Ultra-High Pressure Mineralogy - Physics and Chemistry of the Earth's Deep Interior

688 Pages·1998·465.194 MB·English

by  Russell J Hemley, Ed.

ULTRAHIGH-PRESSURE
MINERALOGY
Physics and Chemistry of the Earth's Deep Interior
Russell J. Hemley, Editor
Geophysical Laboratory
Carnegie Institution of Washington
Washington, DC
This volume was supported in part by
The Center for High Pressure Research
A National Science Foundation
Science and Technology Center
Paul H. Ribbe, Series Editor
Department ofGeological Sciences
Virginia Tech, Blacksburg, Virginia
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COPYRIGHT 1998
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REVIEWS IN MINERALOGY
(Formerly: SHORT COURSE NOTES)
ISSN 0275-0279
Volume 37
ULTRAHIGH-PRESSURE MINERALOGY:
Physics and Chemistry of the Earth's Deep Interior
ISBN 0-939950-48-0
ADDITIONAL COPIES ofthisvolume aswellasothers in
this series maybe obtained atmoderate costfrom:
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ULTRAHIGH-PRESSURE MINERALOGY:
Physics and Chemistry of the Earth's Deep Interior
FOREWORD
This volume was edited by Russell I. Hemley inpreparation for ashort course bythe
same title, organized together with Ho-kwang Mao and sponsored by the Mineralogical
Society of America, December 4-6, 1998onthecampus oftheUniversity of California at
Davis. This is number 37 in the Reviews in Mineralogy series, begun in 1974 and
continuing with vigor, at least into the near future, with volumes on "Uranium
Mineralogy and Geochemistry," on "Sulfate Mineralogy," and on "Natural Zeolites"
planned for 1999 and 2000. Volume 36 (1056 pagesl), "Planetary Materials," edited by
1.1. Papike, appeared earlier this year, and it is certainly not unrelated to the subject of
this volume on the physics and chemistry of the deep interior of one of the planets. Rus
Hemley has highlighted Reviews in Mineralogy Volumes 14, 18, 20 and 29 as
particularly relevant tothe subject matter of"Ultrahigh-Pressure Mineralogy."
Pau[J{. 'l?j66e
Department ofGeological Sciences
Virginia Tech
Blacksburg, VA November 1998
PREFACE
High-pressure mineralogy has historically been avital part of the geosciences, but it
is only in the last few years that the field has emerged as adistinct discipline as aresult
of extraordinary recent developments in high-pressure techniques. The domain of
mineralogy is now no less than the whole Earth, from the deep crust to the inner
core-the entire range of pressures and temperatures under which the planet's
constituents were formed or now exist. The primary goal of this field is to determine the
physical and chemical properties of materials that underlie and control the structural and
thermal state, processes, and evolution oftheplanet. New techniques that have come 'on-
line' within the last couple of years make itpossible to determine such properties under
extreme pressures and temperatures with an accuracy and precision that rival measure-
ments under ambient conditions. These investigations of the behavior of minerals under
extreme conditions link the scale of electrons and nuclei with global processes of the
Earth and other planets in the solar system. It is in this broad sense that the term
'Ultrahigh-Pressure Mineralogy' is used for the title of this volume of Reviews in
Mineralogy.
This volume sets out to summarize, in a tutorial fashion, knowledge in this rapidly
developing area of physical science, the tools for obtaining that knowledge, and the
prospects for future research. The book, divided into three sections, begins with an
overview (Chapter 1)of the remarkable advances in the ability to subject minerals-not
only aspristine single-crystal samples but also complex, natural mineral assemblages-to
extreme pressure-temperature conditions in the laboratory. These advances parallel the
development of an arsenal of analytical methods for measuring mineral behavior under
those conditions. This sets the stage for section two (Chapters 2-8) which focuses on
high-pressure minerals in their geological setting as afunction of depth. This top-down
approach begins with what we know from direct sampling of high-pressure minerals and
rocks brought to the surface to detailed geophysical observations of the vast interior. The
third section (Chapters 9-19) presents the material fundamentals, starting from properties
of achemical nature, such as crystal chemistry, thermochemistry, element partitioning,
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PREFACE
and melting, and moving toward the domain of mineral physics such as melt properties,
equations of state, elasticity, rheology, vibrational dynamics, bonding, electronic
structure, and magnetism.
