Petrogenesis of Metamorphic Rocks

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2 K. Bucher M. Frey Petrogenesis of Metamorphic Rocks 6th Edition Complete Revision of Winkler's Textbook With 93 Figures and 28 Tables Springer-Verlag Berlin Heidelberg GmbH

3 Professor Dr. Kurt Bucher Mineralogisch-Petrographisches Institut Albertstr. 23b D Freiburg im Breisgau Professor Dr. Martin Frey Mineralogisch-Petrographisches Institut Bernoullistr. 30 CH Basel ISBN DOI / ISBN (ebook) CIP data applied for This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer-Verlag Berlin Heidelberg GmbH. Violations are liable for prosecution under the German Copyright Law. Springer-Verlag Berlin Heidelberg 1994 Originally published by Springer-Verlag Berlin Heidelberg New York in 1994 The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Typesetting: Data conversion by Elsner & Behrens GmbH, Oftersheim SPIN: / Printed on acid-free paper

4 Preface Metamorphic rocks are one of the three classes of rocks. Seen on a global scale they constitute the dominant material of the Earth. The understanding of the petrogenesis and significance of metamorphic rocks is, therefore, a fundamental topic of geological education. There are, of course, many different possible ways to lecture on this theme. This book addresses rock metamorphism from a relatively pragmatic view point. It has been written for the senior undergraduate or graduate student who needs practical knowledge of how to interpret various groups of minerals found in metamorphic rocks. The book is also of interest for the non-specialist and non-petrologist professional who is interested in learning more about the geological messages that metamorphic mineral assemblages are sending, as well as pressure and temperature conditions of formation. The book is organized into two parts. The first part introduces the different types of metamorphism, defines some names, terms and graphs used to describe metamorphic rocks, and discusses principal aspects of metamorphic processes. Part I introduces the causes of metamorphism on various scales in time and space, and some principles of chemical reactions in rocks that accompany metamorphism, but without treating these principles in detail, and presenting the thermodynamic basis for quantitative analysis of reactions and their equilibria in metamorphism. Part I also presents concepts of metamorphic grade or intensity of metamorphism, such as the metamorphic-facies concept. Also, a brief presentation of techniques and methods for estimating pressure and temperature conditions at which metamorphic rocks once were formed a long time ago can be found in Part I (geothermobarometry). Part II deals systematically with prograde metamorphism of six different classes of bulk rock compositions. The categories of rock compositions treated cover most of the sedimentary, igneous and metamorphic precursor material that is commonly encountered. Some more exotic rock compositions, for example ironstones, evaporites, laterites and manganese-rich rocks are not covered by the book. Part II can, in principle, be used alone, provided that the reader is familiar with common types of petrologic phase diagrams. Part II makes extensive use of computed phase diagrams. The routine computation of phase diagrams is one of the major

5 VI Preface developments in petrology of the last few years. It was made possible by a continuous and tremendous effort by scientists in experimental laboratories, who have vastly expanded the database of material of geological interest through phase equilibria and thermochemical studies. Advanced mathematical and thermodynamic analysis of the experimental data resulted in the compilation of thermodynamic data of phase components of geologic substances and in the development of solution models for solid mineral solutions and gas mixtures at high pressures and temperatures. Finally, several computer software packages developed during recent years make the computation of phase diagrams convenient and easy. Computation of phase diagrams is becoming increasingly widespread among geologists, and as the reader will see, this book in its present form could not have been written 5 years ago. In general, the book focusses on the interpretation and significance of mineral assemblages and chemical reactions in metamorphic rocks. Several important topics concerning metamorphism and metamorphic rocks are not covered by this book. These topics include metamorphic micro-structures and their interpretation, deformation and metamorphism, geodynamic aspects of metamorphism and the thermodynamic basis for the quantitative treatment of chemical reactions in rocks. The references are cited at the end of each chapter, the lists of references include a selection of important papers and books on the subject covered by the respective chapter that are highly recommended for further reading. The bibliography includes classical papers in the field as well as more recent contributions that may help to provide access to research in specialized fields via the references cited in the listed research (e.g. granulite-facies metamorphism of pelitic rocks etc.). Many of the phase diagram figures show numbered reaction equilibria that are formulated and listed in tables. Reaction numbers are also frequently used in the text. We recommend copying the tables with the reaction stoichiometries and keeping them on hand, which will help eliminate the need to flip back and forth between text and reaction tables. We also strongly recommend regular reading of current issues of scientific journals that arrive at your library. In the field of metamorphic petrology, the Journal of Metamorphic Geology is essential reading and a few of the other particularly relevant journals are Journal of Petrology, Contributions to Mineralogy and Petrology, American Mineralogist, European Journal of Mineralogy, Mineralogical Magazine, Lithos, Chemical Geology and Earth and Planetary Science Letters. Freiburg and Basel (March 1994) Kurt Bucher and Martin Frey

