ALBERT

Beschreibung / Inhaltsverzeichnis: Unlike sedimentation and volcanism, active metamorphism is not directly observable. Metamorphic petrologists therefore must infer what constitutes the process of metamorphism by examining the products of metamorphic events. The purpose of this volume is to review the use of a powerful probe into metamorphic process: mineral assemblages and the composition of minerals. Put very simply, this volume attempts to answer the question: "What can we learn about metamorphism through the study of minerals in metamorphic rocks?" It is not an encyclopedic summary of metamorphic mineral assemblages; instead it attempts to present basic research strategies and examples of their application. Moreover, in order to limit and unify the subject matter, it concentrates on the chemical aspects of metamorphism and regrettably ignores other important kinds of studies of metamorphic rocks and minerals conducted by structural geologists, structural petrologists, and geophysicists. An overview of the chemical aspects of modern metamorphic petrology is timely because it brings together three areas of research which have reached maturity only in the last 25 years: (1) chemical analysis of minerals by microanalytical techniques; (2) application of reversible and irreversible thermodynamics to petrology; and (3) laboratory phase equilibrium experiments involving metamorphic minerals. Chemical thermodynamics is the formal mathematical framework which links measurable variables (i.e., mineral composition) to metamorphic variables which cannot be directly measured (i.e., chemical potential, pressure, temperature, fluid composition). Results of phase equilibrium studies involving metamorphic minerals at metamorphic pressures and temperatures (together with calorimetric and heat capacity data) permit these links to be quantitative. It is the union of analysis, theory, and laboratory experiment which allows the modern metamorphic petrologist to make sophisticated inferences about conditions of metamorphism and the factors which control these conditions. This union is the principal subject of the volume. The volume is organized much in the same way that one might approach a research project involving metamorphic rocks. Initially those chemical components which characterize the composition of minerals in the assemblages under consideration must be identified. In addition, the reaction relationships among components must be systematically characterized. The reaction relationships rationalize the prograde changes in mineralogy which rocks experience during metamorphism and, furthermore, form the basis for extracting information about intensive variables during metamorphism. Chapters 1-3 summarize strategies for identifying components in metamorphic minerals and for formulating chemical reactions among them. Chapter 4 develops, from classical thermodynamics, those equations which can be used to explicitly relate mineral composition to other variables of interest such as metamorphic pressure, temperature, and chemical potentials of volatile species in any metamorphic fluid phase. Chapter 5 is specifically devoted to geologic thermometry and barometry, and Chapter 6 reviews strategies for the determination of metamorphic fluid composition. Petrologists should not be content with simply calculating and cataloguing values of metamorphic pressure, temperature, and fluid composition. In order to characterize the process of metamorphism, we must try to understand what controls these measured values and the manner in which they evolve during metamorphism both as rocks are heated and buried and as rocks are cooled and uplifted. Chapter 7 explores how two concepts buffering and infiltration -- can act as general controls on fluid composition, mineral composition, and temperature during metamorphic events. In addition, this chapter develops procedures which can be used to evaluate the relative importance of buffering versus infiltration in the evolution of specific rocks. Chapter 8 demonstrates how integrated petrologic and stable isotope studies may be used, in principle, to reconstruct the prograde pressure-temperature-infiltration history of metamorphic rocks. Chapter 9 discusses the use of mineral inclusions and compositional zoning in minerals in evaluating both prograde and post-peak P-T paths of certain mineral assemblages. In addition, compositional zoning is considered as an indicator of cooling rates during post-peak uplift. Thus between Chapter I and Chapter 9 we go from the first step of describing a metamorphic mineral assemblage through a reconstruction of the physical state in which it crystallized to an analysis of what factors controlled that state and how it evolved with time. The contents of the volume reflect two themes which underlie modern research in metamorphic petrology. The first of these is an ever-increasing emphasis on the quantitative characterization of metamorphism. Current research less involves description and classification than calculation of intensive and