Petrogenesis of Metamorphic Rocks

Petrogenesis of Metamorphic Rocks

Springer-Verlag Berlin Heidelberg GmbH

Kurt Bucher Martin Frey ( t) Petrogenesis of Metamorphic Rocks 7th Completely Revised and Updated Edition With 99 Figures and 25 Tables Springer

Professor Dr. Kurt Bucher University of Freiburg Institute of Mineralogy, Petrology and Geochemistry Albertstr. 23b 79104 Freiburg i. Br. Germany E-mail: bucher@uni-freiburg.de Web site: http://www.minpet.uni-freiburg.de Professor Dr. Martin Frey <t) ISBN 978-3-662-04916-7 Library of Congress Cataloging-in-Publication Data Bucher, Kurt, 1946- Petrogenesis of metamorphic rocks / Kurt Bucher, Martin Frey. - 7th, completely revised and updated ed. p. cm. Includes bibliographical references and index. ISBN 978-3-662-04916-7 ISBN 978-3-662-04914-3 (ebook) DOI 10.1007/978-3-662-04914-3 1. Rocks, Metamorphic. I. Frey, Martin, 1940- II. Title. QE475.A2 B84 2002 552'A-dc21 2002070560 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-V erlag Berlin Heidelberg GmbH. Viola-tions are liable for prosecution under the German Copyright Law. http://www.springer.de Springer-Verlag Berlin Heidelberg 2002 Origina1ly published by Springer-Verlag Berlin Heidelberg New York in 2002 Softcover reprint ofthe hardcover 7th edition 2002 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. Production: PRO EDIT GmbH, Heidelberg, Germany Cover-Design: Erich Kirchner, Heidelberg, Germany Typesetting: K + V Fotosatz, Beerfelden, Germany Printed on acid-free paper SPIN 11375746 32/3111/Di 54321

Preface to Sixth Edition 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 this theme. This book addresses rock metamorphism from a relatively pragmatic viewpoint. 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 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 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 ther-

VI Preface to Sixth Edition mochemical 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 were developed during recent years that 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 been written 5 years ago. In general, the book focuses 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

Preface to Seventh Edition The new edition of Petrogenesis of Metamorphic Rocks has several completely revised chapters and all chapters have updated references and redrawn figures. The chapters on metamorphic grade and metamorphism of ultramafic rocks have been rewritten. Also, the introduction and definitions have experienced some major changes. An important new addition is the reference made to important websites for metamorphic petrology tutorials, software, mail bases, and more. The links to these sites may fail to work over time. We will try to maintain and update metamorphism-related links at our own website: http://www.minpet. uni -freiburg.de. We encourage you to regularly read (or glance through) the 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, Geofluids, American Mineralogist, European Journal of Mineralogy, Lithos, Chemical Geology and Earth and Planetary Science Letters. The work on the second edition of Petrogenesis of Metamorphic Rocks was deeply affected by the unexpected and tragic death of Martin Frey. He died in an accident during a hike in the Swiss Alps on September 10, 2000, a few months after celebrating his 60th birthday. It was not far from his beloved Lukmanier field area that he fell over a cliff during a steep descent and died from severe injuries. It was a clear Sunday in early fall and the message that reached us at Lukmanier Pass Hospiz during a mapping field course deeply shocked all of us. Martin was a very open and generous colleague and it was a great pleasure for me to first work in his Institute in Basel as Assistant Professor and later, during my stays in Oslo and Freiburg, to write and edit Petrogenesis of Metamorphic Rocks together with him. His e-mails and chats on the phone were always cheerful highlights of my working days. I miss him very much. Freiburg, December 2001 Kurt Bucher

VIII Acknowledgments Acknowledgments The revision of this book benefited from software help provided by Jamie Connolly (ETH Zurich) and Christian de Capitani (Basel). The patience of the Freiburg students in following my convoluted lectures and their helpful suggestions for improvement of the text are gratefully acknowledged. Very useful suggestions, comments and corrections were also supplied by Bernard Evans (and his students), B. Storre and H. Kawinski. Also, various discussions on the "Geometamorphism Mailbase" were useful for the improvement of the book. One round of discussion was, in fact, directly related to Fig. 2.1 of the sixth edition. Martin Engi provided the P-T contour map of the Central Alps. Martin Engi and Dave Pattison are thanked for stimulating dialogues on amphibolites and granulites. Christian de Capitani instructed me in the latest developments regarding the "pseudosection virus" that is rapidly infecting the geometamorphism community.

