Petrogenesis of Metamorphic Rocks PDF
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Petrogenesis of Metamorphic Rocks Petrogenesis of Metamorphic Rocks Third Edition Helmut G. F. Winkler English Editor Edgar Froese Springer-Verlag Berlin. Heidelberg. New York Helmut G. F. Winkler Professor and Director, Institute of Mineralogy and Petrology University of Gottingen, Germany Edited by Edgar Froese Geological Survey Ottawa, Canada ~~tJGER STUD~ f:::t>1"'Cf-J Design: Peter Klemke, Berlin Library of Congress Cataloging in Publication Data Winkler, Helmut G. F. 1915- Petrogenesis of metamorphic rocks. Includes bibliographical references. 1. Rocks, Metamorphic. l. Title. QE475.A2W5613 1974 552'.4 74-2179 All rights reserved No part of this book may be translated or reproduced in any form without written permission from Springer-Verlag. © 1974 by Springer-Verlag New York Inc. ISBN-13: 978-1-4612-9830-4 e-ISBN-13: 978-1-4612-9828-1 DOl: 10.1007/978-1-4612-9828-1 Preface to the Third Edition The first edition of this book was published in 1965 and its French translation in 1966. The revised second edition followed in 1967 and its Russian translation became available in 1969. Since then, many new petrographic observations and experimental data elucidat ing reactions in metamorphic rocks have made a new approach in the study of metamorphic transformation desirable and possible. It is felt that this new approach, attempted in this book, leads to a better unders tanding of rock metamorphism. The concept of metamorphic facies and subfacies considers asso ciations of mineral assemblages from diverse bulk compositions as characteristic of a certain pressure-temperature range. As new petrographic observations accumulated, it became increasingly difficult to accommodate this information within a manageable framework of metamorphic facies and subfacies. Instead, it turned out that mineral assemblages due to reactions in common rocks of a particular composi tion provide suitable indicators of metamorphic conditions. Metamorphic zones, defined on the basis of mineral reactions, very effectively display the evolution of metamorphic rocks. Thus the im portance of reactions in metamorphic rocks is emphasized. Experimen tal calibration of mineral reactions makes it possible to distinguish reac tions which are of petrogenetic significance from those which are not. This distinction provides guidance in petrographic investigations un dertaken with the object of deducing the physical conditions of metamorphism. Within a metamorphic terrain, points indicating the same reac tion constitute a line or a band, here designated by the term isoreac tion-grad. Points along the isoreaction-grad represent metamorphic conditions (P, T, Pvolatiles) corresponding to the pertinent reaction. As the term implies, an isoreaction-grad is defined by a specific reaction and is therefore more significant than an isograd based on the ap pearance or disappearance of a mineral or mineral assemblage not rel ated to a specific reaction. Thus this presentation of the principles of rock metamorphism differs from that of previous editions: mineral reactions in several rock groups of common composition (mafic, ultramafic, pelitic, marly, and v vi Preface to the Third Edition dolomitic) are treated in separate chapters. For each compositional group, the various mineral reactions that take place during the course of metamorphism are discussed. Large divisions of metamorphic grade, also defined on the basis of mineral reactions in common rocks, pro vide a convenient overview of metamorphic conditions. These divi sions are designated as very-low, low, intermediate, and high-grade metamorphism. The new concept is straightforward in its application. It has been used successfully in the field by the author's coworkers and others. It is hoped that this book will provide some guidance in the petrographic studies of metamorphic terrains: only rocks having certain composi tions need be examined in great detail. Instead of extensive investiga tions, only selected petrographic observations aimed at specific targets are required to deduce physical conditions of metamorphism. In order to choose the right targets within a given metamorphic setting, Chapter 15 should be consulted because it furnishes a key for the determination of metamorphic grades and major isoreaction-grads and isograds in common rocks. The references are predominantly to recent literature in order to save space. There is no intention to underrate the value of older publications, and the student is advised to consult the reference lists given in recent publications. For the sake of convenience, all references are grouped together at the end of each chapter. This book stresses the chemical, mineralogical and physicochemical aspects of metamorphism. The fabric of rocks is not treated but attention is called to the books by Sprey [Metamorphic Tex tures. Pergamon Press, Oxford. 1969] and Turner and Weiss [Structural Analysis of MetamorphiC Tectonics. New York. 1963]. Field relations in specific metamorphic regions are not considered in detail; this has been done by Turner [Metampornic Petrology. McGraw-Hill Book Com pany, New York. 1968] and by Miyashiro (Metamorphism and Metamorphic Belts. George Allen & Unwin, London, 1973). However, this book furnishes the basis for field investigations yielding petrogenetically significant data. I am grateful for oral and written discussions, for expert guidance on field trips, and for early communication of most recent observations to so many people in various countries that all cannot be acknowledged individually. I also express my gratitude to my young colleagues at the University of Goettingen, especially Drs. P. Metz, K.