978) 



* Recalculation of data from Wada and Hattori ( 1978) using equation 1 1 from Mariotti et al. ( 198 1 ), and 
assuming f=0.6 and initial substrate &*N = -1.5 %o when phytoplankton biomass # 5 N is approximately 
-12 %o. 



GEOPHYSICAL LABORATORY 



121 



associated with ammonium assimilation is 
not species specific. We conclude that the 
rate-limiting step in ammonium assimila- 
tion for high and for low ammonium con- 
centrations is similar among different or- 
ganisms. 

Potential sites of an isotope effect (i.e., 
the rate-limiting step) for ammonium as- 
similation are depicted in Fig. 78. The 
equilibrium isotope effect between NH 4 + 
andNI^ is -19.2 %o at 25°C (Hermes etai, 
1985). The 15 N is concentrated in NH 4 + , 
whereas 14 N is enriched in the NH 3 . In cal- 
culating the kinetic isotope effect of 
alanine and glutamate dehydrogenase from 
bovine liver. Weiss et al. (1988) corrected 
the observed values to account for equilib- 
rium isotope effects during the deprotona- 
tion of NH 4 \ because the actual substrate 
for the enzyme is NH 3 . Therefore, the iso- 
tope effects for alanine and glutamate 
dehydrogenase are inverse, +8%o and 
+2 %o(±l %6), respectively. Assimilation of 
ammonia with a # 5 N of -19 by these en- 
zymes would yield # 5 N values for bacterial 
cells of - 1 7 .2 %o and - 1 1 .2 %c, respectively. 
Isotope fractionation for V. harveyi grown 
on 20 mM NH 4 + (ca. -15 %o) is between 
these values. Alanine dehydrogenase may 
be involved in V. harveyi ammonium as- 
similation, however, its activity was not 
assayed in our cultures. 

We are presently measuring the isotope 
fractionation by glutamine synthetase. Also 
inherent in determining the isotope frac- 
tionation of GS is the pre-equilibrium iso- 
tope effect between NH 3 and NH 4 \ because 
NH 3 is the species taken up by the enzyme. 
The rate controlling steps of many chemi- 
cal reactions are preceded by rapid and 




high 

[NH+J 

DIFFUSION 



■ 3 ^ ... >4 
potential isotope effect 



low 

[NHJ] 

ACTIVE TRANSPORT 



Fig. 78. Schematic diagram of the pathways for 
ammonium assimilation in a bacterial cell show- 
ing the potential sites of isotope effects. Values for 
isotope fractionation are explained in the text. 

reversible pre-equilibria (Bigeleison and 
Wolfsberg, 1958). Glutamine synthetase 
was assayed at two pH values to determine 
the effect of this pre-equilibrium on the 
measured fractionation of the reaction. At 
pH 7.0, where less than 1 % of the total N is 
NH 3 , the isotope fractionation (e) for both 
the pre-equilibrium step and the enzyme 
reaction itself is -8.0 ± 0.3 %o (r 2 = 0.95; n 
= 1 3). At pH 8.6, where a greater proportion 
of the total N is NH 3 , the total fractionation 
is -123 ± 0.5 %o (r 2 = 0.94; n = 9). Accord- 
ingly, the fractionation by GS itself was 
determined by calculations modified from 
Bigeleison and Wolfsberg (1958): 



total equilibrium GS* 



(5) 



At pH 7.0 and 8.6, respectively, inverse 



122 



CARNEGIE INSTITUTION 



isotope effects of +10.8 and +3.0 were cal- 
culated. Both values have a similar direc- 
tion and magnitude as those measured by 
Weiss et al (1988) for ADH and GDH. 

Therefore, at lower ammonium concen- 
trations the observed isotope fractionation 
for V. harveyi is a result of some other 
process involved in the ammonium assimi- 
latory pathway. Bacteria obtain ammonium 
across cell membranes by physical diffu- 
sion of NI^ or by active (i.e., energy de- 
pendent) transport of NH 4 + (Kleiner, 1985). 
Nothing is known about isotope effects 
associated with active NH 4 + transport, al- 
though Marotti et al. (1982) found no iso- 
tope fractionation during the active uptake 
of NO3- into plant cells. Conversely, the 
isotope effect during the diffusion NH 3 
may be as large as -29 %o (See Hermes et 
al., 1985). At low NH 4 + concentrations, 
diffusion may be the rate-limiting step in 
assimilation. 

The relatively large isotope fractiona- 
tion associated with ammonium assimila- 
tion by heterotrophic marine bacteria can 
have a major influence on the nitrogen 
isotope ratio of suspended and sedimentary 
organic matter in estuarine and coastal 
environments. With our results, nitrogen 
isotopes may be useful in addressing eco- 
logical questions concerning the role of 
heterotrophic bacteria in marine nitrogen 
cycling. 



References 



Altabet, M. A., Variations in nitrogen isotopic 
composition among particle classes: Implica- 
tion for particle transformation and flux in the 



open ocean, Deep Sea Res., 35, 535-544, 1988. 

Bender, R. A., K. A. Janssen, A. D. Resnick, M. 
Blumenberg, F. Foor, and B. Magasanik, Bio- 
chemical parameters of glutamine synthetase 
from Klebsiella aerogenes, J. Bacterid., 129 
(2), 1001-1009, 1977. 

Biegeleison, J., and M. Wolfsberg, Theoretical 
and experimental aspects of isotope effects in 
chemical kinetics, in Advances in Chemical 
Physics, I. Prigogine, ed., Interscience Publish- 
ers, Inc., New York, 1958. 

Delwiche, C. C, and P. L. Steyn-, Nitrogen isotope 
fractionation in soils and microbial reactions, 
Environ. Sci. Technoi, 4, 929-939, 1970. 

Ducklow, H. W., Production and fate of bacteria in 
the oceans, BioScience, 33(8), 494-501, 1983. 

Eppley, R. W., R. W. Holmes, and J. D. H. Strick- 
land, Sinking rates of marine phytoplankton 
measured with fluorometer, /. Exp. Mar. Biol. 
Ecol, 1, 191-208, 1967. 

Fuhrman, J. A., Close coupling between release 
and uptake of dissolved free amino acids in 
seawater studied by an isotope dilution approach, 
Mar. Ecol. Prog. Ser., 37, 45-52, 1987. 

Hermes, J. D., P. M. Weiss, and W. W. Cleland, 
Use of nitrogen- 15 isotope effects to determine 
the chemical mechanism of phenylalanine 
ammonium-lyase, Biochem., 24, 2959-2967, 
1985. 

Hollibaugh, J. T., A. B. Carruthers, J. A. Fuhrman, 
and F. Azam, Cycling of organic nitrogen in 
marine plankton communities studied in en- 
closed water columns, Mar. Biol., 59, 15-21, 
1980. 

Kleiner, D. , Bacterial ammonium transport, FEMS 
Microbiol. Rev., 32, 87-100, 1985. 

Macko, S. A., M. L. Fogel (Estep), P. E. Hare, and 
T. C. Hoering, Isotope fractionation of nitrogen 
and carbon in the synthesis of amino acids by 
microorganisms, Chem. Geol. (IGS), 65, 79-92, 
1987. 

Mariotti, A., J. C. Germon, P. Hubert, P. Kaiser, R. 
Letolle, A. Tardieux, and P. Tardieux, Experi- 
mental determination of nitrogen kinetic isotope 
fractionation, some principles; illustration for 
the denitrification and nitrification processes, 
Plant and Soil., 62, 413-430, 1981. 

Mariotti, A., F. Mariotti, M.-L. Champigny, N. 
Amarger, and A. Moyse, Nitrogen isotope frac- 



GEOPHYSICAL LABORATORY 



123 



donation associated with nitrate reduction activ- 
ity and uptake of N0 3 * by pearl millet, Plant 
Physiol, 69, 880-884, 1982 

Sanwal, B. D., and M. Lata, The occurrence of two 
different glutamic dehydrogenases in neurospora, 
Can. J. Microbiol, 7, 319-328, 1961. 

Sigleo, A. C, and S. A. Macko, Stable isotope and 
amino acid composition of estuarine dissolved 
colloidal material, in Mar. Estuar. Geochem. A. 
C. Siegleo and A. Hattori, eds., Lewis Publish- 
ing Inc., Chelsea, Michigan, pp. 29-46, 1985. 

Solorzano, L., Determination of ammonium in 
natural water by the phenol hypochlorite method, 
Limnol Oceanogr., 14, 799-800, 1969. 

Velinsky, D. J., L. A. Cifuentes, J. R. Pennock, J. 
H. Sharp, and M. F. Fogel., Determination of the 
isotope composition of ammonium-nitrogen at 
the natural abundance level from estuarine 
waters, Mar. Chem., in press, 1989. 

Wada, E., and A. Hattori, Nitrogen isotope effects 
in the assimilation of inorganic nitrogenous 
compounds by marine diatoms, Geomicrobiol. 
J., 1(1), 85-101, 1978. 

Wheeler, P. A., and D. L. Kirchman., Utilization 
of inorganic and organic nitrogen by bacteria in 
marine systems, Limnol. Oceanogr., 31(5), 998- 
1009, 1986. 

Weiss, P. M., C. Y. Chen, W. W. Cleland, and P. 
F. Cook, Use of primary deuterium and 15 N 
isotope effects to deduce the relative rates of 
steps in the mechanisms of alanine and gluta- 
mate dehydrogenases, Biochemistry, 27, 4814- 
4822, 1988. 



Dissolved Nitrogen Isotopic Distribu- 
tion in the Black Sea 

David J. Velinsky, Marilyn L. Fogel, and 
Bradley M. Tebo* 

The Black Sea is the world's largest, 
present-day, anoxic marine basin (Fig. 79). 
As a result of intense water column strati- 
fication, the flux of oxygen to the bottom 
waters is not sufficient for the complete 
oxidation of surface-derived organic mat- 
ter. Below approximately 200 m, bacteria 
use alternate electron acceptors, including 
iron and manganese oxides, nitrate and 
most importantly sulfate, to oxidize or- 
ganic matter during respiration. Because 
sulfate is the most abundant oxidant after 
oxygen, microbial respiration is dominated 
by sulfate reduction in the deep waters and 
sediments of the Black Sea. 

During the oxidation of organic matter 
coupled to sulfate reduction, organically 
bound nitrogen is converted to ammonium. 




Fig. 79. Black Sea station location map. 



* Scripps Institution of Oceanography, La Jolla, 
CA 92093. 



124 



CARNEGIE INSTITUTION 



Richards (1965) described a steady state 
stoichiometric model for the production of 
ammonium during anaerobic oxidation of 
organic matter (Table 16). These reactions, 
coupled with the sluggish mixing of Black 
Sea deep waters, result in the buildup of 
ammonium in the waters below approxi- 
mately 100 m. As the ammonium diffuses 
upward in the water column across the 
oxygen-sulfide boundary, it undergoes 
important transformations that affect bio- 
logical production and possibly also trace 
metal distributions. For example, ammo- 
nium can serve as an energy source for 
aerobic chemosynthetic production of or- 
ganic matter (Brewer and Murray, 1973). 
In the process of nitrification, chemoau- 
totrophic bacteria convert ammonium to 



nitrite and nitrate, which can subsequently 
be reduced to nitrogen gas via denitrifica- 
tion in tightly coupled reactions (Hattori, 
1982). In addition, because of the broad 
zone of low oxygen concentration observed 
just above the oxygen/sulfide interface 
during the 1988 expedition to the Black 
Sea, it has been postulated that nitrate can 
serve as an electron acceptor for both 
ammonium and dissolved manganese oxi- 
dation (Murray etaL, 1989). Thus there are 
potentially both aerobic and anaerobic 
processes taking place near the interface 
that can consume ammonium and limit its 
availability as a nutrient in the overlying 
waters. 

Isotope tracers at the natural abundance 
level have been used to determine the flow 



Table 16. Steady-State Stoichiometric Model for the Oxidation of Organic Matter 



1) Oxygen Respiration: 



(CH 2 O) 106 (NH 3 ) 16 H 3 PO 4 + 106 2 <=> 106 C0 2 + 16 NH, + HLPO, + 106 H.O (1) 



Ammonia is oxidized to nitrate (i.e., nitrification): 
16NH3 + 32 2 16HN0 3 +16Hp 

2) Nitrate Reduction and Denitrification: 

(CH 2 O) 106 (NH 3 ) 1< H 3 PO 4 + 84.8 HN0 3 

<=> 106 CO, + 42.4 N 2 + 16 NH, + H 3 P0 4 + 148.4 H 2 

Also, the NFL, released can be oxidized by HN0 3 : 
5NH 3 +3HN0 3 <=>4N 2 + 9H 2 

3) Sulfate Reduction: 

(CH 2 O) 106 (NH 3 ) 16 H 3 PO 4 + 53 S0 4 > 

<=> 106 C0 2 + 53 S 2 +16 NH 3 + H 3 P0 4 + 106 H.O 



(la) 



(2) 



(2a) 



(3) 



GEOPHYSICAL LABORATORY 



125 



and reactions for both carbon and nitrogen 
in estuarine and open ocean environments 
(Cifuentes et aL, 1988a; Mariotti et ai, 
1984; Altabet, 1988). Processes such as 
algal assimilation of nitrogen (e.g., NH 4 + , 
N0 3 \ and N0 2 ), nitrification, denitrifica- 
tion and possibly organic decomposition 
can be followed with stable isotope tracers. 
Overall, the isotopic composition of both 
the dissolved and particulate pool of nitro- 
gen is determined by the isotopic composi- 
tion of the source material and any related 
isotopic fractionation in its formation or 
decomposition. To understand better the 
reaction pathways of the nitrogen, particu- 
larly near the oxygen-sulfide interface in 
stratified waters, the stable N isotope 
composition (# 5 N) of dissolved ammo- 
nium and nitrate were determined from 
water samples taken from the Black Sea. 
Along with particulate nitrogen isotopic 
data, the transformations of nitrogen can be 
further elucidated. This information is ex- 
tremely important in the understanding of 
the isotope biogeochemistry of material 
formed in the oxic surface waters and 
deposited in euxinic environments like the 
Black Sea. Once the variability and proc- 
esses related to the formation of the nitro- 
gen isotopic composition of particulate 
matter are understood, a more thorough 
interpretation of the # 5 N distribution in the 
sedimentary record can be made (Rau et 
aU 1987). 

Samples for nitrogen isotopic composi- 
tion of dissolved ammonium and nitrate 
were obtained during the 1988 Black Sea 
Oceanographic Expedition on leg 3 (June 
3-16, 1988). Two stations (Fig. 79) were 
occupied and water samples were taken 



from the R/V Knorr for full water column 
chemistry, Station 2 (BS3-2; 42°50'N 
32WE) and Station 6 (BS3-6; 43°04'N 
34WE). 

The method for the preparation and 
nitrogen isotopic determination of dissolved 
ammonium is described in Velinsky et al. 
(1989). Briefly, an aliquot of the sample is 
adjusted to pH>9 using 6 M NaOH and 
distilled with a rapid steam distillation 
apparatus. The distilled ammonia is col- 
lected in a dilute acid trap and removed 
from solution by ion-exchange onto a zeo- 
lite. The nitrogen isotopic composition of 
dissolved nitrate is accomplished by the 
method described by Mariotti and Letolle 
(1978) and Horrigan et al. (unpublished). 
Dissolved nitrate is reduced to ammonia 
using Devarda's Alloy (Cu-Al-Zn) in a 
basic solution. The ammonia generated is 
distilled with a conventional distillation 
apparatus, into a dilute acid and zeolite trap 
(Velinsky et aL, 1989). The zeolite and 
particulate N is analyzed for the nitrogen 
isotopic composition (# 5 N) of both ammo- 
nium and nitrate by a modified Dumas 
combustion technique (Macko, 1981). The 
data are reported in the standard <5 notation 
{i.e., # 5 N = [(K^A^J-lllO* where R 
= 15 N/ 14 N} and the ratios are reported against 
air (# 5 N = 0). Precision of replicate samples 
for ammonium and nitrate isotopic analy- 
sis is approximately ±0.5 %o and + 1 .0 %o , 
respectively. 

The concentration and isotopic compo- 
sition of dissolved ammonium and nitrate 
varied with depth in the water column 
(Figs. 80 and 81). Ammonium concentra- 
tions (Fig. 80) in the surface waters (0-80 
m) were close to the detection limit and 



126 



CARNEGIE INSTITUTION 



NH* (uM) a 
20 40 60 80 100 



500 



1000 



sz 

a. 
a> 
Q 



1500 




NH5 (uM) - 
20 40 60 80 100 



2000 



J I L 



Station 2 



J I i i i 



500 - 



1000 - 



SI 

Q 



1500 - 



2000 - 




01 23456789 10 
5 15 N Q 



Fig. 80. Concentration and nitrogen isotopic composition of dissolved ammonium with depth in the 
Black Sea at Stations 2 and 6. 



reflected biological uptake. Below 80 m, 
with the onset of sulfate reduction, ammo- 
nium concentrations increased from less 
than 0.2 to about 20 fiM at 200 m and up to 
90 jiM by 2000 m. Nitrate concentrations 
exhibited a broad maximum of 6.5 ^M near 
the middle of the sub-oxic zone (Fig. 8 1 ). A 
slight overlap between nitrate and ammo- 
nium distributions near 85 m was indica- 
tive of the oxidation of ammonium to ni- 
trate. The presence of nitrite which is an 
intermediate in the oxidation of ammo- 
nium to nitrate during nitrification is fur- 
ther evidence for this process (Murray et 



aU 1989a,b). 

The distribution of isotopic ratios of 
ammonium and nitrate are presented in 
Figs. 80 and 81 . The # 5 N of ammonium at 
depths greater than 500 m was uniform for 
both stations (1.71 ±0.16%c,n=9). Above 
500 m dramatic shifts occurred in the nitro- 
gen isotopic composition of ammonium. 
As the concentration of ammonium de- 
creased toward the interface, the # 5 N of 
ammonium increased. At station 6 for 
example, the # 5 N increased from ca. 1 .9 %o 
at 500 m to 9.0 %o at 95 m. A similar 
distribution was observed at station 2. The 



GEOPHYSICAL LABORATORY 



127 



DIN (jiM) 
4 8 12 16 20 24 

r— i — i — i — |— i — I — I — i — I — I — i — r~ 



50 



■B 
a. 
o 
Q 



100 



150 



200 




Station 6 

J I I I I I I I L 



— flj- NH>M) 
— ♦- 5 15 NO 



3 
(>iM) 



6 NH 4 



01 23456789 10 
6 15 N 

Fig. 81. Concentrations and nitrogen isotopic 
composition of dissolved ammonium and nitrate 
in the upper water column of the Black Sea at 
Station 6. (DIN = dissolved inorganic nitrogen) 

more positive isotope ratios for ammonium 
are indicative of isotopic fractionation 
during the consumption or oxidation of 
ammonium (see below). 

The # 5 N of nitrate also changed consid- 
erably with depth. At station 6, the # 5 N of 
nitrate increased with depth from 4.2 %o at 
50 m to 9.8 %o just below the nitrate con- 
centration maximum. Bazylinski et al. 
( 1 988) measured maximum denitrification 
rates below this maximum at station 2 
during leg 2 (May 1988). The transforma- 
tion of nitrate to N 2 by denitrification 
(Table 16) induces a large isotopic frac- 
tionation (r, where e = (a-l)10 3 ) of ap- 
proximately -30 %o (Cline and Kaplan, 
1975). Therefore, the residual nitrate should 



be enriched in 15 N. The more positive # 5 N 
values of nitrate below the nitrate concen- 
tration maximum could be explained by 
high denitrification rates at depth. Similar 
observations of # 5 N of nitrate and denitri- 
fication zones occurred at station 2 (data 
not shown). 

An advection-dif fusion model was used 
to calculate the consumption or production 
of ammonium in the water column of the 
Black Sea with a final goal of understand- 
ing isotope fractionation and biogeochemi- 
cal processes in nitrogen cycling. This 
model is similar to that developed by Craig 
(1969) and Craig and Weiss (1970). Be- 
cause the data set for station 6 is more 
complete, only this station was used for the 
advection-diffusion model. 

The general equation for the advection, 
diffusion and reaction of a chemical spe- 
cies within a water system is (Craig, 1969): 



Kd 2 C/dz 2 -codC/dz + J = 0. 



(1) 



This particular form of the equation as- 
sumes steady state conditions where K is 
the vertical eddy diffusion coefficient, co is 
the vertical advection velocity, J is the 
production or consumption of ammonium 
(C). It assumes only vertical water move- 
ment (i.e., where z is positive upward) and 
is valid only in the linear portion of the 
potential temperature-salinity profile. In 
this case, J [equation (1)] was fitted by an 
exponential term (J = J o e /iz ), where fi is the 
decay constant for ammonium consump- 
tion or production with depth (z). The 
equation was first solved in terms of K/co 
(Craig, 1969) for stable conservative ele- 
ments (i.e., potential temperature and 



128 



CARNEGIE INSTITUTION 



salinity). Kl co is a mixing parameter for 
species that do not undergo any reaction 
during two end-member mixing. Once K/co 
was determined, the model was solved for 
stable nonconservative species (i.e., am- 
monium) in terms of JJco and ji. The use of 
this type of model and its limitations is 
discussed by Craig ( 1 969), Craig and Weiss 
(1970) and Spencer and Brewer (1971). 

The solution of equation (1), fitted to 
the salinity data, yielded a K/co of 127 m, 
which is in excellent agreement with the 
results of Spencer and Brewer (1971). The 
model was run for a constant / and expo- 
nentially fitted J (see above) and both solu- 
tions gave similar results. The median / 
within our mixing interval (90 to 800 m) is 
-3.8 • 10 2 /zM NH 4 + /kg yr, where \i = -2.80 
km 1 . The negative sign means that ammo- 
nium was being consumed. This median 
consumption rate occurs at a depth of 390 
m below the surface. Fig. 82 shows the 
fitted data with an exponentially decreas- 
ing J and with a model run with 7 = 0. The 
consumption rate of -3.8 • 10 2 juM NH 4 7kg 
yr was approximately three times lower 
than that derived by Brewer and Murray 
(1973). Station to station variability and 
different mixing intervals could be the 
reason for this difference (Spencer and 
Brewer, 1971; Murray etal., 1989). In any 
case, the ammonium taken up in this inter- 
val, could be oxidized via nitrification or 
consumed by other chemoautotrophic or 
heterotrophic bacteria around the interface. 
Both of these processes are enzymatically 
mediated, thus a normal isotope effect (i.e., 
14 N is taken up at a faster rate then 15 N) was 
expected. 

Qualitatively, the ammonium in the 
mixing interval became more enriched in 



NH>M) 



20 



40 60 80 

~1 1 1 1 1 T 



300 



^ 600 

E 



Q. 

CD 

Q 



900 



1200 



1500 




Fig. 82. Advection-diffusion model results for 
both predicted ammonium concentrations 
assuming J decreases exponentially with depth 
(predicted) and with no production or consump- 
tion (/ = 0). 

15 N compared to that in bottom waters (Fig. 
80). In other words, as ammonium was 
consumed, the residual ammonium became 
enriched in 15 N. Isotopic fractionation by 
bacteria has been determined by Hoch et 
ai, (this Report) for the bacterium Vibrio 
harveyi. Fractionation values, £, varied 
between -15 to -22 %o during growth on 
ammonium as the sole nitrogen source. 
Chemosynthetic uptake by bacteria of 
ammonium near the interface of the Black 
Sea (Brewer and Murray, 1973) is therefore 



GEOPHYSICAL LABORATORY 



129 



associated with a normal isotope effect 
because the residual ammonium becomes 
increasingly heavier as it was consumed. 
Our calculations, based on a closed system, 
yielded a fractionation, e, of -3.7 %o be- 
tween the mixing interval of 90 to 800 m. 
Closed system calculations will yield 
smaller isotope fractionations than those 
calculated from open system models, 
because 14 N is constantly diffusing upward 
and reacting faster (i.e., an open system) 
than 15 N. We are presently developing an 
advection diffusion model taking into ac- 
count isotopic fractionation during the 
uptake of ammonium. This type of equa- 
tion has been used to model the isotopic 
composition of nitrate in the low oxygen 
zone of the North East Pacific (Cline and 
Kaplan, 1975). 

In summary, two distinct processes 
appear to be occurring near the interface (< 
200 m) of the Black Sea; 1) denitrification 
and 2) chemosynthetic production of or- 
ganic matter. Both processes result in dis- 
tinct isotopic ratios for both ammonium 
and nitrate. Below the nitrate concentration 
maximum, the concentration of nitrate 
decreases due to denitrification. This is 
further evidenced by the increase in 15 N 
below the nitrate concentration maximum 
(Fig. 81). Ammonium concentrations start 
to increase because sulfate reduction and 
related ammonium production (Table 16) 
were faster then both transport and con- 
sumption. However, our model results 
show that there is a net consumption of am- 
monium most likely associated with bacte- 
rial chemosynthetic production near the 
interface. As the bacteria consume ammo- 
nium, the residual ammonium becomes in- 



creasingly enriched in 15 N. 

The nitrogen isotope fractionation dur- 
ing the chemosynthetic uptake of dissolved 
ammonium was calculated using closed 
system assumptions. While the fractiona- 
tion for closed system calculations yielded 
an e of -3.7, calculations based on more 
realistic open system assumptions will yield 
a slightly greater fractionation value. It will 
be of interest to compare these results with 
model calculations from other anoxic envi- 
ronments such as the Framvaren Fjord and 
the Saanich Inlet. These data would help 
eventually determine the controls on the 
isotopic composition of material formed in 
the water column and eventually buried in 
anoxic marine environments. 



References 

Altabet, M. A., Variations in nitrogen isotopic 
composition between sinking and suspended 
particles: implications for nitrogen cycling and 
particle transformation in the open ocean, Deep 
Sea Res., 35, 535-554, 1988. 

Bazylinski, D. A., B. L. Howes, and H. W. Jan- 
nasch, Denitrification, nitrogen fixation and 
nitrous oxide concentrations through the Black 
Sea oxic-anoxic interface, EOS, 69, 1241, 1988. 

Brewer, P. G., and J. W. Murray, Carbon, nitrogen 
and phosphorus in the Black Sea, Deep Sea Res., 
20, 803-818, 1973. 

Cifuentes, L. A., J. H. Sharp, and M. L. Fogel, 
Stable carbon and nitrogen isotope biogeochem- 
istry in the Delaware estuary, Limnol. Oceanogr., 
33, 1102-1115, 1988a. 

Cifuentes, L. A., M. L. Fogel, J. R. Pennock, and 
J. H. Sharp, Seasonal variations in the stable 
nitrogen isotope ratio of ammonium in the Dela- 
ware Estuary, Annual Report of the Director of 
the Geophysical Laboratory, Carnegie Instn. 
Washington, 1987-1988, Geophysical Labora- 
tory, Washington, D. C, 114-121, 1988. 



130 



CARNEGIE INSTITUTION 



Cline, J. D., and I. R. Kaplan, Isotopic fractiona- 
tion of dissolved nitrate during denitrification in 
the eastern tropical North Pacific Ocean, Mar. 
Chem., 5,271-299, 1975. 

Craig, H., Abyssal carbon and radiocarbon in the 
Pacific,/. Geophys Res., 74, 5491-5506, 1969. 

Craig, H., and R. F. Weiss, The Geosecs 1969 
intercalibration station: Introduction, hydro- 
graphic features, and total C0 2 -0 2 relationships, 
J. Geophys. Res., 75, 1641-1647, 1970. 

Macko, S. A., Stable nitrogen isotope ratios as 
tracers of organic geochemical processes, Ph. D. 
dissertation, Univ. of Texas at Austin, 1981. 

Mariotti, A., C. Lancelot, and G. Billens, Natural 
isotopic composition of nitrogen as a tracer of 
origin for suspended organic matter in the Scheldt 
Estuary, Geochim. Cosmochim. Acta, 48, 549- 
555, 1984. 

Mariotti, A. and R. Letolle, Analyse isotopique de 
l'asote au niveau des abondances naturelles, 
Analusis, 6, 421, 1978. 

Murray, J. W., H. W. Jannasch, S. Honjo, R. F. 
Anderson, W. S. Reeburgh, Z. Top, G. E. Frie- 
derich, L. A. Codispoti, and E. Izdar, Unex- 
pected changes in the oxic/anoxic interface in 
the Black Sea, Nature, 338, 411-413, 1989a. 

Murray, J. W., and E. Izdar, The 1988 Black Sea 
oceanographic expedition: Overview and new 
discoveries, Oceanography, 1, 15-21, 1989b. 

Rau, G. H., M. A. Arthur, and W. E. Dean, 15 N/ 14 N 
variations in Cretaceous Atlantic sedimentary 
sequences: implications for past changes in 
marine nitrogen biogeochemistry, Earth Planet. 
Sci. Lett., 82, 269-279, 1987. 

Richards, F. A., Anoxic basins and fjords, in 
Chemical Oceanography, J. P. Riley and G. 
Skirrow, eds., pp. 1-41. Academic Press, New 
York, 1965. 

Spencer, D.W., and P. G. Brewer, Vertical advec- 
tion diffusion and redox potentials as controls on 
the distribution of manganese and other trace 
metals dissolved in waters of the Black Sea, J. 
Geophys. Res., 76, 5877-5892, 1971. 

Velinsky, D. J., J. R. Pennock, J. H. Sharp, L. A. 
Cifuentes, and M. L. Fogel, Determination of 
the isotopic abundance of dissolved ammonium- 
nitrogen from estuarine waters at the natural 
abundance level, Mar. Chem, 26, 351-362, 
1989. 



mlneralogical and oxygen isotope 
Analyses of Manganese Oxides Precipi- 
tated by Spores of a Marine Bacterium 

Kevin W. Mandernack, Marilyn L. Fogel, 
Bradley M. Tebo* 
and Jeffrey Post" 

Manganese(II) [Mn(II)] oxidation in the 
environment is generally catalyzed by 
bacteria (Nealson etal., 1988). The mecha- 
nism of this process, however, is poorly 
understood, as are the products of micro- 
bial Mn oxidation. In recent experiments, 
Hastings and Emerson (1986) utilized the 
catalytic properties of spores of a marine 
bacillus (SG-1) to perform laboratory Mn 
(II) oxidation experiments under environ- 
mentally significant conditions of pH and 
Mn (II) concentration. They concluded that 
the concentration of Mn (II) in seawater 
and the oxidation state of marine Mn ox- 
ides are controlled by the rapid precipita- 
tion of hausmannite (Mn 3 4 ), which can be 
microbially mediated. The Mn^ rapidly 
undergoes abiotic disproportionation to 
Mn0 2 because of low Mn(II) concentra- 
tions typically found in the marine environ- 
ment. 

