Petrogenesis of Metamorphic Rocks

Petrogenesis of Metamorphic Rocks

(Parte 1 de 7)

Petrogenesis of Metamorphic Rocks Petrogenesis of Metamorphic Rocks

Kurt Bucher Rodney Grapes

Petrogenesis of Metamorphic Rocks

Prof.Dr. Kurt Bucher University Freiburg Mineralogy Geochemistry Albertstr. 23 B 79104 Freiburg Germany bucher@uni-freiburg.de

Prof. Rodney Grapes Department of Earth and Environmental Sciences Korea University Seoul Korea grapes@korea.ac.kr

ISBN 978-3-540-74168-8 e-ISBN 978-3-540-74169-5 DOI 10.1007/978-3-540-74169-5 Springer Heidelberg Dordrecht London New York

Library of Congress Control Number: 2011930841

# Springer-Verlag Berlin Heidelberg 2011 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. Violations are liable to prosecution under the German Copyright Law. Theuse of general descriptive names, registerednames, trademarks, etc.in thispublicationdoesnot 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.

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Preface

This new edition of “Petrogenesis of Metamorphic Rocks” has several completely revised chapters and all chapters have updated references and redrawn figures. All chapters of Part I of the book have been rewritten. Also, the chapters “Introduction” and “Grade” have undergone several major changes. The references made to important web sites relating to metamorphic petrology tutorials, software, mail base, etc have been updated and extended. However, it should be noted that some of the links to these sites may fail to work in the future. A large number of new figures showing assemblage stability diagrams have been computed using the Theriak/ Domino software by Ch. de Capitani of the University of Basel.

We encourage you to regularly read (or at least glance through) current issues of scientific journals in your library either online or paper copies. In the field of metamorphic petrology, the Journal of Metamorphic Geology is essential reading and some of the other particularly relevant journals include, Journal of Petrology, Contributions to Mineralogy and Petrology, Geofluids, American Mineralogist, European Journal of Mineralogy, Lithos, Chemical Geology and Earth and Planetary Science Letters.

Freiburg, Germany Kurt Bucher Seoul, South Korea Rodney Grapes November 2010

Contents

1 Definition, Conditions and Types of Metamorphism3
1.1 Conditions of Metamorphism4
1.1.1 Low-Temperature Limit of Metamorphism4
1.1.2 High-Temperature Limit of Metamorphism5
1.1.3 Low-Pressure Limit of Metamorphism7
1.1.4 High-Pressure Limit of Metamorphism7
1.2 Types of Metamorphism8
1.2.1 Orogenic Metamorphism8
1.2.2 Ocean-Floor Metamorphism1
1.2.3 Other Types of Regional Metamorphism1
1.2.4 Contact Metamorphism13
1.2.5 Cataclastic Metamorphism14
1.2.6 Hydrothermal Metamorphism14
1.2.7 Other Types of Small-Scale Metamorphism16
References and Further Reading17
2 Metamorphic Rocks21
2.1 Primary Material of Metamorphic Rocks2
of Metamorphic Rocks23
Rocks and Their Protoliths25
2.2 The Structure of Metamorphic Rocks26
2.3 Classification and Names of Metamorphic Rocks29
2.3.1 Rock Names Referring to the Structure31
2.3.2 Names for High-Strain Rocks32
2.3.3 Special Terms3
2.3.4 Modal Composition of Rocks35
2.3.5 Names Related to the Origin of the Protolith35
2.4 Mineral Assemblages and Mineral Parageneses36

Part I Introduction and General Aspects of Metamorphism 2.1.1 Chemical Composition of Protoliths 2.1.2 Chemical Composition Classes of Metamorphic vii