The Review thus moves from the complexity of rocks to their mineral components
and finally to fundamental properties arising directly from the play of electrons and
nuclei. The following themes crosscut itschapters.
Composition of the mantle and core. Our knowledge of the composition of the
Earth inpart is rooted in information oncosmochemical abundances of the elements and
observations from the geological record. But an additional and essential part of this
enterprise is the utilization of the growing information supplied by mineral physics and
chemistry in detailed comparison with geophysical (e.g. seismological) observations for
the bulk of the planet. There is now detailed information from a variety of sources
concerning crust-mantle interactions in subduction (Liou et aI., Chapter 2; Mysen et aI.,
Chapter 3). Petrological, geochemical, and isotope studies indicate a mantle having
significant lateral variability (McDonough and Rudnick, Chapter 4). The extent of
chemical homogeneity versus layering with depth in the mantle, aquestion as old as the
recognition of the mantle itself, is afirst-order issue that threads its way throughout the
book. Agee (Chapter 5) analyzes competing models interms ofmineral physics, focusing
on the origin of seismic discontinuities in the upper mantle. Bina (Chapter 6) examines
theconstraints forthe lower mantle, with particular emphasis given tothe variation ofthe
density and bulk sound velocity with depth through to the core-mantle boundary region
(Jeanloz and Williams, Chapter 7). Stixrude and Brown (Chapter 8) examine bounds on
the composition ofthecore.
Mineral elasticity and the link to seismology. The advent of new techniques is
raising questions of the mineralogy and compositionofthe deep interior to anew level.
As aresult of recent advances in seismology, the depth-dependence of seismic velocities
and acoustic discontinuities have been determined with high precision, lateral
heterogeneities in the planet have been resolved, and directional anisotropy has been
determined (Chapters 6 and 7). The first-order problem of constraining the composition
and temperature as a function of depth alone is being redefined by high-resolution
velocity determinations that define lateral chemical or thermal variations. As discussed
by Liebermann and Li (Chapter IS), measurements of acoustic velocities can now be
carried out simultaneously at pressures that are an order of magnitude higher, and at
temperatures that are afactor oftwo higher, than those possible just afew years ago. The
tools are in hand to extend such studies to related properties of silicate melts (Dingwell,
Chapter 13).Remarkably, the solid inner core is elasticaiIy anisotropic (Chapter.8);with
developments in computational methods, condensed-matter theory now provides robust
and surprising predictions for this effect (Stixrude et aI., Chapter 19), and with very
recent experimental advances, elasticity measurements of core material at core pressures
can beperformed directly (Chapters 1and 15).
Mantle dynamics. The Earth is a dynamic planet: the rheological properties of
minerals define the dynamic flow and texture of material within the Earth. Measurement
of rheological properties at mantle pressures is a significant challenge that can now be
addressed (Weidner, Chapter 16). Deviatoric stresses down to 0.1 GPa to pressures
approaching 300 GPa can be quantified inhigh-pressure cells using synchrotron radiation
(Chapter 1). The stress levels are an appropriate scale for understanding earthquake
genesis, including the nature of earthquakes that occur at great depth in subducted slabs
(deep-focus earthquakes) as these slabs travel through the Earth's mantle. Newly
developed high-pressure, high-precision x-ray tools such as monochromatic radiation
with modern detectors with short time resolution and employing long duration times are
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PREFACE
now possible with third-generation synchrotron sources to study the rheology of deep
Earth materials under pressure (Chapter 1).
Fate of subducting slabs. One of the principal interactions between the Earth's
interior and surface is subduction of lithosphere into the mantle, resulting in arc
volcanoes, chemical heterogeneity in the mantle, as well as deep-focus earthquakes
(Chapters 2 and 3). Among the key chemical processes associated with subduction is the
role of water inthe recycling process (Prewitt and Downs, Chapter 9), which atshallower
levels is essential for understanding arc volcanism. Mass and energy transport processes
govern global recycling of organic and inorganic materials, integration of these
constituents in the Earth's interior, the evolution (chemically and physically) of
descending slabs near convergent plate boundaries, and the fate of materials below and
above the descending slab. Chapters 5 and 6 discuss the evidence for entrainment and
passage of slabs through the 670 km discontinuity, and the possibility of remnant slabs in
the anomalous D" region near the core-mantle boundary (Chapter 7). The ultimate fate of
the materials cycled to such depths may affect interactions at the core-mantle boundary
and may also hold clues to the initiation of diapiric rise. The evolution and fate of a
subducting slab can now be addressed by experimental simulation of slab conditions,
including in situ monitoring of a simulated slab in high-pressure apparatus in situ x-ray
and spectroscopic techniques. The chemistry of volatiles changes appreciably under deep
Earth conditions: they can be structurally bound under pressure (Prewitt and Downs,
Chapter 9).