Hastings and Emerson's (1986) work 
supports the model of Hem and Lind ( 1 983) 
in which manganese oxidation is believed 
to occur in two steps (Fig. 83). In the 
laboratory at 25 °C, the initial product is 
hausmannite, which can spontaneously pro- 
tonate to manganite, y-MnOOH (Murray et 



Scripps Institution of Oceanography, La Jolla, 
CA 92093 

Smithsonian Institution, Washington, D. C. 
20550 



GEOPHYSICAL LABORATORY 



131 




Fig. 83. [Taken from Hastings and Emerson, 1986]. 
Dissolved Mn 2+ activity - pH equilibrium relation- 
ships in aerated solutions (based on the work of 
Hem and Lind, 1983). Each line represents the 
equilibrium for the reaction written. Based on 
these lines and with Mn and pH values, it is 
possible to predict which Mn phase is thermody- 
namically stable. A solution with Mn and pH 
values to the right of line 2 would be expected to 
precipitate Mn 3 4 . Data points from Hem and 
Lind (1983), Murray etai, 1985 and Hastings and 
Emerson (1986; referred to this figure as "this 
study") are shown as well as the field which 
represents typical seawater Mn concentration and 
pH. 



ai, 1985; Piper ef al., 1984). Theoretically, 
Mn0 2 , which has an oxidation state of 4+, 
results from a disproportionation of Mn 3 4 . 
In laboratory experiments that lasted up to 
9 months, however, the highest oxidation 
state observed was 3+ except under more 
extreme conditions of high temperature or 
pH (Murray etai, 1985). This fact is rather 
enigmatic considering that manganese in 
the oceans is usually highly oxidized 
(Kalhorn and Emerson, 1984; Murray et 
al. y 1984; Piper et al„ 1984). Hastings and 
Emerson (1986) suspected that more oxi- 
dized phases did not form in their experi- 



ments because of high concentrations of 
dissolved Mn(II). 

Representative strains of bacteria that 
could be responsible for Mn oxidation in 
the ocean have been observed to precipitate 
high-oxidation state manganese oxides 
(>3+), even at high dissolved Mn(II) con- 
centrations in solution (Tebo> unpublished 
results). Because of the uncertainties that 
persist in the mechanisms of Mn oxide 
formation by these bacteria, we examined 
these processes with oxygen isotope tracer 
and x-ray powder diffraction studies on an 
array of oxides precipitated by SG- 1 spores . 

The oxygen isotopic composition of 
dissolved atmospheric oxygen is very dif- 
ferent from that of water. Thus, the relative 
proportions of these two oxygen sources to 
Mn oxides can be traced. Molecular oxy- 
gen in air has a # 8 of +23.5, whereas 
seawater has a 5 18 value of around %o 
(Kroopnick and Craig, 1976). The percent- 
age of oxygen in Mn oxides derived from 
both H 2 and 2 can be predicted depend- 
ing on the mechanism that is proposed for 
manganese oxide formation. The model of 
Hem and Lind (1983), for example, pre- 
dicts that 25% of the oxygen in hausman- 
nite should come from dissolved 2 . In 
contrast, Mn0 2 minerals formed by direct 
precipitation from seawater without an 
intermediate would be expected to have 
50% of the oxygen from dissolved 2 , as in 
the following equation: 

Mn 2+ + 1/2 2 + H 2 <=> Mn0 2 + 2H + . (1) 

In this paper preliminary results of 
mineralogical and stable oxygen isotope 
investigations of Mn oxides produced by 



132 



CARNEGIE INSTITUTION 



SG-1 spores in buffered seawater or deion- 
ized distilled water with varying Mn con- 
centration and temperature are presented. 
The dual approach is useful for (1) estab- 
lishing the identity of the mineral phase 
formed under given conditions, and (2) 
determining the portion of the oxygen at- 
oms in the Mn oxide product that is derived 



from either dissolved oxygen or water 

The marine bacillus bacterium SG-1 is 
unique since only spores,. a dormant non- 
metabolic resting stage in the life cycle of 
the bacterium, are capable of oxidation 
while the growing vegetative cells are not 
(Nealson and Ford, 1980; Rosson and Ne- 
alson, 1982). SG-1 is able to oxidize Mn(II) 



Table 17. Mineralogy of Mn Oxides Produced by SG-1 Spores 



[Mn (11)1 


3°C 


RT 


50°C 


70°C 


Seawater 10 uM 


todorkite(?) 


ND 


ND 


ND 


100 uM 


buserite— > 
birnessite 


buserite — > 
birnessite 


todokorite(?) 


todorokite(?) 


ImM 


todorokite(?) 


todorokite(?) 


todorokite(?) 


hausmannite 


10 mM 


U 


manganite, 


manganite & 
feitknechtite(?), 


hausmannite, 

trace 
manganite & 






MnC0 3 (?) 


hausmannite 


trace MnC0 3 


Distilled HpiOuM 


birnessite(?) 
8.9A phase 


ND 


ND 


ND 


100 uM 


buserite — » 
birnessite 


buserite — > 
birnessite 


U (10A phase) 


hausmannite 


ImM 


ND 


feitknechtite(?), 
manganite 


hausmannite 


hausmannite 


10 mM 


feitknechtite -» 


manganite > 


hausmannite 


hausmannite 




manganite, 


hausmannite 


trace manganite 






groutite (?) 









RT = Room temperature 

ND = Not determined 

U = Unknown phase 

? = Tentative identification 

-> = Process that apparently occurred upon drying 



GEOPHYSICAL LABORATORY 



133 



over a wide range of temperatures (2-80°C) 
and Mn concentrations (10 nM to 10 mM), 
in both seawater and distilled water. The 
use of SG-1 spores as a catalyst permitted 
sufficient amounts of manganese oxides to 
form within a short time frame so that the 
objectives of this study could be met. SG- 

1 was grown to a fully sporulated state in a 
20 mM HEPES buffered (pH 7.5) seawater 
medium containing 0.5 g yeast extract and 

2 g peptone per liter and 100 fjM MnC^. 
The spores were harvested by centrifuga- 
tion and purified to remove any remaining 
vegetative cells and cell debris. 

The SG-1 produced Mn oxides were 
prepared in 0.22 jjm filtered seawater (SW) 



or in deionized-distilled water (DW). 
Additions of 1 M MnSO d and 1 M HEPES 
buffer (20 mM final concentration, pH 8.0) 
were followed by inoculation with SG-1 
spores (Table 17). The oxides were pre- 
pared during 2 week incubations. The ox- 
ides that were formed were collected by 
centrifugation and washed with DW. They 
were stored wet and frozen until analysis. 
Powder x-ray diffraction patterns were 
collected for the oxides at the Smithsonian 
Institution on a Scintag™ automated dif- 
fractometer with copper K a radiation. The 
oxides were analyzed wet because drying 
can change the crystal structure of certain 
manganese oxides (Paterson et al., 1986). 




Fig. 84. Transmission electron micrographs of spores before (A) and after (B) organic matter extraction. 
Spores in Figure 84a were grown at 3°C in lOmM Mn. Spores in Figure 84b were grown at 25°C in 
100^m Mn. Note the amorphous Mn minerals coating the spore wall. In Figure 84a, two different types 
of Mn minerals are present: wavey sheets and granular material. 



134 



CARNEGIE INSTITUTION 



Some of the oxides were finely crystalline 
or poorly ordered, and consequently could 
not be positively identified. Table 17 shows 
the inferred mineralogy based on the XRPD 
results and the conditions under which the 
oxides formed. Transmission electron 
microscopy was performed on several of 
the samples at the Department of Earth 
Sciences, Johns Hopkins University, by Jill 
Banfield (Fig. 84). 

The microbially -produced oxides were 
extracted to remove organic material prior 
to # 8 determination. The method that 
proved the most efficient without altering 
the isotopic composition of the oxides was 
a modification of a DNA purification pro- 
cedure, followed by hypochlorite treatment 
at 4°C. Frozen cells with oxide coatings 
were sequentially extracted with phenol, 
chloroform, and methanol with a final wash 
with DW. This final residue was treated 
with dilute (3%) hypochlorite overnight at 
4°C. The oxide was washed extensively 
with DW and dried in vacuo at 50°C. 

The fluorination method with BrF 5 was 
used for determining the # 8 of silicates 



14.72 5.53 
200.0 



<0 

CL160.0 
O 



f0.06 



CO 

— 40.0 \- 



0.0 



d-spacing, A 

3.42 2.49 

- 1 1 — 



1.97 



H 80 AS 
CO 



^120.0 J\ii> tt Mh»^^ 60 3 




' ' ' ' 




100 



16 26 36 

26, degree 



Fig. 85. X-ray powder diffraction pattern of man- 
ganese mineral before (10A peak) and after (7 A 
peak) drying. Spores were cultured in distilled 
water at 3°C in 0. 1 mM Mn 



(Clayton and Mayeda, 1963). For most 
analyses duplicate samples of 3 to 7.5 mg 
of Mn oxide were reacted at 600°C for > 1 8 
hr for the highest yields. The error of the 
analysis for the c5 18 of technical grade 
Mn0 2 was ±0.5 %o. 

Broad interpretations can be made from 
Table 17 regarding Mn oxide mineral for- 
mation. In general, hausmannite formed at 
high temperatures and higher Mn concen- 
trations in both DW and SW. Subsamples 
collected from the 10 mM DW and SW 
preparations after 4 days incubation at 50 
and 70 °C were essentially completely com- 
posed of hausmannite (data not shown). 
Conversely, those that incubated for 2 weeks 
usually contained a significant amount of 
manganite (Mn(ITI)). The shift in mineral 
structure with time may indicate that the 
hausmannite was protonating to manganite 
as indicated in reaction 2. Protonation may 
occur faster at lower temperatures, as the 
oxides from 10 mM solutions at room 
temperatures were composed mostly of 
manganite. 

In general, higher oxidation state ox- 
ides were observed to form under condi- 
tions of lower Mn concentration and lower 
temperature. Qualitatively, this is what 
would be predicted from thermodynamics 
(Fig. 83). Buserite was evidently precipi- 
tated at 100 jUM Mn at 3°C and room 
temperature in both waters. The XRPD 
patterns for these samples showed the 
characteristic collapse of a 10A peak to 7 A 
upon drying (Fig. 85). The 7 A phase is 
presumed to have a birnessite-type struc- 
ture. 

Manganese minerals from the seawater 
incubations appeared as buserite or re- 



GEOPHYSICAL LABORATORY 



135 



Table 18. Isotope Ratios of Manganese Minerals Precipitated from SG-1 Spores 



[Mn] Medium 7 


°c 


fl^Hp 


5 18 2 


fl'OMin 


%np 


%o 2 










Hausmannite 








ImM 


DW 


50 


-9.5 


23.5 


-10.3 


100 





10 mM 


DW 


70 


-9.5 


23.5 


-11.9 


100 





ImM 


SW 


70 


0.0 


23.5 
Birnessite 


2.5 


89 


11 


ImM 


DW 


25 


-9.5 


23.5 
Todorokite 


-0.2 


72 


28 


100 ^iM 


SW 


25 


0.0 


23.5 


7.7 


67 


33 


ImM 


SW 


50 


0.0 


23.5 


8.9 


62 


38 



sembled a disordered todorokite with a 
fixed d-spacing near 10 A. Todorokite was 
tentatively identified based on the charac- 
teristic 10A peak both before and after 
drying. Todorokite-like phases were only 
observed in the sea water incubations, and 
therefore the interaction with the other 
cations in seawater may be significant in 
the mineral formation. 

Spores were cultured in distilled water 
or seawater with air as the source of oxy- 
gen. The source of the oxygen to the man- 
ganese minerals and therefore, the mecha- 
nism of formation, was elucidated using 
the following mass balance equation: 



(&*0 np)(% O from H 2 0) 
+ (^O 2 )(% O from Cg 
-9 % Mn oxide 



(2) 



The determination is approximate as there 
is a ±0.5 %o uncertainty in the isotopic 
analysis of the Mn oxide. The calculation 
also assumes negligible isotopic fractiona- 
tion in the incorporation of both water and 
dissolved 2 . Studies with slightly l ^-en- 
riched water and oxygen in comparable 
minerals gave similar results with the same 
equation (Tebo et al. y 1987). 

The percentage of H 2 0-derived oxygen 
in the minerals decreased with increasing 
oxidation state (Table 18). The # 8 of 
hausmannite was always slightly more 
negative than that of the water in which the 
precipitation occurred. Based on equation 
(1), all of the oxygen in the mineral must 
have originated from water, unless the 
mineral freely exchanged its oxygens with 
water. The possibility of rapid and total 



136 



CARNEGIE INSTITUTION 



exchange of the isotopic signature in the 
manganese minerals was tested previously 
(Tebo etal, 1987). Only 10% of the oxy- 
gens in manganite exchanged after 12 
months. One hausmannite sample contain- 
ing manganite yielded a ^ 8 that was +2.5 
more positive than that of the water. Tebo et 
al. (1987) had previously measured the 
isotopic composition of synthetic mangan- 
ite, and concluded that approximately 75% 
of its oxygen came from water and the 
remaining portion from dissolved 2 . 

The higher oxidation state oxides con- 
tain between 62 to 72% oxygen from water 
and the remainder from dissolved oxygen 
(28-38%). Because no dissolved oxygen 
signal was measured in the Mn 3 4 , the 
reaction mechanism for Mn oxidation must 
be different from that proposed by Hem 
and Lind (1983) and Hastings and Emerson 
(1986). Equation (1) and the following 
equation are closer representations of the 
reaction mechanism indicated by isotopic 
analysis: 



Mn 2+ + 1/4 2 + 3/2 H 2 
<=> Mn(III)OOH + 2H + . 



(3) 



The minerals formed by the spores were 
commonly mixtures of mineral phases 
(Table 17). Accordingly, the variability in 
the isotopic results for a particular set of 
growth conditions is most likely the bypro- 
duct of the analysis of these mixtures. 

In summary, both x-ray powder diffrac- 
tion and isotopic tracer studies confirm that 
manganese oxides are precipitated by a 
different mechanism from that proposed 
previously for chemical precipitates and 
for spore catalyzed oxides. No traces of 



hausmannite or manganite were found in 
minerals precipitated at low Mn concentra- 
tion. If hausmannite were the initial prod- 
uct in the formation of the higher oxidation 
state oxides, oxygen bonds in the crystal 
lattice must be broken and reformed during 
the rearrangement of structure to buserite 
or todorokite. The involvement of molecu- 
lar oxygen is indicated by isotopic ratios of 
these two oxides, rather than in the initial 
formation of hausmannite itself. With bet- 
ter quantitative mineral identification we 
should be able to determine whether Mn 
oxidation mechanisms for chemically 
driven systems are the same as those cata- 
lyzed by living organisms. 



References 

Clayton, R. N., and T. K. Mayeda, The use of 
bromine pentafluoride in the extraction of oxy- 
gen from oxides and silicates for isotopic 
analysis, Geochim. Cosmochim. Acta, 27, 43- 
52, 1963. 

Hastings, D., and S. Emerson, Oxidation of 
maganese by spores of a marine Bacillus: ki- 
netic and thermodynamic considerations, Geo- 
chim. Cosmochim. Acta, 50, 1819-1824, 1986. 

Hem, J. D., Redox coprecipitation mechanisms of 
manganese oxides: particulates in water, in Ad- 
vances in Chemistry, Series No. 189, M. C. 
Kavanaugh and J. O. Lecke, eds., American 
Chemical Society, Washington, D. C, pp. 45- 
72, 1980. 

Hem, J. D., and C. J. Lind, Nonequilibrium models 
for predicting forms of precipitated manganese 
oxides, Geochim. Cosmochim. Acta, 47, 2037- 
2046, 1983. 

Kalhorn, S., and S. Emerson, The oxidation state 
of manganese in surface sediments of the Pa- 
cific Ocean, Geochim. Cosmochim. Acta, 48, 
897-902, 1984. 

Kroopnick, P. and H. Craig, Oxygen isotope frac- 



GEOPHYSICAL LABORATORY 



137 



tionation in dissolved oxygen in the deep sea, 
Earth Planet. Sci. Lett., 32, 375-388, 1976. 

Murray, J. W, L. S. Balistrieri, and B. Paul, The 
oxidation state of manganese in marine sedi- 
ments and ferromanganese nodules, Geochim. 
Cosmochim.Acta,48, 1237-1247, 1984. 

Nealson, K. H., and J. Ford, Surface enhancement 
of bacterial manganese oxidation: Implications 
for aquatic environments, Geomicrobiol. J., 2, 
21-37, 1980. 

Nealson, K. H, B. M. Tebo, and R. A. Rosson, 
Occurrence and mechanisms of microbial oxi- 
dation of manganese, Adv. Appl. Microbiol., 33, 
279-318, 1988. 

Paterson, E, J. L. Bunch, and D. R. Clark, Cation 
exchange in synthetic manganates: I. alkylam- 
monium exchange in a synthetic 
phyllomanganate, Clay Minerals, 21, 949-955, 
1986. 

Piper, D. Z, J. R. Basler, and J. L. Bischoff, 
Oxidation state of marine manganese nodules, 
Geochim. Cosmochim. Acta, 48, 2347-2355, 
1984. 

Rosson, R. A., and K. H. Nealson, Manganese 
binding and oxidation by spores of a marine 
bacillus, J.Bacteriol., 151, 1027-1034, 1982. 

Tebo, B. M, M. L. Fogel, A. T. Stone, and K. W. 
Mandernack, Oxygen isotope tracers of manga- 
nese oxide precipitation, EOS, 68, 1702, 1987. 



Separation and Purification of Phos- 
phates for Oxygen Isotope Analysis 

Ellen K. Wright and Thomas C. Hoering 

Oxygen isotope analysis of biogenic, 
marine phosphates is a potentially power- 
ful tool for determining the temperature of 
ancient oceans because phosphates are more 
resistant towards isotope exchange during 
diagenesis than the conventionally-used 
carbonates. However, published tempera- 
tures deduced from analyses of phosphates 
indicate several problems. Some of these 



are clearly extrinsic such as unknown iso- 
topic composition of the ocean water 
through time. However, others may be 
inherent in the analytical methods and these 
problems will be discussed here. 

There are stringent requirements for an 
analytical method designed to measure 
stable oxygen isotope ratios in geological 
materials. First, all steps must be either 
quantitative, in order to avoid isotope frac- 
tionation due to incomplete yields, or else 
a reproducible fraction of the sample must 
be converted. Second, there must be no 
addition of extraneous oxygen through 
contamination, memory effects, or isotope 
exchange induced during the analysis. 
Three, the final product to be introduced 
into the mass spectrometer must be free of 
spectral contaminants. These criteria were 
used in the design of an analytical method 
for the isotopic analysis of phosphates. As 
will be seen below, requirements one and 
three are probably met, but two presents 
difficulties. 

A published method (Tudge, 1960) 
involves bringing the phosphate into solu- 
tion with nitric acid and then oxidizing any 
organic matter with potassium permanga- 
nate. This is followed by three successive 
purification steps wherein the sample is 
first precipitated as ammonium phospho- 
molybdate which is filtered, dissolved and 
precipitated as magnesium ammonium 
phosphate. This compound is dissolved 
and finally precipitated as bismuth phos- 
phate, which is heated to remove water of 
crystallization. Oxygen is extracted from 
anhydrous bismuth phosphate by reaction 
with bromine pentafluoride at 250°C. The 



138 



CARNEGIE INSTITUTION 



oxygen is then converted to carbon dioxide 
for analysis in the mass spectrometer. 

This method can be considerably sim- 
plified by substituting the lengthy precipi- 
tation and dissolution steps with an ion 
exchange separation method and then pre- 
cipitating non-hydrating silver phosphate 
instead of bismuth phosphate. In the first 
step, 30 to 60 mg of a calcium phosphate 
sample (-200 jjM P0 4 ) is dissolved in 2 ml 
of 2 molar HF (digestion time -24 hours). 
Calcium ions are precipitated as calcium 
fluoride and are removed by centrifuga- 
tion. The resulting solution is pipetted off, 
and the residue is rinsed in 2 ml distilled 
water, centrifuged again, and the rinse water 
pipetted off and added to the solution. 

The solution is neutralized with potas- 
sium hydroxide ~ 2.2 ml of 2 molar solu- 
tion) and added to a disposable ion ex- 
change column (6 ml volume) packed with 
a strong base anion exchange resin in the 
hydroxide form [Amberlite™ IRA- 
400(OH)]. The column is rinsed with dis- 
tilled water until neutral and free of fluo- 
ride ions. Then the phosphate is eluted with 
20-30 ml 0.5 Molar ammonium nitrate. 
The eluate is added to an ammoniacal solu- 
tion of silver nitrate and precipitated as 
silver phosphate according to the method 
of Firsching (1961). 

The phosphate concentration in the 
eluate was monitored by the method of 
Parsons etal. (1984a). Collecting fractions 
of eluate from a 200 U.M P0 4 sample showed 
peak concentrations of phosphate ions 
between 1 and 12 ml eluate and only traces 
after 14 ml eluate. Care should be taken that 
all fluoride ions are removed from the 
column in the rinse step as fluoride inter- 



feres with formation of the blue color, which 
is used to monitor the phosphate concentra- 
tion. 

A large sample of potassium dihydro- 
gen phosphate, KH 2 P0 4 (> 99.97% pure) 
has been reserved as a oxygen isotope 
reference material. This compound is not 
hygroscopic and does not form a hydrate. 
Oxygen isotope analyses were done first on 
the potassium dihydrogen phosphate, then 
on silver phosphate precipitated directly 
from potassium dihydrogen phosphate, then 
on silver phosphate precipitated from po- 
tassium hydrogen phosphate processed 
through the anion exchange column, and 
finally on bismuth phosphate precipitated 
directly from potassium hydrogen phos- 
phate. Each of these compounds was re- 
acted with an excess of bromine pen- 
tafluoride at 300°C according to the proce- 
dure of Clayton and Mayeda (1963) to 
yield oxygen. The oxygen was converted to 
carbon dioxide by reaction with hot graph- 
ite. Also several samples of National Bu- 
reau of Standards phosphate standards (NBS 
120b and NBS 120c) were processed 
through the columns and the isotopic val- 
ues compared with the published values of 
Shemesheftf/. (1983). 



Results 

The results are shown in Table 19. A 
sample of quartz, that had been analyzed 
previously in several laboratories, was used 
as a control. The published value for & s O of 
this material is +7.18 %o relative to Stan- 
dard Mean Ocean Water. The value shown 
in Table 19 agrees within the precision of 



GEOPHYSICAL LABORATORY 



139 



measurement, proving that the extraction 
system and the mass spectrometry are 
functioning properly. The mean # 8 of the 
potassium dihydro gen phosphate reference 
material (11.91 %o) was higher than the 
mean # 8 values of several batches of 
silver phosphate (11.76 to 10.05 %6) and 
bismuth phosphate (10.55 %6) precipitated 
directly from this reagent. The standard 
deviation of the potassium dihydrogen 
phosphate (0.2 %c) was comparable with a 
standard deviation of 0.2 %o for the quartz 
run on the same extraction system. How- 
ever, the standard deviation increased for 
the secondary precipitates (0.3 and 0.4 %c 
for the silver phosphates and 0.5 %o for the 
bismuth phosphate) and was highest for the 



column processed silver phosphates (0.6 to 
1.0 %6). The mean # 8 of the column 
processed NBS 120b standard was 19.81 
%o with a standard deviation of 0.8 %c. The 
published values of Shemesh et al. (1983) 
are 20.1 %o and a standard deviation of 0.3 
%o. 

The decrease of # 8 values and the 
increase in the variance of the the silver 
phosphate precipitated from the potassium 
dihydrogen phosphate reference material 
may be caused by contaminants. Silver 
phosphate precipitated from phosphate ions 
purified by the ion exchange column has a 
different color (greenish or brownish yel- 
low) and smaller crystal size than silver 
phosphate precipitated directly in an 



Table 19. Summary of means and standard deviations of # 8 of silver phosphate, bismuth phos- 
phate, and quartz. 



Compound 


Yield(%) 


mean 


Yield(% ) 


s.d.(%o) 


N 




precipitate 


# 8 (0%o) 


co 2 






KH 2 P0 4 




11.91 


102 


0.2 


7 


Ag 3 P0 4 * 


100 


11.76 


104 


0.4 


8 


Ag 3 P0 4 * 


100 


11.21 


104 


0.3 


7 


Ag 3 P0 4 * (silica free) 


100 


10.75 


103 


0.4 


7 


Ag 3 P0 4 * (column) 


98 


11.55 


104 


0.7 


6 


Ag 3 P0 4 * (column) 


98 


10.05 


103 


1.0 


8 


BiPO* 

4 


99 


10.55 


105 


0.5 


8 


Ag 3 P0 4 (from NBS 120b) 


98 


19.81 


100 


0.8 


12 


Ag 3 P0 4 (from NBS 120c) 


98 


19.94 


101 


0.6 


7 


Si0 2 » 




6.99 


101 


0.2 


21 



& s O = {^QptOJ^O/ 1 *®^ - 1 } x 1000 where the subscript x refers to the unknown sample and 
std refers to standard Mean Ocean water. 

* denotes that the compound is derived from the KH 2 PO A isotope reference material. 

• the published value for # 8 of quartz is +7.18 %o 



140 



CARNEGIE INSTITUTION 



ammoniacal solution from pure potassium 
dihydrogen phosphate. Possible contami- 
nants are small inclusions of silver chloride 
and coatings of organic matter and silica on 
the silver phosphate crystals. The chloride 
ions stem from the ion exchange resin. The 
Amberlite™ IRA-400(OH) resin is mainly 
in. the hydroxide form. However, a small 
amount of chloride ions is present, and 
attempts to eliminate it by flushing the 
resin with potassium hydroxide solution 
caused decomposition of the resin before 
complete elimination of the chloride. 

The organic coatings stem from un- 
avoidable decomposition of the anion ex- 
change resin. Combustion of a silver phos- 
phate sample that was derived from a col- 
umn processed NBS 120c sample showed 
the presence of 0.3 weight percent carbon. 
The & 2 C of the carbon was -31 %o. This low 
value is indicative of petrochemicals that 
were used to manufacture the exchange 
resin, and not of sedimentary carbonates 
contained in the NBS 1 20c sample, or from 
dissolved carbon dioxide co-precipitated 
as silver carbonate. Traces of silica were 
detected by microprobe analysis in some 
batches of silver phosphate. This contami- 
nant would yield oxygen upon reaction 
with bromine pentafluoride. Silica was 
detected in the ammonium hydroxide used 
in the final precipitation step by the colo- 
rometric method of Parsons etal. (1984b). 
Silica-free ammonium hydroxide was pro- 
duced by dissolving ammonia gas from a 
cylinder into distilled water and storing the 
solution in a Teflon™ bottle. Microprobe 
analysis of column processed and directly 
precipitated silver phosphate samples 
showed no detectable silica levels when 



silica-free ammonium hydroxide was used 
in the precipitation step. 



Discussion 

The silver phosphate procedure for 
analyzing oxygen is promising, although 
several problems remain to be solved. It is 
definitely easier and more rapid than previ- 
ous methods and more amenable to proc- 
essing large numbers of samples. The pre- 
cision of measurement has steadily im- 
proved until it now rivals that of the bis- 
muth phosphate method, although there 
seems to be a constant bias between the two 
methods. The procedure fulfills two of the 
three criteria described in the introduction. 
The wet chemistry steps are monitored by 
a sensitive and specific colorometric 
method. No losses of phosphate were de- 
tected in any of them. Firshing's (1961) 
method for precipitating silver phosphate 
is quantitative and accurate. The bromine 
pentafluoride method of Clayton and 
Mayeda (1963) has been used on silicates 
for many years and found to be completely 
reliable. Quantitative yields of carbon di- 
oxide are obtained from pure silver phos- 
phate by this method. The reproducible 
results on the control sample of quartz are 
encouraging. 

The source of of the variance is most 
likely due to small and variable amounts of 
contaminants that are precipitated with the 
silver phosphate and yield oxygen on reac- 
tion with bromine pentafluoride. Future 
work will focus on finding the source of 
this contamination and methods for elimi- 
nating it. Reasons for the systematic differ- 



GEOPHYSICAL LABORATORY 



141 



ences between the silver phosphate and the 
bismuth phosphate will be sought. 

It is unlikely that the problem is due to 
isotopic exchange of phosphate with water 
during the course of the analysis. Keisch et 
al. (1958), Bunton etal. (1961), andTudge 
(1960) have shown that the phosphate ion 
is inert to exchange under all of the condi- 
tions used in this study. 



References 

Bunton, C. A., D. R. Llewellyn, C. A. Vernon, and 
V. A. Welch, The reactions of organic phos- 
phates. Part IV. Oxygen exchange between and 
water and orthophosphatic acid, /. Chem. Soc. 
London, 1636-1640, 1961. 

Clayton, R. N., and T. K. Mayeda, The use of 
bromine pentafluoride in the extraction of oxy- 
gen from oxides and silicates for isotopic analysis, 



Geochim. Cosmochim. Acta., 27, 43-54, 1963. 

Firsching, F. H., Precipitation of silver phosphate 
from homogeneous solution, Anal. Chem., 33, 
873-87, 1961. 

Keisch, B., J. W. Kennedy., and A. C. Wahl, The 
exchange of oxygen between phosphoric acid 
and water, /. Amer. Chem. Soc, 80, 4778-4782, 
1958. 

Parsons, T. R., Y. Maita, and C. M. Lalli, Determi- 
nation of phosphate, in A Manual for Chemical 
and Biological Methods for Seawater Analysis, 
Pergamon Press, New York, 22-25, 1984a. 

Parsons, T. R., Y. Maita, and C. M. Lalli, Determi- 
nation of silica, in A Manual for Chemical and 
Biological Methods for Seawater Analysis, Per- 
gamon Press, New York, 25-28, 1984b. 

Shemesh, A., Y. Kolodny, and B. Luz, Oxygen 
isotope variations in phosphate of biogenic 
apatites, II. Phosphorite rock, Earth Plan. Sci. 
Let., 64, 405-416, 1983. 

Tudge, A. P., A method of analysis of oxygen 
isotopes in orthophosphates - its use in the 
measurement of paleotemperatures, Geochim. 
Cosmochim. Acta., 18, 81-83, 1960. 