Assemblages39
Fraction Line39
2.5.2 The Mole Fraction Triangle41
2.5.3 Projections43
References and Further Reading5
3 Metamorphic Processes57
3.1 Principles of Metamorphic Reactions58
3.2 Pressure and Temperature Changes in Crust and Mantle65
3.2.1 General Aspects65
3.2.2 Heat Flow and Geotherms6
3.2.3 Temperature Changes and Metamorphic Reactions71
3.2.4 Pressure Changes in Rocks72
3.3 Gases and Fluids74
3.4 Time Scale of Metamorphism76
3.5 Pressure–Temperature–Time Paths and Reaction History7
3.6 Chemical Reactions in Metamorphic Rocks81
3.6.1 Reactions Among Solid-Phase Components82
3.6.2 Reactions Involving Volatiles as Reacting Species83
3.7 Reaction Progress9
3.8 Phase Diagrams102
3.8.1 Phase Diagrams, General Comments and Software102
3.8.2 The Phase Rule103
Systems After the Method of Schreinemakers105
3.8.4 Use of Phase Diagrams, an Example109
References and Further Reading113
4 Metamorphic Grade119
4.1 General Considerations119
4.2 Index Minerals and Mineral Zones120
4.3 Metamorphic Facies122
4.3.1 Origin of the Facies Concept122
4.3.2 Metamorphic Facies Scheme124
4.3.3 Pressure–Temperature Conditions of Metamorphic Facies131
4.4 Isograds131
4.4.1 The Isograd Concept131
4.4.2 Zone Boundaries, Isograds and Reaction-Isograds133
4.4.3 Assessing Isograds, Isobars and Isotherms135
4.5 Bathozones and Bathograds139
4.6 Petrogenetic Grid141
4.6.1 Polymorphic Transitions142

2.5 Graphical Representation of Metamorphic Mineral 2.5.1 Mole Numbers, Mole Fractions and the Mole 3.8.3 Construction of Phase Diagrams for Multicomponent viii Contents

4.7.1 Concept and General Principle147
4.7.2 Assumptions and Precautions149
4.7.3 Exchange Reactions153
4.7.4 Net-Transfer158
4.7.5 Miscibility Gaps and Solvus Thermometry162
4.7.6 Uncertainties in Thermobarometry166
Calculations (MET)167
4.8 Gibbs Method168
4.9 Assemblage Stability Diagrams170
4.10 More P–T Tools171
4.10.1 Reactions Involving Fluid Species171
4.10.2 P–T Tools for Very Low Grade Rocks173
References and Further Reading174

4.7 Geothermobarometry ........................ ...................... 146 4.7.7 Thermobarometry Using Multi-equilibrium

5 Metamorphism of Ultramafic Rocks191
5.1 Introduction191
5.2 Ultramafic Rocks191
5.2.1 Rock Types193
5.2.2 Chemical Composition194
5.3 Metamorphism in the MSH System196
5.3.1 Chemographic Relations in the MSH System196
Hydrated Harzburgite198
5.4 Metamorphism in the CMASH System202
Lherzolite202
to Cooling204
5.5 Isograds in Ultramafic Rocks204
5.6 Mineral Assemblages in the Uppermost Mantle206
5.7 Serpentinization of Peridotite208
5.8 Ultramafic Rocks at High Temperature210
5.9 Thermometry and Geobarometry in Ultramafic Rocks211
5.10 Carbonate-Bearing Ultramafic Rocks212
5.10.1 Metamorphism of Ophicarbonate Rocks212
5.10.2 Soapstone and Sagvandite215
5.1 Open System Reactions in Ultramafic Rocks219
5.12 Potassium-Bearing Peridotites221
References and Further Reading221

Part I Metamorphism of Specific Rock Types 5.3.2 Progressive Metamorphism of Maximum 5.4.1 Progressive Metamorphism of Hydrated Al-Bearing 5.4.2 Effects of Rapid Decompression and Uplift Prior Contents ix

6.1 Introduction225
6.1.1 Rocks225
6.1.2 Minerals and Rock Composition227
6.1.3 Chemographic Relationships228
6.2 Orogenic Metamorphism of Siliceous Dolomite230
6.2.1 Modal Evolution Model232
6.3 Orogenic Metamorphism of Limestone233
6.4 Contact Metamorphism of Dolomites235
6.4.1 Modal Evolution Model238
6.5 Contact Metamorphism of Limestones239
6.6 Isograds and Zone Boundaries in Marbles243
Decompression Paths244
6.8 Marbles Beyond the CMS-HC System246
6.8.1 Fluorine247
6.8.2 Aluminium248
6.8.3 Potassium248
6.8.4 Sodium251
6.9 Thermobarometry of Marbles251
6.9.1 Calcite–Dolomite Miscibility Gap252
of Carbonate Rocks252
References and Further Reading253
7 Metamorphism of Pelitic Rocks (Metapelites)257
7.1 Metapelitic Rocks257
7.2 Pelitic Sediments257
7.2.1 General257
7.2.2 Chemical Composition258
7.2.3 Mineralogy258
7.3 Pre-metamorphic Changes in Pelitic Sediments258
7.4 Intermediate-Pressure Metamorphism of Pelitic Rocks259
7.4.1 Chemical Composition and Chemography259
7.4.2 Mineral Assemblages at the Beginning of Metamorphism260
7.4.3 The ASH System262
7.4.4 Metamorphism in the FASH System264
7.4.5 Mica-Involving Reactions267
7.4.6 Metamorphism in the KFMASH System (AFM System)269
7.5 Low-Pressure Metamorphism of Pelites278
7.5.1 FASH System278
7.5.2 KFMASH System280
Granulites284