Melting. Understanding pressure-induced changes in viscosity and other physical
properties of melts is crucial for chemical differentiation processes ranging from models
of the magma ocean in the Earth's early history to the formation of magmatic ore
deposits. (Chapter 13). Recent evidence suggests that melting may take place at great
depth in the mantle. Seismic observations of alow-velocity zone and seismic anisotropy
at the base of the mantle have given rise to debate about the existence of regions of
partial melt deep in the mantle (Chapter 7). Deep melting is also important for mantle
convection from subduction of the lithosphere to the rising of hot mantle plumes. Very
recent advances in determination of melting relations of mantle and core materials with
laser-heating techniques are beginning to provide accurate constraints (Shen and Heinz,
Chapter 12).Sometimes lost in the debate onmelting curves isthe fact that adecade ago,
there simply were no data for most Earth materials, only guesses and (at best)
approximate models. Moreover, it isnow possible to carry out in situ melting studies on
multi-cornponanr systems, including natural assemblages, to deep mantle conditions.
These results address whether or not partial melting is responsible for the observed
seismic anomalies atthe base ofthe mantle andprovide constraints for mantle convection
models (Chapter 7).
The enigma of the Earth's core. The composition, structure, formation, evolution,
and current dynamic state of the Earth's core is an area of tremendous excitement
(Chapter 8). The keys to understanding the available geophysical data are the material
properties of liquid and crystalline iron under core conditions. New synchrotron-based
methods and new developments in theory are being applied to determine all of the
pertinent physical properties, and in conjunction with seismological and geodynamic
data, to develop a full understanding of the core and its interactions with the mantle
(Chapter 7). There has been considerable progress in determining the melting and phase
relations of iron into the megabar range with new techniques (Chapter 12). Constraints
are also obtained from theory (Chapter 19). These results feed into geophysical models
for the outer and inner core flow, structural state, evolution, and the geodynamo.
Moreover, there is remarkable evidence that the Earth's inner core rotates at adifferent
rate than the rest ofthe Earth. This evidence inturn rests onthe observation that the inner
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PREFACE
core is elastically anisotropic, a subject of current experimental and theoretical study
from thestandpoint of mineral physics, asdescribed above.
The thermodynamic framework. Whole Earth processes must be grounded in
accurate thermodynamic descriptions of phase equilibria in multi-component systems, as
discussed byNavrotsky (Chapter 10).New developments inthis area include increasingly
accurate equations of state (Duffy andWang, Chapter 14)required for modeling ofphase
equilibria as well as for direct comparison with seismic density profiles through the
planet. Recent developments in in situ vibrational spectroscopy and theoretical models
provide ameans for independently testing available thermochemical data and ameans for
extending those data to high pressures and temperatures (Gillet et aI., Chapter 17).
Accurate determinations of crystal structures provide abasis for understanding thermo-
chemical trends (Chapter 9). Systematics for understanding solid-solution behavior and
element partitioning are now available, at least to the uppermost regions of the lower
mantle (Fei, Chapter 11).New measurements for dense hydrous phases are beginning to
provide answers to fundamental questions regarding their stability of hydrous phases in
the mantle (Chapters 3 and 9) and the partitioning of hydrogen and oxygen between the
mantle andcore (Chapter 8).
Novel physical phenomena at ultrahigh pressures. One ofthe key recent findings in
high-pressure research is the remarkable effect of pressure on the chemistry of the
elements, atconditions ranging from deep metamorphism of crustal minerals (Chapter 2)
to "contact metamorphism" at the core-mantle boundary (Chapter 7). Pressure-induced
changes in Earth materials represent forefront problems in condensed-matter physics.
New crystal structures appear and the chemistry of volatiles changes (Chapter 9).