GEOPHYSICAL LABORATORY 143 



Scientific Highlights of the 

Geophysical Laboratory 

1905-1989 

H. S. Yoder, Jr. 



Table of Contents 



1. Introduction 144 

2. Experimental Petrology 147 

3. Hydrothermal Techniques 155 

4. High-pressure Apparatus 157 

5. Ore Petrology 159 

6. X-ray Crystallography 161 

7. Spectral Mineralogy 163 

8. Field Petrology 165 

9. Statistical Petrology 167 

10. Extraterrestrial Petrology 168 

11. Volcanology 172 

12. Geophysics 174 

13. Geochemistry 177 

14. Thermodynamics and Calorimetry 181 

15. Heat and Mass Transfer and Kinetics 183 

16. Geochronology 187 

17. Stable Isotopes 189 

18. Biogeochemistry 192 

19. War-time Studies 194 

20. Closing Remarks 196 



144 



CARNEGIE INSTITUTION 



1. Introduction 

The concept of a geophysical labora- 
tory was initiated by Clarence King at the 
U. S. Geological Survey in 1882. The 
laboratory was placed under the direction 
of Carl Barus, and continued until govern- 
ment funds were cut off in 1 892. Work was 
resumed in 1900 under the direction of 
George F. Becker, a field geologist with a 
background in physics and mathematics, 
and some support for its staff was obtained 
in 1904 from the newly formed Carnegie 
Institution of Washington (CIW). An 
Advisory Committee in Geophysics had 
been set up in the Institution in 1 902, mainly 
at the instigation of Charles D. Walcott, 
then Director of the U. S. Geological Sur- 
vey, who also served as Secretary of the 
Executive Committee of the Board of Trus- 
tees of CIW. Charles R. Van Hise, who had 
drawn up the plan for the work of the 
U.S.G.S. geophysics group, served with T. 
C. Chamberlin, Carl Barus, A. A. Michel- 
son, C. D. Walcott and R. S. Woodward 
(Chairman) on the Advisory Committee. 

A proposal for an independent, pri- 
vately endowed geophysical laboratory was 
hastily prepared for the Committee by 
Becker. A subcommittee was formed in 
July, 1902, consisting of Chamberlin, Van 
Hise, and Woodward to prepare a more 
detailed report on the problems to be inves- 
tigated from both physical and chemical 
viewpoints. Van Hise and Becker were 
sent to Europe in 1903 to consult their 
colleagues on the continent about forming 
a new laboratory. In addition to the reports 
of Van Hise and Becker, the Trustees re- 
ceived a detailed outline of suggested 



geophysical investigations on 1 October 
1903 from Frank D. Adams, Whitman 
Cross, Joseph P. Iddings, James F. Kemp, 
Alfred C. Lane, Louis V. Pirsson, H. S. 
Washington, and John E. Wolff. (That 
outline eventually served as the charge to 
the new laboratory). Because Becker's 
plan required a large proportion of the CIW 
budget, the more modest plan of Van Hise, 
focusing on geochemical and petrological 
research, was deemed more acceptable. As 
a result, Becker's deputy, Arthur L. Day, 
was asked to submit a proposal whereby 
small grants could foster programs from 
which a larger scale endeavor might evolve. 

Day received a grant in 1904 to enlarge 
his studies onpetrogenesis at the U.S.G.S., 
and a grant was made to Becker for the 
analysis of the strain relations in the flow 
and rupture of rocks. These two tests of the 
practicability of experimental solutions to 
geological problems proved successful. 
Later that year, R. S. Woodward, a member 
of the geophysics subcommittee, succeeded 
to the presidency of CIW, and he urged the 
Board of Trustees to approve the construc- 
tion of a geophysical laboratory. On 12 
December 1905, Woodward, with the help 
of Walcott, succeeded in getting the 
Trustee 's approval, and within a few months, 
Day was named as its first Director. 

The news of the authorization did not 
please Mr. Andrew Carnegie, who believed 
the exceptional investigator should be 
supported in his own environment. Others 
were equally unhappy with the proposed 
specific program of work. The physico- 
chemical study of mineral solutions at high 
temperatures was considered by Becker a 
mere "detail" in the general need to under- 



GEOPHYSICAL LABORATORY 



145 



stand the behavior of matter under the 
extreme conditions in the earth. Neverthe- 
less, the following broad program outlined 
in 1902, reviewed and rededicated by Day 
in 1927, has served the Geophysical Labo- 
ratory well for over 80 years, 

"The crust of the lithosphere has thus far 
been the chief field of geology in the 
narrower sense, since it contains the rock 
record of the earth's past; and geological 
studies have been directed chiefly to read- 
ing and mapping this record, but the record 
needs to be interpreted on broader and 
deeper lines based on a profounder knowl- 
edge of physical laws. To this end the data 
of geology need to be correlated and uni- 
fied under these laws on an experimental 
basis .... 

"Some of the salient problems of the outer 
lithosphere are the origin and maintenance 
of the continental platforms . . . and a 
whole group of intricate questions of a 
chemical and chemico-physical nature, 
including the flow of rocks, the destruction 
and genesis of minerals, the functions of 
included water and gases, the internal trans- 
fer of material, the origin of ore deposits, 
the evolution and absorption of heat, and 
other phenomena that involved the effects 
of temperature, pressure, tension and re- 
sultant distortion upon chemical changes 
and mineralogical aggregations. 
"These questions of the earth's outer part 
are inseparably bound up with those of the 
interior, and here the problems involve the 
most extreme and the least known condi- 
tions and make their strongest demand for 
experimental light. The themes here are 
the kinds and distribution of the lithic and 
metallic materials in the deep interior, the 
states of matter; the distribution of mass 
and of density, and the consequent distri- 
bution of pressure; the origin and distribu- 
tion of heat; ... the secular redistribution 
of heat within the earth and its loss from 
the surface; the possible relations of redis- 
tribution of internal heat to vulcanism and 



to deformation and similar profound prob- 
lems. 

"A series of specific laboratory questions 
arise from these, e.g., the effect of pressure 
on the melting point of rocks carried to as 
high temperatures and pressures and 
through as wide range of materials, as 
possible to develop the laws of constancy 
or of variation; the effect of temperature 
and pressure on thermal conductivity as 
indicated above, and on elasticity, espe- 
cially as involved in the transmission of 
seismic tremors." 

In subsequent years all of the recommended 
areas of geophysical research have been 
investigated by the staff. 

The land for the new building in the 
Azadia area of the District of Columbia 
was obtained in March of 1906, construc- 
tion began in June of that year from plans 
prepared in 1904, and the building was 
occupied on 7 June 1 907. The design of the 
massive structural walls resulted from 
Day's experience at the Physikalisch-Tech- 
nische Reichanstalt in Berlin, where pass- 
ing streetcars caused the galvanometers to 
vibrate, Another innovative feature was 
the erection of the machine shop on a 
floating slab independent of the building. 

The staff was recruited primarily from 
the U.S.G.S. At the end of the first year of 
operation in the new building, the staff 
consisted of 3 physicists (A. L. Day, J. K.. 
Clement, W. P. White), a chemist (E. T. 
Allen), 2 physical chemists (E. S. Shep- 
herd, G. A. Rankin), and 2 petrologists (F. 
E. Wright, E. S. Larsen, Jr.). Grants were 
alsomadebyCIWtoG.F.Becker(U.S.G.S.) 
and F. D. Adams (McGill Univ.) in geo- 
physics and to T. C. Chamberlin (Univ. of 
Chicago) and H. S. Washington (Locust, N. 
J.) in geology. 



146 



CARNEGIE INSTITUTION 



Year 



■■/■■/■•A Biogeochemistry 




10 



20 



30 



40 



50 60 

Percent 



70 



80 



90 



100 



Fig. 1. Change in proportional effort of regular Geophysical Laboratory staff (not including Fellows or 
Visiting Investigators) in various fields of research with time and directorship. (George W. Morey served 
as Acting Director, 1952- 1953; Robert B. Sosman served as Acting Director, 1918-1920, for Arthur L. 
Day). 



GEOPHYSICAL LABORATORY 



147 



Over the years, more than 2100 papers 
have been issued from the Geophysical 
Laboratory, but this represents only one 
measure of the contribution of the staff. 
The ebb and tide of the focus of the work 
has indeed been great. Figure 1 gives a 
crude picture of the change in effort of the 
regular staff throughout the years. The 
effort assigned to various fields is some- 
what arbitrary in view of the overlap and 
integration of the fields. The designated 
fields, however, serve as focal points on 
which to summarize the following high- 
lights of the work. It is evident the Geo- 
physical Laboratory has responded dynami- 
cally to the needs of the science, develop- 
ing the most rewarding directions as they 
evolved. It is also evident that it is the 
individual staff members who have made 
the concept of interdisciplinary research so 
successful. In accord with the original 
wishes of Mr. Andrew Carnegie, the sup- 
port of exceptional individuals has resulted 
in a record of discovery and invention that 
is extraordinary. 



2. Experimental Petrology 



Igneous Petrology 

The charter for the Geophysical Labo- 
ratory, as recorded in the report of the 
Advisory Committee on Geophysics, 
clearly stated the need to unify geological 
field observations under physical and 
chemical laws on an experimental basis. 
They believed geologists wanted to know: 



"...the melting points of rocks, the tem- 
peratures at which rocks crystallize from 
magma, the relative specific gravities of 
melted and crystallized rocks, the effects 
of slow cooling upon the crystallization of 
rocks with and without pressure, the solu- 
tion of one kind of rock in another, and, in 
short, all the phenomena which concern 
the transformation of magma to crystal- 
lized rock and of crystallized rock to 
magma." 

That statement appeared in Year Book 
No. 2 of CIW for 1903, which included a 
detailed plan of investigation (pp. 195- 
201). It has served as the principal guide- 
line for the core program of the Geophysi- 
cal Laboratory for 84 years. 

The experimental approach to those 
goals was immediately beset with prob- 
lems of the most fundamental nature. There 
was no generally acceptable temperature 
scale above 200°C and standard calibration 
points had not been established even though 
several boiling and melting points were 
commonly used up to about 1100°C 
(Sosman, 1952). Primary pressure calibra- 
tion was available only to 2 kbar. There 
was, however, considerable knowledge 
about the composition of rocks and the ten 
most important oxides had been identified 
by chemical analyses. The main advantage 
lay with the incredible intuition and per- 
ception of the geological advisors who had 
acquired a remarkable qualitative sense 
about how rocks were formed. 

The most abundant mineral in the crust 
of the earth is plagioclase, and the Ab-An 
system had been selected for study at the 
U.S.G.S. in the formative years of a geo- 
physical laboratory. That first step in a 



148 



CARNEGIE INSTITUTION 



much broader scheme of investigation of 
the common rock-forming minerals was 
undertaken by Day (1906-1935) 1 , Allen 
(1907-1932) and Iddings (Univ. of Chi- 
cago) with the financial support of CIW. 
The results were published in 1 905 as paper 
No. 1 of the new Geophysical Laboratory. 
The liquidus was determined by the heat- 
ing curve method from An 100 to An 26 v the 
remainder of the now classical solid solu- 
tion loop was deduced as Roozeboom's 
Type I. The temperature calibration was 
based on the Reichsanstalt scale for the 
melting of Cd, Zn, Hg, and Cu. Platinum- 
Rhodium thermocouples were employed 
with a Pt-wound resistance furnace. Be- 
cause of the great difficulty in determining 
the exact temperature of complete melting, 
Shepherd (1904-1946) and Rankin (1907- 
1916) devised a new method in 1 909 for the 
CaO-Si0 2 , MgO-Si0 2 , and Al 2 3 -Si0 2 
systems in which the liquid was quenched 
from a known temperature to a glass and 
examined optically for crystals. The new 
technique was applied in a reexamination 
of the plagioclase system in 1913 by N. L. 
Bowen (1910-1919; 1920-1937; 1947- 
1952), who proved that the solid solution 
loop was indeed as deduced. He also showed 
that the depression and rise of the melting 
temperatures of the endmembers An and 
Ab, respectively, were in close agreement 
withRaoult's Law of vapor pressure. Thus, 
plagioclase may be considered an ideal 
solution, however, the conditions under 



1 Numbers in bold-face type are the years during which the 
Staff Member or Fellow officially served the Geophysical 
Laboratory. The single years in text type is for a reference 
or an Annual Report citation, most of which are listed in the 
"Indices of the Annual Reports of the Director of the Geo- 
physical Laboratory" and the "Publication List of the Geo- 
physical Laboratory." 



which it deviates from ideality remains a 
principal focus of today. The new Geo- 
physical Laboratory temperature scale 
(discussed at the end of this section), cali- 
brated with lithium metasilicate, diopside 
and anorthite, was applied in those experi- 
ments. 

In the short time of seven years, Bowen 
had at his disposal the data for Ne-An, 2 Ab- 
An, Di-Fo-Qz, An-Fo-Qz (Anderson, 1912- 

1918, 1915), Di-Ab-An, and CaO-AL/V 
Si0 2 (Rankin and Wright, 1906-1944, 
1915). From these few data and a large 
measure of genius Bowen produced "The 
later stages of the evolution of the igneous 
rocks." In 1922, he published "The reac- 
tion principal in pedogenesis," which Pentti 
Eskola (1921) of Finland later called "the 
most important contribution to petrology 
of the present century." With only the 
additional information in CaO-MgO-Al 2 3 
(Rankin and Merwin, 1906-1946, 1916), 
MgO-AL/^-SiC^ (Rankin and Merwin, 
1918), CaO-MgO-Si0 2 (Ferguson, 1912- 

1919, and Merwin, 1919); Ak-Geh 
(Ferguson and Buddington, 1919-1920, 
1 920) and the immiscibility studies of Greig 
(1922-1960, 1927) in FeO-Fe^-ALft- 
Si0 2 , Bowen assembled all his previous 
petrological discussions in a set of Prince- 
ton lectures published in 1928 as "The 
Evolution of the Igneous Rocks." Although 
Bowen expressed his great prejudice for 
the well established theory of crystal frac- 
tionation as the guiding principle in ac- 
counting for the diversity of rocks, he also 



2 Bowen's Ph.D was granted in 1912 by the Massachusetts 
Institute of Technology in part for his study of Ne-An at the 
Geophysical Laboratory between 1910 and 1912. He ap- 
pears to have been the Laboratory's first "Predoctoral Fel- 
low." 



GEOPHYSICAL LABORATORY 



149 



provided the theory for testing alternative 
views. No other book has had a greater 
influence on the course of petrology. On 
the fiftieth anniversary of Bowen's book, a 
review of the same questions raised by 
Bowen was made (Yoder, 1948 — , 1979), 
and it was evident that he had indeed dis- 
cussed the critical issues still relevant to- 
day. 

Most of the other staff members not as 
geologically inclined as Bowen and his 
associates chose to pursue a plan whereby 
oxide systems, rather than mineral systems 
were investigated. By taking each of the 
principal oxides alone, then two at a time, 
successively adding other components, the 
melting behavior of the multicomponent 
rock can be ascertained. Because there are 
about 10 oxides essential to rocks, there 
would be 45 binary, 120 ternary, 210 quar- 
ternary, and 252 quinary systems. Clearly 
judicious choices were necessary, because 
not all of these systems are pertinent to 
rock-forming processes. Some systems 
were of exceptional industrial importance, 
however, and a few staff members deviated 
from the principal goals initially set. It was 
fortunate indeed they did, because some of 
the studies resulted in the establishment of 
the optical glass industry in the U. S. (see 
section on Wartime Studies), solution of 
the clinker problem in Portland cement, 
increased metal yields in the steel industry 
by adjusting the slag compositions, and 
others have been important to the high- 
temperature refractories industry. 

During the first thirty years, there was a 
special effort to deal with the oxidation 
states of iron, starting with Sosman (1908- 
1928) and his associates. In experiments 



on the Na 2 0-Fe 2 3 -Si0 2 system involving 
acmite and hematite, Bowen et al. (1930) 
pointed out that the liquids actually con- 
tained some FeO. From this experience, 
Bowen and Schairer ( 1927-1970) set out to 
ensure that equilibrium was obtained on 
FeO-Si0 2 (1932). The successful break- 
through in dealing with iron came as a 
result of using an iron crucible held in a 
purified stream of nitrogen. The equilibria 
were well defined as long as native Fe was 
present, even though the Fe 2 3 content of 
the liquids varied in a systematic way. With 
this new technique, reproducible results 
were obtained by them, with the help of 
Posnjak (1913-1947), on Ln-Fa, CaO-FeO- 
Si0 2 , MgO-FeO-Si0 2 , Ab-Fa, and Ne-FeO- 
Qz. Later, Schairer (1942) completed a 
major portion of the very complex system 
CaO-FeO-Al 2 3 -Si0 2 , for which he in- 
vented the summary "flow sheet" to de- 
scribe the major courses of fractionation of 
liquids. As will be seen in the section on 
Hydrothermal Studies, the next break- 
through at the Laboratory in controlling the 
oxidation state of iron was through the 
oxygen buffer technique devised by Eug- 
ster (1952-1958, 1957). A major tool for 
petrologists was provided by Lindsley 
(1960-1970) who calibrated the coexisting 
pairs of Fe-Ti oxides for use as thermome- 
ters and oxygen barometers. Because the 
oxidation state of iron has a profound influ- 
ence on the differentiation trend of a magma, 
the quantitative measure of the partial pres- 
sure of oxygen with minerals of wide spread 
occurrence has been of exceptional value. 
For systems requiring only Fe 2 3 Hucken- 
holz (1966-1973) and Yoder (1971) mixed 
Pt0 2 in the starting materials held in Pt 



150 



CARNEGIE INSTITUTION 



tubes to ensure an excess of oxygen for the 
study of andradite and fenidiopside at high 
pressures. Another method for maintain- 
ing the partial pressure of oxygen, devel- 
oped elsewhere (Darken and Gurry, 1945) 
was the use of mixtures of gases, such as 
C0 2 -H 2 . Eventually it was possible to 
define the Mg-Fe fractionation trends for 
the major rock-forming phases as a func- 
tion of /(0 2 ) and T. 

Characterization of the principal rock- 
forming minerals and investigation of their 
stability relations has been an ongoing 
program of the Geophysical Laboratory. 
After the determination of Ne-Ks-Qz, 
"petrogeny's residua system," by Schairer 
and Bowen in 1935, the course of phase 
equilibria research was set for years to 
come. Systematically, Schairer and col- 
leagues added the endmembers of each of 
the phases formed early in magma (e.g., 
forsterite, anorthite, diopside, and enstatite) 
to the relevant joins in the residua system. 
The ternary feldspars required consider- 
able effort because of their complex stabil- 
ity relations at various pressures and even 
more complex structural changes. The 
sluggish growth problems were overcome 
when suitable hydrothermal pressure ves- 
sels were developed. 3 The Ab-Or-H 2 
system was studied by Bowen and Tuttle 
(1947-1953, 1950) in preparation for their 
classic work on the granite system. The 
ternary feldspars were investigated by 
Yoder, Stewart (1955-1957) and Smith 
1954-1957) (1957) at P(U 2 0) = 5 kbar to 
avoid the incongruent melting of sanidine 
and to achieve a suitable rate of reaction. In 

3 The development of techniques and apparatus is given in 
the following sections on Hydrothermal Techniques and 
High-pressure Apparatus. 



the course of that work a direct method was 
established for obtaining the water content 
of the liquid as defined by the phase equili- 
bria. The melting relations of Ab-An were 
worked out by Lindsley (1968) at lOand 20 
kbar after Bell (1964-1989) and Roseboom 
(1956-1959) (1965) provided the P-T dia- 
gram for Ab up to 50 kbar while Hays 
(1965-1966, 1967) was investigating the 
P-T diagram for An and related phases up 
to 35 kbar. It became evident that plagio- 
clase was not a stable phase at pressures 
above about 32 kbar. 

In a similar way, the stability regions of 
the olivines, pyroxenes, spinels, melilites, 
and an array of feldspathoids were mapped 
out by many staff members and their asso- 
ciates at atmospheric pressure as well as at 
mantle pressures. Those phases found to 
be stable only at high pressures, e.g., jade- 
ite, pyrope, sodium melilite, provided new 
constraints on the origin of rocks in which 
they occur, particularly in solid solution. It 
was essential that the stability relations of 
each of the major mineral groups be well 
defined before their interrelationships as 
assemblages in rocks could be tackled. 
(Space does not permit a detailed account 
of the investigations of each of these major 
mineral groups even though staff members 
played leading roles in defining their sta- 
bility relations.) Impatience, however, 
usually led to somewhat premature ven- 
tures into the study of more complex as- 
semblages. One successful venture is given 
in the following example. 

After extensive experimental experi- 
ence with feldspars and pyroxenes, the 
time was considered appropriate to put 
these two major mineral groups together as 



GEOPHYSICAL LABORATORY 



151 



they are found in basalt. Study of the 
multicomponent system one component at 
a time would require an unreasonable 
amount of time. For this reason a less 
rigorous approach was taken in which the 
natural igneous rock, presumed to have 
been at one time all liquid, could be treated 
as a single bulk composition in the multi- 
component system. On this basis Yoder 
and Tilley (1931, 1955-1967) examined 
various natural basalt types and their high 
pressure analogues. The results were pub- 
lished in 1962 under the title "Origin of 
basalt magmas: an experimental study of 
natural and synthetic rock systems." Ac- 
cording to the Institute for Scientific Infor- 
mation, it was the most quoted paper in 43 
core earth science journals in the period 
1961-1980. Their model, the generalized 
basalt tetrahedron, still serves as a guide for 
testing other theories of basalt magma 
generation. 

Attention turned to the petrology of the 
mantle in the 40-200 km depth range when 
the Boyd-England (1926-1971) high-pres- 
sure apparatus was developed. During the 
very active period 1960-1970, Boyd 
(1953—) and colleagues determined the 
melting curves for Di, Ab, En, Fo, and Jd. 
In addition, the stability fields of pyrope, 
coesite, and jadeite were defined in early 
studies. The transformation of basalt to 
eclogite was outlined by Yoder and Tilley 
in 1961. O'Hara (1962-1963) worked out 
the melting relations of natural garnet peri- 
dotite at 30 kbar and B. T. C. Davis (1962- 
1965) provided the liquidus for Di-Py-Fo 
at 40 kbar. The critical observation that 
eclogite (equivalent to basalt) was at the 
minimum melting composition of ompha- 
cite-garnet was based on O'Hara's study of 



that join at 30 kbar with purified natural 
minerals and B. T. C. Davis' work on Di-Py 
at 40 kbar. The solvus on the Di-En join 
was measured by B. T. C. Davis and Boyd 
(1966) at 30 kbar, and they applied it as a 
geothermometer to the pyroxenes in nod- 
ules from kimberlites. A particularly im- 
portant phase diagram was published by 
Boyd (1970) for the system Wo-En-Cor in 
which the alumina content of orthopyrox- 
ene was later (1973) calibrated as a geobar- 
ometer. During this time, the limits of 
alumina content of diopside were defined 
on the solvus of the join Di-Jd by Bell and 
B. T. C. Davis (1969) who had earlier 
determined the melting relations of that 
system. All of these studies and related 
investigations had indeed generated a new 
outlook on the origin of magmas, the depths 
of metamorphism, and placed constraints 
on the plethora of earth models that erupted 
with the rise of plate tectonics. 

The lower mantle and core captured the 
attention of some of the staff and a large 
number of Postdoctoral Fellows and Guest 
Investigators when the diamond-anvil cell 
became a practical tool. The phase stabili- 
ties and equations of state of the metals and 
major oxide components of the earth were 
studied first, some to pressures near the 
center of the inner core. Next, combina- 
tions such as CaSi0 3 - and (Mg,Fe)Si0 3 - 
perovskite were investigated, and then Aip 3 
was added to the system. The samples were 
heated with a YAG 4 laser at each pressure 
increment to accelerate the phase transi- 
tions. Phase diagrams were generated for 

4 The yttrium aluminum garnet (YAG) was first synthesized 
by Yoder and M. L. Keith (1947-1950) in 1949 at the 
Geophysical Laboratory in a study of spessartite-yttrogar- 
net. 



152 



CARNEGIE INSTITUTION 



MgO-FeO-Si0 2 up to 700 kbar by T. Yagi 
(1976-1978), Bell, and Mao (1972—, 
1979). The partitioning of Mg and Fe 
between the various solid solutions placed 
great constraints on the geochemical mod- 
els of the earth. When the equations of state 
of the various structures were fitted to 
similar equations inferred from seismic 
data (Preferred Reference Earth Model), it 
became evident that the lower mantle was 
dominated by two perovskite structures, 
mostly an orthorhombic ferromagnesian 
silicate perovskite and a cubic calcium 
silicate perovskite (CaSi0 3 ) as a minor 
phase. After the sharp phase transition 
between spinel and perovskite + magne- 
siowiistite was discovered, Mao (1988) 
proposed a model wherein the 670-km 
seismic discontinuity is a phase-transition- 
driven, chemical-composition boundary. 
Because magnesiowustite strongly parti- 
tions iron relative to silicate perovskite, 
Mao, Bell and T. Yagi constructed a new 
fractionation model of the earth whereby 
the magnesiowustite would sink toward 
the center and lose some of its iron to the 
core by chemical reduction or dispropor- 
tionation. The excitement generated by 
these difficult and laborious experiments 
on the interior of the earth rivals that of the 
returned lunar samples. 

Although much of the emphasis was 
placed on understanding the interrelation- 
ships of the crystalline phases, their melt- 
ing behavior was, from a thermodynamic 
point of view, highly dependent on the 
character of the liquid. For this reason, 
characterization of the liquid became a 
major focus. The techniques for the meas- 
urement of density, viscosity, thermal ex- 



pansion compressibility, refractive index, 
and heat contents were developed, but 
understanding why they varied with com- 
position required knowledge of the liquid 
structure. With the advent of spectroscopic 
tools, the local short-range structure of the 
"amorphous" liquid could be ascertained. 
The structural units were identified and 
simple coordination rules developed. A 
model emerged that could be used to ra- 
tionalize the chemical, physical and thermo- 
dynamic properties of melts. The model 
was achieved by systematically examining 
the melt structure of simple systems. The 
work of B. O. Mysen (1972—) and D. 
Virgo (1971 — ) and associates on systems 
with the common rock forming oxides, 
with and without volatiles, resulted in a 
book by Mysen (1988) on the "Structure 
and Properties of Silicate Melts." 

Temperature Scale. The very first prac- 
tical problem to be faced by the staff of the 
Geophysical Laboratory was the calibra- 
tion of a temperature scale above about 
1100°C, there being no internationally 
accepted scale in 1905. Because of Day's 
experience at the Physikalisch-Technische 
Reichanstalt in Berlin, the first apparatus 
installed was the nitrogen-gas thermome- 
ter. With a new design for improved accu- 
racy of measurement, Day and Sosman 
gave accurate data for a scale from 300° to 
630°C with a direct determination of the 
boiling point of sulfur. The scale was then 
extended by them in 1910 to the palladium 
melting point of 1 549.2°C. The fixed points 
were corrected from the constant-volume 
nitrogen scale to an absolute thermody- 
namic scale and expressed by Johnston 



GEOPHYSICAL LABORATORY 



153 



(1908-1916) and Adams (1910-1952) 

(1914) as an e.m.f. for copper-constantan 
and platinum-rhodium thermocouples from 
0°to 1755°C. The principal fixed points for 
gold, copper, diopside, and palladium be- 
came known as the Geophysical Labora- 
tory scale, 5 and it is still used today. The 
melting point of platinum, 1755°C, was 
based on the incremental difference of 
optical pyrometer measurements of the 
Bureau of Standards between palladium 
and platinum. 

After WWI, an international confer- 
ence met and the International Tempera- 
ture Scale of 1927 was adopted. Silver was 
set 0.3° higher; gold, 0.4° higher, palla- 
dium, 5.5° higher, and the major change 
was that platinum became 1773°C. In spite 
of these recommendations, the scientists at 
the Geophysical Laboratory retained their 
own scale because of their belief in its 
thermodynamic foundation and for consis- 
tency with their previously published phase 
diagrams. In the meantime, physicists noted 
certain discrepancies in the physical con- 
stants related to the International Tempera- 
ture Scale. A new international committee 
met in 1939, but WWII intervened and 
their results were not published until 1948. 
The changes nearly restored the fixed val- 
ues below 1550°C to those of the Geo- 
physical Laboratory scale. One significant 
change related to the extrapolation to the 
melting point of cristobalite which would 
require a change from 1713°C to 1723°C. 
Nevertheless, the values for diopside 
(1391. 5°C) and pseudo-wollastonite 
(1544±2°C), anorthite (1553±2°C), and 

5 The fixed boiling and melting points below gold are listed 
by Sosman (p. 522, 1952). 



cristobalite (1713±5°C) have all been re- 
tained by the Geophysical Laboratory as 
calibration points not only for consistency 
but also because they are within the errors 
of experimental determination of the Inter- 
national Temperature Scale, which is still 
subject to change. It would be useful to 
ascertain in the near future the melting 
point for the important endmember min- 
eral forsterite that is still known only as 
1890±20°C. The corrections to the e.m.f. 
of thermocouples used at high pressures, 
recently studied but subject to debate, also 
remain an important subject for reinvesti- 
gation. In principle, the triple points of 
mineral phase changes may serve as an 
adequate P-T scale for interlaboratory 
comparisons. 



Metamorphic Petrology 

Prior to WWII there were only a few 
studies concerned with metamorphism at 
the Geophysical Laboratory, even though 
an extensive program had been laid out by 
the Advisory Committee. Van Hise had 
already completed his enormous (1286 
pages) "Treatise on Metamorphism" for 
the U.S.G.S. in 1904 and was well prepared 
to advise the CIW. Some of the thermody- 
namic principles were stated by Johnston 
andNiggli (1912-1913) (1913), and Eskola 
(1922) described the sequence of meta- 
morphic rocks at a limestone-granite con- 
tact. A major mapping study of the meta- 
morphic zones of Dutchess Co., N. Y,. was 
made by Barth (1929-1936, 1936). He 
demonstrated that the rocks were appar- 
ently at equilibrium because the assem- 



154 



CARNEGIE INSTITUTION 



blages accounted for the bulk composition 
at each stage of the metamorphism of the 
argillaceous sediments. 

The principal delay in tackling experi- 
mentally the metamorphic facies of Eskola 
as well as Bo wen's petrogenetic grid was 
the lack of apparatus to contain the hydrous 
minerals. That problem was subsequently 
solved (see next section) by Bowen and 
Tuttle (1949) who published the first sys- 
tematic study on the P-T stability of some 
of the critical metamorphic minerals in 
MgO-Si0 2 -H 2 0. Shortly thereafter a se- 
ries of papers appeared on systems defin- 
ing the stability fields of chlorite, cordier- 
ite, muscovite, biotite, chloritoid, stauro- 
lite, garnets, and especially the AL^SiC^ 
polymorphs. 

Serious objections to the facies and 
isograd concepts were raised by Yoder 
(1952) in a study of MgO-Al 2 3 -Si0 2 -H 2 
in which representatives of all the then 
defined facies were found to be stable at the 
same P and T. He also raised the issue of 
the role of water in metamorphism (Yoder, 
1955) in regard to its presence in excess as 
a free phase or where it was "deficient" 
relative to the most hydrous assemblage. 
The open vs. closed system with volatiles 
became the major issue of the day. A 
significant contribution to the problem was 
made by H. J. Greenwood (1959-1963) 
from experiments on analcite-H 2 0-Argon, 
Ct-Qz-H 2 0, and others. The influence of 
P(H 2 0) less than P was clearly demon- 
strated for those simple but highly informa- 
tive reactions. 