extensive variables attained during metatamorphism. This volume hopefully serves as a text in the quantitative study of the chemical aspects of metamorphism. As a corollary to the emphasis placed on quantitative methods, we can see increasing attention paid to analytical as opposed to graphical treatments of mineral equilibria. Graphical representations, while undeniably valuable, can consider two (or at most three) independent variables. Analytical treatment of mineral equilibria is attractive because it rigorously keeps track of all variables pertinent to an equilibrium assemblage. The second theme is an increasing interest in the dynamics of metamorphism. Metamorphism obviously is not a static process -- it involves changes in pressure, temperature, mineral and fluid composition, etc. The classical static approach to quantitative metamorphic petrology, though, searches for the physical conditions of a unique pressure-temperature state which a rock or mineral assemblage records. Mineral equilibria are used to estimate single values of pressure, temperature, and fluid composition -- a sort of snapshot of what conditions were like. If mineral assemblages indeed represent a fossilized metamorphic state, then calculated P, T, Xi' however, simply represent a single point along the P-T-Xi-time path which a rock followed during metamorphism. Chapters 2, 7, 8, and 9 reflect an increasing interest among petrologists in the entire P-T-Xi-time path (or at least in more than one point along it). We can expect to see less satisfaction in the future with the snapshot model of metamorphism and more effort devoted to characterizing metamorphism as a dynamic process. Thus the volume not only summarizes time-honored current practices in quantitative metamorphic petrology, but hopefully also identifies some paths which may be followed in the future.

Beschreibung / Inhaltsverzeichnis: The development of modern isotope geochemistry is without doubt attributed to the efforts, begun in the 1930's and 1940's, of Harold Urey (Columbia University and the University of Chicago) and Alfred O.C. Nier (University of Minnesota). Urey provided the ideas, theoretical foundation, the drive, and the enthusiasm, but none of this would have made a major impact on Earth Sciences without the marvelous instrument developed by Nier and later modified and improved upon by Urey, Epstein, McKinney, and McCrea at the University of Chicago. Harold Urey's interest in isotope chemistry goes back to the late 1920's when he and I.I. Rabi returned from Europe and established themselves at Columbia to introduce the then brand-new concepts of quantum mechanics to students in the United States. Urey, of course, rapidly made an impact with his discovery of deuterium in 1932, the 'magical' year in which the neutron and positron were also discovered. Urey followed up his initial important discovery with many other experimental and theoretical contributions to isotope chemistry. During this period, Al Nier developed the most sophisticated mass spectrometer then available anywhere in the world, and made a series of surveys of the isotopic ratios of as many elements as he could. Through these studies, which were carried out mainly to obtain accurate atomic weights of the various elements, Nier and his co-workers clearly demonstrated that there were some fairly large variations in the isotopic ratios of the lighter elements. However, the first inkling of a true application to the Earth Sciences didn't come until 1946 when Urey presented his Royal Society of London lecture on 'The Thermodynamic Properties of Isotopic Substances' (now a classic paper referenced in most of the published papers on stable isotope geochemistry). With the information discovered by Nier and his co-workers that limestones were about 3 percent richer in 18O than ocean water, and with his calculations of the temperature coefficient for the isotope exchange reaction between CaCO3 and H2O, Urey realized that it might be possible to apply these concepts to determining the paleotemperatures of the oceans. Urey was never one to overlook important scientific problems, regardless of the field of scientific inquiry involved. In fact, he always admonished his students to 'work only on truly important problems!' Urey, then a Professor at the University of Chicago, decided to take a hard look into the experimental problems of developing an oxygen isotope paleotemperature scale. Although the necessary accuracy had not yet been attained, the design of the Nier instrument seemed to offer a good possibility, with suitable modifications, of making the kinds of precise measurements necessary for a sufficiently accurate determination of the 18O/16O ratios of both CaCO3 (limestone) and ocean water. Enormous efforts would be required to do this, because even if all the mass spectrometric problems could be solved, every analytical and experimental procedure would have to be invented from scratch, including the experimental calibration of the temperature coefficient of the equilibrium fractionation