Pressure-induced electronic transitions and magnetic collapse in transition metal ions
strongly affect mineral properties and partitioning of major, minor, and trace elements
(Chapter 11). Evidence for these transitions from experiment (Chapter 18) and theory
(Chapter 19) is important for developing models for Earth formation and chemical
differentiation. The conventional view of structurally and chemically complex minerals
ofthe crust giving way to simple, close-packed structures ofthe deep mantle and asimple
iron core isbeing replaced by anew chemical picture wherein dense silicates, oxides, and
metals exhibit unusual electronic and magnetic properties and chemistry. In the end, this
framework must dovetail with seismological observations indicating an interior of
considerable regional variability, both radially and laterally depending on depth (e.g.
Chapters 6and 7).
New classes of global models. Information concerning the chemical and physical
properties of Earth materials athigh pressures and temperatures is being integrated with
geophysical and geochemical data to create a more comprehensive global view of the
state, processes, and history of the Earth. In particular, models of the Earth's interior are
being developed that reflect the details contained in the seismic record but are bounded
by laboratory information onthe physics and chemistry ofthe constituent materials. Such
"Reference Earth Models" includes the development of reference data sets and modeling
codes. Tools that produce seismological profiles from hypothesized mineralogies
(Chapters 4 and 5) are now possible, as are tools for testing these models against
'reference' seismological data sets (Chapter 6). These models incorporate the known
properties of the Earth, such as crust and lithosphere structure, and thus have both an
Earth-materials and seismological orientation.
Other planets. The Earth cannot be understood without considering the rest of the
solar system. The terrestrial planets of our solar system share acommon origin, and our
understanding of the formation of the Earth is tied to our understanding of the formation
of its terrestrial neighbors, particularly with respect to evaluating the roles of
homogeneous and heterogeneous processes during accretion. As a result of recent
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PREFACE
developments in space exploration, as well as in the scope of future planetary missions,
we have new geophysical and geochemical data for the other terrestrial planets. Models
for the accretion history of the Earth can now be reevaluated in relation to this new data.
Experiments on known Earth materials provide the thermodynamic data necessary to
calculate the high-pressure mineralogy of model compositions for the interior of Mars
and Venus. Notably, the outer planets have the same volatile components as the Earth,
just different abundances. Studies of the outer planets provide both an additional
perspective on our own planet as well as a vast area of opportunity for application of
these newly developed experimental techniques (Chapter 1and 17).
New techniques in the geosciences. The utility of synchrotron radiation techniques
in mineralogy has exceeded the expectations of even the most optimistic. New
spectroscopic methods developed for high-pressure mineralogy are now available for
characterizing small samples from other types of experiments. For example, the same
techniques developed for insitu studies athigh pressures andtemperatures arebeing used
to investigate microscopic inclusions such ascoesite inhigh-pressure metamorphic rocks
(Chapter 2) and deep-mantle samples as inclusions in diamond (Chapter 3). With the
availability of a new generation of synchrotron radiation sources (Chapter 1) and
spectroscopic techniques (Chapter 17), a systematic application of new methods,
including microtomographic x-ray analysis of whole rock samples, is now becoming
routinely possible.
Contributions in technology. Finally, there are implications beyond the geosciences.
Mineralogy has historically has led many to conceptual and technical developments used
in other fields, including metallurgy and materials science, and the new area of ultrahigh
pressure mineralogy continues this tradition. As pointed out in Chapter 1,many high-
pressure techniques have their origins in geoscience laboratories, and in many respects,
geoscience leads development of high-pressure techniques in physics, chemistry, and
materials science. New developments include the application of synthetic diamond for
new classes of 'large-volume' high-pressure cells. Interestingly, information on diamond
stability, including its metastable growth, feeds back directly on efforts to grow large
diamonds for the next generation of such high-pressure devices (Chapter 1). Micro-
analytical techniques, such as micro-spectroscopy and x-ray diffraction, developed for
high-pressure research are now used outside of this field ofresearch as well. The study of
minerals and mineral analogs under pressure is leading to new materials. As in the
synthesis ofdiamond itself, these same scientific approaches promise the development of
novel, technological materials.