The apparent loss of large volumes of 
water during the metamorphism of some 
sediments and the gain of water by other 



rocks, implied an active flow of fluids. 
Oxygen isotopic evidence and phase analy- 
sis led D. Rumble (1969-1971; 1973—) 
and associates to estimate that the volume 
of fluid that flowed through a calc- silicate 
bed at Beaver Brook, N. FL, was from 1 .5 to 
4.0 times the rock volume. Their paper 
(1982) emphasized the process of rock- 
fluid interaction, but the proportions of 
fluid to rock are still being debated vigor- 
ously. The concept of reaction progress 
variables espoused by J. M. Ferry (1975- 
1977) have been helpful in understanding 
the process. More recently, the flow of 
fluids has been related to structure by C. P. 
Chamberlain (1985-1987). The transport 
of heat with fluid was documented by 
comparing the isotherms deduced from the 
metamorphic reactions with the oxygen 
isotopic data. The mapping of channeled, 
hot, fluid-flow regions is potentially a valu- 
able tool for ore prospecting. 

The extensive studies on the amphi- 
boles at the Geophysical Laboratory per- 
tain to both metamorphic and igneous rocks. 
In general, the role of amphibole in meta- 
morphism is confined to low P(H 2 0) and 
relatively low temperatures, whereas most 
amphiboles appear on the liquidus above a 
few kbar P(H 2 0) Although Allen and 
Clement (1904-1907) (1908) found water 
to be a component in tremolite, its struc- 
tural role deduced by Schaller (1916) was 
confirmed by Posnjak and Bowen (1931), 
and a previous report of its formation from 
a dry melt was withdrawn. A few years 
later, fluoroamphiboles were formed inad- 
vertently when NaF was used as a flux to 
grow orthopyroxenes. (That study laid the 
groundwork for a later extensive program 



GEOPHYSICAL LABORATORY 



155 



at the U. S. Bureau of Mines for the pos- 
sible production of synthetic asbestos.) The 
first systematic P-T studies of tremolite 
and pargasite were made by Boyd (1954). 
A complex hornblende was produced from 
a tholeiite basalt by Yoder and Tilley (1956), 
and its stability field outlined up to 10 kbar. 
The study by staff and associates of most of 
the critical endmember amphiboles fol- 
lowed: magnesioriebeckite, arfvedsonite, 
glaucophane, ferropargasite, richterite, 
ferrorichterite, K-richerite, anthophyllite, 
cummingtonite, and aluminous anthophyl- 
lite. The breakdown of amphibole at high 
pressures (20-30 kbar) was first suggested 
from thermodynamic calculations by 
Greenwood (1 963), but it was several years 
before the general concept was demon- 
strated experimentally by others. The 
possible storage of water in the mantle then 
shifted from the amphiboles to the micas 
and hydrous forms of commonly anhy- 
drous minerals (e.g., hydrogarnets). 



3. Hydrothermal Techniques 

Before 1900 some 80 mineral species 
had been synthesized, but not under con- 
trolled and reproducible conditions. The 
devices used for synthesis were generally 
gun barrels closed by brazing, welding, or 
a screw on cap. A pressure vessel having a 
screw-on-cap fitted with a flat metal washer, 
made in about 1900, was brought to the 
Geophysical Laboratory by E. T. Allen 
from the U. S. Geological Survey. Few 
experiments were tried before WWI be- 
cause the devices were unreliable even at 
low pressures. The review of hydrothermal 



mineral formation by G. W. Morey (1912- 
1957) and Paul Niggli in 1913, however, 
registered the strong interest in pursuing 
those experiments. Further stimulus was 
provided by the analyses of gases at Kilauea 
volcano, Hawaii, by Day and Shepherd 
who found H 2 a principal component. In 
1917 Morey and Earl Ingerson (1935-1947), 
no doubt inspired by the demonstration by 
Day and Shepherd of H 2 in the gases of 
Kilauea, designed a pressure vessel with a 
contained copper or silver washer that would 
retain reliably pressures somewhat over 1 
kbar. With that apparatus Morey and C. N. 
Fenner (1910-1937) investigated the 
K 2 Si0 3 -Si0 2 -H 2 system up to 1000°C and 
about 340 bar by the isothermal polybaric 
saturation method. Their detailed exposi- 
tion of theory and experimental methods 
recorded a major advance in hydrothermal 
studies. There followed a series of experi- 
ments in the "Morey bomb" on the simple 
oxide systems with H 2 0. 

The next breakthrough came with the F. 
H. Smyth (1919-1925) and L. H. Adams 
(1923) device in which HOOT and 1 kbar 
could be sustained with a C0 2 -gas me- 
dium. With the same device, R. W. 
Goranson (1926-1951) achieved the first 
systematic results on the melt curves of the 
rock-forming silicates, albite-H 2 and 
sanidine-H 2 0, as well as the melting curve 
for granite-H 2 0. These dramatic experi- 
ments would appear to be the last major de- 
velopments in experimental apparatus prior 
to WWII. Fortunately, Morey had also de- 
scribed a new design forhis pressure vessel 
that was to lay fallow throughout the war. 
He adapted P. W. Bridgeman's unsupported- 
area principle to the closure and connected 



156 



CARNEGIE INSTITUTION 



a H 2 pump directly to the Morey bomb, 
thereby controlling the water pressure in- 
dependently of the temperature. 

A review of the Geophysical 
Laboratory's programs after WWII by the 
staff and a large host of external colleagues 
greatly emphasized the need to pursue 
hydrothermal systems. An inventive and 
imaginative investigator employed at the 
Laboratory during the war under an Office 
of Scientific Research and Development 
contract, O. F. Tuttle, was hired to help 
Morey and N. L. Bowen carry out this 
mission. The hot-seal apparatus, eventu- 
ally called the Tuttle apparatus, and the 
cold-seal pressure vessels soon were de- 
veloped by Tuttle, using alloys found supe- 
rior for machine gun barrel liners during 
WWII research at the Geophysical Labora- 
tory (see section on War-time Studies). The 
cold-seal, pressure vessels, also called "rod 
bombs" or "test-tube bombs" depending 
on their position in, or orientation of, the 
furnace, remain the most widely used ves- 
sels for hydrothermal investigation today. 
A simple, cold-seal, pressure-vessel bench 
employing an intensifier was built by Yoder 
for operation to 850°C, and 5 kbar for runs 
of one month or more duration. The sealed- 
platinum-tube technique, first introduced 
at the Laboratory by P. Eskola in 1922, was 
used for a wide range of gases in addition to 
Hfi. 

Because of the inherent limitations of 
the externally-healed pressure vessels, 
Yoder constructed in 1949 an internally - 
heated, gas-media pressure vessel that could 
sustain 1650°C and 10 kbar for months. 
These conditions were adequate for the 
entire range of temperatures and pressures 



in the continental crust within which 99% 
of the rocks observed crystallized. With 
the experience gained from investigations 
on pure mineral systems, Yoder and C. E. 
Tilley initiated in 1956 a study of natural 
igneous rocks with and without water. In 
the same apparatus, sulfur-bearing systems 
were studied in gold tubes by Kullerud and 
Yoder. 

Other new techniques were developed 
rapidly thereafter. For examples, the con- 
trol of oxygen fugacity by a series of min- 
eral buffers was demonstrated by Eugster 
in 1956. The buffers initially consisted of 
iron oxides whose stability had been deter- 
mined by Darken and Gurry (1945). For 
pairs of oxides in equilibrium, the P(0 2 ) is 
fixed for a given temperature and pressure. 
By surrounding a sample contained in Pt, a 
metal that is permeable to hydrogen, with 
water and a pair of oxides held in an outer 
gold tube that is relatively impermeable to 
hydrogen, the oxygen pressure can be 
maintained. Eugster 's first demonstration 
of the technique was in determining the 
stability of the iron-rich endmember mica, 
annite, between 0.5 and 2 kbar. The tech- 
nique was adopted rapidly worldwide and 
continues to be a principal method for 
investigating redox reactions with a large 
range of buffers. The equilibrium estab- 
lished through the Pt membrane is of a 
restricted type because the gas phase over 
the buffer has a different composition that 
than over the sample. Nevertheless, the 
simplicity of the technique and wide range 
of application have had a major impact on 
igneous and metamorphic petrology. In 
1976, J. D. Frantz (1972- ) redesigned the 
Shaw apparatus for controlling the H 2 fu- 



GEOPHYSICAL LABORATORY 



157 



gacity. The influence of gas mixtures, such 
as C0 2 and H 2 0, on metamorphic reactions 
was outlined by H. J. Greenwood, after he 
resolved the gas-mixing problem that frus- 
trated previous attempts to measure these 
effects. 

With the above-described devices it was 
thenpossible to establish the stability ranges 
of most of the common rock-forming 
minerals that contained a volatile compo- 
nent. The Postdoctoral Fellows carried 
these techniques to other parts of the world, 
and hydrothermal studies evolved expo- 
nentially. The attainment of those condi- 
tions to be found in the mantle and core 
required new concepts and these are out- 
lined in the next section. 



4. High-Pressure Apparatus 

The effect of pressure on the melting 
"point" of rocks has been a high priority 
question since the inception of CIW. The 
compressibility studies of T. W. Richards 
and W. N. Stull (1903) at Harvard Univer- 
sity were supported by CIW, probably on 
the recommendation of C. Barus, a mem- 
ber of the Advisory Committee on Geo- 
physics. [Barus (1893) was the first to 
obtain an estimate of the change of melting 
"point" of diabase with pressure from 
measurements of the volume change, melt- 
ing temperature, and heat of melting.] In 
1906 P. W. Bridgman began his experi- 
ments at Harvard on a range of materials to 
ascertain the change of physical properties 
with pressure. About the same time, John 
Johnston began to develop apparatus for 
sustaining both high temperature and high 



pressure for geological applications at the 
Geophysical Laboratory. The limits ob- 
tained were 400° C at 2 kbar, and Johnston 
and L. H. Adams (1911) were able to report 
on the melting point changes with pressure 
of Sn, Bi, Cd, and Pb. The study of the 
compressibility of major rock-forming 
minerals and rocks, however, remained of 
central interest. The measurements on 
dunite and basaltic glass were especially 
pertinent to theories of the constitution of 
the mantle. By 1923 Smyth and Adams had 
achieved 1400°C at 1 kbar, and the range 
was later extended in the same apparatus to 
940°C and 3.7 kbar by Goranson. In this 
time period, the manganin pressure gauge 
and its calibration was perfected by Adams 
and his colleagues as well as valves and 
other high-pressure fittings critical to the 
success of high-pressure experiments. 
Nevertheless, the trial-and-error stage of 
testing metals and packings continued. The 
availability of an on-site machine shop and 
direct accessibility to imaginative instru- 
ment makers contributed immeasurably to 
the development of new high-pressure 
techniques. 

After WWII, Yoder sustained 1650°C 
and 1 kbar by 1 949 in an internally-heated, 
gas-media apparatus. In 1956 substantial 
increases in pressure and temperature were 
achieved by F. R. Boyd, Jr. and J. L. Eng- 
land who had adapted the Griggs and 
Kennedy design of Bridgman's (1935) 
carbide-piston "squeezer". They attained 
800° at 10 kbar and 600° at 50 kbar, illus- 
trating the breakdown of nepheline to jade- 
ite and an unidentified phase. 

The exciting announcement of Loring 
Coes (Norton Co., Worcester, MA) that he 



/ 



158 



CARNEGIE INSTITUTION 



had synthesized a large number of "high- 
pressure" minerals others had struggled 
unsuccessfully to obtain, came in 1953. He 
had devised a solid-media, high-pressure 
apparatus in which a hot-pressed Al^ 
core supported by steel bands and tungsten 
carbide pistons were used. His experi- 
ments were made up to 1000°C and 45 kbar 
in that device. Because of its obvious 
applicability to many geological questions, 
the Coes apparatus was the basis for an 
improved chamber assembly designed by 
Boyd and England (1958, 1960) that could 
sustain 1750°C and 50 kbar. The main 
breakthroughs were in fitting a thermo- 
couple up to the sample and in providing 
adequate support for a reuseable tungsten 
carbide core. Immediately after the an- 
nouncement of the details of diamond 
synthesis by the General Electric Co. in 
1 959, Boyd and England successfully made 
diamonds in their apparatus. That highly 
successful design has been used by hun- 
dreds of investigators around the world on 
mineralogical and petrological problems 
in the mantle. Extension of the range to 1 00 
kbar was accomplished by them through a 
two-stage device in which the piston was 
supported by a substance such as KBr, that 
undergoes a phase change, thereby main- 
taining the support pressure at the phase 
change. 

On the basis of Bridgman's anvil con- 
cept, Weir et al. (1959) at the National 
Bureau of Standards patented a miniature 
device in which the sample is squeezed 
between two opposing diamond anvils, for 
pressures up to 160 kbar at relatively low 
temperatures (< 175°C). Substantial im- 
provements by H-k. Mao and P. M. Bell in 



1978 led to the production of 1.72 Mbar, 
verified by three different methods of cali- 
bration. In subsequent years, pressures 
beyond those in the center of the earth (3.5 
Mbar) were achieved and the current rec- 
ord is 5.5 Mbar. The observation of plastic 
flow in diamond during one super pressure 
experiment raised an array of theoretical 
questions. The sample in the high-pres- 
sure, diamond-anvil cell can be heated to 
3500°C with an appropriate laser beam to 
which diamond is transparent. The trans- 
parency of the diamond was a great advan- 
tage for observing absorption, scattering, 
and diffraction by the sample at pressure 
with Mbssbauer, x-ray diffraction, Raman, 
optical, infrared and other spectral devices. 
The versatility of the Mao-Bell diamond 
cell has resulted in an explosion of studies 
on specific materials in the earth at ambient 
conditions and generated a host of opportu- 
nities for the chemist and physicist. 

In spite of the availability of equipment 
that reproduces the entire range of P-T 
conditions in the earth, their exploitation in 
general systematic studies of phase equili- 
bria have been slow in the geological 
community. The current trend toward 
development of large-volume devices for 
sustaining high pressures and high tem- 
peratures appears to be driven by the desire 
to understand those properties of the earth's 
mantle and core that require measurement 
of larger volume specimens. For examples, 
measurement of sound velocity, rheology, 
partitioning in multiphase assemblages, 
single crystals for structural study, and 
particularly those measurements requiring 
a constant and uniform temperature cur- 
rently require larger volumes than can be 



GEOPHYSICAL LABORATORY 



159 



accommodated in the diamond-anvil cell 
without special facilities. 

Pressure calibration has been a difficult 
problem in itself. The primary calibration 
of force per unit area is dependent on an 
evaluation of the friction on the piston. A 
rotating, free piston loaded with weights 
was used at the Laboratory for many years 
up to 10 kbar. Secondary calibrations were 
usually dependent on abrupt volume 
changes in a simple material. The melting 
of ice VI to water at room temperature was 
given as 9630 bar at 25 °C by Adams (1931). 
The freezing pressure of Hg at 0°C was 
taken as 7492 bar, and the transformation 
pressure of CC1 4 1 — » II was taken as 3326 
bar (Bridgman, 1911, 1914). As higher 
pressures were developed the transforma- 
tion of Bi I -> II (25.2 kbar at 25°C) was 
employed by Boyd and England. The tran- 
sition of Till -» m (37.15 kbar at 29°C) 
was also used by Boyd and England ( 1 958) 
indirectly by measuring its abrupt change 
in electrical resistence in a silver chloride 
cell. 

When the pressure range exceeded 50 
kbar, the limit of the tungsten carbide core, 
it was necessary to turn to still other meth- 
ods. The shift in the lattice constants of 
certain metals (Au, Ag, Cu, Mo, Pd, Pt) was 
used as the primary pressure calibration. 
The shift of the ruby Rj fluorescence line 
became the new secondary calibration in 
the diamond-cell apparatus. Because the 
ruby fluorescence weakened above 1 Mbar, 
it was necessary to return to the primary 
method of using force per unit area, with a 
substantial loss in accuracy, or to the mul- 
tiple use of calibrated metals. It is likely 
that new calibrations will be required as the 



investigation of certain ranges of pressure 
involved with major seismic discontinui- 
ties in the earth progresses. 

The leadership of the Geophysical 
Laboratory in developing high-pressure 
techniques has been maintained through- 
out its existence. Although geology is 
often described as an applied science, the 
geologists at the Laboratory have provided 
the basic physics and chemistry in the ex- 
treme regions of pressure and temperature 
for use in other sciences. Challenges to 
existing theory have been proposed by 
experimentation under the core and mantle 
conditions in the earth, and the feedback to 
the basic sciences has been rewarding. The 
analysis of a geological problem by isolat- 
ing and evaluating the effect of each sig- 
nificant variable appears to be an effective 
way to understand multivariate natural 
phenomena. 



5. Ore Petrology 

The plans submitted in 1903 by Dr. C. 
R. Van Hise for a geophysical laboratory 
included the need for 

"experimental studies on underground 
solutions and the artificial reproduction of 
natural minerals [that] will lead to correct 
theories of ore deposition and also give 
results of practical value, the magnitude of 
which cannot now be estimated." 

Although Van Hise championed but one of 
the several schools of ore deposition, the 
recommendation was clear. Within a few 
years of the opening of the laboratory build- 
ing, papers appeared on the characteriza- 



160 



CARNEGIE INSTITUTION 



tion of sulfides, the analytical procedures 
for determining sulfur, and on the physical 
chemistry of sulfide systems. For example, 
the chemistry of the secondary enrichment 
of copper sulfides was unraveled by E. G. 
Zies (1913-1949), E. T. Allen, and H. E. 
Merwin in 1916. The studies of Allen and 
Zies (1919) on the chemistry of hot springs 
was applied by Fenner (1933) to ores de- 
rived from igneous origins. In the same 
year, Bowen ( 1 933) proposed that the heavy 
metals would be concentrated in the resid- 
ual fractions of a differentiating magma. It 
became evident that hot springs were an 
end product of ore deposition as well as 
indicators of volcanic activity. 

A benchmark paper on the Cu-Fe-S 
system by Merwin and Lombard (1915- 
1927) appeared in 1937. They laid out the 
technique for holding synthetic and natural 
samples at a defined vapor pressure of 
sulfur (455 mm) and temperature in silica- 
glass (vitreosil) tubes. The phase diagram 
was of great importance to economic ge- 
ologists because it helped to constrain the 
temperatures and pressures of ore forma- 
tion. With continued investigation, the 
system has been found to be exceptionally 
complex, and it remains one of the most 
intensively studied systems even today. 
The concept of buffers was clearly defined 
even though the "equilibrium" obtained 
was of a restrictive type, the buffer and 
sample being at different temperatures. 

Merwin and Lombard had recognized 
many of the problems arising from the 
inability to quench the run products. The 
unmixing of solid solutions in the FeS-ZnS 
system had been determined quantitatively 
as a function of temperature by Kullerud 



(1954-1970). After he joined the Geo- 
physical Laboratory he applied this impor- 
tant principle of geothermometry to other 
systems and to the estimation of the tem- 
perature of formation of natural ores. During 
a highly inventive period, techniques were 
evolved by Kullerud (1971) for dealing 
with sulfur and selenium systems, beyond 
the limitations of silica-glass tubes, up to 
1400°C. Kullerud and his colleagues 
showed that essentially all sulfide and se- 
lenide systems exhibited liquid immisci- 
bility. The first high-pressure-temperature 
diagram for a sulfide, pyrite, was achieved 
by Kullerud and Yoder (1959). Their ob- 
servation of incongruent melting in pyrite 
clearly showed that it could not be a mag- 
matic phase in either basalts or rhyolites. A 
similar conclusion was reached forpentlan- 
dite in a study by Kullerud (1963). The 
phase diagram for the economically impor- 
tant system Cu-Fe-Ni-S was established by 
J. R. Craig (1965-1967) and Kullerud 
(1969). 

The systematic study of the synthetic 
sulfide systems have yielded information 
on the stability of mineral assemblages in a 
wide range of ore bodies. Not infrequently, 
the discovery of synthetic phases preceded 
their discovery as minerals in the ore body! 
The temperature gradients in the ore bod- 
ies, as determined by sulfide geothermom- 
etry, have been especially useful in explo- 
ration. The rapid response of some of the 
sulfides to changes in temperature in the 
laboratory have brought special insight into 
the metamorphism of ore bodies, a concern 
ofVanHiseasearlyas 1900. Re-equilibra- 
tion to temperatures as low as 200°C for 
some sulfides has been useful in generating 



GEOPHYSICAL LABORATORY 



161 



a scale of closure for determining the kinet- 
ics of the cooling of the ore body (Kullerud, 
1967). 

The interrelationships of sulfides and 
silicates, the essence of ore petrology, did 
not get underway until the early 1960's. 
Kullerud and Yoder, after considering the 
zones around the Bodenmais, Bavaria, ore 
body, reacted sulfur with fayalite and ob- 
tained pyrrhotite, magnetite, and quartz. 
From these and other experiments with 
various iron-bearing silicates, the concept 
of sulfurization emerged that helped ex- 
plain the apparent high-grade metamor- 
phic aureoles around low-temperature ore 
bodies. This concept was also demon- 
strated and applied to the interrelationship 
of sulfides and carbonates as well as sul- 
fides and oxides. In the latter case, Kullerud 
and colleagues produced a new type of 
omission solid solution in magnetite when 
reacted with sulfur. 

The magmatic ores, especially those 
occurring in the layered igneous intrusions, 
have been of more recent concern. With an 
exceptionally wide range of experience in 
the layered intrusions of the world, Irvine 
(1972 — ) and his colleagues characterized 
the Pt-Pd ores of the Stillwater Complex of 
Montana. The detailed analyses of the J-M 
reef illustrated how magma mixing and 
double diffusive convection play a major 
role in the deposition of ores high in the 
layered sections of silicate rocks. 



6. X-ray Crystallography 

The program in crystal structure deter- 
mination was initiated at the Geophysical 



Laboratory in 1919, just seven years after 
Laue's discovery of x-ray diffraction, by 
Ralph W. G. Wyckoff (1919-1927), who 
had been invited to the Laboratory by Day 
during a visit to Cornell. Atomic arrange- 
ments were initially deduced intuitively 
and then tested by the few measured reflec- 
tions. Wyckoff derived a complete analyti- 
cal expression of Schoenflies space group 
theory to define all the possible arrange- 
ments and used the x-ray information to 
select the correct structure. In this way he 
worked out the relatively simple structures 
of the calcite group, dolomite, aragonite, 
periclase, quartz, wiistite, and zircon. The 
first structure to be determined at high 
temperature from powder x-ray-diffraction 
data was high cristobalite (Wyckoff, 1 925). 
With the help of Wyckoff, C. J. Ksanda 
(1914-1940), a Swiss-trained instrument 
maker, designed the twin-gas tubes for x- 
ray generation. Wyckoff joined with Eu- 
gene Posnjak (1913-1947) to prove the 
validity of Werner's coordination theory. 
When Wyckoff departed to work at the 
Rockefeller Institute on organic crystals, T. 
F. W. Barth joined the staff in 1929. He 
worked with Posnjak on the spinel prob- 
lem, which resulted in their recognition in 
1931 of "variate atom equipoints" - that is, 
crystallographically equivalent sites that 
could be occupied by chemically different 
atoms. It was the key idea in understanding 
many crystal structures, especially the 
aluminosilicates. 

According to Donnay et al. (Yearbook 
68, pp. 278-283), only the Geophysical 
Laboratory and Caltech had x-ray crystal- 
lography programs carried on continuously 
from 1919 to 1969. This activity continues 



162 



CARNEGIE INSTITUTION 



at the Geophysical Laboratory and Caltech 
in 1989. 

The sulfide minerals were the focus of 
attention of George Tunell (1925-1947). 
He determined the structures of tenorite, 
calaverite, sylvanite and krennerite. He 
also derived the Lorenz correction factor 
for equi -inclination Weissenberg films, 
essential for use of the intensities of dif- 
fracted x-rays. The Patterson-Tunell sten- 
cils were a very popular aid for the compu- 
tation of Fourier synthesis prior to the 
computer era. 

With the arrival of the powder x-ray 
diffractometer in 1949, the identification 
and characterization of synthetic mineral 
phases, primarily carried out under the 
microscope, was supplemented by the use 
of comparative powder patterns. The cell 
dimensions and volumes of the alkali feld- 
spar solid-solution series were determined 
and the existence of a high-order transition 
established by Gabrielle Donnay (1950- 
1952;1955-1960;1963-1970) and L. H. 
Adams. The first applications of general- 
ized symmetry to magnetic-structure de- 
terminations were made by J. D. H. Don- 
nay (Visiting Investigator) with colleagues 
at the Brookhaven National Laboratory. 
The Donnays were especially successful in 
relating morphology to structure, which 
led to additional generalizations of the Law 
of Bravais. These studies were followed 
with the discovery of the relationship be- 
tween crystallographic axes and morpho- 
logical features of the calcite skeleton, 
termed biocrystals, in Echinodermata. 

During his tenure as a Postdoctoral 
Fellow, J. V. Smith (1951-1954) pursued 
crystallographic studies of paracelsian,me- 



lilite, and alkali feldspars, much of the 
latter in collaboration with W. S. MacKenzie 
(1951-1952; 1953-1957). Smith also pro- 
vided the theoretical and structural basis 
for polymorphism in the micas with Yoder. 
Although a staff member for only a brief 
period, Charles W. Burnham (1963-1966) 
refined the structures of sillimanite, kyanite, 
and mullite. He compared in detail the 
crystal structures of orthoferrosilite, clinof- 
errosilite, and ferrosilite HI, and pointed 
out differences in these polymorphs that 
have not yet been fully explained. In addi- 
tion, he provided several computer pro- 
grams whose successors are still being used 
in crystallographic studies. A wide range 
of crystal structures among the common 
rock -forming minerals were refined by L. 
W. Finger (1967 — ). He also developed 
computer reduction programs for the elec- 
tron microprobe, automated the x-ray dif- 
fractometer, and contributed many tech- 
niques for resolving the more complex 
mineral structures. Finger and R. M. Hazen 
(1976 — ) initiated single-crystal, diamond- 
cell techniques that resulted in the accurate 
measurement of both compressibility (to 
200 kbar) and thermal expansion (to 
1000°C). From these techniques the con- 
cepts of cation polyhedral analysis as a 
function of pressure and temperature 
evolved. 

Current studies include the adaptation, 
initiallybyFinger,A.Jephcoat(1982-1989), 
and H-k. Mao, of synchrotron radiation to 
structure determination of very small single 
crystals held at pressure in the diamond 
cell and the characterization, primarily by 
Finger and Hazen, of the structures of phases 
with high-temperature superconducting 



GEOPHYSICAL LABORATORY 



163 



properties. C. T. Prewitt (1986 — ) joined 
the Laboratory as Director and collabo- 
rated with Finger and Hazen on a variety of 
projects including the first structure deter- 
minations of high-temperature supercon- 
ductors and high-pressure silicate struc- 
tures containing octahedrally-coordinated 
silicon that were synthesized in the cubic- 
anvil apparatus at SUNY Stony Brook. As 
part of his involvement in the superconduc- 
tor research, Hazen wrote a book, "The 
Breakthrough", which gives an account of 
the discovery of the 1-2-3 high-T c super- 
conductor and subsequent attempts by dif- 
ferent research groups to develop the dis- 
covery. 

In addition to their individual pioneer- 
ing efforts, the hallmark of the crystallog- 
raphers at the Geophysical Laboratory has 
been their cooperative response to the needs 
of other staff members in characterizing 
the common rock-forming minerals and 
especially the minute synthetic phases 
produced. The determination of crystal 
structure at a range of conditions and its 
relationship to physical and chemical prop- 
erties constitutes a major and essential 
contribution to the success of the Geo- 
physical Laboratory's mineralogical inves- 
tigations. 



7. Spectral Mineralogy 

The field of mineral physics at the 
Geophysical Laboratory evolved mainly 
from initial efforts in mineral optics, arc- 
Raman, and x-ray crystallography, followed 
in the 1970's by Mossbauer, laser-Raman 
and infrared spectroscopy, and in the 1 980's 



by the entire array of spectral tools of 
modem day physics and chemistry. 

An early pioneer in the U. S. in the 
application of microscopy to mineralogi- 
cal and penological problems was F. E. 
Wright. His design of apetrographic micro- 
scope was adopted by a leading U. S. 
manufacturer and his improvements sub- 
stantially advanced its use. His book on 
"The methods of petro graphic-microscope 
research" in 1911 had great influence in 
promoting the quantitative measurement 
of the optical properties of crystals. An- 
other major contributor to crystal optics 
was H. E. Merwin. He developed with E. 
S. Larsen (1907-1909) special immersion 
media of unusually high refraction using 
mixtures of amorphous sulfur and sele- 
nium. His dispersion method for measur- 
ing refractive indices of grains in immer- 
sion liquids is still widely used. Because of 
his demonstration of the relationship of 
index of refraction, density, and composi- 
tion of glasses, he contributed to many of 
the phase equilibria studies of the Labora- 
tory. 

Some of the earliest studies of the Raman 
effect, discovered in 1928, were carried out 
in the U. S. by J. H. Hibben (1928-1939). 
He provided detailed treatises on inorganic 
compounds in 1933 and on organic com- 
pounds in 1939. His principal successes 
were in the speciation of organic com- 
pounds, and he made a special effort to 
apply the technique to the petroleum indus- 
try. The low intensity of the Raman effect 
using an arc lamp and photographic plates 
was eventually enhanced with the advent 
of laser light sources and photoelectric cell 
recording of the spectra. Applications to 



164 



CARNEGIE INSTITUTION 



the common rock-forming minerals and 
their melts did not begin until the arrival of 
Postdoctoral Fellow S. K. Sharma (1977- 
1980) who installed a modern Raman spec- 
trometer and a variety of laser sources with 
the help of his colleagues J. D. Frantz and 
D. Virgo. Another Raman system fitted 
with a microscope was added, and a multi- 
channel detector was introduced by Mao, 
Bell and Hemley (1984 — ). These refine- 
ments led to the techniques of single-crys- 
tal, micro-Raman spectroscopy as well as 
ultra high-pressure optical spectroscopy. 
An outpouring of highly innovative studies 
at pressures in the megabar range yielded 
an array of studies of crystallized gases, 
new mantle-phase structures, as well as 
coordination changes in common miner- 
als. The crystallized gases became the 
"hydrostatic" media for subsequent dia- 
mond-anvil experiments and initiated the 
race to make metallic hydrogen. With 
these new instruments for sustaining rec- 
ord pressures, the winning of that race by 
Hemley and Mao appears to have been 
achieved in 1988 and documented above 
2.5 Mbar. 

The application of Mossbauer tech- 
niques to atom site preference problems 
was carried out by D. Virgo. Landmark 
studies of the Fe-Mg ordering in olivines 
(with L. Finger) and anthophyllite (with F. 
A. Seifert, 1973-1974) included an impor- 
tant estimate of the kinetics of the process 
over a range of pressure and temperature. 
The resulting time-temperature-transfor- 
mation plots are useful in defining the later 
stages of the cooling path of a metamorphic 
rock. 