Contents Part I 1 1.1 1.1.1 1.1.2 1.1.3 1.1.4 1.2 1.2.1 1.2.2 1.2.3 1.2.4 1.2.5 Definition, Conditions and Types of Metamorphism.... Conditions of Metamorphism.... Low-Temperature Limit of Metamorphism.... High-Temperature Limit of Metamorphism.... Low-Pressure Limit of Metamorphism.... High-Pressure Limit of Metamorphism.... Types of Metamorphism.... Orogenic Metamorphism.... Ocean-Floor Metamorphism.... Other Types of Regional Metamorphism.... Contact Metamorphism.... Other Types of Small-Scale Metamorphism.... References...................................... 3 3 3 4 6 6 7 7 8 10 10 11 13 2 2.1 2.1.1 2.1.2 2.2 2.3 2.3.1 2.3.2 2.3.3 2.3.4 2.3.5 2.4 2.5 2.5.1 2.5.2 Metamorphic Rocks.... Primary Material of Metamorphic Rocks.... Chemical Composition of Protoliths of Metamorphic Rocks. Chemical Composition Classes of Metamorphic Rocks and Their Protoliths.... Structure of Metamorphic Rocks.... Classification and Names of Metamorphic Rocks.... Rock Names Referring to the Structure.... Names for High-Strain Rocks.... Special Terms.... Modal Composition of Rocks.... Names Related to the Origin of the Protolith.... Mineral Assemblages and Mineral Parageneses.... Graphic Representation of Metamorphic Mineral Assemblages.... Mole Numbers, Mole Fractions and the Mole Fraction Line.. The Mole Fraction Triangle......................... 17 18 19 21 22 24 24 25 26 28 28 29 32 32 34

X Contents 2.5.3 2.5.3.1 2.5.3.2 2.5.3.3 2.5.3.4 2.5.3.5 Projections.... Simple Projections.... Complex Projections.... AFM Projections.... ACF Projections.... Other Projections.... References...................................... 36 36 39 41 45 47 47 3 3.1 3.2 3.2.1 3.2.2 3.2.2.1 3.2.3 3.2.4 3.3 3.4 3.5 3.6 3.6.1 3.6.1.1 3.6.1.2 3.6.1.3 3.6.1.4 3.6.2 3.6.2.1 3.6.2.2 3.6.2.3 3.6.2.4 3.6.2.5 3.6.2.6 3.6.2.7 3.6.2.8 3.7 3.8 3.8.1 3.8.2 3.8.2.1 3.8.3 3.8.4 Metamorphic Processes.... Principles of Metamorphic Reactions.... Pressure and Temperature Changes in Crust and Mantle.... 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.... Reactions Involving Sulfur.... Reactions Involving Halogens.... Complex Mixed Volatile Reactions and Fluids.... Reactions Involving Minerals and Dissolved Components in Aqueous Solutions.... Reaction Progress.... Phase Diagrams.... Phase Diagrams, General Comments and Software.... The Phase Rule.... Phase Rule in Reactive Systems.... Construction of Phase Diagrams for Multicomponent Systems After the Method of Schreinemakers.... Use of Phase Diagrams, an Example.... References...................................... 49 50 57 57 58 61 62 64 65 67 68 73 73 73 73 73 74 75 75 78 78 81 82 83 83 85 86 89 89 90 91 92 96 99