-H. Nitsch, and B. Storre, who contributed many experimental results and discussions. Most of all, I am grateful to my friend Dr. Edgar Froese of the Geologi cal Survey of Canada. He corrected, in fact, edited, my English version of the manuscript and improved it also through critical remarks and suggestions. Mrs. Ingeborg Tradel was so kind to undertake the task of Preface to the Third Edition vii typing the English manuscript. Finally, I cordially thank my wife Ur sula for her gentle understanding during the many long days extending over the several years that I spent sitting at my desk. Goettingen, September 1973 Helmut G. F. Winkler Contents Preface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v 1. Definition and Types of Metamorphism ................... . 2. From Diagenesis to Metamorphism. . . . . . . . . . . . . . . . . . . . . . . . . 9 3 . Factors of Metamorphism ............................... 15 General Considerations .......................... . . . .. 15 The Composition of the Fluid Phase . . . . . . . . . . . . . . . . . . . .. 19 Directed Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 23 4. Mineral Parageneses: The Building Blocks of Metamorphic Rocks. 27 5. Graphical Representation of Metamorphic Mineral Parageneses . .. 30 Composition Plotting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 30 ACF Diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 34 A'FK Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 40 How Are ACF and A'FK Diagrams Used? . . . . . . . . . . . . . . . .. 44 AFM Diagrams ..................................... 47 6. Classification Principles: Metamorphic Facies versus Metamorphic Grade. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 54 7. The Four Divisions of Metamorphic Grade. . . . . . . . . . . . . . . . . .. 63 General Considerations .......................... . . . .. 63 The Terms Isograd and Isoreaction-Grad . . . . . . . . . . . . . . . . .. 65 The Division of Very-Low-Grade Metamorphism ........... 66 The Division of Low-Grade Metamorphism . . . . . . . . . . . . . . .. 73 The Change from Low-Grade to Medium-Grade Metamorphism. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 74 The Change from Medium-Grade to High-Grade Metamorphism .............................. . . . .. 81 Granulite-High Grade; Regional Hypersthene Zone. . . . . . . .. 86 Pressure Divisions of the Metamorphic Grades ............. 87 Problems with the Al2SiOs Species. . . . . . . . . . . . . . . . . . . . .. 90 8. General Characteristics of Metamorphic Terrains. . . . . . . . . . . . .. 95 Metamorphic Zones in Contact Aureoles. . . . . . . . . . . . . . . . .. 95 Metamorphic Zones in Regional Metamorphism ............ 100 Paired Metamorphic Belts ............................. 107 9. Metamorphic Reactions in Carbonate Rocks ................. 109 General Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 109 Metamorphism of Siliceous Dolomitic Limestones .......... 111 Formation of Wollastonite. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 125 ix x Contents Metamorphism of Carbonates at Very High Temperature and Very Low Pressure .............................. 130 10. Metamorphism of Marls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 136 11. Metamorphism of Ultramafic Rocks: Systems MgO-Si02- C02- H20 and MgO-CaO-Si02 -H20. . . . . . . . . .. 148 12. Metamorphism of Mafic Rocks. . . . . . . . . . . . . . . . . . . . . . . . . . .. 160 Transformations Except Those of Very-Low-Grade Metamorphism at Low Pressures. . . . . . . . . . . . . . . . . . .. 160 Very-Low-Grade Metamorphism at Low Pressures .......... 172 Evaluation of Metamorphic Changes at Very-Low Grade. . . . .. 180 The Role of CO2 in Very-Low-Grade Metamorphism ......... 191 13. Very-Low-Grade Metamorphism of Graywackes .............. 195 14. Metamorphism ofPelites ................................ 197 General Statement .................................. 197 Metamorphism of Pelitic Rocks at Very-Low and Low-Grade.. 197 Metamorphism of Pelitic Rocks at Medium-and High-Grade .. 211 15. A Key to Determine Metamorphic Grades and Major Isoreaction-Grads or Isograds in Common Rocks .......... 228 Very-Low-Grade Metamorphism ....................... " 229 Low-Grade ....................................... " 231 Medium-and High-Grade ............................ " 234 Geothermometers and Geobarometers ................... 240 Sequences of Isoreaction-Grads or Isograds ................ 241 16. Regional Hypersthene Zone (Granolite High Grade) ............ 245 Nomenclature and Mineralogical Features of "Granulites" .... 245 Metamorphism of Granolites and Related Granoblastites ..... 252 Petrogenetic Considerations .......................... " 260 17. Eclogites............................................. 264 18. Anatexis, Formation of Migmatites, and Origin of Granitic Magmas ......................................... 271 Anatexis: General Considerations ....................... 273 Experimental Anatexis of Rocks Composed of Alkali Feldspar, Plagioclase, and Quartz. . . . . . . . . . . . . . . . . . . . . . . . . .. 289 Experimental Anatexis of Rocks Composed of Plagioclase and Quartz but Lacking Alkali Feldspar ............... " 295 Formation of Migmatites ............................ " 301 Formation of Granitic Magmas by Anatexis ................ 306 Appendix: Nomenclature of Common Metamorphic Rocks .......... 312 Names of Important Rock Groups. . . . . . . . . . . . . . . . . . . . . .. 312 Prefixes ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 314 Classification ....................................... 315 Index .................................................... 317 Petrogenesis of Metamorphic Rocks
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