One of the ultimate goals of vibrational 
spectroscopy is in deriving the thermody- 



namic properties of crystals that can be 
used in calculating their phase relations. A 
major step forward was taken in 1985 by 
Hofmeister (1983-1987) and colleagues in 
modifying a Fourier-transform, far-infra- 
red spectrometer with a beam condenser, 
an He-cooled bolometer, and a diamond 
cell in order to obtain high-pressure spec- 
tra. From the data collected in the modified 
apparatus, combined with the data from the 
Raman active bands, the heat capacity and 
the Griineisen parameters could be ob- 
tained. The equation of state for the Mg-Fe 
olivines in particular will be at hand when 
the temperature effects are investigated. 

Brillouin/scattering from a five-pass, 
interferometer was used by Mao, Bell, and 
other colleagues to obtain the pressure 
dependence of longitudinal- and transverse- 
acoustic velocities and refractive index in 
solid hydrogen and deuterium for the pur- 
pose of obtaining its equation of state. 
These techniques can now be applied to the 
principal mantle phases to obtain their 
elastic parameters that are so important to 
the seismologist. 

The important problem of heat transfer 
by radiation in the earth was examined by 
S. P. Clark, Jr. (1957-1962). The strong 
onset of photon absorption in natural oli- 
vine appeared to be an important process 
that influenced the thermal regime in the 
earth. With dual-beam, crystal-field spec- 
tra H-k. Mao and P. M. Bell showed that the 
radiation window broadened with pres- 
sure, but the shift of the absorption edge 
with pressure blocked the radiative trans- 
fer. 

Because of the enormous advantage of 
the intense, parallel x-rays from a synchro- 
tron source, Mao, Hemley, and colleagues 



GEOPHYSICAL LABORATORY 



165 



have developed the appropriate devices for 
carrying out diffraction at high pressures at 
the National Synchrotron Light Source at 
the Brookhaven National Laboratory, Up- 
ton, NY. The intense beam, properly colli- 
mated, is ideal for high-resolution, low- 
atomic-weight elements, and small sample 
diffraction. The determination of the crys- 
tal structures of solid hydrogen and helium, 
for example, has been a major contribution 
to fundamental physics. The structures of 
oxides and silicate-perovskites, critical in 
the mantle, and those of iron and nickel- 
iron alloys at core pressures have also been 
ascertained in the diamond cell. These 
impressive experiments have been ac- 
claimed by the entire scientific community. 
The assembly in the 1970's and 1980's 
under one roof of the wide range of tools 
described, supplemented by the use of elec- 
tron spin resonance, nuclear magnetic reso- 
nance devices, and transmission electron 
microscopes at other institutions, have 
resulted in a major revolution at the Geo- 
physical Laboratory and in the field of 
mineralogy. The quantitative approach to 
mineralogy in which mineral properties are 
characterized in order to obtain thermody- 
namic parameters is of critical importance 
in understanding materials under the ex- 
treme range of conditions in the earth, 
particularly where the direct measurement 
of thermodynamic parameters is not yet 
possible. Theoretical computational meth- 
ods for predicting structural, thermody- 
namic, and elastic properties has been 
developed by Hemley for minerals under 
these extreme conditions. In combination 
with the on-going experimental mineral 
physics research, a sound theoretical basis 



for interpreting condensed phase behavior 
is developing. 



8. Field Petrology 

Throughout the years, field measure- 
ments have been an integral part of the 
experimental program. Most staff mem- 
bers have collected their own samples to 
test new concepts, but the help of col- 
leagues, especially in the U. S. Geological 
Survey, has also been vital. The generosity 
of museum curators has also been essential 
in obtaining materials with the appropriate 
properties for meaningful experiments. 

Some staff members have relied heav- 
ily on detailed mapping for the develop- 
ment of ideas. The analytical work of H. S. 
Washington (1912-1934) and E. G. Zies, 
for examples, was guided by first hand 
experience in the field. The classic studies 
of Fenner at Gardiner River, Yellowstone 
National Park, Wyoming, and Katmai, 
Alaska, are still highlighted. No doubt his 
work was well remembered by some of the 
officials of Yellowstone National Park, who 
watched with "considerable apprehension" 
as Fenner began drilling operations in 1929 
several hundred feet west of Old Faithful 
geyser. The study of that core as well as one 
from Norris Basin recorded the rock altera- 
tion, which correlated well with the results 
of Allen's analyses of the discharge waters. 

Fenner 's papers gave rise to an extended 
debate on the roles of assimilation and 
magma mixing. He was a strong advocate 
of superheat, and he believed that an ade- 
quate heat content was necessary in the 
magma for assimilation to be a major proc- 



166 



CARNEGIE INSTITUTION 



ess. Bowen, on the other hand, assigned a 
minor role to assimilation because he did 
not believe superheat prevailed. Perhaps 
the more widely known Fenner-Bowen 
debate was in regard to the fractionation 
trends of magmas. Whereas Fenner's field 
studies led him to believe iron was concen- 
trated in intermediate liquids, Bowen was 
persuaded on experimental grounds that 
iron was removed continuously through 
the stages of fractionation. The iron-en- 
richment trend through ferrogabbro be- 
came labelled the Fenner trend, and the 
basalt — » andesite — > dacite — > rhyolite 
series was designated as the Bowen trend. 
Later work by E. F. Osborn (1938-1945; 
1973-1977) in which iron oxidation was 
taken into account, has shown that both 
trends can result depending on the condi- 
tions. 

A major contribution to the granite 
problem resulted from the extensive col- 
lections of granites by F. Chayes (1947- 
1986). His techniques of modal analysis 
provided critical evidence that related the 
mineralogical composition of these rocks 
to the minimum melting diagram of Tuttle 
and Bowen (1958). The persuasive argu- 
ment that liquid was involved in the gen- 
eration of rhyolites and granites was made, 
but whether they arose by partial melting or 
fractionation depended on other criteria. 
Various granites have been distinguished 
by both modal and chemical analyses, yet 
attempts to relate the pyroxene-, pyroxene- 
amphibole-, amphibole, mica-amphibole-, 
mica-, two-mica-bearing granites have not 
been rewarding. The search for chemically 
equivalent granites having different miner- 



alogy has not as yet been successful, so the 
question of heteromorphism in granites 
remains open. 

Layered intrusions have provided criti- 
cal tests for many theories purporting to 
relate magmas. Careful field observations 
by T. N. Irvine have yielded many new 
ideas. Before arriving at the Geophysical 
Laboratory, he had made detailed studies of 
layered intrusions on Duke Island (Alaska) 
and Muskox (N.W.T.), Canada. Subse- 
quent studies included Skaergaard, Still- 
water, Bushveld, and other classic areas. 
As a result of these experiences he charac- 
terized the processes resulting from new 
magma influxes, side-wall accumulation, 
mass slumping, density currents, troughs, 
double-diffusive convection, and accounted 
for compaction effects, metasomatic ex- 
change, replacement reactions, and the 
products of magma mixing. Debate has 
been vigorous, but the thoroughness of his 
documentation, supported by laboratory 
model experiments, have stimulated ef- 
forts in field studies by others. 

The collection and identification of ul- 
trabasic xenoliths from alkaline rocks has 
been a major interest of F. R. Boyd. On the 
basis of many thousands of electron micro- 
probe analyses of coexisting minerals in 
nodules collected from kimberlite pipes in 
southern Africa, Boyd and associates were 
able to define the depth and temperature of 
origin of the nodules. From these data and 
the constraints of high-pressure experimen- 
tal studies, Boyd was able to construct a 
section of the mantle under the Kaapvaal 
Craton and adjoining younger rocks. The 
model illustrates the lithosphere-astheno- 



GEOPHYSICAL LABORATORY 



167 



sphere boundary at about 150 km with a 
root zone extending to 200 km under the 
craton. The root zone extended into the 
stability field of diamond and is also marked 
by the presence of low-Ca garnets. From 
these field and mineralogical studies ex- 
tending over twenty-years, a unique struc- 
tural and chemical model has emerged that 
will no doubt be further supported as the 
great variety of nodules are characterized. 
The metasomatic effects, recrystallization, 
deformation, and kinetic responses to the 
dynamics of eruption of the nodules are 
currently under investigation. 

The classical studies of T. F. W. Barth in 
1936 on the "metamorphism" of paleozoic 
sediments in Dutchess Co., N. Y., resulted 
in the definition of a new class of rocks 
called "syntectic". His detailed minera- 
logical and petrological studies outlined 
the passage of sediment -> slate — > schist 
— » gneiss — » augen gneiss -> intrusive 
granite. During these events the rocks were 
"heated and stewed in liquids of magmatic 
and anatectic origin". The role of fluids 
became an important aspect of the mapping 
by Rumble and associates of metamorphic 
rocks of New Hampshire. He developed a 
dynamic model for the flow of fluids through 
rocks during metamorphism from stable 
isotope data. His recognition of hydrother- 
mal graphite as the core marker of fluid 
transport generated a wide variety of inves- 
tigations. 

The staff members of the Geophysical 
Laboratory are convinced that experiments 
derived from, guided by and tested with 
field relations result in principles of lasting 



value. The field-laboratory-field process is 
reiterated until an acceptable interpretation 
of the geological field observations is ob- 
tained. 



9. Statistical Petrology 

Four years were required for H. S. 
Washington to compile the "Chemical 
Analyses of Igneous Rocks" that had been 
published during the period 1884-1913. 
He personally recalculated all the CIPW 
(Cross, /ddings, Pirsson, Washington) 
norms of the rocks. The monumental work 
appeared in 1917 with the statement that 
rock analyses were "indispensable", and 
"the study of igneous rocks is in large part 
the study of silicate solutions and their 
equilibria, often complicated by the pres- 
ence of volatile components, and is thus 
regarded as essentially a special branch of 
physical chemistry". The CIPW norms 
contributed greatly to the classification of 
igneous rocks, but more importantly re- 
duced the chemical analysis of a rock to 
simple endmember components that could 
be experimentally investigated. The nor- 
mative system incorporates an enormous 
amount of petrologic intuition and percep- 
tiveness derived from field experience. The 
assignment of the analyzed constituents 
was made in an order that reflected field 
knowledge of the physicochemical behav- 
ior of rocks not yet demonstrated experi- 
mentally in 1902! 

A "Manual of the Chemical Analyses of 
Rocks" was also published by Washington 
in 1904, revised through three subsequent 



168 



CARNEGIE INSTITUTION 



editions, with due acknowledgment of the 
advice of his friend W. F. Hillebrand, a 
chemist at the U. S. Geological Survey at 
that time. That manual served a generation 
of analysts in the production of high quality 
rock analyses. 

The explosion of analytical data after 
WWII presented a challenge of the first 
order that was met primarily by the remark- 
able developments in electronic data stor- 
age and retrieval at first confined to nu- 
merical data. An early compilation of over 
1 6,000 analyses of Cenozoic volcanic rocks 
by Felix Chayes, a petrologist, proved 
extremely useful both in research and as a 
guide to further work. As soon as it became 
apparent that large quantities of non-nu- 
merical data could be effectively stored, 
sorted, and selectively retrieved in digital 
form, Chayes turned his efforts to system- 
atic development of a world data base for 
igneous petrology. He developed a suitable 
international organization for the construc- 
tion and maintenance of such a base. Cur- 
rently, the International Geological Corre- 
lation Project 263 and a Subcommission of 
the International Union of Geology share 
responsibility for the base, version 2 of 
which is distributed by World Data Center 
A. 

Current estimates of the number of 
published rock analyses range from 65,000 
to over 100,000. It is evident that a more 
intensive effort will be required to use the 
information now available. The eventual 
correlation of phase assemblage (mineral- 
ogy) with chemical composition, not yet 
done for a single rock type, is essential for 
the future progress of petrology. The least- 
squares approximation technique pioneered 



by W. B. Bryan (1967-1970), Chayes and 
Finger (1969) was a major contribution to 
the estimation of these important relation- 
ships. 

Another important problem, still largely 
unresolved, results from ratio formation, in 
particular, the percentage form of state- 
ment used in reporting rock analyses. For 
example, the closure resulting from divid- 
ing the amount of each constituent by the 
sum of all imparts special properties to the 
interrelationships of the constituents. 
Chayes summarized these properties in a 
manual for students called "Ratio Correla- 
tion" in 1971. Chayes' extensive experi- 
ence in the modal analysis of rocks, men- 
tioned in the section of Field Petrology, 
was recorded in "Petrographic Modal 
Analysis" (1956) in which he showed that 
the point-counting of minerals in thin sec- 
tions gave an accurate estimate of their 
volumes in rocks, and he provided experi- 
mental evaluation of the number of points 
and sections required to achieve appropri- 
ate precision. 



10. Extraterrestrial Petrology 



Meteorites 

The nickel-iron core of the Earth was at 
one time believed to be surrounded by a 
zone of mixed iron and silicate, pallasite. 
Because of the supposed similarity be- 
tween some meteorites and the interior of 
the earth, the pallasites were studied both 
for their structure and range of composition 
by Adams and Washington (1924). The 



GEOPHYSICAL LABORATORY 



169 



meteorites also contribute to an understand- 
ing of the origin and history of the solar 
system. For this reason S. P. Clark, Jr. and 
Kullerud undertook a study of Fe-Ni-S and 
Fe-Ni-P to establish a buffered system of 
taenite andkamacite with troilite or schreib- 
ersite in order to derive the temperature of 
formation of the meteorites. While in resi- 
dence, P. Ramdohr (1960-1962, 1964) 
examined over 340 polished sections of 
stony meteorites to characterize in a sys- 
tematic way the mineralogy of the opaque 
phases. In typical fashion, he discovered 
many new minerals as well as previously 
described minerals hitherto not previously 
observed in meteorites. The Fe-Cr-S sys- 
tem was studied by El Goresy (1967-1968) 
and Kullerud to account for the Cr-bearing 
compounds in meteorites. They found the 
sulfides responded more readily to shock 
impact than silicates thereby explaining 
their disequilibrium relations. 

Over the years the Allende carbona- 
ceous chondrite received the special atten- 
tion of the staff because of its potential 
applications to the early evolution of plan- 
ets of alleged chondritic composition. The 
P-T diagram for the Allende meteorite up to 
30 kbar with and without H 2 was investi- 
gated by Kushiro (1962-1965, 1968-1969, 
1971-1976, 1978-1987) and M. G. Seitz 
(1971-1974). They demonstrated that 
separation of the phases would yield the 
layered structure presumed for the earth. 
Other experiments dealt with the partition- 
ing of elements between the metal, oxide 
and silicate portions. The amino acids 
were identified by Cronin (1974-1975, 
1975) and some notion of the process 
whereby abiotic organic compounds could 



be formed from the precursor compounds 
in the meteorite. The partitioning of boron 
was achieved through an etching technique 
that revealed the spallation recoil tracks in 
whitlockite. The high concentration of 
boron and other volatile elements in a 
meteorite alleged to have formed at high 
temperatures remains a mystery. The fas- 
saite of the Allende meteorite was interest- 
ing because it was found to be iron free and 
contain trivalent titanium, confirmed by 
high-resolution optical spectra. The chemi- 
cal incompatibility of its oxidation state 
with other minerals in the meteorite, such 
as metallic iron and andradite, was evident. 
Meteorites frequently contain minerals 
formed at high pressures through shock. 
For this reason they are important in under- 
standing the phase changes that take place 
at depth in the earth's mantle. The discov- 
ery of ringwoodite, the spinel form of oli- 
vine, indicated to N. Boctor (1977-1980), 
Mao and Bell that the pressure was be- 
tween 100 and 225 kbar during impact 
metamorphism. The presence of majorite 
in association with ringwoodite suggested 
to them that a large pressure gradient ex- 
isted in the order of 100 kbar to > 300 kbar. 
Other features such as veins of inhomo- 
geneous glass from incipient melting, frac- 
turing, undulatory extinction, and mosaic- 
ity are also indicative of high shock pres- 
sures. 



Lunar Samples 

The return of the successful Apollo 
missions with samples of the moon begin- 
ning in 1969 provided one of the most 



170 



CARNEGIE INSTITUTION 



exciting scientific opportunities for the 
following decade. The incredibly fresh and 
unaltered character of the rocks greatly 
facilitated their study, but the fine grain and 
shock metamorphism of the minerals were 
the principal challenges. The characteriza- 
tion of the fine-grained material generated 
a new array of techniques and the unique 
conditions of rock formation on the moon 
led to the new field of comparative petrol- 
ogy. Needless to say, the daily excitement 
of discovery has not been equaled by the 
arrival of any other set of specimens. The 
initial stages of inquiry were predominantly 
detailed mineralogical studies, followed 
by experimental studies of both the natural 
samples and synthetic analogues, and then 
the testing of various models of the moon's 
composition and structure. The entire ar- 
ray of sample types (rocks, breccias, glass 
fragments, and soils), was investigated by 
the staff members. 

Because of the special skills of the staff, 
the opaque minerals received detailed at- 
tention. Ilmenite was the major opaque 
phase, but members of the chromite- 
ulvospinel series, the newly discovered 
armalcolite series, as well as troilite and 
metallic iron alloy were studied. (Armal- 
colite was also discovered independently 
by several laboratories, and subsequently 
named by combining the initial letters of 
the names of the astronauts Armstrong, 
A/drin, and Collins.) Haggerty (1968-1971) 
found that the spinels were bimodal at 
some sites, but other samples exhibited a 
complete series of solid solutions. A new 
pyroxenoid was discovered by Lindsley, 
which he then prepared synthetically at 
high pressures. The new phase, pyroxfer- 



roite, is apparently metastable and had 
persisted in that state for at least 3 b.y. ! The 
olivines also appeared to be bimodal in 
some samples. The Cr content of olivine 
was more than twice that of earth olivines, 
and more importantly, was in a reduced 
state (Haggerty et al., 1970). The first 
demonstration of Fe-Mg ordering in any 
olivine was made by Finger on the lunar 
material. 

The pyroxenes were studied in excep- 
tional detail by Boyd, whose electron micro- 
probe data clearly reflected their chaotic 
crystallization behavior. The zoning of the 
pigeonites and oscillatory augite rims, for 
example, suggested cooling and mixing 
with new magma batches. Two distinct 
rate-determining steps were found by Virgo 
in the cooling of two lunar pigeonites. A 
steady state of Fe-Mg ordering was achieved 
at about 810°C involving a few hours of 
time, then an exceptionally slow rate to 
about 480°C below which no further an- 
nealing was possible. (The 57 Fe resonance 
spectroscopy technique for determining 
valence state and geometrical configura- 
tion of iron in a crystal structure had been 
previously proved useful in kinetic studies 
of terrestrial pyroxenes). The plagioclases 
contained Fe 2+ and its site preference was 
determined by Finger. The range of shock 
features in the plagioclase were particu- 
larly impressive. The lunar glasses were 
studied with the new high-resolution, opti- 
cal-spectra apparatus of Bell and Mao. 
Some of the glasses were igneous in origin 
and others formed from the meteorite 
impacts. Various colored glasses were found 
to result from the reduced states of Fe and 
Ti. A particularly exciting event, although 



GEOPHYSICAL LABORATORY 



171 



short lived, was the discovery of "rust" 
(goethite and akaganeite) on some of the 
lunar specimens, eventually attributed to 
accidental contamination in the earth's 
atmosphere. The event was not only an 
exhibit of the great care taken by the ob- 
servers, but also of the advanced state of the 
art of characterizing fine materials. 

The experimentalists also contributed 
to the understanding of the formation on 
the moon of the principal rock types, called 
basalts and anorthosites even though they 
were quite different in composition and 
mineralogy from their earth-bound name- 
sakes. Because of the extreme rarity of the 
lunar samples, Muan and Schairer (1969) 
made a synthetic analogue and studied its 
behavior at a series of temperatures in iron 
crucibles. This "basalt" composition 
yielded pyroxene on the liquidus at 1 1 85° C 
and had a solidus between 1075°-1090°C 
with plagioclase and ilmenite. These val- 
ues are not greatly different from those of 
some earth basalts. Later, as more material 
became available, lunar samples themselves 
were studied at a range of P and T by 
Kushiro and Hodges (1973-1974). Of the 
three models of lunar composition they 
tested, the model composition of Ganapa- 
thy and Anders (1974) appeared to fit the 
observations best. A most interesting ob- 
servation of Bell and Mao in support of the 
high-pressure experiments was recogni- 
tion that a spinel + two-pyroxene symplec- 
tite in olivine had the bulk composition of 
garnet. The reaction of garnet and olivine 
to the symplectite assemblage had been 
previously demonstrated to be a high-pres- 
sure reaction. Another set of pioneering 
experiments was performed by M. G. Seitz. 



He was concerned about the chemical frac- 
tionation that resulted from the volatiza- 
tion of materials during the impact events. 
He showed in a vacuum furnace that all of 
the alkalies and some of the iron was lost by 
volatilization in short heating events. These 
experiments were precursory to the major 
program of study, described below, most 
pertinent to the origin of the solar system. 



Condensation Petrology 

An understanding of the evolutionary 
processes of the solar system require data 
on the P, T, and composition at various 
times and places as the solar nebula col- 
lapses. The fundamental issue is whether 
the minerals formed by direct condensa- 
tion from a gas or by crystallization from an 
intermediate liquid phase of the proto-solar 
system. Experiments conducted at the 
Geophysical Laboratory by Mysen, Virgo, 
and Kushiro bear on these processes. The 
materials found in meteorites are believed 
to be representative of the oldest solar 
system material. For this reason, they 
worked on the very low-pressure region of 
stability for minerals such as akermanite, 
diopside, corundum, spinel, and hibonite, 
found in the carbonaceous chondrites. By 
means of a Knudsen-cell technique, in a 
high-vacuum, high-temperature furnace, 
they established the P-T curves separating 
the crystal, vapor, and liquid regions. From 
the experimental results, they suggest that 
for the solar-gas composition, the pressure 
would have to exceed 10 2 bar for liquid to 
form, increasing with decreasing oxygen 
fugacity. In general, it appears that the 



172 



CARNEGIE INSTITUTION 



early solar nebula resulted from gas-crystal 
reactions in the absence of melting at pres- 
sures below 10" 4 bar and at an/(0 2 ) at least 
3 orders of magnitude below that of the 
iron-wiistite buffer. In short, these dra- 
matic experiments place severe constraints 
on the collapse of the solar nebula and 
emphasize the systematic chemical differ- 
ences between the terrestrial planets as a 
function of their distance from the sun. 

Other constraints are placed on the 
gaseous planets by experiments in a totally 
different realm. Materials that are nor- 
mally gaseous condense to form liquids 
and crystals at high pressures . Studies up to 
5.5 Mbar are particularly pertinent to the 
early evolution of the solar system as well 
as the interior of Jupiter, for example. The 
P-V curves for crystalline hydrogen, deu- 
terium, argon, neon, xenon, and oxygen 
have been determined, and, in some cases, 
their crystalline structure determined with 
synchrotron-generated radiation. The first 
single-crystal structure determination of n- 
H 2 at 54 kbar by Hazen et al. (1987) with 
conventional x-ray diffraction was of fun- 
damental interest to condensed-matter and 
planetary physicists. In addition, methane 
and water, important in the Giant Planets 
were also studied. In this way Mao, Hem- 
ley, and a large number of colleagues were 
able to set limits on the conditions required 
to collapse these gases in the nebula. 



11. VOLCANOLOGY 

In 1902, when the CIW was only five 
months old, the city of St. Pierre, Martin- 
ique, was destroyed by the eruptions of 



Mount Pelee. The event no doubt helped 
persuade the Board of Trustees of the need 
for a geophysical laboratory that would 
investigate the phenomena of volcanic 
eruption. Field and analytical investiga- 
tions of the rocks from an active volcanic 
region by H. S. Washington (1906) were 
promptly supported by CIW. His mono- 
graph on "The Roman Comagmatic Re- 
gion" (-Italian petrographic province) 
presented a detailed description of the many 
rare lavas characterized by the presence of 
leucite. In 1911 the Hawaiian Volcano 
Observatory was founded by T. A. Jaggar 
(MIT) in collaboration with R. A. Daly 
(Harvard), the Volcano Research Associa- 
tion of Hawaii, and the Geophysical Labo- 
ratory. The measurement of the tempera- 
ture of the lava lake in Kilauea and the role 
of gas in the flowing lavas were undertaken 
by E. S. Shepherd and F. A. Perret that year. 
These epoch-making studies involved the 
collection, via a cable across the lava lake, 
of an iron bucket dip sample of the lava and 
immersion of a thermocouple pipe in the 
bubbling lake itself. In the summers of 
1911 and 1912, Day and Shepherd col- 
lected and analyzed the gases in the active 
part of the Halemaumau crater of Kiluaea. 
They clearly demonstrated that water was 
an original component of the lava, contrary 
to the prevailing view of the nonaqueous 
quality of magmatic gases. Furthermore, 
they attributed the loss of gas as the reason 
for the structural change from Pahoehoe 
lava to Aa lava. 

Day and Allen next turned to Lassen 
Peak, CA., after its catastrophic outbreak 
in May of 1915, the first eruption from a 
volcano within the continental boundaries 



GEOPHYSICAL LABORATORY 



173 



of the U. S. in the memory of then living 
men. In addition to the description of the 
eruptive activity, they focused on the types 
of hot springs and fumeroles with field and 
laboratory measurements. The change from 
springs of acid character transporting py- 
rite, to those of alkaline character was at- 
tributed to the interaction of the hot waters 
with the silicate rocks. 

In the meantime, Mount Katmai, Alaska, 
had erupted during June, 1912, but it was 
1916 before an expedition, organized by R. 
F. Griggs and supported by the National 
Geographic Society, reached the area. On 
that and subsequent expeditions to the Valley 
of Ten Thousand Smokes were C. N. Fen- 
ner, E. G. Zies, and E. T. Allen, who col- 
lected rocks, fumerole encrustations, meas- 
ured the temperature of the hot springs, 
aspirated exhalations for the "insoluble" 
gases, and helped in the geologic mapping. 
They concluded that the vast sheet of sili- 
ceous rocks were not lavas but were of 
pyroclastic origin, ejected as rhyolitic 
pumice through the fractured valley floor. 
The fumeroles (100°-650°C) were, there- 
fore, of deep seated origin and decreased in 
temperature with time. Through succes- 
sive observations, the mineralogy of the 
encrustations changed as the temperature 
dropped, and because many economic 
minerals were formed, a relationship of ore 
deposits to volcanic exhalations was estab- 
lished. The analyses of the gases collected 
showed the highest contents of HC1 and HF 
that had ever been detected. The hybrid 
nature of the rocks (also found at Lassen 
Peak) led Fenner to believe that a super- 
heated rhyolite magma melted fragments 
of old andesitic lavas and incorporated 



them into the Erupted pumice and ash. The 
detailed analytical work, tied closely to the 
mineralogy and geology, established the 
value of a multidisciplinary approach to 
geologic problems. 

In the course of these studies, Morey 
(1922) provided a new theory for the in- 
crease in pressure of a cooling hydrous 
magma, based on the continuity and uni- 
variancy of the crystal + liquid + gas curve 
in the KN0 3 -H 2 system. Some forty 
years later Yoder (1965) pointed out that 
most magmas were not saturated or uni- 
variant and that explosive volcanism re- 
sulted from an incremental drop in pressure 
when gas was liberated from an initially 
undersaturated magma. This concept arose 
out of an experimental study of the syn- 
thetic basalt system diopside-anorthite-HjO 
at 5 and 10 kbar. 

Four major studies in volcanology by F. 
A. Perret, an associate of the Geophysical 
Laboratory, were supported by the CIW. 
Detailed descriptive monographs were 
published on the Vesuvius eruption of 1 906, 
the eruptions of Mt. Pelee, the volcano- 
seismic crises at Montserrat, and finally, 
because Perret was obliged to stay in the U. 
S. during WWII, a compendium of his 
studies of volcanoes around the world. 
These unique contributions record the 
observations of one of the world's most 
perceptive students of volcanic activity. 

The remarkable hydrothermal activity 
of Yellowstone National Park was described 
in another classic study by Allen and Day 
(1935), in which is recorded the physical 
and chemical changes of the fumeroles, 
geysers and thermal springs over a period 
of seven years. The relationship of hot 



174 



CARNEGIE INSTITUTION 



springs to fumeroles was defined and the 
differences in rock alteration from the acid, 
mixed, and alkaline types contrasted. They 
identified superheated water up to 138°C, 
which gave rise to violent effervescence, 
and they contributed to the problem of 
discharge and its relation to rainfall. 

A further contribution to the study of 
hot springs and geysers was made by T. F. 
W. Barth who carried out the laboratory 
study of samples collected in Iceland. The 
work was done during the summers of 1 934 
and 1937, but publication was held up for 
eight years while Barth was detained in 
occupied Norway. 

Note should be made of the extensive 
field and chemical investigation by E. G. 
Zies of the domes of the active volcano 
Santiaguito and its ancient edifice Santa 
Maria in Guatemala. Unfortunately, fail- 
ing health prevented him from bringing 
those studies, mentioned in a series of nine 
abstracts, to the publication stage. The 
combination of Zies' analytical skills and 
H. E. Merwin's keen microscopy had gen- 
erated a detailed picture of the mixing of 
magmas and the digestion of individual 
crystals. 

The last major work on volcanic activ- 
ity supported in part by the Laboratory was 
F. R. Boyd's study of the welded tuffs and 
flows in the rhyolite plateau of the Yellow- 
stone National Park, Wyoming. Boyd 
mapped the plateau, determined its strati- 
graphy, and, most importantly, discovered 
the Yellowstone caldera. His thermody- 
namic analysis combined with experimen- 
tal evidence showed that tuffs can have 
temperatures of emplacement sufficiently 
high for them to weld. 



More pages have been written by the 
staff on volcanology than any other field of 
endeavor. Other projects on active volca- 
noes have been undertaken by the staff in 
recent years, but the field studies have been 
primarily for the purpose of keeping touch 
with the principal problems uncovered by 
other workers. Field work has always been 
encouraged at the Geophysical Laboratory 
in order to investigate experimentally the 
significant problems whose solution may 
be applied broadly. 



12. Geophysics 

Although the name of the Geophysical 
Laboratory implies that a large component 
of the work would involve geophysics, the 
classical fields of endeavor now included 
under the term have played a small role 
over the years. For brief periods, however, 
gravity, heat flow, electrical conductivity, 
thermal conductivity, density, magnetism, 
tectonophysics, oceanography and seismol- 
ogy, have all been investigated. Some of 
these studies were cooperative with the 
Department of Terrestrial Magnetism, 
which was established in 1903. It initially 
dominated the field of magnetism, comple- 
mentary to the national bureaus, and was a 
pioneer in explosion seismology after 
WWII. 