Contents 4 4.1 4.2 4.3 4.3.1 4.3.2 4.3.2.1 4.3.2.2 4.3.2.3 4.3.2.4 4.3.2.5 4.3.2.6 4.3.3 4.4 4.4.1 4.4.2 4.4.3 4.5 4.6 4.6.1 4.6.1.1 4.6.1.2 4.6.1.3 4.7 4.7.1 4.7.2 4.7.2.1 4.7.2.2 4.7.2.3 4.7.2.4 4.7.2.5 4.7.2.6 4.7.2.7 4.7.2.8 4.7.3 4.7.3.1 4.7.3.2 4.7.3.3 4.7.4 4.7.4.1 4.7.4.2 4.7.4.3 4.7.4.4 4.7.5 4.7.5.1 4.7.5.2 Metamorphic Grade.... General Considerations.... Index Minerals and Mineral Zones.... Metamorphic Facies.... Origin of the Facies Concept.... Metamorphic Facies Scheme.... Sub-Blueschist -Greenschist Facies.... Greenschist Facies.... Amphibolite Facies.... Granulite Facies.... Blueschist Facies.... Eclogite Facies.... Pressure-Temperature Conditions of Metamorphic Facies... Isograds and Reaction Isograds.... Origin and History of the Isograd Concept.... Zone Boundaries, Isograds and Reaction Isograds.... Assessing Isograds, Isobars and Isotherms.... Bathozones and Bathograds.... Petrogenetic Grid.... Polymorphic Transitions.... Andalusite-Kyanite-Sillimanite.... Calcite-Aragonite.... Quartz-Coesite.... Geothermobarometry.... Concept and General Principle.... Assumptions and Precautions.... Question of Equilibrium.... Retrograde Effects.... Quality of Calibration.... Long Extrapolations in P-T.... Sensitivity of Thermo barometry.... Variable Structural State.... Effect of Other Components.... Estimation of Fe 2 + /Fe 3 + in Mineral Analysis.... Exchange Reactions.... Garnet-Clinopyroxene.... Garnet-Biotite.... Isotopic Exchange Thermometry.... Net Transfer.... Garnet-Aluminosilicate-Quartz-Plagioclase (GASP).... Garnet-Rutile-Aluminosilicate-Ilmenite-Quartz (GRAIL).... Clinopyroxene-Plagioclase-Quartz.... Sphalerite-Pyrrhotite-Pyrite.... Miscibility Gaps and Solvus Thermometry.... Orthopyroxene-Clinopyroxene.... Plagioclase-Alkali Feldspar.... XI 105 105 106 107 107 109 111 112 112 113 114 114 115 116 116 117 119 122 125 127 127 128 130 130 131 134 134 135 135 135 136 136 136 137 138 139 141 142 143 145 146 146 147 147 148 149

XII Contents 4.7.5.3 Calcite-Dolomite................................. 150 4.7.5.4 Muscovite-Paragonite.............................. 150 4.7.6 Uncertainties in Thermobarometry.................... 151 4.7.7 Thermobarometry Using Multiequilibrium Calculations (MET)............................... 152 4.8 Gibbs Method................................... 154 4.9 Assemblage Stability Diagrams....................... 155 4.10 More P-T Tools.................................. 156 4.10.1 Reactions Involving Fluid Species..................... 156 4.10.1.1 Phengite-Biotite-K-Feldspar-Quartz................... 156 4.10.1.2 Magnetite-Ilmenite Equilibria and the "Quilf" System...... 157 4.10.2 P-T Tools for Very Low-Grade Rocks.................. 158 4.10.2.1 Fluid Inclusions.................................. 158 4.10.2.2 Vitrinite Reflectance............................... 159 4.10.2.3 Conodont Color Alteration Index (CAl)................ 159 References...................................... 160 Part II s 5.1 5.2 5.2.1 5.2.2 5.3 5.3.1 5.3.2 5.4 5.4.1 5.4.2 5.5 5.6 5.7 5.8 5.9 5.10 5.10.1 5.10.2 Metamorphism of Ultramafic Rocks..................... 171 Introduction.................................... 171 Metamorphic Ultramafic Rocks...................... 171 Rock Types..................................... 172 Chemical Composition............................. 173 Metamorphism in the MSH System.................... 175 Chemographic Relations in the MSH System............. 175 Progressive Metamorphism of Maximum Hydrated Harzburgite..................................... 176 Metamorphism in the CMASH System................. 179 Progressive Metamorphism of Hydrated Al-Bearing Lherzolites...................................... 179 Effects of Rapid Decompression and Uplift Prior to Cooling. 182 Isograds in Ultramafic Rocks........................ 182 Mineral Assemblages in the Uppermost Mantle........... 183 Serpentinization of Peridotites....................... 184 Reactions in Ultramafic Rocks at High Temperatures...... 185 Thermometry and Geobarometry in Ultramafic Rocks..... 188 Carbonate-Bearing Ultramafic Rocks.................. 188 Metamorphism of Ophicarbonate Rocks................ 189 Soapstone and Sagvandite.......................... 192 References...................................... 193