6 Acknowledgements KB started the work on this book during his Oslo period and it was completed at the University of Freiburg. During the process of writing this book, parts of the text were taught to student courses at the University of Oslo and Freiburg. The patience of the students in following the lectures at various stages and their helpful comments are gratefully acknowledged. KB thanks the Institute fur Mineralogie und Petrographie, ETH ZUrich, where Chapter 5 was written. Chapter 9 was written during another sabbatical that was partly spent at Johns Hopkins University. MF thanks the Department of Geology, Stanford University, where Chapter 4 was written during a sabbatical. KB also wishes to thank John Schumacher for help and useful comments and suggestions. KB is indebted to Ernie Perkins and James Connolly, who provided various versions of their phase diagram software and showed great interest in the book project. MF is grateful to Steven Bohlen for reviewing Chapter 4, to Christian de Capitani for help in computing phase diagrams of Chapter 8 and for reviewing Chapter 8, and to Meinert Rahn for drafting of the figures of Chapters 1, 4, 8 and 10. One of the authors, Kurt Bucher, has also published under his extended name Bucher-Nurminen but found it more convenient to simplify his name for the textbook and he will continue this practice in future publications. We hope this will not be the cause of much confusion.

7 Contents Part I Basic Principles Definition, Limits and Types of Metamorphism Limits of Metamorphism Types of Metamorphism Orogenic Metamorphism Ocean-Floor Metamorphism Other Types of Regional Metamorphism Contact Metamorphism Other Types of Small-Scale Metamorphism References Metamorphic Rocks Primary Material of Metamorphic Rocks Chemical Composition of Protoliths of Metamorphic Rocks The Seven Chemical Composition Classes of Metamorphic Rocks and Their Protoliths The Structure of Metamorphic Rocks Classification and Names of Metamorphic Rocks Structurally Defined Rock Names Special Terms The Modal Composition Systematics Names Related to the Origin of the Proto lith Mineral Assemblages and Mineral Parageneses Graphical Representation of Metamorphic Mineral Assemblages Mole Numbers, Mole Fractions and the Mole Fraction Line The Mole Fraction Triangle Projections References Metamorphic Process Principles of Metamorphic Reactions Pressure and Temperature Changes in Crust and Mantle

8 X Contents General Aspects Heat Flow and Geotherms Transient Geotherms Temperature Changes and Metamorphic Reactions Pressure Changes in Rocks Gases and Fluids Time Scale of Metamorphism Pressure-Temperature-Time Paths and Reaction History Chemical Reactions in Metamorphic Rocks Reactions Among Solid Phase Components Phase Transitions, Polymorphic Reactions Net-Transfer Reactions Exchange Reactions Exsolution Reactions/Solvus Reactions Reactions Involving Volatiles as Reacting Species Dehydration Reactions Decarbonatization Reactions Mixed Volatile Reactions Oxidation/Reduction Reactions Sulfidation Reactions Reactions Involving Halogens Complex Mixed Volatile Reactions and Fluids Reactions Involving Minerals and Dissolved Components in Aqueous Solutions Reactions Progress Phase Diagrams Significance of Phase Diagrams The Phase Rule Construction of Phase Diagrams for Multicomponent Systems After the Method of Schreinemakers References and Further Reading Metamorphic Grade General Considerations Index Minerals and Mineral Zones Metamorphic Facies Subgreenschist Facies Greenschist Facies Amphibolite Facies Granulite Facies Blueschist Facies Eclogite Facies