Gravity 

One of the many interests of F. E. Wright 
was the difference in gravity between the 
earth and moon and the resulting differ- 



GEOPHYSICAL LABORATORY 



175 



ences in geomorphology and isostatic 
compensation. Pursuing this interest, he 
persuaded F. A. Vening Meinesz in 1928 to 
install his pendulum for making gravity 
determinations at sea on a U. S. submarine. 
From subsequent measurements, they 
concluded that some oceanic deeps were 
uncompensated whereas the Mississippi 
delta was practically compensated in spite 
of the enormous load of sediment laid down 
each year. Inspired by the facility of occu- 
pying a large number of stations at sea, 
Wright and J. L. England developed an 
improved torsion gravity meter mounted 
on a truck so that twenty or more stations 
could be occupied in a day. Although most 
of the stations occupied were in the eastern 
U. S., the apparatus was set up in 1940 on 
an active volcano in Guatemala to assess 
the changes in the magma chamber in 
conjunction with other geophysical meas- 
urements. 



Heat Flow 

An early attempt (1912) to measure the 
thermal gradient in the crust was made by 
J. Johnston and L. H. Adams. They used 
both mercury thermometers and an electri- 
cal resistance thermometer in wells as deep 
as 5230 feet. It was believed that such 
measurements might also have economic 
importance in identifying layers rich in 
coal or oil, indicated by a higher tempera- 
ture gradient. An opportunity for measur- 
ing heat flow in long tunnels occurred in 
the construction of the Arlberg and Taverin 
tunnels in Austria. With the underground 
temperature observations and the labora- 



tory measurement of thermal conductivity 
of the various rocks, S. P. Clark, Jr. found 
that relatively high geothermal fluxes ex- 
tend into the eastern Alps. More recently 
the relatively high heat flow (2.2 meal/ 
cm 2 sec) in Arizona was investigated by 
Bell and R. F. Roy (Harvard), who related 
the results to the gravity and seismology 
data of the region. 



Geotherm 

The problem of the cooling of a primi- 
tive earth was undertaken by L. H. Adams 
(1924) after the revealing calculations of 
Holmes (1916) and Jeffreys (1924). He 
generated a "most probable" geotherm 
down to 300 Km, assuming the age of the 
earth was 1.6 b.y., the generation of radio- 
active heat was constant, and the earth was 
covered with a substantial molten layer. 
Urry (1949) also calculated the geotherms 
for the earth at various times taking into 
account the exponential decay of radioac- 
tive elements and the variation of surface 
heat flow with time. Later, Clark (1961) 
derived geotherms as a function of time for 
various models calculated with the aid of a 
digital computer. He concluded that the 
distribution of radioactivity cannot be in- 
ferred from the near surface heat flow. 
Furthermore, the variability of heat flow 
cannot be attributed to different degrees of 
concentration of radioactivity in the outer 
few hundred kilometers of an initially 
homogeneous earth. An innovative ap- 
proach to the geotherms was found by F. R. 
Boyd, Jr. by applying the pyroxene geobar- 
ometer and geothermometer. On the basis 



176 



CARNEGIE INSTITUTION 



of the composition of coexisting pyroxenes 
in nodules from kimberlites, he obtained a 
quantitative measure of the geotherm. In 
general, the geotherm derived from the 
nodules substantiates the geophysical esti- 
mates based on surface heat flow. His 
results also showed that cratons have been 
cool relative to oceanic plates for at least 3 
b.y. One surprising result was an inflection 
in the geotherm under northern Lesotho 
that may be attributed to a region of partial 
melting. 



Tectonophysics 

Prior to the opening of the Geophysical 
Laboratory and during its formative pe- 
riod, grants were made to F. D. Adams 
(1902-1912) by CIW to study the flow of 
rocks. A 1 20-ton press was set up at McGill 
University to investigate the deformation 
of marble, granite, diabase, and other rock 
types at temperatures up to 1000°C. One of 
the goals was to understand the origins of 
crystalline schists, a subject of special 
concern to Van Hise who served on the 
CIW Advisory Committee in Geophysics. 
A theoretical interpretation of the flow in 
stressed solids by R. W. Goranson, using 
thermodynamic potential relations for dif- 
ferent physical conditions, was corrobo- 
rated by experimental studies. Those ex- 
periments were not published, presumably 
because of Goranson's assignments during 
WW II, but support for his theory was 
provided by the more detailed laboratory 
studies ofD. Griggs (Harvard). For a five- 
year period, two Postdoctoral Fellows from 
Yale undertook a field and experimental 
program relating the conditions of flow to 



the resultant plastic strain. On the basis of 
these and other studies, E. Hansen (1964- 
1968) developed the concept of "strain 
fades" recorded in a book with that name. 



Oceanography 

The discovery of the high radium con- 
tent of ocean bottom samples collected by 
the auxiliary brigantine Carnegie led C. S. 
Piggot (1925-1947) to develop a device for 
coring ocean bottom sediments in 1935. 
Using a gun-fired sample tube and hoisting 
gear built at the Geophysical Laboratory, 
he obtained cores with the cooperation of 
the crews on the ship Atlantis (Woods Hole 
Oceanographic Institution). Cores up to 
ten feet in length were recovered from 
depths as great as 2700 fathoms. Changes 
in the orientation of the earth's magnetic 
field with depth in those cores were studied 
at DTM. 



Magnetism 

The pressure effect on the critical tem- 
perature of magnetization of iron was found 
to be negligible up to 3.6 kbar by L. H. 
Adams and J. W. Green (1931). They 
concluded that the nickel-iron core had 
little influence on the earth's magnetic field 
because the core temperature was well 
above the Curie point! The Curie point was 
investigated for a large number of materi- 
als by Posnjak during 1936-1937, and the 
effects of solid solution on the magnetic 
properties of spinels were the subject of 
investigation for many years to follow. 



GEOPHYSICAL LABORATORY 



177 



Seismology 

Of special significance was the theo- 
retical contribution of L. H. Adams and E. 
D. Williamson (1914-1923) in 1923 when 
they deduced a formula that related the 
compressibility and density of rocks to the 
seismic velocities of the longitudinal and 
shear waves. In this way the laboratory 
measurement of the density and compressi- 
bility of rocks and minerals constrained the 
kinds and proportion of phases in earth 
where the seismic velocities were known. 
Observational seismology had been rec- 
ommended by the Van Hise Committee as 
early as 1903 and proposed on numerous 
occasions thereafter. The Director of the 
Geophysical Laboratory, A. L. Day was 
appointed chairman of the CIW Advisory 
Committee in Seismology in 1921 . On his 
Committee's recommendation, a program 
of study was outlined and a Seismology 
Laboratory built in Pasadena, California, 
in 1926 in cooperation with the California 
Institute of Technology. The studies were 
administered by the Committee until 1 Jan 
1937 when the Seismological Laboratory 
was turned over to Caltech. That Labora- 
tory was primarily concerned with natural 
earthquakes; however, following WWII, 
the DTM initiated a cooperative program 
in explosion seismology. Three members 
of the Geophysical Laboratory staff, J. W. 
Greig, J. L. England, and G. L. Davis 
(1941-1978), helped select the seismome- 
ter sites for their geological advantages and 
on occasion occupied those sites to receive 
signals from quarry blasts and the destruc- 
tion of old military explosives, for ex- 



amples. In another more recent coopera- 
tive project with DTM, the velocity of 
transmission of both longitudinal and shear 
waves in partially molten peridotite was 
measured directly up to 10 kbar by T. 
Murase (1976-1980) and colleagues. 



13. Geochemistry 

In the formative stages of the Geophysi- 
cal Laboratory, the major debate about its 
program of work concerned physical meas- 
urements, promoted by G. F. Becker, and 
chemical measurements, advocated by C. 
R. Van Hise. A compromise resulted in 
physical chemistry, with the emphasis on 
chemistry, a position strongly supported by 
C. D. Walcott who was Director of the 
USGS and Secretary of the CIW Board of 
Trustees. There was no disagreement on 
the great need for application of the quan- 
titative principles of physics and chemistry 
to the science of geology. Although, geo- 
chemistry, loosely defined, pervades most 
aspects of geology, the following high- 
lights of the work of the Geophysical Labo- 
ratory are restricted to only a few investiga- 
tions highly dependent on chemistry. 



Element Partitioning 

The accuracy and precision of the analy- 
sis of the minutest amounts of an element 
has reached an exceptionally high state 
with the wide variety of techniques avail- 
able. Nevertheless, the analysis of a min- 
eral, a unique combination of elements, 



178 



CARNEGIE INSTITUTION 



still requires research — it is not a routine 
matter. The data produced are of a most 
fundamental character in determining P, T, 
time, and reaction path of the mineral and 
its host rock. Analytical chemistry, how- 
ever, has greatly outstripped the calibra- 
tion of those data in defining the conditions 
endured by the rock. 

Phase equilibria studies have defined 
limits of solid solution for a large number 
of the common rock-forming minerals. 
Some of those studies have already been 
mentioned in the section on Experimental 
Petrology; however, the minor and trace 
elements would appear to be a more accu- 
rate measure of conditions because they 
tend to obey the thermodynamic laws of 
dilute solution. The emphasis, therefore, 
has been on the partitioning of elements 
such as Ni, Cr, Ti, alkali metals, alkaline 
earths, and various rare earths for crystal- 
liquid, crystal-vapor, as well as crystal- 
crystal equilibria. The major productive 
period was 1970-1980, and perhaps the 
principal reason for the diminution of inter- 
est after 1980 can be attributed to the reali- 
zation that the partitioning coefficients were 
much more sensitive to bulk composition 
than previously envisaged. The enormity 
of the task of calibrating trace elements 
then acquired dimensions beyond the scope 
of a small laboratory dedicated to pioneer- 
ing ventures. 

In 1953, Eugster and colleagues initi- 
ated some experiments on the partitioning 
of Cs, Tl, and K between sanidine and a 
fluid phase at a series of temperatures from 
500° to 800°C and 1 and 2 kbar. Cesium, 
for example, more readily entered the sani- 
dine structure at high temperatures than at 



low temperatures when Cs/K was 0.0002 
to 0.01, but the enrichment was much less 
than observed in nature. Eugster attributed 
the difference to the great enhancement 
that results from fractional crystallization. 
These experiments appear to be the first 
direct determination of the distribution 
factors of minor elements in silicates. 

The technique that facilitated the meas- 
urement of crystal-liquid partition coeffi- 
cients was fission-track mapping on mus- 
covite or on emulsions, which when devel- 
oped revealed the concentration of the 
radioactive element. Seitz described the 
method in 1973 for the partitioning of 235 U 
and 230 Th between diopside and a liquid in 
Di- Ab- An, a simple basalt system. He used 
less than 30 ppm of the spikes and con- 
cluded that the activity coefficients were 
independent of concentration. In another 
series of experiments he examined the 
partitioning of 151 Sm between diopside and 
the simple basalt liquid to compare with the 
previous results of Kushiro and Masuda 
( 1 970) on clinopyroxene in a natural basal- 
tic liquid. He found that the coefficients in 
synthetic systems were considerably lower 
than those in the natural system. Although 
he indicated that chemical and physical 
conditions affect the measurements, he also 
attributed the higher values in the natural 
system to non-equilibrium conditions. 

Subsequent detailed studies by Mysen 
(1976) and his associates clearly demon- 
strated that the concentration range of 
Henry's law behavior was limited, and the 
partition coefficients became composition- 
ally dependent. In the course of a few 
years, it was shown that the partition coef- 
ficients were dependent on pressure, tern- 



GEOPHYSICAL LABORATORY 



179 



perature, bulk composition, presence of 
other phases, and on the available sites in a 
crystal for specific trace elements. Even 
the structure of the melt was found by 
My sen and Virgo (1980) to influence the 
partition coefficients. To all those factors 
can be added the influence of/(0 2 ) mdf(S 2 ) 
on the partitioning of Ni between olivine 
and iron sulfide melt. The calibration of 
any partition coefficient indeed required 
careful control of all the variables. 

Throughout the productive period, a 
wide range of natural rocks were melted at 
various conditions to determine specific 
partition coefficients in an empirical ap- 
proach to defining their conditions of for- 
mation. Some of the rock types investi- 
gated included basalt, kimberlite, perido- 
tite, komatiite, and other ultramafic rocks, 
primarily for the purpose of relating pre- 
sumed source rocks to their partial melts. It 
became evident that the partial melts, as 
represented by the alkali basalts, were much 
too enriched in the light rare earths to have 
been generated from such sources by even 
small degrees of melting (Harrison, 1977- 
1979, 1979). That conclusion gave strong 
support to the concept that metasomatism 
plays an important role in the mantle. 

Aside from the many experiments on 
crystal-crystal partitioning, two ingenious 
investigations on liquid-liquid and crystal- 
vapor partitioning must be mentioned. In 
1975, Watson (1975-1977) measured the 
partitioning of spiked elements in coexist- 
ing immiscible liquids in the K^O-Al^- 
FeO-Si0 2 system. The compositions of the 
quenched glasses were determined by elec- 
tron microprobe. From these data, he 
concluded that deviations from Henry's 



law were confirmed for several of the ele- 
ments; there are cation interaction effects; 
and that there are distinct differences be- 
tween the ways various cations are accom- 
modated in the acid melt relative to the 
iron-rich melt. The results provided a useful 
test of speculations on the origin of mafic- 
felsic associations such as basalt and rhy- 
olite. 

The partitioning of elements between a 
water-rich vapor and the constituent miner- 
als of a garnet peridotite was investigated 
by Mysen (1978). With the beta-track 
technique he measured the partition of Ce, 
Sm, and Tm in its minerals and obtained the 
trace element content of the coexisting 
vapor by mass balance. He demonstrated 
that the REE patterns were highly pressure 
dependent. In summary, it was clear that 
the REE content of the crystals are similar 
to the depleted nodules from the mantle and 
that the metasomatizing fluid in the mantle 
was, therefore, probably similar to that 
observed in the experiments. 



Mineral Solubility 

The initial studies on the solubility of 
minerals were carried out in 1915 on KN0 3 
and KC1 by L. H. Adams, who was inter- 
ested in freezing point depression in dilute 
solution. He used an interferometer, rather 
than the customary refractometer, to achieve 
higher precision in the analysis of the solu- 
tions. About the same time, Johnston and 
Williamson, paying particular attention to 
the species dissolved in the solution, inves- 
tigated the solubility of calcite. During the 
depression years and up to WWII, consid- 



180 



CARNEGIE INSTITUTION 



erable efforts were made in studying the 
simple systems NaCl-H 2 0, K 2 S0 4 -H 2 0, 
B 2 3 -H 2 0, and KCl-Hp, with emphasis 
on obtaining thermodynamic properties. 
With the development of high-pressure 
equipment, P-V-T data were developed for 
common salt solutions. One significant 
breakthrough was the study by Goranson 
(1936) of Ab-H 2 in which he determined 
the solubility of water in silicate melt, that 
is, the high-temperature end of the three- 
phase solubility curve. Other staff mem- 
bers focussed on the CaS0 4 -H 2 system 
with various salts in order to understand the 
deposition of gypsum and anhydrite in salt 
water. Posnjak (1941) came to the conclu- 
sion that gypsum was most likely to be 
deposited from ocean water and might be 
converted to anhydrite after deposition. 

During those years attempts were made 
to resolve the experimental problems of 
determining solubility at high P and T by 
developing a stirring and filtering device 
(Morey and Burlew 1936-1952, 1938) so 
that the fluid could be quenched independ- 
ently of the crystals. The increase in solu- 
bility with water pressure was of special 
interest, and in one study the weight of 
solids dissolved in the fluid reached almost 
half. Much of the theory for the solubility 
curves had already been worked out, how- 
ever, a paper by Morey and Niggli (1913) 
was instrumental in guiding the laboratory 
research. It was not until 1940 that Morey 
and Fleischer (1936-1938) provided the 
background for two-volatile systems, such 
as K 2 0-Si0 2 -C0 2 -H 2 0, that are so impor- 
tant to the entire range of geological prob- 
lems. Some of the stimulus for the study of 
the solubility of minerals in aqueous solu- 



tions no doubt came from the detailed stud- 
ies of other staff members on the study of 
sublimates around fumeroles and volca- 
noes. 

After WWII and with the development 
of many new tools for generating P and T 
and characterizing products, attention again 
turned to the P-V-T of simple aqueous 
solutions. Morey was then able to study 
Na 2 0-Si0 2 -H 2 0, which exhibited retro- 
grade solubility: The solubility of sodium 
disilicate fell to almost zero at the first 
critical end point, but became important 
again at the upper part of the solubility 
curve. The determination of the solubility 
of quartz in steam up to 600°C and 2 kbar 
was of practical importance in relation to 
the fouling of turbine blades as well as in 
the understanding of the formation of quartz 
veins. Morey and Hesselgesser (1949- 
1953) demonstrated that the solubility of 
some minerals was incongruent in the vapor 
phase - a property that became of special 
significance in metasomatism. In this post 
war period, Yoder (1958) studied the melt- 
ing curves of Ab-H 2 0, Sa-H 2 0, Di-H 2 0, 
An-H 2 0, Ne-H 2 and Qz-H 2 up to 10 
kbar, but none of the systems showed a 
second critical end point on the solubility 
curve. 

The next major thrust was on the solu- 
bility of ore minerals in aqueous solution. 
A new apparatus was developed by H. L. 
Barnes (1956-1960) in which he could 
sample and analyze the gas phase from a 
reaction vessel at P and T. In this way, he 
obtained quantitative solubility measure- 
ments of sphalerite (ZnS) in H 2 S- saturated 
water. In addition, he found evidence that 
a bisulfide complex was the most probable 



GEOPHYSICAL LABORATORY 



181 



transport mechanism for sphalerite. Bar- 
nes also observed that adding NaOH to the 
ZnS-H 2 S-H 2 system did not change the 
phase relations significantly; however, in a 
study with Ernst, it was demonstrated that 
NaOH lowered the stability of brucite, for 
example, in a major way. 

After an almost ten-year hiatus, solubil- 
ity work again resumed in the new dia- 
mond-anvil, high-pressure cell. By direct, 
visual observation, the solubility of gyp- 
sum was measured up to 8 kbar by A. Van 
Valkenburg (1975-1980) and his colleagues 
Mao and Bell. They also observed the 
phase CaC0 3 6H 2 0, ikaite, which had been 
found in a carbonatite deposit submerged 
in arctic waters. 

With the development of infiltration 
models for mass transport in hydrothermal 
rock systems, the need for mineral solubil- 
ity data became acute. Because fluid inclu- 
sions in many ore deposits contained chlo- 
rides, geothermal well waters are often 
brines, and evaporate minerals are associ- 
ated with copper porphyry deposits, Frantz 
and his colleagues investigated simple 
systems in the presence of HC1. Study of 
the reaction of HC1 with talc, hausmannite, 
albite and hematite resulted in the conclu- 
sion that the metals were dominantly asso- 
ciated, e.g., MgCl 2 °, above 400° to 600°C 
at 1 and 2 kbar. With knowledge of the 
associated species, accurate solubility in- 
formation could be calculated for those 
minerals investigated and a host of others. 

In view of the above importance of 
ionization behavior of electrolytes, Frantz 
joined with W. L. Marshall (Oak Ridge 
National Laboratory) to measure the elec- 
trical conductance of salt solutions as a 



function of pressure and temperature. A 
large array of simple systems were investi- 
gated, including carbonates, hydroxides, 
and fluorides. The results were immedi- 
ately applicable to steam-generated corro- 
sion in nuclear power plants in addition to 
their fundamental importance to the prin- 
ciples of element concentration in ore 
deposits. Current research is focusing on 
the determination of the PVT properties of 
mixed volatiles in which synthetic, fluid- 
inclusion techniques are used. Methods 
are being developed for the accurate analy- 
sis of individual fluid inclusions in the 
silicates coexisting with ore minerals with 
new sophisticated microanalytical tech- 
niques. Concurrently, a high-pressure cell 
has been designed to examine the Raman 
spectra of solutions at 600°C and 4 kbar to 
ascertain the species transporting the vari- 
ous metals important in ore deposits. 



14. Thermodynamics and Calorimetry 

The first director, A. L. Day, while at- 
tending Yale occupied an office in the same 
building as J. Willard Gibbs, and presuma- 
bly Gibbs influenced Day's scientific fo- 
cus. Later, on returning from Germany, 
Day served as the personal emissary of the 
Berlin Physical Society, advising Gibbs of 
his election as president of the Society, 
which Gibbs declined for reasons of age. It 
is no wonder, therefore, that thermody- 
namics became a major factor in the work 
of the Geophysical Laboratory. Intensive 
study sessions were conducted by mem- 
bers of the staff, and several members 
achieved international recognition for their 



182 



CARNEGIE INSTITUTION 



interpretation and application of thermo- 
dynamic principles. After a series of pa- 
pers on laws of chemical equilibria, hetero- 
geneous equilibria, and phase rule prob- 
lems, G. W. Morey (1912-1957) was asked 
to contribute an article to the "Commentary 
on the Scientific Writings of J. Willard 
Gibbs." Another major contributor to 
thermodynamics was George Tunell, re- 
nown for his careful exposition and explicit 
derivations, particularly in regard to open 
systems. 

The definition of activity, chemical 
potential, and related thermodynamic quan- 
tities, especially their variation with tem- 
perature and pressure was the principal 
area of expertise of L. H. Adams. A treatise 
on the "Thermodynamic relations in multi- 
component systems" by R. W. Goranson 
was published by CIW. He, too, was in- 
volved in the thermodynamic treatment of 
activity as it applied to solutions. But for 
the practical PVT relations in solutions, 
whether they were organic or inorganic, 
one turned to R. E. Gibson (1924-1946). 
Experimentalists consulted Morey for 
application of Schreinemaker's principles, 
especially the Morey-Schreinemaker's 
coincidence theorem, in the solution of 
their phase diagrams. 

It was N. L. Bowen who led the way in 
using the phase diagram to derive thermo- 
dynamic properties. The diopside-anorthite 
system is often used to illustrate those 
principles, and his diopside-albite-anorthite 
system is the current model for describing 
thermodynamic functions. The theoretical 
guidance of thermodynamic principles was 
evident throughout all the work of the 
Geophysical Laboratory. 



The experimental determination of th- 
ermodynamic properties was at various 
times a significant part of the work of the 
Laboratory. The construction of a calo- 
rimeter was in the hands of W. P. White 
(1904-1935), who was best known for the 
White double potentiometer adopted by 
the leading manufacturer of precision elec- 
trical measuring devices. White was greatly 
concerned with the factors that resulted in 
high precision and accuracy, and his mono- 
graph in the American Chemical Society 
Series on "The Modem Calorimeter" rec- 
ords detailed analysis of each facet of the 
experiment. He provided specific heats for 
the various forms of silica and some sili- 
cates, including the feldspars, in which a 
drop calorimeter was used. 

Calorimetry was considered a high pri- 
ority subject of investigation after WWII. 
A hydrofluoric-acid-solution calorimeter 
was built by F. C. Kracek (1923-1956) and 
his colleagues T. G. Sahama (1947-1949) 
and K. J. Neuvonen (1948-1950), with 
improvements on the successful Bureau of 
Mines (Berkeley, CA) design. At that time 
jadeite was under intense study from both 
a theoretical and experimental viewpoint, 
so the thermodynamic data for the critical 
reaction nepheline + albite — > jadeite were 
obtained. With the newly determined heats 
of formation as well as the determination of 
the other relevant parameters by other 
workers at the Laboratory, L. H. Adams 
was able to calculate the pressure-tempera- 
ture curve of stability for jadeite, as yet not 
synthesized in the laboratory. In short 
order, the heats of formation of the plagio- 
clases, alkali feldspars, olivines, and the 
hypersthenes followed. One of the divi- 



GEOPHYSICAL LABORATORY 



183 



dends of the calorimetry program not re- 
corded, was the large number of purified 
mineral separates prepared that were valu- 
able in related studies. 

With the material and financial help of 
the Geophysical Laboratory, T. G. Sahama 
was able to build his own calorimeter at the 
University of Helsinki and continue min- 
eralogical studies with K. J. Neuvonen. In 
more recent years the determination of 
thermodynamic properties has been car- 
ried out by calculation from more funda- 
mental parameters. The elegant work of A. 
H. Hofmeister (1983-1987), who used the 
spectral methods of mineralogy, is outlined 
in the section on Mineral Physics. The 
thermochemical properties of silicate 
glasses and liquids was of special interest 
to Pascal Richet (1983-1984) in collabora- 
tion with his colleague in France, Y. Bot- 
tinga. 



15. Heat and Mass Transport 
and Kinetics 

In all of the phase equilibrium studies 
carried out at the Geophysical Laboratory, 
much effort was expended in achieving 
equilibrium conditions. The products of 
such reproducible experiments were to be 
applied to rocks, which were assumed to 
approach closely equilibrium in the earth. 
In addition, if the end products of an equi- 
librium process were known, the non-equi- 
librium paths could be deduced. It is fortu- 
nate that rocks retain some of their non- 
equilibrium features, thereby revealing the 
path to their present state of closure. Some 
of the factors that provide evidence of path, 



such as heat and mass transport properties 
as well as process rates, have been investi- 
gated by the staff. For convenience, the 
studies are grouped under diffusion, reac- 
tion kinetics, crystal growth and dissolu- 
tion, metasomatism, and heat transfer. 



Diffusion 

One of the earliest measurements of 
diffusion in silicate liquids was made by 
Bowen (1921). He studied the interdiffu- 
sion against gravity (to avoid convection) 
between a buoyant layer of plagioclase 
liquid over a denser diopside liquid at about 
1500°C. After holding the liquids for a 
period of time, they were quenched, and the 
compositions of glass were determined at 
various levels by measuring their refrac- 
tive indices, which had been previously 
calibrated with mixtures of known compo- 
sition. From the diffusion profiles an 
"average diffusivity" was calculated. 
Bowen concluded that the formation of 
border phases of large bodies of igneous 
rocks by diffusion could not be considered 
possible in the time available for a cooling 
magma. On the other hand, the formation 
of reaction rims about inclusions could be 
attributed to diffusion. 

A similar experiment was carried out by 
Yoder (1973) between liquids of basalt and 
rhyolite compositions at 1200°C and 
P^O) = 1 kbar. The gradients of the major 
elements after quenching were determined 
by electron microprobe. He noted the strong 
coupling of the fluxes of major compo- 
nents and suggested that the structural units 
in the liquid were related to subspecies of 



184 



CARNEGIE INSTITUTION 



the minerals. 

The self diffusion of 45 Ca in diopside at 
one atmosphere (McCallister 1973-1975, 
1978-1979, Brady 1978-1979, and Mysen, 
1979) and up to 30 kbar (Watson, 1979) 
were especially informative experiments 
in regard to exsolution and homogeniza- 
tion processes in pyroxenes. The study of 
the coupled diffusion of Mg and Fe in 
olivine by Misener (1971-1972, 1972) was 
carried out at a series of temperatures for 
the purpose of relating diffusion to the 
creep rate. The interdiffusion coefficient 
was found to be sensitive to composition 
and crystallographic orientation. With the 
available creep data, Misener was able to 
demonstrate that the rate-controlling step 
was not the volume diffusion of cations. 
Similar coupled diffusion experiments were 
done by Boctor and Brady (1979) involv- 
ing S in HgSe (tiemannite). 

The diffusion of those elements used in 
geochronology received considerable at- 
tention. For example, the discordant ages 
that fit a chord across the concordia curve 
in a plot of 207 Pb/ 235 U vs 206 Pb/ 23 ^ were 
attributed by Tilton (1956-1965) to the 
continuous volume diffusion of Pb from 
the minerals measured. The paradox of 
lead loss at the same time on all continents 
from rocks of the same age was thereby 
resolved. Other studies included the gain 
and loss of argon in albite (Laughlin and 
Yoder, 1971 ) and the disequilibrium distri- 
bution of Th in diopside (Seitz, 1974). The 
technique of preparing fission-track maps 
developed by Seitz was successful in ob- 
taining data on the diffusion of Th, U, and 
O in diopside and fluorapatite. In coopera- 
tive studies with DTM, the diffusion of Sr 
in basalt liquid, studied by Hofmann( 1974), 



was especially pertinent to the small scale 
heterogeniety of the mantle as well as to 
applications to Rb-Sr geochronology of 
magmatic rocks. 



Reaction Kinetics 

The compositions of exsolved pyrox- 
enes place limits on their conditions of 
formation and give valuable information 
on the cooling history of the host rock. In 
a laboratory study of a synthetic solid solu- 
tion of Di-En, McCallister measured the 
rate of exsolution between 1225°C and 
1300°C. The observed changes in textures 
suggested to him that nucleation and growth 
occur above 1300°C, whereas spinodal 
decomposition, dependent solely on inter- 
diffusion kinetics, is the appropriate mecha- 
nism at lower temperatures. Additional 
annealing experiments yielded the useful 
observations, substantiated by bright-field 
micrographs, that rapid exsolution produces 
irregular lamellae (spinodal decomposi- 
tion), whereas slow exsolution has regular 
lamellae that lie within the coherent solvus. 

Another major contribution to the cool- 
ing rate problem was made by Seifert and 
Virgo (1975). By determining the Mg-Fe 
distribution with Mossbauer spectra in 
anthophyllite at P(H 2 0)=2 kbar, 400°- 
720°C, and various times, they were able to 
calibrate the order-disorder parameters. In 
this way the cooling rates of natural an- 
thophyllites could be ascertained. These 
experiments were seminal to a large range 
of studies on the rates of metamorphic 
events. 

Other studies included the influence of 
Zn and Pb on the transformation rates of 



GEOPHYSICAL LABORATORY 



185 



metacinnabar to cinnabar (Boctor and 
McCallister, 1979), the influence of poros- 
ity on the reaction rate of periclase and 
quartz to form forsterite (Brady, 1979), and 
the rate of homogenization of zoned gar- 
nets from metamorphic zones (Muncill, 
1983-1989, and Chamberlain, 1986). The 
latter study is being applied in New Eng- 
land in order to obtain the cooling rates 
after peak metamorphism. 



Crystal Growth and Dissolution 

In 1916 Becker and Day demonstrated 
by experiment the linear force of growing 
crystals. They refuted earlier failures by 
showing that the load increased crystal 
solubility, so it was necessary to maintain 
supersaturation for growth. A crystal- 
growth apparatus was designed by Hostetter 
(1912-1919) in 1919 in which separate 
thermostats held the source fluid at a higher 
temperature than the growing crystals. 
Whereas the growing of crystals under 
equilibrium conditions was the essence of 
obtaining phase equilibria diagrams, the 
growing of large crystals was only under- 
taken in regard to special measurements. 