A number of books have reviewed certain aspects of the material covered in this
volume. Although many are cited in the chapters, some of the key publications are listed
here. Among the most recent are the proceedings of the US-Iapan seminar on high-
pressure mineral physics, Properties ofEarth and Planetary Materials atHigh Pressures
and Temperatures, edited by M.H. Manghnani and T. Yagi [American Geophysical
Union, Washington, D.C., 1998], which contains numerous recent developments, and
earlier volumes in the series contain landmark papers in the field. Very recent
developments in high-pressure research are given in Review of High-Pressure Science
and Technology, Vol. 7,edited byM.Nakahara [Japan Society forHigh-Pressure Science
and Technology, Kyoto, 1998].T.I. Ahrens' Mineral Physics and Crystallography [AGU
Reference Shelf, Vol. 2,American Geophysical Union, Washington, D.C., 1995]contains
useful tabulations of data as well as introductions to both properties and techniques.
Equations of State of Solids for Geophysics and Ceramic Science, by O.L. Anderson
[Oxford University Press, New York, 1995]isanimportant recent resource.
Earlier books include the following. Previous volumes of Reviews of Mineralogy
provide useful pedagogic background, particularly Volume 14, Microscopic to
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PREFACE
Macroscopic, edited by S.W. Kieffer and A. Navrotsky; Volume 18, Spectroscopic
Methods, edited by F.C. Hawthorne; Volume 20,Modern Powder Diffraction, edited by
D.L. Bish and I.E. Post; and Volume 29, Silica, edited by P.I. Heaney et al. L.G. Liu and
W.A. Bassett [Elements, Oxides, Silicates, Oxford University Press, New York, 1986]
provided an encyclopedic overview of the high P-T properties of mantle and core
materials generally in the sub-megabar range (mostly <30 GPa), summarizing data to
1986. D.L. Anderson's Theory of the Earth [Blackwell, Boston, 1989] and A.E.
Ringwood's earlier Composition and Petrology of the Earth's Mantle [McGraw-Hill,
New York, 1975] defined integrated views of thedeep interior with information available
at that time. The classic, early papers in the field have been compiled by T.I. Shankland
and J.D. Bass in Elastic Properties and Equations of State [American Geophysical
Union, Washington, D.C., 1988].
Finally, I thank the following people for their help with this project. As is evident,
this is the product of 34 authors, all very busy people who put aside other tasks to
complete their chapters, sometimes with ridiculous deadlines. I am indebted toDave Mao
for much help with the organization and planning. Gordon Brown suggested the idea, and
was persistent in his encouragement. The effort was supported by the NSF Center for
High Pressure Research; itsstaff and especially the members of itsExecutive Committee,
Don Weidner (Director), Charlie Prewitt, Bob Liebermann, and Alex Navrotsky,
contributed to many aspects of the project. Dave Mao, Martin Wilding, and Alex
Navrotsky helped with the short course. A number of additional people contributed
immeasurably incompleting the volume: Steve Gramsch, James Badro, Viktor Struzhkin,
Maddury Somayazulu, Merri Wolf, and Amanda Davis. And last, but actually first, I
thank Paul Ribbe, who manages to put together these volumes with seeming
effortlessness, uniform excellence, andever good cheer, year after year after year.
~usse[[J.j{em[ey
Geophysical Laboratory
Centerfor High Pressure Research
Carnegie Institution of Washington
Washington, DC November 1998
V111
Table of Contents
1 NEW WINDOWS ONTHE EARTH'S DEEP INTERIOR
Ho-kwang Mao, R. J. Hemley
INTRODUCTION 1
~~~:~c~F~~~ls:~~fo~~~~~~:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::~
New opportunities and beyond 3