9 Contents XI Pressure-Temperature Conditions of Metamorphic Facies Isograds and Reaction-Isograds Bathozones and Bathograds Pretogenetic Grid Geothermobarometry Assumptions and Precautions Exchange Reactions Solvus Relations Polymorphic Transitions Net-Transfer Reactions Reactions Involving Fluid Species Thermobarometry Using Multi-Equilibrium Calculations Other Methods Uncertainties in Thermobarometry References Part II Metamorphism of Different Rock Compositions 5 Metamorphism of Ultramafic Rocks Introduction Metamorphic Ultramafic Rocks Rock Types Chemical Composition Metamorphism in the MSH System Chemographic Relations in the MSH System Progressive Metamorphism of Maximum Hydrated Harzburgite Metamorphism in the CMASH System Progressive Metamorphism of Hydrated Al-Bearing Lherzolites Effects of Rapid Decompression and Uplift Prior to Cooling Isograds in Ultramafic Rocks Mineral Assemblages in the Uppermost Mantle Serpentinization of Peridotites Reactions in Ultramafic Rocks at High Temperatures Thermometry and Geobarometry in Ultramafic Rocks Carbonate-Bearing Ultramafic Rocks Metamorphism of Ophicarbonate Rocks Soapstones and Sagvandites References and Further Reading

10 XII Contents 6 Metamorphism of Dolomites and Limestones Introduction General Chemical Composition Chemographic Relationships Orogenic Metamorphism of Dolomites Orogenic Metamorphism of Limestones Contact Metamorphism of Dolomites Contact Metamorphism of Limestones Isograds and Zone Boundaries in Marbles Metamorphic Reactions Along Isothermal Decompression Paths Marbles Beyond the CMS-HC System Fluorine Aluminium Potassium Sodium Thermobarometry in Marbles Calcite-Aragonite Phase Transition Calcite-Dolomite Miscibility Gap References and Further Reading Metamorphism of Pelitic Rocks (Metapelites) Meta pelitic Rocks Pelitic Sediments General The Chemical Composition Mineralogy Pre-Metamorphic Changes in Pelitic Sediments Orogenic Intermediate-Pressure Metamorphism of Pelitic Rocks (± Ky-Geotherm) Chemical Composition and Chemographies Mineral Assemblages at the Beginning of Metamorphism Phase Relationships in the ASH System Metamorphism in the FASH System Mica-Involving Reactions Metamorphism in the KFMASH System (AFM System) Low-Pressure Metamorphism of Pelites KFASH System KFMASH System Cordierite-Garnet-Spinel Equilibria Very High-Temperature Metamorphism of Pelites- Metapelitic Granulites Partial Melting and Migmatites

11 Contents XIII Granulites Metamorphism of Very Mg-Rich "Pelites" High-Pressure-Low Temperature Metamorphism Additional Components in Metapelites References and Further Reading Metamorphism of Marls General Orogenic Metamorphism of Al-Poor Marls Phase Relationships in the KCMAS-HC System Prograde Metamorphism in the KCMAS-HC System at Low Xco Orogenic Metamorphism of Al-Rich Marls Phase Relationships in the CAS-HC System Phase Relationships in the KNCAS-HC System Prograde Metamorphism at Low Xco Prograde Metamorphism at Very Low Xc References and Further Reading Metamorphism of Mafic Rocks Mafic Rocks Geological Occurrence Hydration of Igneous Mafic Rocks Chemical and Mineralogical Composition of Mafic Rocks Chemographic Relationships and the AFC Projection Overview on the Metamorphism of Mafic Rocks Subgreenschist Facies Metamorphism General Aspects and a Field Example Metamorphism in the CASH and NCMASH Systems The Transition to the Greenschist Facies Greenschist Facies Metamorphism Introduction Mineralogical Changes Within the Greenschist Facies Reactions in the CMASH-System Reactions Including Micas Greenschist-Amphibolite Facies Transition Amphibolite Facies Metamorphism Introduction Mineralogical Changes Within the Amphibolite Facies Low-Pressure Series Amphibolites Amphibolite-Granulite Facies Transition

12 XIV Contents 9.6 Granulite Facies and Mafic Granulites Blueschist Facies Metamorphism Introduction Reactions and Assemblages Eclogite Facies Metamorphism Eclogites Reactions and Assemblages Amphibolite and Granulite to Eclogite Facies Transition Reactions in Eclogites Eclogite Facies in Non-Basaltic Mafic Rocks Blueschist and Eclogite Facies Metamorphism of an Olivine Gabbro, a Case History from the Central Alps References Metamorphism of Granitoids Introduction Presence of Prehnite and Pumpellyite Quartz Textures Presence of Stilpnomelane The Microcline/Sanidine Transformation Isograd Granitoid Rocks in the Eclogite Facies and the Blueschist Facies References and Further Reading Appendix: Symbols for Rock-Forming Minerals Subject Index