The persistence of staff members in 
obtaining phases that are difficult to grow 
is the source of many legends. One ex- 
ample, is the incredible patience of J. F. 
Schairer in determining the melting point 
of albite. The liquid of appropriate compo- 
sition has to be prepared at a temperature 
high enough to dissolve the A1 2 3 , but not 
too high to volatilize the Na. The liquid is 
quenched to a glass, crushed to homoge- 
nize, and remelted at successively lower 
temperatures. The process of "acclimat- 



ing" the liquid structure to that close to 
crystalline albite results in a glass that will 
produce the appropriate crystalline struc- 
ture just below the melting point. Only 
after a five-year effort, was Schairer satis- 
fied that he knew the exact melting point of 
albite ! In the difficult synthesis of pyrope, 
Boyd and England (1959) resorted to seed- 
ing, and its field of stability at high pres- 
sures was accurately delineated. Similarly, 
iron cordierite was grown in the system 
FeO-Al 2 3 -Si0 2 , where previous attempts 
failed, merely by crushing a natural iron 
cordierite in the same room, thereby pro- 
viding inadvertently sufficient dust for 
seeds! 

A highly sophisticated apparatus has 
recently been assembled by Muncill (1988) 
for the exact measurement of growth rates 
of crystals in melt. He measured the iso- 
thermal growth kinetics of plagioclase in a 
haplogranodiorite melt at P(H 2 0)=2 kbar. 
The growth rate curves were well modeled 
by a modification of the theory of Muncill 
and Lasaga (1987) fox a simple system, and 
the endmember mineral growth curves can 
now be used to calculate growth rates in 
multicomponent systems. One of the divi- 
dends of the study was a videotape that 
shows the in situ growth and melting of 
plagioclase and other minerals that led to a 
visual appreciation of the generation of 
textures in igneous rocks. 

The dissolution of crystals in melt is 
important to the process of assimilation 
and provides a test of theories of disequili- 
brium melting. Minerals were separated 
from a spinel lherzolite and ground into 
spheres by Scarfe (1978-1980), E. 
Takahashi (1979-1981) and Yoder (1980) 
and held in an alkali basalt melt at high 



186 



CARNEGIE INSTITUTION 



pressures and temperatures. By measuring 
the change in diameter of the spheres it was 
found that the rate of dissolution of Gr > 
Cpx > OPx > Sp > 01 at the range of 
conditions examined. In general, the rate 
of dissolution was inversely proportional 
to the enthalpy of melting. The results are 
pertinent to the digestion of mantle xeno- 
liths by basaltic magmas during their rapid 
ascent to the surface. In another series of 
experiments by Muncill and Dingwell 
(1984-1986) the minerals stable in granitic 
melts dissolved much more slowly under 
anhydrous conditions than when volatiles 
were present. 



Metasomatism 

The rocks that result from the transport 
of various volatile and nonvolatile compo- 
nents are usually explained by the diffusion 
of components through a static solvent. 
For example, mineral textures at metamor- 
phic isograds are often accounted for in this 
way. A different model, first proposed by 
Korzhinskii (1936) involves the transport 
of material by the flow of a solvent in 
response to gradients of fluid pressure. To 
obtain quantitative information on such 
infiltration mass transport, J. D. Frantz and 
A. Weisbrod (1972-1973) studied the K 2 0- 
AljOj-SiOj-HjO-HCl system in 1973 to 
identify the sequence of zones of assem- 
blages, the nature of the boundaries or 
"fronts", and calculate the relative rates of 
progression of those fronts. They showed 
that infiltration metasomatism was ade- 
quate for long distance transport if there 
was an adequate fluid pressure gradient, 



which may remain unchanged regardless 
of the thickness of the reaction zones. These 
elegant computations were particularly 
instructive in predicting reaction paths and 
the relative velocities of the fronts and 
hence the relative thickness of the zones. 
Frantz and Weisbrod took into account the 
important volume term, introducing a po- 
rosity factor, and concluded that unless the 
rock expands, the infiltration process stops 
when the pores are filled. Although the 
infiltration theory is usually applied to 
metamorphic rocks, Irvine ( 1 980) described 
the same process for postcumulus mag- 
matic metasomatism to account for the 
observed compositional variations in the 
cyclical units of the Muskox intrusion. 

In contrast to the graphical solution of 
Frantz and Weisbrod, a general mathemati- 
cal model for mass transfer by both infiltra- 
tion and diffusion was considered by Frantz 
and Mao (1974) for a multicomponent 
system. As a demonstration of their theory, 
the system MgO-Si0 2 -H 2 0-HCl was ex- 
amined analytically by them using new and 
published values of the solubility of the 
phases and taking porosity, tortuosity, and 
diffusion coefficients into account. The 
calculations yielded zone sequences and 
thicknesses for various times. Further work 
included the more complex system CaO- 
MgO-Si0 2 -H 2 0-C0 2 in which they were 
able to calculate the sequence of zones and 
the modal abundance of each of the phases 
in each zone with the diffusion-infiltration 
model. 

In an attempt to deal with the multicom- 
ponent natural systems, R. C. Fletcher and 
R. J. Vidale (now Buden) (1974-1975) 
proposed in 1975 a finite-difference model 



GEOPHYSICAL LABORATORY 



187 



for combined diffusion-infiltration metaso- 
matism. The results were applicable to a 
wide variety of reactions between fluid- 
filled cracks and country rock and between 
incompatible rock assemblages. 

Heat transfer 

One of the important modes of heat 
transfer, resulting in metamorphism or 
magma generation, is from an external 
planar source. To obtain quantitative infor- 
mation on the rates of heat transfer that 
determine the width of metamorphic zones 
and the rate of magma production, Yoder 
devised an apparatus for measuring, during 
a constant heat flux, the heat transfer prop- 
erties in advance of melting and during the 
partial-melting process for a binary sys- 
tem. Detailed temperature profiles were 
obtained as a function of time. It was found 
that the melting process was decoupled 
from the rapid establishment of the thermal 
gradient. No evidence was observed for 
convection even though the properties of 
the system closely approached those of 
natural magmas except for linear scale. 
The results were well represented by a 
theoretical model, deduced by Finger and 
Muncill, from which the effective thermal 
diffusivities could be calculated. The chal- 
lenge of future experiments is to evaluate 
quantitatively the combined heat and mass 
transfer, but that project awaits a suitable 
theory for guidance. 



16. Geochronology 

The determination of the age of miner- 
als by the ratio of lead to uranium and 



thorium was a well established principle by 
1 928 , but a number of difficulties in analy- 
sis remained. Methods for the chemical 
analysis of these elements was given in 
detail by C. N. Fenner. In the following 
year, he and C. S. Piggot enlisted the help 
of F. W. Aston (Cambridge), in making the 
first calculation of a mineral (thorian uranin- 
ite) age on the basis of the specific isotopes 
of lead determined by mass spectroscopy. 
The discrepancy between the Pb-U age and 
Pb-Th age, however, led them to believe 
that the assumed U-Th equivalence factor 
may be in error. Although the radioactivity 
of ocean sediments became a major interest 
of C. S. Piggot and of W. D. Urry (1938- 
1949), the age determination of minerals 
was dominated by others until after WWII. 
A program for the determination of the 
age of minerals was initiated as a collabo- 
rative effort with DTM in 1950. The goal 
was to develop techniques and equipment 
for determining the age of several common 
minerals in the same rock for which differ- 
ent methods could yield completely inde- 
pendent ages. Granites of Precambrian age 
were chosen from which almost a dozen 
major and accessory minerals were ex- 
tracted. The methods focused on the accu- 
rate measure of the naturally occurring 
radioactive elements having long half-lives. 
The parent and daughter elements were 
concentrated from each separated mineral 
by ion-exchange resins after spiking the 
sample with a known amount of a tracer 
isotope and digesting it in acid. In this way 
the absolute concentration of the isotopes 
in the mineral could be ascertained by 
analysis in a mass spectrometer. The min- 
eral separation and solution chemistry was 
performed by Davis at the Geophysical 



188 



CARNEGIE INSTITUTION 



Laboratory and the mass spectrometry was 
carried out mainly by others at DTM 
(Aldrich,Wetherill,Tilton). In 1956Tilton 
transferred from DTM to the Geophysical 
Laboratory, and the close cooperation of 
both groups, with a growing tide of Post- 
doctoral Fellows and Guest Investigators, 
was even more effective. 

During the 1950-1955 period efforts 
were concentrated on methods. With the 
increased sensitivity of the isotope dilution 
technique, the decay scheme of 87 Rb to 87 Sr 
was applied successfully to the Li -bearing 
micas. The 40 K/ 40 Ca and 40 K/ 40 Ar clocks 
were slowly being developed. The discrep- 
ancies between the various clocks were 
attributed to radiation damage in the zir- 
cons, differential leaching in acids, and the 
transfer of Pb between minerals. These 
problems were investigated in great detail. 
The highest ages appeared to be given by 
the Rb-Sr clock, whereas the lowest age 
was found by the Th-Pb method. It was 
deduced that the Rb half-life used in the 
calculation was apparently too low, so a 
new half-life was found by assuming the U- 
Pb age was correct in a mineral giving 
concordant ages from six locations having 
a range of ages. Values of the half-life were 
calculated from the "Rb/^Sr from Rb- 
bearing minerals at the same localities. 
The new Rb half-life so determined geol- 
ogically, eliminated some of the previous 
discordance, and it remains the present-day 
value. 

With improved techniques, it became 
possible to begin applying the results to the 
solution of geological problems. In 1957, 
after discovering large groups of ancient 
rocks, the concept developed that the old- 
est rocks were the "nucleus" of a continent 



and younger belts of rocks were subse- 
quently added on. Because of the different 
responses of specific minerals to metamor- 
phism, it became possible to identify the 
age of the critical events in the geologic 
history of a region. In 1958 a major prob- 
lem among discordant age values was re- 
solved. Wetherill (1956) had shown in a 
plot of ^Pb/^U vs. ^Pb/^Uthat the vari- 
ous measurements could be related by a 
line of "concordia". The line was inter- 
preted by Tilton as the locus of apparent 
ages resulting from the continuous loss by 
diffusion of Pb. It was this discovery that 
cleared the way for geological application 
on a grand scale. Subsequently, the zones 
of various ages mapped for the U. S. and 
Canada were confirmed, and the concept of 
the slow accretion of a continent began to 
take shape. 

Discordant ages continued to plague the 
analysts, but each time the cause of the 
discordancy was resolved greater insight 
into geologic processes emerged. Studies 
of contact aureoles and eventually regional 
metamorphic grades illustrated that tem- 
perature affected the diffusion of radioac- 
tive daughter elements. The apparent ages 
could then be used for mapping thermal 
zones in a metamorphosed region. 

When the amphiboles and pyroxenes 
became useful indicators of age, a new 
range of petrological problems could be 
tackled. For example, the exceptionally 
low concentration of U in dunites and 
websterites suggested that the heat flow in 
the oceans had to arise from another source 
rock; eclogite appeared to be adequate. On 
the other hand, the hornblende-bearing 
peridotites in some of the islands had enough 
K to yield the appropriate heat flow. In 



GEOPHYSICAL LABORATORY 



189 



addition, the isotopic analysis of Pb indi- 
cated that the basalts of the oceanic islands 
were from heterogeneous sources. 

With the arrival of T. Krogh (1966- 
1975) the major thrust of the work turned to 
the Grenville controversy. The value of 
analyzing the whole rock as a closed sys- 
tem instead of individual minerals became 
appreciated. As belts of ages were identi- 
fied, the region appeared to have analogues 
with the modern-day, island-arc volcanic 
zones. The Grenville front was interpreted 
as an ancient plate boundary where a major 
metamorphic event took place 1500-1800 
m.y. ago with a second major dislocation 
about 1000 m.y. ago. 

In the next ten years (1968-1978) at 
least three major improvements in tech- 
nique took place. Krogh invented a new 
dissolution method for zircons in which a 
teflon-lined pressure vessel was used at 
220° C. X-ray fluorescence became a stan- 
dard tool for ascertaining the suitability of 
samples for Rb-Sr analysis. The produc- 
tion and purification (Krogh and Davis, 
1975) of the ^Pb spike (with the help of the 
Holifield National Laboratory) greatly 
improved the precision of the clocks based 
on lead. [The use of the 205 Pb spike was 
apparently developed independently at the 
same time by Tera and Wasserburg ( 1 975)] . 
With these improvements the ages of zir- 
cons inkimberlites were measured by Davis. 
The African diamond pipes were found to 
be around 90 m.y. old and two groups of 
pipes at Yakutsk, U.S.S.R., were 402-443 
m.y. and 360-344 m.y. Other studies in- 
cluded the dating of many other geologi- 
cally significant formations . 



With the resignation of Krogh in 1975 
and the retirement of Davis in 1978, the 
geochronology program was reevaluated. 
It was evident that the Geophysical Labo- 
ratory had served its role in pioneering new 
methods and contributing new concepts to 
the solution of geologic problems depend- 
ent on knowledge of accurate isotopic 
compositions. The existence of more than 
50 laboratories in the U. S. devoted to the 
dating of rocks and minerals, many headed 
up by past associates, indicated the field 
was well established, and it was appropri- 
ate for the Laboratory to invest its limited 
resources in new opportunities. 



17. Stable Isotopes 

The stable isotopes of the five elements 
sulfur, carbon, hydrogen, oxygen, and nitro- 
gen (the SCHON, or "beautiful" system) 
provide a special set of tools to investigate 
both organic and inorganic processes in the 
earth. The stable isotope program at the 
Geophysical Laboratory evolved after the 
arrival of T. C. Hoering (1959 — ). In a very 
short time, he built a mass spectrometer, 
with the help of colleagues at DTM, and 
began applying the C and O isotopes to the 
solution of organic problems. (The appara- 
tus, with several stages of improvement, 
served the staff well for exactly 30 years!) 



Carbon 

The fractionation of C by algae was 
studied by Abelson (1953-1971) and Hoer- 



190 



CARNEGIE INSTITUTION 



ing (1959) and found to be consistent with 
the general observation that 13 C/ 12 C has a 
lower ratio than carbonate or C0 2 in the 
environment. They examined a large array 
of separated, individual amino acids with 
marked isotopic differences, which they 
attributed to the different biosynthetic path- 
ways by which its constituents are incorpo- 
rated into the algae. Fatty acids are the 
precursors of petroleum, which is depleted 
in 13 C relative to whole modern organisms. 
That depletion was correlated with the low 
,3 C in the fatty acids of living organisms 
(both plants and animals) examined by 
Parker (1961-1963). In a study of the 
organisms of a Texas bay, Parker produced 
one of the first investigations of an ecosys- 
tem in which isotopes were used as tracers 
of complex food webs. Even the reduced 
carbon in Precambrian sediments had rela- 
tively low ratios of 13 C/ 12 C, according to 
Hoering 's studies. From then on, isotopes 
became a common tool in studying the 
processes in living and fossil organic mate- 
rial. 



Oxygen 

Hoering set out to evaluate the effects of 
T, P, and X on the isotopic fractionation of 
oxygen. The solubility of C0 2 in H 2 0, for 
example, resulted in fractionation. Pres- 
sure, on the other hand, was found not to be 
an important variable up to 4 kbar. This 
systematic study was soon set aside be- 
cause of the demand to resolve igneous 
penological problems. The lavas of Ice- 
land, Snake River Plain, and rocks from the 
Island Arcs were examined for evidence of 
sediment contamination and their reaction 



with meteoric waters, which result in 18 
enrichment and depletion, respectively. 
These results led to a study of the exchange 
of oxygen between silicates and C0 2 and 
2 by Muehlenbachs (1971-1974) and 
Kushiro. The value of oxygen isotope 
analysis was rapidly recognized by the 
metamorphic petrologists, and experiments 
were designed to test the control of fluid 
composition by the buffering effects of 
local mineral assemblages in metamorphic 
rocks. Even the exchange of oxygen be- 
tween fossils and minerals in metamorphic 
rocks were measured (Rumble, Hoering, 
and Boucot, 1978). The oxygen isotopes 
were then used to test the permeability of 
rocks during metamorphism, and eventu- 
ally in the mapping of the principal hy- 
drothermal pathways in a region. With an 
ever growing demand for data on a host of 
problems another mass spectrometer de- 
voted to both carbon and oxygen was ac- 
quired, and the oldest machine was modi- 
fied to investigate nitrogen isotopes. A 
dramatic new development by Z. Sharp 
(1987-1989) in technique for liberating the 
oxygen in a mineral on a microscale by 
laser heating will bring a new dimension to 
the application of oxygen isotopes to geo- 
logical problems. 



Hydrogen 

The second mass spectrometer to be 
acquired was a special type dedicated to 
measuring hydrogen and deuterium. Be- 
ginning in 1977, Estep (now Fogel, 
1977 — ) and Hoering studied the fractiona- 
tion of hydrogen isotopes in cultures of 
microalgae. They discovered several bio- 



GEOPHYSICAL LABORATORY 



191 



logical processes governing the isotope 
effect when a cell converts water in the 
medium to organic matter. Such informa- 
tion was necessary for interpreting hydro- 
gen isotopes in the organic matter of sedi- 
mentary rocks. For example, marine or- 
ganisms produce a larger effect than fresh- 
water forms, therefore the source of or- 
ganic matter in a sediment may be identi- 
fied. Hydrogen isotopes in lipids were 
shown to be particularly promising in trac- 
ing the sources of plant matter contributed 
to sediments and petroleum. 



Nitrogen 

In many parts of the ocean, nitrogen is a 
limiting nutrient and determines the amount 
of growth. Variations of 15 N/ 14 N can be 
used as tracers in the biogeochemical cycle. 
Hoering and Ford (1960) studied the iso- 
tope fractionation during the fixation of N 2 
for four species of bacterium cultured in the 
laboratory, and they could account for the 
depletions in the heavy isotope in natural 
populations. After a hiatus of almost twenty 
years, the processes of nitrate assimilation 
and reduction by blue-green algae attracted 
the attention of Macko (1981-1983) and 
colleagues. Whereas the fractionation of 
isotopes was small in the fixation of mo- 
lecular nitrogen, the effect was large by 
contrast when the source of nitrogen avail- 
able was in the form of a nitrate. In a 
collaborative effort of all the members of 
the Biogeochemical Group, individual 
amino acids were separated from cultured 
microorganisms in order to determine the 
isotopic effects during biochemical syn- 
thesis. Hare and Estep (now Fogel) (1983) 



later explored these differences in biosyn- 
thesis to trace metabolism of diets and 
subsequent diagenesis of modern and fos- 
sil animal bones. 

In a broad survey of coastal and estuar- 
ian sediments, nitrogen isotopes were used 
to track the mixing and recycling of organic 
matter in the nearshore environments. 
Although the processes are indeed com- 
plex, Cifuentes (1984-1988) and colleagues 
were able to correlate some of the changes 
with the processes that tended to consume 
nitrogen. These results spurred the search 
for more details on the course of nitrogen in 
the diets of living organisms. In addition, 
the value of using several isotope systems 
was recognized as each system contributed 
to the definition of the environmental con- 
ditions. The multiple use of isotopes was 
applied on a grand scale in a study of the 
Delaware estuary. The continuing study 
has already documented the dramatic sea- 
sonal changes that take place in the waters 
and sediments of the estuary. 



Sulfur 

New technique usually opens the door 
to new opportunities, and the use of sulfur 
isotopes is exemplary. Sabels (1962) and 
Hoering in 1963 found that S could be 
liberated as SF 6 with the halogen fluorides, 
and its isotopes measured in the mass spec- 
trometer. The precision in the available 
mass spectrometer was not sufficient to 
warrant a major study on the ore minerals. 
In 1983, however, in a new mass spec- 
trometer fitted with four detectors, Hoering 
was able to measure the four stable isotopes 
of S ( 32 S, 33 S, 34 S, and 36 S) simultaneously. 



192 



CARNEGIE INSTITUTION 



The first applications were to metamorphic 
rocks in which the alteration of pyrite to 
pyrrhotite could be studied The flow of 
fluids from a nearby igneous body were 
believed to be responsible for the desulfuri- 
zation process. 

Hoering determined the isotopic com- 
position of the sulfur in sedimentary barites 
(BaS0 4 ) and pyrite from the Archean of 
southern India. The values for the barite 
contrast sharply with that of contemporary 
seawater and appeared to fall in the range 
for igneous rocks. The values of the coex- 
isting pyrite were even more anomalous. 
One of the factors Hoering thought might 
be important in explaining the results, prior 
to the emergence of the sulfur-reducing 
bacteria about 2.8 b.y. ago, was the role of 
atmospheric oxygen in the nonbiological 
oxidation of reduced sulfur molecules. 
Other isotopic systems are now being 
applied to resolve this fascinating paradox 
in ancient environments. 

It is anticipated that any future study 
will require the use of all the pertinent 
stable isotope systems, whether the prob- 
lem be in sedimentary, igneous, or meta- 
morphic rocks. The advantage in having 
several dedicated mass spectrometers under 
one roof at the Geophysical Laboratory 
means there is no impediment to examin- 
ing the same sample with all the appropri- 
ate isotopic systems, and to integrating all 
the observations by one or several investi- 
gators. 

18. BlOGEOCHEMISTRY 

The application of organic chemistry to 
geological problems at the Geophysical 



Laboratory arose out of the research inter- 
ests of the newly arrived Director, Philip H. 
Abelson (1953-1971). He used paper 
chromatography to demonstrate that fos- 
sils as old as 300 million years retained 
amino acids from some of their original 
proteins. Abelson also determined that the 
breakdown of amino acids in fossils could 
be simulated in the laboratory by substitut- 
ing elevated temperatures for geological 
time, thereby demonstrating their potential 
as stratigraphic markers and geochronom- 
etric tools. These "chemical fossils" com- 
plemented the classical methods of paleon- 
tology. The book "Biochemistry of Amino 
Acids," edited by P. E. Hare (1963— ), T. C. 
Hoering, and F. King, Jr. (1970-1974), has 
been the definitive work on the subject. 

All the amino acids in proteins exist in 
two configuration that are mirror images, 
or optical isomers, designated D and L. 
Hare was successful in separating these 
isomers with gas chromatography andhigh- 
pressure liquid chromatography. He learned 
that biologically produced amino acids, 
which are dominantly L, transformed spon- 
taneously to D abiologically as a function 
of time. Hare developed these observa- 
tions into a method for dating fossils as old 
as 20 million years. 

From the early paper chromatography, 
the techniques have evolved to very-high- 
resolution capillary gas chromatography, 
high-pressure liquid chromatography and 
eventually to a combination of gas-chro- 
matographic and mass spectrometric meth- 
ods. A field-portable, liquid chromato- 
graph was made by Hare to measure amino 
stratigraphic sections on site. The fluores- 
cent derivatives of NH 2 groups were used 



GEOPHYSICAL LABORATORY 



193 



by Hare to analyze for amino acids, pep- 
tides, and proteins at an unprecedented low 
concentration. With this technique he set a 
limit of less than one part per trillion of 
amino acids in the returned lunar soil. That 
method was not only useful in the analysis 
of fluid inclusions in igneous and meta- 
morphic rocks, but also in the characteriza- 
tion of blood. 

The study of amino acids in fossils was 
followed by investigations of the fatty ac- 
ids, fatty alcohols, humic acids, prophy- 
rins, kerogen and steranes by Hoering. Of 
special interest was the demonstration in 
the laboratory of the reaction of glucose 
and amino acids to produce melanoidin, a 
product closely related to humic acid, a 
significant fraction of the organic material 
in Holocene sediments. The work outlined 
the pathway whereby organic matter is 
effectively removed from the biological 
carbon cycle and preserved without further 
metabolization by micro-organisms. 

The organic compounds in mildly meta- 
morphosed Precambrian rocks were stud- 
ied by Hoering. He discovered with the use 
of 13 C/ 12 C that the extractable organic 
compounds could be attributed to biologi- 
cal origin. The insoluble fraction, kerogen, 
yielded similar carbon isotope ratios, but 
the relationship of soluble to the insoluble 
fractions remained obscure because of 
potential contamination by modem organ- 
isms. Subsequent laboratory experiments 
on the thermal breakdown of kerogen pro- 
vided a mechanism for the production of 
the high-molecular weight components 
found in petroleum (Hoering, 1984). The 
hydropyrolysis of shales and other rocks 
resulted in a method, now standard in the 



petroleum industry, for evaluating their 
potential for petroleum generation. 

As a result of Hoering 's skills in mass 
spectrometry, the Laboratory has devel- 
oped dedicated facilities for measuring the 
stable isotopes of C, H, O, N, and S. For 
example M. Fogel traced the food chains 
with hydrogen isotopes. The specific algae 
on which a snail had been feeding could be 
identified in confirmation of the adage "you 
are what you eat." In another important 
study, Fogel showed with stable isotopes 
that modem blue-green algae and bacteria 
growing in C0 2 -rich hot springs exhibited 
the same depletion in 13 C as in Precambrian 
stromatolites formed by the same types of 
organisms. She demonstrated that the 
atmosphere in Precambrian times was, 
therefore, probably enriched in C0 2 by 
several percent relative to the present day 
atmosphere. 

In an unprecedented collaboration be- 
tween the Geophysical Laboratory and the 
Carnegie Institution of Washington's De- 
partment of Plant Biology at Stanford, Fogel 
and Joseph Berry solved one of stable- 
isotope geochemistry's oldest problems, 
the "Dole Effect", that was identified in 
1936. Atmospheric oxygen is anomalously 
enriched in the heavy isotope, 18 0, and 
previous studies could not account for this 
effect. Berry and Fogel discovered that a 
large isotope fractionation occurred during 
the uptake of 2 in photorespiration, a 
process that accompanies the photosynthe- 
sis reaction, and thus they could account 
for the isotope enrichment. 

The presence of a group in biogeochem- 
istry in a geophysical laboratory has yielded 
many unanticipated dividends. The stable 



194 



CARNEGIE INSTITUTION 



isotope facilities initially developed by them 
have been applied to a wide range of prob- 
lems in sedimentary, igneous, and meta- 
morphic petrology. Their techniques and 
cooperation have contributed to the under- 
standing of ore deposits, meteorites, and an 
unusual array of mineralogical problems. 
They are indeed exemplary of the outstand- 
ing results that can be achieved through the 
Carnegie concept of supporting scholars in 
fields of their own choice. 



19. War-time Studies 



World War I 

Before hostilities began in 1914, it 
became evident that the U.S. would be cut 
off from the European sources of optical 
glass. Five American companies under- 
took to make optical glass but the quality 
was not satisfactory by the time the U.S. 
entered the war. Because of the critical 
need for high quality optical glass for mili- 
tary fire-control instruments, methods for 
its manufacture on a large scale had to be 
developed. The Council of National De- 
fense appealed to the Geophysical Labora- 
tory for help because it had been engaged 
for many years in the study of silicate 
liquids, similar to optical glass, at very high 
temperatures. It was the only organization 
in the country with a staff trained in the 
fundamentals necessary for the manufac- 
ture of optical glass. 

In April 1917 groups of staff members 
were sent to the various plants and assigned 
the responsibility for their operations, 
whereas others remained at the Laboratory 



to deal with specific problems. The coop- 
erative attitude of the companies and the 
direct liaison with the Army through the 
commissioning of F. E. Wright greatly 
facilitated the task. The expenses incurred 
were covered by CIW and no compensa- 
tion was ever received for their work. The 
Director, A. L. Day, was eventually desig- 
nated as "in charge of optical glass produc- 
tion, War Industries Board." After the 
armistice, the records show that 95% of all 
optical glass manufactured in the U.S. 
during the war had been made under the 
supervision of the staff of the Laboratory. 
The manufacturing problems were 
eventually resolved by putting the secre- 
tive cook-book glass making methods on a 
scientific base. Formulae were devised so 
that glasses of the appropriate index of 
refraction or other optical constants could 
be prepared from the necessary constitu- 
ents with a minimum of trial and error. 
Even the barium-rich glasses for aerial 
camera lenses were made on short notice. 
Most important contributions were made 
by Adams and Williamson (1919), who 
deduced the laws for relieving stress in 
glass by annealing, and Roberts (1917- 
1947, 1919), who by direct experiment was 
able to formulate cooling schedules for the 
glass pots. Sosman (1925) had investi- 
gated some of the principles governing the 
corrosion of the fire clays used in the pots 
by the molten glass. Other problems such 
as high dispersion due to successive iron 
content, stones from the digestion of un- 
suitable clay pots, cords and striations aris- 
ing from poor stirring, and strain from 
rolling were all investigated. Over 20 papers 
were published by the staff on glass making 
for the benefit of the future U.S. glass 



GEOPHYSICAL LABORATORY 



195 



industry. Of these, the monograph on the 
properties of glass by G. W. Morey (1938) 
revised in 1954, remains a standard refer- 
ence work. Although none of the 20 scien- 
tifically-trained staff had previous experi- 
ence with the manufacture of glass, all used 
their basic knowledge of silicates to put this 
new U.S. industry on a sound basis. 

The skills of the chemists at the Labora- 
tory were also put to use on the fixation of 
nitrogen for the manufacture of explosives. 
Experimental work on the Bucher-cyanide 
process and the Haber-process were begun 
in the summer of 1918, and, therefore, had 
not proceeded far before the end of the war. 
As repugnant as the task may have been, 
the Laboratory also investigated some of 
the physical constants of mustard "gas" in 
response to a military request. 



World War II 

The president of CIW, Vannevar Bush, 
helped establish the National Defense 
Research Committee in 1940 and served as 
its chairman. On the 28 June 1941 Bush 
became Director of the Office of Scientific 
Research and Development (OSRD) that 
organized and directed most of the research 
efforts during the war. In that summer a 
comprehensive program of defense research 
was organized to be centered at the Geo- 
physical Laboratory. Some of the staff 
began to collect information from military 
and other sources for delineating the lines 
of research. After the declaration of war in 
December, the entire staff, supplemented 
by thirty temporary employees, and all of 
the resources of the Laboratory were de- 
voted to the tasks ahead. 



The Director, L. H. Adams, was ap- 
pointed chairman of the committee for 
investigating the erosion of gun barrels due 
to high-pressure, hot, propellant gases re- 
leased on firing. As the research pro- 
ceeded, studies were concentrated on the 
caliber-50, rapid-fire, aircraft gun where 
means to counteract severe swaging of the 
lands and thermal expansion of the barrel 
became the principal focus. The system- 
atic studies included analysis of the corro- 
sion products of the steel barrels and the 
propellant gases. By means of isotopically 
labeled nitrogen in the explosive charge 
and use of the National Bureau of Stan- 
dards mass spectrometer, tracer studies 
revealed the depth of penetration of the 
gases. Experiments were carried out in 
high-pressure vessels on controlled explo- 
sions to ascertain the internal ballistics and 
chemical products. Metal with high, hot- 
hardness, as well as resistance to gas ero- 
sion were inserted as short liners in barrels 
at the origin of rifling. The liners were then 
tested on a firing range on the Potomac 
River or in firing ranges installed under the 
tennis courts (now volley ball court) be- 
hind the Laboratory. The superior metal 
was found to be the cobalt-based alloy, 
stellite, and it became a most useful mate- 
rial for making hydrothermal pressure 
vessels after the war. 