factor between calcite and water at low temperatures. To carry out this formidable study, Urey gathered around himself a remarkable group of students, postdoctoral fellows, and technicians, as well as his paleontologist colleague Heinz Lowenstam. With Sam Epstein at the center of the effort and acting as the principal driving force, the rest, as they say, 'is history.' The marvelous nature of the Nier-Urey mass spectrometer is attested to by the fact that the basic design is still being used, and that there are now hundreds of laboratories throughout the world where this kind of work is being done. For example, the original instrument built by Sam Epstein and Chuck McKinney at Caltech in 1953 is still in use and has to date produced more than 90,000 analyses. University, government, and industrial laboratories have found these instruments to be an indispensable tool. Enormous and widely varying application of the original concepts have been made throughout the whole panoply of Earth, Atmospheric, and Planetary Sciences. In the present volume we concentrate on an important sub-field of this effort. That particular sub-field was inaugurated in Urey's laboratories at Chicago by Peter Baertschi and Sol Silverman, who developed the fluorination technique for extracting oxygen from silicate rocks and minerals. This technique was later refined and improved in the late 1950's by Sam Epstein, Hugh Taylor, Bob Clayton, and Toshiko Mayeda, and has become the prime analytical method for studying the oxygen isotope composition of rocks and minerals. The original concepts and potentialities of high-temperature oxygen isotope geochemistry were developed by Samuel Epstein and his first student, Bob Clayton. Also, Bob Clayton, A.E.J. Engel, and Sam Epstein carried out the first application of these techniques to the study of ore deposits. The first useful experimental calibrations of the high-temperature oxygen isotope geothermometers quartz-calcite-magnetite-H2O were carried out initially by Bob Clayton, and later with his first student Jim O'Neil. In the meantime, Sam Epstein and his second student, Hugh Taylor, had begun a systematic study of 18O/16O variations in igneous and metamorphic rocks, and were the first to point out the regular order of 18O/16O fractionations among coexisting minerals, as well as their potential use as geochemical tracers of petrologic processes. During this period, a parallel development of sulfur isotope geochemistry was being carried out by Harry Thode and his group at McMaster University in Canada. They developed all the mass spectrometric and extraction techniques for this element, and also provided the theoretical and experimental foundation for understanding the equilibrium and kinetic isotope chemistry of sulfur. Starting from these beginnings, most of which took place either at the University of Chicago, Caltech, or McMaster University (but also with important input from Irving Friedman's laboratory at the U.S. Geological Survey, from Athol Rafter's laboratory in New Zealand, and from Columbia, Penn State, and the Vernadsky Institute in Moscow), there followed during the decades of the late 60's, 70's, and early 80's the development and maturing of the sub-field of high-temperature stable isotope geochemistry. This discipline is now recognized as an indispensable adjunct to all studies of igneous and metamorphic rocks and meteorites, particularly in cases where fluid-rock interactions are a major focus of the study. The twin sciences of ore deposits and the study of hydrothermal systems, both largely concerned with such fluid-rock interactions, have been profoundly and completely transformed. Virtually no issue of Economic Geology now appears without 3 or 4 papers dealing with stable isotope variations. No one writes papers on the development of the hydrosphere, hydrothermal alteration, ore deposits, melt-fluid-solid interactions, etc. without taking into account the ideas and concepts of stable isotope geochemistry. Although the present volume represents only a first effort to fill the need for a general survey of this sub-field for students and for workers in other disciplines, and although it is still obviously not completely comprehensive, it should give the interested student an idea of the present 'state-of-the-art' in the field. It should also provide an entry into the pertinent literature, as well as some understanding of the basic concepts and potential applications. Some thought went into the arrangement and choice of chapters for this volume. The first three chapters focus on the theory and experimental data base for equilibrium, disequilibrium, and kinetics of stable isotope exchange reactions among geologically important minerals and fluids. The fourth chapter discusses the primordial oxygen isotope variations in the solar system prior to formation of the Earth, along with a discussion of isotopic anomalies in meteorites. The fifth chapter discusses isotopic variations in the Earth's mantle and the sixth chapter reviews the variations in the isotopic