Contents XIII 6 Metamorphism of Dolomites and Limestones.............. 197 6.1 Introduction.................................... 197 6.1.1 General........................................ 197 6.1.2 Chemical Composition............................. 197 6.1.3 Chemographic Relationships........................ 198 6.2 Orogenic Metamorphism of Dolomites................. 200 6.3 Orogenic Metamorphism of Limestones................ 202 6.4 Contact Metamorphism of Dolomites.................. 204 6.5 Contact Metamorphism of Limestones................. 206 6.6 Isograds and Zone Boundaries in Marbles.............. 207 6.7 Metamorphic Reactions Along Isothermal Decompression Paths.............................. 209 6.8 Marbles Beyond the CMS-HC System.................. 211 6.8.1 Fluorine........................................ 211 6.8.2 Aluminum...................................... 212 6.8.3 Potassium...................................... 212 6.8.4 Sodium........................................ 213 6.9 Thermobarometry in Marbles........................ 214 6.9.1 Calcite-Aragonite Phase Transition.................... 214 6.9.2 Calcite-Dolomite Miscibility Gap..................... 214 References...................................... 214 7 Metamorphism of Pelitic Rocks (Metapelites).............. 217 7.1 Metapelitic Rocks................................. 217 7.2 Pelitic Sediments................................. 217 7.2.1 General........................................ 217 7.2.2 Chemical Composition............................. 218 7.2.3 Mineralogy..................................... 218 7.3 Pre-metamorphic Changes in Pelitic Sediments........... 219 7.4 Intermediate-Pressure Metamorphism of Pelitic Rocks..... 219 7.4.1 Chemical Composition and Chemographies............. 220 7.4.2 Mineral Assemblages at the Beginning of Metamorphism... 220 7.4.3 The ASH System................................. 221 7.4.4 Metamorphism in the FASH System................... 224 7.4.5 Mica-Involving Reactions........................... 227 7.4.6 Metamorphism in the KFMASH System (AFM System)..... 230 7.5 Low-Pressure Metamorphism of Pelites................. 235 7.5.1 KFASH System................................... 236 7.5.2 KFMASH System................................. 238 7.5.3 Cordierite-Garnet-Spinel Equilibria.................... 240 7.6 Very High-Temperature Metamorphism of Pelites- Metapelitic Granulites............................. 242 7.6.1 Partial Melting and Migmatites...................... 242 7.6.2 Granulites...................................... 244

XIV Contents 7.7 7.8 7.9 Metamorphism of Very Mg-Rich "Pelites".... High-Pressure-Low-Temperature Metamorphism.... Additional Components in Metapelites.... References.... 247 249 252 254 8 8.1 8.2 8.2.1 8.2.2 8.3 8.3.1 8.3.2 8.3.2.1 8.3.2.2 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 Xco,.... References.... 259 259 259 260 262 264 265 267 270 271 275 9 9.1 9.1.1 9.1.2 9.1.3 9.2 9.3 9.3.1 9.3.2 9.3.3 9.4 9.4.1 9.4.2 9.4.2.1 9.4.2.2 9.4.3 9.5 9.5.1 9.5.2 9.5.3 9.5.4 9.6 9.7 9.7.1 9.7.2 Metamorphism of Mafic Rocks.... Mafic Rocks.... Hydration of Igneous Mafic Rocks.... Chemical and Mineralogical Composition of Mafic Rocks... Chemographic Relationships and the ACF Projection.... Overview of the Metamorphism of Mafic Rocks.... Subgreenschist Facies Metamorphism.... General Aspects and a Field Example.... Metamorphism in the CASH and NCMASH Systems.... 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.... Granulite Facies and Mafic Granulites.... Blueschist Facies Metamorphism.... Introduction.... Reactions and Assemblages.... 279 279 280 281 283 288 291 291 293 299 299 299 300 300 302 303 304 304 305 306 308 309 311 311 313

Contents 9.8 9.8.1 9.8.2 9.8.2.1 9.8.2.2 9.8.3 9.8.3.1 Eclogite Facies Metamorphism.... Eclogites.... Reactions and Assemblages.... Amphibolite and Granulite to Eclogite Facies Transition.... Reactions in Eclogites.... Eclogite Facies in Nonbasaltic Mafic Rocks.... Blueschist and Eclogite Facies Metamorphism of an Olivine Gabbro: a Case History from the Central Alps.... References...................................... XV 316 316 318 318 320 320 321 324 10 10.1 10.2 10.3 10.4 10.5 Metamorphism of Granitoid Rocks.... Introduction.... Presence of Prehnite and Pumpellyite.... Presence of Stilpnomelane.... The Microcline/Sanidine Transformation Isograd.... Granitoid Rocks in the Eclogite Facies and the Blueschist Facies.... References...................................... 329 329 329 330 330 331 332 List of Abbreviations...................................... 335 Subject Index........................................... 337