Another group was concerned with the 
electroplating of chromium inside the bar- 
rel after the liner, in cooperation with the 
electroplating group at the National Bu- 
reau of Standards. Because it was not 
practical to machine a taper in the large 
number of barrels required, a method was 
designed to taper the plating, with increas- 
ing thickness of the plate toward the muzzle. 



196 



CARNEGIE INSTITUTION 



In this way, constriction of the bore com- 
pensated for the thermal expansion of the 
barrel during firing. The increased life and 
accuracy was documented by test firing on 
the Geophysical Laboratory ranges. The 
barrel adapted for military use, still being 
manufactured today, contains a short stel- 
lite liner and a chrome-plated, tapered 
bore. 

Several of the staff members were also 
helpful at DTM in the development of the 
proximity fuze for artillery shells. That 
device was considered to be "the most 
important technical improvement in weap- 
onry to come out of World War H." 

Almost five years of the life of the 
Geophysical Laboratory were devoted to 
the war work. The regular staff was paid by 
CIW; however, the costs of the temporary 
employees and extra expenses were pro- 
vided by the government. In 1946 the war 
work was phased out, the reports written, 
and a comprehensive review undertaken of 
the scientific programs in the light of the 
irreversible changes brought about by World 
Warn. 



20. Closing Remarks 

The most important factor in the gen- 
eration of new ideas at the Geophysical 
Laboratory has been the freedom of choice 
to follow whatever the staff member be- 
lieves to be important in the solution of a 
geological problem. The scientist's over- 
riding goal was to achieve an understand- 
ing of the problem so that the critical vari- 
ables could be recognized, evaluated, and 
formulated into general concepts useful in 
solving other problems. The intent, there- 



fore, was to seek knowledge that has broad 
application to the major problems of the 
earth. Because no researcher can predict 
how a fundamental discovery might be 
applied to future societal needs or prob- 
lems, there is no test for relevance or appli- 
cability applied to the work at the Geo- 
physical Laboratory as is made in indus- 
trial organizations. That freedom to follow 
whatever is critical to the solution of prob- 
lems is why the Geophysical Laboratory 
has remained unique among research or- 
ganizations. The price of such a generous 
measure of scientific freedom is greater 
personal responsibility to produce and 
greater accountability. Although peer 
review provides for continual testing, the 
responsibility to produce was self gener- 
ated and was expressed by the high motiva- 
tion and involvement of the staff. 



Addendum 

Most histories record the biased views 
of a single observer moderated by the writ- 
ten records and evaluations of others. It is 
difficult to subdue the enthusiasm, admira- 
tion and pride the author has for the Geo- 
physical Laboratory and its past and pres- 
ent staff members. Having known almost 
all of the early staff members and experi- 
enced directly slightly more than half of the 
life of the Laboratory, the author might be 
forgiven for any excessive claims of dis- 
covery attributed to the staff. All science is 
built on the discoveries of others, and it is 
not always evident who arrives at the pin- 
nacle of an idea first, demonstrates its proof, 
applies the solution to a geological prob- 
lem, or capitalizes on its promotion. The 



GEOPHYSICAL LABORATORY 



197 



personal satisfaction of contributing to the 
growth of science is adequate reward in 
itself. 

The scientific history presented above 
was prepared on short notice, with a mini- 
mum of time for reflection, preparatory to 



the departure of the staff from the Geo- 
physical Laboratory building on 280 1 Upton 
St., N. W., Washington, D. C. to a new 
building on the DTM campus. It is antici- 
pated that a more detailed, documented 
history will be prepared in the future. 



GEOPHYSICAL LABORATORY 



199 



Publications 

Reprints of the numbered publications listed below are available, except where noted, at no 
charge from the Librarian, Geophysical Laboratory, 2801 Upton St., N.W, Washington, D.C. 
20008-3898, U.S.A. Please give reprint number(s) when ordering. 



Angel, R. J., High-pressure structure of anorthite, 
Am. Mineral., 73, 1 1 14-1 1 19, 1988 (G.L. Paper 
2089). 

Angel, R. J., and L. W. Finger, Polymorphism of 
nickel sulfate hexahydrate, Acta Crystallogr ., 
Sect.C,44, 1869-1873, 1988 (G.L. Paper 2094). 

Angel, R. J., T. Gasparik, and L. W. Finger, 
Crystal structure of a Cr^-bearing pyroxene, 
Am. Mineral, 74, 599-603, 1989 (G.L. Paper 
2123). 

Angel, R. J., S. A. T. Redfern, and N. L. Ross, 
Spontaneous strain below the /I -PA transition in 
anorthite at pressure, Phys. Chem. Minerals, 16, 
539-544, 1989 (G. L. Paper 2122). 

Angel, R. J., L. W. Finger, R. M. Hazen, M. 
Kanzaki, D. J. Weidner, R. C. Liebermann, and 
D. R. Veblen, Structure and twinning of single- 
crystal MgSi0 3 garnet synthesized at 17 GPa 
and 1800°C, Am. Mineral., 74, 509-512, 1989 
(G.L. Paper 2120). 

Arashi, H., O. Shimomura, T.Yagi, S. Akimoto, 
and Y. Kudoh, P-T phase diagram of Zr0 2 deter- 
mined by in situ X-ray diffraction measurements 
at high pressures and high temperatures, in 
Advances in Ceramics, Vol. 24: Science and 
Technology ofZirconia HI, The American Ce- 
ramic Society, Inc., Westerville, Ohio, pp. 493- 
500, 1988 (No reprints available from Geo- 
physical Laboratory). 

Boctor, N. Z., and G. Kullerud, Phase relations in 
the mercury-selenium sulfur system at 200° to 
700°C, J. Solid State Chem., in press. 

Boyd, F. R., Where do we go from here?, in 
Kimberlite and Related Rocks, Proceedings of 
the Fourth International Kimberlite Conference, 
Perth, Australia, August, 1986, J. Ross, ed., 
Geological Society of Australia, Special Publi- 
cation No. 14, Vol. 2, Blackwell Scientific Pubns, 
Carleton, Victoria, Australia, pp. 1239-1251, 
1989 (G.L. Paper 2142; no reprints available for 
distribution). 



Boyd, F. R., Compositional distinction between 
oceanic and cratonic lithosphere, Earth Planet. 
Sci. Lett., in press. 

Chamberlain, C. P., P. H. Zeitler, and M. Q. Jan, 
The dynamics of the suture between the Kohis- 
tan Island arc and the Indian plate in the Hima- 
laya of Pakistan, /. Metamorphic Geol., 7, 135- 
149, 1989. 

Chamberlain, C. P., and M. Q. Jan, Petrologic 
constraints on the tectonic development of the 
Nanga Parbut - Haramosh Massif, Himalayas, 
Spec. Pap. - Geol. Soc. Amer., in press. 

Chamberlain, C. P., and D. Rumble, Thermal 
anomalies in a regional metamorphic terrane: 
An isotopic study of the role of fluids, /. Petrol., 
29, 1215-1232, 1988 (G.L. Paper 2129). 

Chamberlain, C. P., and D. Rumble, III, The 
influence of fluids on the thermal history of a 
metamorphic terrane, New Hampshire, USA. /. 
Geol. Soc. London (Spec. Issue), in press. 

Chayes, F., The Delesse relation in a concentri- 
cally zoned sphere. I. The section-number bias, 
Math. Geol, 21, 319-329, 1989 (G.L. Paper 
2134). 

Cifuentes, L. A., J. H. Sharp, and M. L. Fogel, 
Stable carbon and nitrogen isotope 
biogeochemistry in the Delaware Estuary, 
Limnol. and Oceanogr., 33, 1102-1115, 1988 
(G.L. Paper 2095). 

Day, H. W., and C. P. Chamberlain, Implications 
of thermal and baric structure for controls on 
metamorphism in northern New England, J. 
Geol. Soc. London, in press. 

Dingwell, D. B., The structures and properties of 
fluorine-rich magmas: a review of experimental 
studies, in Recent Advances in the Geology of 
Granite-Related Mineral Deposits, Proceedings 
of the CIM Conference on Granite-Related 
Mineral Deposits, Halifax, Canada, September, 
1985, R. P. Taylor and D. F. Strong, eds., CIM 
Bull Spec Vol. 39, pp. 1-12, The Canadian 



200 



CARNEGIE INSTITUTION 



Institute of Mining and Metallurgy, Montreal 
1988 (G.L. Paper 2098). 

Dymek, R. R, S. C. Brothers, and C. M. Schiffries, 
Pedogenesis of ultramafic metamorphic rocks 
from the 3800 Ma Isua Supracrustal Belt, West 
Greenland, /. Petrol, 29, 1353-1397, 1988. 

Finger, L. W., R. M. Hazen, and R. J. Hemley, 
BaCuSi 2 6 . A new cyclosilicate with four- 
membered tetrahedral rings, Am. Mineral., 74, 
952-955, 1989 (G.L. Paper 2131). 

Fogel, M. L., E. K. Sprague, A. P. Gize, and R. W. 
Frey, Diagenesis of organic matter in Georgia 
salt marshes, Estuarine, Coastal Shelf Science, 
28, 211-230, 1989 (G.L. Paper 2115). 

Frantz, J. D., Y. G. Zhang, D. D. Hickmott, and T. 
C. Hoering, Hydrothermal reactions involving 
equilibrium between minerals and mixed vola- 
tiles. 1. Techniques for experimentally loading 
and analyzing gases and their application to 
synthetic fluid inclusions, Chem. GeoL, in press. 

Guy, R. D., J. A. Berry, M. L. Fogel, and T. C. 
Hoering, Differential fractionation of oxygen 
isotopes by cyanide-resistant and cyanide-sen- 
sitive respiration in plants, Planta, 177, 483- 
491, 1989 (G.L. Paper 2138). 

Hare, P. E., Chiral mobile phases for the enanti- 
omeric resolution of amino acids, in Chromato- 
graphic Chiral Separations, L. J. Crane and M. 
Zief, eds., Marcel Dekker, New York, pp. 165- 
177, 1988 (G.L. Paper 2105). 

Hare, P. E., and P. A. St. John, Detection limits for 
amino acids in environmental samples, in De- 
tection in Analytical Chemistry: Importance, 
Theory, and Practice, L. A. Curie, ed., ACS 
Symposium Series 361, American Chemical 
Society, Washington, D.C., Chapt. 15., pp. 275- 
285, 1988 (G.L. Paper 2106; no reprints avail- 
able for distribution). 

Hare, P. E., Detection limits in amino acid analy- 
sis: An overview, in Methods in Protein Se- 
quence Analysis, (Proceedings of the 7th Inter- 
national Conference, Berlin, July 3-8, 1988), B. 
Wittman-Liebold, ed., Springer- Verlag, New 
York, Chapt. 1.1, pp. 2-9, 1989 (G.L. Paper 
2141; no reprints available for distribution). 

Hazen, R. M., A useful fiction: polyhedral model- 
ing of mineral properties, Am. J. Sci., Special 
("Wones") Volume, 288-A, 242-269, 1988 (G.L. 
Paper 2059). 



Hazen, R. M., Understanding perovskites of bene- 
fit to science and industry - an interdisciplinary 
approach, Earth in Space, 1, No. 3,. 8-10, 1988 
(G.L. Paper 21 12; no reprints available for dis- 
tribution). 

Hazen, R. M., and Z. D. Sharp, Compressibility of 
sodalite and scapolite, Am. Mineral., 73, 1120- 
1 122, 1988 (G.L. Paper 2088). 

Hazen, R. M., and L. W. Finger, High-pressure 
crystal chemistry of andradite and pyrope: 
Revised procedures for high-pressure diffrac- 
tion experiments, Am. Mineral., 74, 352-359, 
1989 (G.L. Paper 2114). 

Hazen, R. M., L. W. Finger, and D. E. Morris, 
Crystal structure of DyBa 2 Cu 4 O g : A new 77 K 
bulk superconductor, Appl. Phys. Lett., 4, 1057- 
1059, 1989 (G.L. Paper 2113). 

Hazen, R. M., The Breakthrough: The Race for 
the Superconductor, Summit Books, New York, 
1988; Ballantine/Science, New York, 1989. 
Foreign editions: Superconductors: The Break- 
through, Unwin Hyman Ltd., London, 1988; La 
Course Aux Supraconducteurs, Librairie Plon, 
Paris, 1989; De Dag Dat de Wetenschap Wild 
Werd, Uitgeverij Lannoo, Tielt, The Nether- 
lands, 1989 (G.L.Paper 2073; obtainable by 
purchase only from the publishers). 

Hemley, R. J., R. E. Cohen, A. Yeganeh-Haeri, H. 
K. Mao, D. J. Weidner, and E. Ito, Raman 
spectroscopy and lattice dynamics of MgSi0 3 - 
perovskite at high pressure, in Perovskite: A 
Structure of Great Interest to Geophysics and 
Materials Science, A. Navrotsky and D. J. 
Weidner, eds., American Geophysical Union, 
Washington, D. C, pp. 35-53, 1989 (G.L. Paper 
2111). 

Hemley, R. J., A. P. Jephcoat, C. S. Zha, H. K. 
Mao, L. W. Finger, and D. E. Cox, Equation of 
state of solid neon from X-ray diffraction meas- 
urements to 1 10 GPa, in International AIR APT 
Conference,XIth,Kiev, USSR, July 12-17, 1987, 
Vol. 3. High Pressure Science and Technology: 
Proceedings, N. V. Novikov and Ye M. 
Chistyakov, eds., Naukova Dumka, Kiev, pp. 
211-217, 1989 (G.L. Paper 2135; no reprints 
available for distribution). 

Hemley, R. J., L. C. Chen, and H. K. Mao, New 
transformations between crystalline and amor- 
phous ice, Nature, 338, 638-640, 1989 (G.L. 
Paper 2124). 



GEOPHYSICAL LABORATORY 



201 



Hemley, R. J., C. S. Zha, A. P. Jephcoat, H. K. 
Mao, L. W. Finger, and D. E. Cox, X-ray diffrac- 
tion and equation of state of solid neon to 1 10 
GPa,Phys.Rev.B,39, 11820-11827, 1989(G.L. 
Paper 21 18). 

Hickmott, D. D., and N. Shimizu, Trace element 
zoning in garnets from the Kwoiek area, British 
Columbia: Possible influence of interface kinet- 
ics in metamorphism, Contrib. Mineral. Petrol., 
in press (No reprints will be available from 
Geophysical Laboratory). 

Hoering, T. C, Isomers of the monomethyl, acy- 
clic hydrocarbons in the Messel shale and in 
petroleums, Cour. Forsch.Senkenberg, 107 ', 79- 
87, 1988 (G.L. Paper 2116). 

Hofmeister, A. M, J. Xu, H. K. Mao, P. M. Bell, 
and T. C. Hoering, Thermodynamics of Fe-Mg 
olivines at mantle pressures: Mid- and far- 
infrared spectroscopy at high pressure, Am. 
Mineral., 74, 281-306, 1989 (G.L. Paper 2097). 

Irvine, T. N., A global convection framework: 
Evidence for symmetry and stratification in the 
Earth's convection system, Econ. Geol., in press. 

Kubicki, J. D., and A. C. Lasaga, Molecular dy- 
namics of SiO z melt and glass: Ionic and cova- 
lent models, Am. Mineral., 73, 941-955, 1988 
(No reprints available from Geophysical Labo- 
ratory). 

Kudoh, Y., E. Ito, and H. Takeda, High-pressure 
structural study on perovskite-type MgSi0 3 - A 
summary, in Perovskite: A Structure of Great 
Interest to Geophysics and Materials Science, A 
Navrotsky andD. J. Weidner, eds., Geophysical 
Monograph 45, American Geophysicial Union, 
Washington, D. C.,pp. 33-34, 1989 (No reprints 
available from Geophysical Laboratory). 

Kushiro, I., Density of basalt magmas at high 
pressures and its petrological application, in 
Advances in Physical Geochemistry, "Physical 
Chemistry of Magma", L. L. Perchuk and I. 
Kushiro, eds., Springer- Verlag, New York, in 
press. 

Kushiro, I., and B. O. My sen, Experimental stud- 
ies of the system Mg^SiO^F^at pressures 10" 2 - 
10" 10 bar and temperatures to 1650'C: Applica- 
tion to condensation and vaporization processes 
in the primitive solar nebula, in Advances in 
Physical Geochemistry, L. L. Perchuk, ed., 
Springer- Verlag, New York, in press. 

Luth, R. W., Natural versus experimental control 



of oxidation state: Effects on the composition 
and speciation of C-O-H fluids, Am. Mineral., 
74, 50-57, 1989 (G.L. Paper 2110). 

Luth, R. W., and G. E. Muncill, Fluorine in alumi- 
nosilicate systems: Phase relations in the system 
NaAlSi 3 8 -CaAl 2 Si 2 O g -F 2 A , Geochim. Cosmo- 
chim. Acta, in press (G.L. Paper 2136). 

Luth, R. W., D. Virgo, F. R. Boyd, and B. J. Wood, 
Ferric iron in mantle-derived garnets: Implica- 
tions for thermobarometry and for the oxidation 
state of the mantle, Contrib. Mineral. Petrol., in 
press. 

Mao, H. K., Static compression of simple molecu- 
lar system in the megabar range, in Simple 
Molecular Systems at Very High Density, Vol. 
186, Proceedings of a NATO Advance Research 
Workshop/European Society Workshop, March 
28-April 6, 1988, Les Houches, France, A. Po- 
lian, P. Loubeyre, and N. Boccara, eds., Plenum 
Publ. Corp., New York, pp. 221-236, 1989 (G.L. 
Paper 2100). 

Mao, H. K., R. J. Hemley, Y. Wu, A. P. Jephcoat, 
L. W. Finger, C. S. Zha, and W. A. Bassett, 
High-pressure phase diagram and equation of 
state of solid helium from single crystal X-ray 
diffraction to 23.3 GPa, Phys. Rev. Lett., 60, 
2649-2652, 1988 (G.L. Paper 2083). 

Mao, H. K., and R. J. Hemley, Optical studies of 
hydrogen above 200 gigapascals: Evidence for 
metallization by band overlap, Science, 244, 
1462-1465, 1989 (G.L. Paper 2130). 

Mao, H. K., L. C. Chen, R. J. Hemley, A. P. 
Jephcoat, Y. Wu, and W. A. Bassett, Stability 
and equation of state of CaSi0 3 -perovskite to 
134 GPa, J. Geophys. Res., in press. 

McMillan, P., and N. Ross, The Raman spectra of 
several orthorhombic calcium oxide perovskites, 
Phys. Chem. Minerals, 16, 21-28, 1988 (No 
reprints available from Geophysical Labora- 
tory). 

Morris, D. E., J. H. Nickel, J. Y. T. Wei, N. G. 
Asmar, J. S. Scott, U. M. Scheven, C. T. Hultgren, 
A. G. Markelz, J. E. Post, P. J. Heaney, D. R. 
Veblen, and R. M. Hazen, Eight new high- 
temperature superconductors with the 1:2:4 
structure, Phys. Rev. B, 39, 7347-7350, 1989 
(G.L. Paper 2127). 

Muncill, G. E., and A. C. Lasaga, Crystal growth 
kinetics of plagioclase in igneous systems: 
Isothermal H 2 0-saturated experiments and 



202 



CARNEGIE INSTITUTION 



extension of a growth model to complex sili- 
cate melts, Am. Mineral., 73, 982-992, 1988 
(G.L. Paper 2087). 

Mysen, B. O., and D. Virgo, Redox equilibria, 
structure, and properties of Fe-bearing alumi- 
nosilicate melts: Relationships among tempera- 
ture, composition, and oxygen fugacity in the 
system Na 2 0-Al 2 3 -Si0 2 -Fe-0, Am. Mineral, 
74, 58-76, 1989 (G.L. Paper 2108). 

Mysen, B. O., Relations between structure, redox 
equilibria of iron, and properties of magmatic 
liquids, in Advances in Physical Geochemistry, 
L. L. Perchuk and I. Kushiro, eds., Springer- 
Verlag, New York, in press. 

Mysen, B. O., Volatiles in magmatic liquids, in 
Progress in Physico-Chemical Petrology (D. S. 
Korzhinskii Memorial Volume), L. L. Perchuk, 
ed., Cambridge University Press, New York, in 
press. 

Mysen, B. O., Distribution of aluminum between 
structural units in peralkaline aluminosilicate 
melts in the systems Li 2 0-Al 2 3 -Si0 2 , Na 2 0- 
Al 2 3 -Si0 2 and K 2 0-Al 2 3 -Si0 2 , Am. 
Mineral., In press. 

Powell, E. N., A. Logan, R. J. Stanton, Jr., D. J. 
Davies, and P. E. Hare, Estimating time-since- 
death from the free amino acid content of the 
mollusc shell: A measure of time averaging in 
modern death assemblages? Description of the 
technique, Palaios, 4, 16-31, 1989 (G.L. Paper 
2140; no reprints available for distribution). 

Prewitt, C. T., Annual Report of the Director of the 
Geophysical Laboratory, Carnegie Instn. Wash- 
ington, 1987-1988, Geophysical Laboratory, 
Washington, D.C., 1988 (G.L. Paper 2102). 

Richet, P., J. A. Xu, and H. K. Mao, Quasi- 
hydrostatic compression of ruby to 500 Kbar, 
Phys. Chem. Minerals , 16, 207-21 1, 1988 (G.L. 
Paper 2071). 

Richet, P., H. K. Mao, and P. M. Bell, Static 
compression and equation of state of CaO to 
1.35 Mbar, J. Geophys. Res., 93, B12, 15279- 
15288, 1988 (G.L. Paper 2099). 

Richet, P., H. K. Mao, and P. M. Bell, Bulk moduli 
of magnesiowustites from static compression 
measurements, /. Geophys. Res., 94, B3, 3037- 
3045, 1989 (G.L. Paper 2109). 

Ross, N. L., and A. Navrotsky, Study of the 
MgGe0 3 polymorphs (orthopyroxene, clinopy- 
roxene, and ilmenite structures) by calorimetry, 



spectroscopy and phase equilibria, Am. Min- 
eral., 73, 1355-1365, 1988 (No reprints avail- 
able from Geophysical Laboratory). 

Ross, N. L., and R. M. Hazen, Single crystal X-ray 
diffraction study of MgSi0 3 perovskite from 77 
to 400 K, Phys. Chem. Minerals, 16, 415-420, 
1989 (G.L. Paper 2119). 

Ross, N. L., J. Ko, and C. T. Prewitt, A new phase 
transition in MnTi0 3 : LiNb0 3 perovskite 
structure, Phys. Chem. Minerals, in press (G.L. 
Paper 2137). 

Rumble, D., HI, and C. P. Chamberlain, Graphite 
vein deposits of New Hampshire, in New Eng- 
land Intercollegiate Geological Conference 
Guidebook, 80th Annual Meeting, W. A. Both- 
ner, ed., University of New Hampshire, Dur- 
ham, NH, pp. 241-255, 1988 (G.L. Paper 2104; 
no reprints available for distribution). 

Rumble, D., in, C. P. Chamberlain, D. K. Zeitler, 
and B. Barriero, Hydrothermal graphite veins 
and Acadian granulite facies metamorphism, 
New Hampshire, USA, in Fluid Movements, 
Element Transport, and the Composition of the 
Crust, D. Bridgwater, ed., Kluwer Academic 
Publ., Dordrecht, in press (G.L. Paper 2128). 

Schiffries, C. M., Liquid- absent fluid inclusions 
and phase equilibria in the system CaCl 2 - NaCl 
- H 2 0, Geochim. Cosmochim. Acta, in press, 
1989. 

Schiffries, C. M., and D. M. Rye, Stable isotope 
systematics of the Bushveld Complex: I. Con- 
straints in magmatic processes in layered intru- 
sions, Am. /. Sci., in press, 1989. 

Schiffries, C. M., amd D. M. Rye, Stable isotope 
systematics of the Bushveld Complex: II. Con- 
straints on hydrothermal processes in layered 
intrusions, Am. J. Sci., in press, 1989. 

Sharp, Z. D., G. R. Helffrich, S. R. Bohlen, andE. 
J. Essene, The stability of sodalite in the system 
NaAlSi0 4 -NaCl, Geochim. Cosmochim. Acta, 
in press (G.L. Paper 2133). 

Sheng, Z. Z., A. M. Hermann, D. C. Vier, S. 
Schultz, S. B. Oseroff, D. J. George, and R. M. 
Hazen, Superconductivity in the Tl-Sr-Ca-Cu- 
O system, Phys. Rev. B, 38, 7074-7076, 1988 
(G.L. Paper 2103) 

Spear, F. S., D. D. Hickmott, and J. Selverstone, 
The metamorphic consequences of thrust em- 
placement, Fall Mountain, New Hampshire, 
Geol.Soc. Am. Bull., in press (No reprints will be 



GEOPHYSICAL LABORATORY 



203 



available from Geophysical Laboratory). 

Stafford, T. W., Jr., and R. A. Tyson, Accelerator 
radiocarbon dates on charcoal, shell, and human 
bone from the Del Mar site, California, Am. 
Antiq., 54, 389-395, 1989 (G.L. Paper 2125). 

Stafford, T. W., Jr., Extraction of organic fractions 
from fossil bones for radiocarbon dating and 
stable isotope analysis, J. Archaeol. Sci. , in 
press. 

Stathoplos, Linda, and P. E. Hare, Amino acids in 
planktonic foraminifera: Are they phylogeneti- 
cally useful? in Origin, Evolution, and Modern 
Aspects of Biomineralization in Plants and 
Animals, Proceedings of the Fifth International 
Symposium on Biomineralization, R. E. Crick, 
ed., Plenum Publ. Co., New York, in press. 

Ulmer, P., The dependence of the Fe 2+ -Mg cation- 
partitioning between olivine and basaltic liquid 
on pressure, temperature, and composition: An 
experimental study to 30 kbars, Contrib. Min- 
eral. Petrol, 101, 261-273, 1989.(G.L. Paper 
2139). 



Velinsky, D. J., J. R. Pennock, J. H. Sharp, L. A. 
Cifuentes, and M. L. Fogel, Determination of 
the isotopic composition of ammonium-nitro- 
gen at the natural abundance level from estuar- 
ine waters, Marine Chemistry, in press (G.L. 
Paper 2126). 

Wood, B. J., and D. Virgo, Upper mantle oxida- 
tion state: Ferric iron contents of lherzolite spi- 
nels by 57 Fe Mossbauer spectroscopy and resul- 
tant oxygen fugacities, Geochim. Cosmochim. 
Acta, 53, 1277-1291, 1989 (G.L. Paper 2121). 

Yoder, H. S., Jr., The great basaltic "floods," 
South African J. Geol., 91 (Alex. L. du Toit 
Memorial Lectures, No. 20), 139-156, 1988 
(G.L. Paper 2085). 

Zhang, Y. G., and J. D. Frantz, Experimental 
determination of the compositional limits of 
immiscibility in the system CaClj-Hj-O-COj at 
high temperatures and pressures using synthetic 
fluid inclusions, Chem. Geol, 74, 289-308, 1989 
(G.L. Paper 2107). 



204 



CARNEGIE INSTITUTION 



Personnel 



July 7, 1988 to June 30, 1989 



Research Staff 



Research Associates 



Charles T. Prewitt, Director 
Peter M. Bell 1 
Francis R. Boyd, Jr. 
Larry W. Finger 
Marilyn L. Fogel 
John D. Frantz 
P. Edgar Hare 
Robert M. Hazen 
Russell J. Hemley 
Thomas C. Hoering 
T. Neil Irvine 
Ho-Kwang Mao 
Bjorn O. My sen 
Douglas Rumble III 
David Virgo 
Hatten S. Yoder, Jr. 



David Velinsky 
Nick Oliver 5 



Postdoctoral Fellows 

Ross Angel 6 
Luis Cifuentes 7 
Donald Hickmott 
Andrew P. Jephcoat 8 
Yasuhiro Kudoh 9 
Robert W.Luth 10 
Nancy Ross 11 
Craig Schiffries 
Zachary Sharp 12 
Peter Ulmer 13 
Yi-gang Zhang 14 



Keck Earth Sciences Research Scholar 



i'112 



Gregory E. Muncill 



Postdoctoral Associates 

Liang-chen Chen 3 
Ming Sheng Peng 4 
Jinfu Shu 
Ellen K. Wright 



Predoctoral Fellows 

Constance Bertka 
Yingwei Fei 
Matthew Hoch 16 
Kevin Mandernack 17 
Linda Stathoplos 18 



Research Interns 
Brad Herman 19 



GEOPHYSICAL LABORATORY 



205 



Virginia Mattingly 20 
William Merrill 21 



Supporting Staff 

Andrew J. Antoszyk, Shop Foreman 
Bobbie Brown, Instrument Maker 22 
Stephen D. Coley, Sr., Instrument Maker 
Roy R. Dingus, Instrument Maker 23 
David J. George, Electronics Technician 
Christos Hadidiacos, Electronics Engineer 
Marjorie E. Imlay, Assistant to the Director 
Lavonne Lela, Librarian 
Harvey J. Lutz, Technician 
Mabel B. Mattingly, Department Secretary 
Mary Moore, Word Processor Operator — 

Receptionist 
Lawrence B. Patrick, Maintenance Super- 
visor 
David Ratliff, Jr., Maintenance Technician 
Pedro J. Roa, Maintenance Technician 
Susan Schmidt, Coordinating Secretary 
John M. Straub, Business Manager 
Mark Vergnetti, Instrument Maker 24 



Visiting Investigators 

Ronald E. Cohen, Naval Research Labora- 
tory 

David H. Freeman, University of Mary- 
land 

Jaidong Ko, SUNY, Stony Brook 

James Kubicki, Yale University 



Julie Kokis, George Washington Univer- 
sity 
Yali Su, University of Maryland 
Bradley Tebo, Scripps Institution of Ocean- 
ography 
Noreen Tuross, Smithsonian Institution 
Donald J.Weidner, SUNY, Stony Brook 



Emeritus 

Hatten S. Yoder, Jr., Director Emeritus 
Felix Chayes, Petrologist Emeritus 



Retired June 30, 1989. 

2 Expiration of Keck Fellowship Arpil 30, 1989. 

3 To June 30, 1989. 

4 FromJuly 1, 1988. 

5 ToJune 1,1989. 

6 To September 30, 1988. 

7 To September 1, 1988. 

8 To February 28, 1989. 

9 From September 1, 1988. 

10 To September 30, 1988. 

n To October 30, 1988. 

12 To June 30, 1989. 

13 To September 30, 1988. 

14 From July 1, 1988 to June 30, 1989. 

15 From July 1, 1988 to June 30, 1989. 

16 FromJuly 1, 1988. 

17 From July 1,1988. 

18 To June 30, 1989. 

19 FromJunel, 1989. 

20 FromJune 1, 1989. 

21 FromJune 1,1989. 

22 FromJuly 1, 1988. 

23 Transferred to D.T.M. February 1989. 

24 From April 1, 1989.