compositions of natural waters on our planet. In Chapters 7, 8, 9 and 10, these isotopic constraints and concepts are applied to various facets of the origin and evolution of igneous rocks, bringing in much material on radiogenic isotopes as well, because these problems require a multi-dimensional attack for their solution. In Chapters 11 and 12, the problems of hydrothermal alteration by meteoric waters and ocean water are considered, together with discussions of the physics and chemistry of hydrothermal systems and the 18O/16O history of ocean water. Finally, in Chapters 13 and 14, these concepts are applied to problems of metamorphic petrology and ore deposits, particularly with respect to the origins of the fluids involved in those processes. It seems clear to us (the editors) that this sub-field of stable isotope geochemistry can only grow and become even more pertinent and dominant in the future. One of the most fruitful areas to pursue is the development of microanalytical techniques so that isotopic analyses can be accurately determined on ever smaller and smaller samples. Such techniques would open up vast new territories for exploitation in every aspect of stable isotope geochemistry. Exciting new methods have recently been developed whereby a few micromoles of CO2 and SO2 can be liberated for isotopic analyses from polished sections of carbonates and sulfides by laser impact. There are also new developments in mass spectrometry like RIMS (resonance ionization mass spectrometry), Fourier transform mass spectrometry and the ion microprobe that offer considerable promise for these purposes. Stable isotope analyses of large-sized samples (even those that must be obtained by reactions of silicates with fluorinating reagents) have now become so routine and so rapid that they represent an 'easy' way to gather a lot of data in a hurry. In fact 'mass production' techniques for rapidly processing samples are starting to become prevalent, so much so that one of the biggest worries in the future may be that a flood of data will overwhelm us and outstrip our abilities to carefully define and carry out sampling strategies, as well as to think carefully and in depth about the data. An organized system of handling the D/H, 13C/12C, 15N/14N, 18O/16O, and 34S/32S data, and/or a computerized data base that could be manipulated and added to would be a useful path to follow in the future, particularly if it were integrated into a larger data base containing radiogenic isotope data, major- and trace-element analyses, electron microprobe data, x-ray crystallographic data, and petrographic data (particularly modal data on mineral abundances in the rocks).

Beschreibung / Inhaltsverzeichnis: This volume of was prepared in conjunction with the Mineralogical Society of America Short Course on Amphiboles and Other Hydrous Pyriboles, Fall, 1981. Had it not been split into two volumes, 9A and 9B, it would have resembled in some respects the Manhattan telephone directory (it is hoped, however, that the content is more readable and relevant to the geological sciences). The length of this collection of papers appears to result from a combination of phenomena. The amphiboles themselves must accept most of the blame: their structural complexity and resulting chemical variability and diversity of petrologic behavior preclude brief description. In addition, while some of these papers are relatively brief summaries of the published literature that easily and quickly can be consumed by students, others are exhaustive (and lengthy) discourses that may not be digestible in one sitting by even the most dedicated amphibole researcher. Finally, it appears that some geologists, probably with justification, love amphiboles so much that they would never have stopped writing had there been no publication deadline. The extremely short time between the preparation of papers and publication of Reviews in Mineralogy and the authors' intimate knowledge of their fields ensure that the papers reflect the very latest in research results. The rapid production of the "Reviews," however, inevitably results in a few errors that might be caught in a more leisurely publication process; the editors apologize for any such errors that are included in this volume. In addition, the sequence of presentation of papers reflects not only the editors' notions of order in the amphibole universe, but also somewhat the order in which papers were received. Although a collection of reviews of this sort cannot claim to give exhaustive coverage to all aspects of a topic, it is hoped that the papers presented here do review most of the important areas of active amphibole research. The papers have been split in a somewhat arbitrary fashion into Volume 9A, Amphiboles and Other Hydrous Pyriboles - Mineralogy, and Volume 9B, Amphiboles: Petrology and Experimental Phase Relations. Everyone is encouraged to purchase both volumes, however, because there is a hefty dose of petrology in 9A (witness the paper by Thompson, for example) and not a little mineralogy in 9B.