PRESSURE AND TEMPERATURE. .4
~:~~-~~~~~~.~~~~c.~~~:~~.~:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::j:':i::::::::::
Variable temperature 15
HIGH-PRESSURE MINERAL PHYSICS AND CHEMISTRy 18
Quenching high P-T samples 18
In situ probes at high pressure and variable temperature 18
New opportunities with synchrotron radiation 21
CONCLUDING PROLEGOMENON 25
ACKNOWLEDGMENTS 26
REFERENCES 28
2 HIGH-PRESSURE MINERALS FROM DEEPLY SUBDUCTED
METAMORPHIC ROCKS
J.G. Liou, R. Y.Zhang, W. G. Ernst, D. Rumble III, S. Maruyama
INTRODUCTION 33
DEFINITION AND poT REGIMES FOR VHP METAMORPHISM 34
GLOBAL DISTRIBUTION OF VHP METAMORPHIC TERRANES 36
The Dora Maira Massif, Western Alps, 35 Ma .4l
The Kokchetav Massif, Northern Kazakhstan, 540-530 Ma .41
The Sulu-Dabie Terrane, East-Central China, 210-240 Ma .42
The Western Gneiss Region, Norway, 408-425 Ma .42
DESCRIPTION OF VHP ROCKS .44
Eclogites from East-Central China .44
Garnet peridotites .44
Metasediments .47
GEOCHEMICAL CHARACTERISTICS-EXAMPLES FROM CHINA .47
Diamond 52
VHP HYDROUS SILICATES 55
Phengitic mica 55
Zoisite and epidote 57
Talc 59
Ti-Clinohumite 62
Nyboite and glaucophane 62
Discussion 63
CHIEFLY DABIE-SULU VHP CARBONATE PHASES 65
Magnesite 65
Dolomite 67
Calcite pseudomorphs after aragonite 69
Phase relations 69
EXSOLUTION LAMELLAE IN DABIE-SULU AND OTHER ROCKS 70
Ilmenite rods in olivine 70
Magnetite lamellae in olivine and clinohumite 73
Ilmenite rods in clinopyroxene 75
K-feldspar lamellae in clinopyroxene 75
Silica rods in omphacite and clinopyroxene 78
Monazite lamellae in apatite 79
OTHER UNUSUAL MINERALS 79
CONCLUSIONS 83
ACKNOWLEDGMENTS 85
REFERENCES················ 85
IX
3
THE UPPER MANTLE NEAR CONVERGENT PLATE BOUNDARIES
B. O. Mysen, P. Ulmer, J.Konzett, M. W. Schmidt
INTRODUCTION 97
SEISMIC DEFINITION OF SUBDUCTION 99
NATURAL EXAMPLES OF THE UPPER MANTLE
NEAR CONVERGENT PLATE BOUNDARIES 99
Accretionary subduction complexes 102
High and very high pressure terranes 102
Peridotite massifs 103
Upper mantle xenoliths 104
Natural evidence for the role of H,O in subduction zones 104
Metasomatically altered xenoliths 105
H,O content of arc magmas and melt inclusions in arc-derived minerals 106
Water contents inferred from experimental phase equilibria 106
Oxygen fugacity in the mantle near convergent plate boundaries 107
PHASE RELATIONS AMONG METASEDIMENTS, GABBRO,
AND ULTRAMAFIC COMPOSITIONS NEAR SUBDUCTION ZONES I08
Phase relations in metabasalt, basalt and metasediments 109
Phase relations in ultramafic compositions 110
Phase relations in mantle compositions with additional components 116
H,O in nominally anhydrous minerals 120
WATER IN PERIDOTITE 120
DENSE HYDROUS MAGNESIUM SILICATES (DHMS) 122
EXPERIMENTAL STUDIES OF METASOMATIC ALTERATION
OF THE MANTLE WEDGE 123
Materials transport-silicate solubility in aqueous solutions 123
Silica enrichment and mineralogical alteration during flushing of the mantle
above subducting slabs 124
Phase relations among K-rich, hydrous phases
-results of metasomatism of peridotite? 125
Phase relations in K,O-Na,O-CaO-MgO-AI,03-SiO,-H,O (KNCMASH) 127
Phase relations in the natural lherzolite system 129
Hydrous potassic phase stability in subduction zone settings 131
CONCLUDING REMARKS 131
REFERENCES 132
4
MINERALOGY AND COMPOSITION OF THE UPPER MANTLE
W. F. McDonough, R. L. Rudnick
INTRODUCTION 139
ROCKS OF THE UPPER MANTLE 139
Peridotites 140
Mafic rocks l51
Inclusions in diamonds 152
THE SAMPLES 153
Orogenic massifs 153
Mantle xenoliths 154
Oceanic peridotites 157
A MODEL COMPOSITION FOR THE UPPER MANTLE 158
ACKNOWLEDGMENTS 159
REFERENCES 159
5 PHASE TRANSFORMATIONS AND SEISMIC STRUCTURE
IN THE UPPER MANTLE AND TRANSITION ZONE
C. B. Agee
INTRODUCTION 165
OLIVINE AND THE Mg,SiO.-Fe,SiO 166
x