6 Metamorphism of Dolomites and Limestones .. ...................... 225 6.7 Metamorphic Reactions Along Isothermal 6.10 High-Pressure and Ultrahigh-Pressure Metamorphism 7.6 High-Temperature Metamorphism of Pelites: Metapelitic x Contents

7.6.2 The Excess Quartz Condition286
7.6.3 Partial Melting and Migmatite288
7.6.4 More About Granulites292
7.7 Metamorphism of Mg-rich “Pelites”296
7.8 High Pressure: Low Temperature Metamorphism of Pelites298
7.9 Additional Components in Metapelites302
References and Further Reading306
8 Metamorphism of Marls315
8.1 General315
8.2 Orogenic Metamorphism of Al-Poor Marls316
8.2.1 Phase Relationships in the KCMAS-HC System317

7.6.1 Cordierite–Garnet–Opx–Spinel–Olivine Equilibria .......... 285 8.2.2 Prograde Metamorphism in the KCMAS-HC

319
8.3 Orogenic Metamorphism of Al-Rich Marls321
8.3.1 Phase Relationships in the CAS-HC System323
8.3.2 Phase Relationships in the KNCAS-HC System325
8.4 Increasing Complexity of Metamarls332
8.5 Low Pressure Metamorphism of Marls3
References and Further Reading336
9 Metamorphism of Mafic Rocks339
9.1 Mafic Rocks339
9.1.1 Hydration of Mafic Rocks340
9.1.2 Chemical and Mineralogical Composition of Mafic Rocks342
9.1.3 Chemographic Relationships and ACF Projection343
9.2 Overview of Metamorphism of Mafic Rocks348
Labradorite System (NCASH System)352
9.3 Subgreenschist Facies Metamorphism353
9.3.1 General Aspects353
9.3.2 Metamorphism in the CMASH and NCMASH Systems356
9.3.3 Transition to Greenschist Facies362
9.4 Greenschist Facies Metamorphism363
9.4.1 Introduction363
9.4.2 Mineralogical Changes Within the Greenschist Facies363
9.4.3 Greenschist–Amphibolite Facies Transition365
9.5 Amphibolite Facies Metamorphism367
9.5.1 Introduction367
9.5.2 Mineralogical Changes Within the Amphibolite Facies367
9.5.3 Low-Pressure Series Amphibolites368
9.5.4 Amphibolite–Granulite Facies Transition370
9.6 Granulite Facies and Mafic Granulites371

System at Low XCO 9.2.1 Plagioclase in Mafic Rocks, Equilibria in the Contents xi

9.7.1 Introduction374
9.7.2 Reactions and Assemblages374
9.8 Eclogite Facies Metamorphism378
9.8.1 Eclogites378
9.8.2 Reactions and Assemblages380
9.8.3 Eclogite Facies in Gabbroic Rocks383
References and Further Reading387
10 Metamorphism of Quartzofeldspathic Rocks395
10.1 Quartzofeldsapthic Rocks395
10.2 Metagraywackes395
10.2.1 Introduction395
Compositions397
10.2.3 Orogenic Metamorphism of Metagraywackes398
and Metapsammites400
10.3 Granitoids406
10.3.1 Prehnite and Pumpellyite406
10.3.2 Stilpnomelane406
10.3.3 The Microcline–Sanidine Isograd407
10.3.4 Eclogite and Blueschist Facies Granitoids408
10.3.5 Migmatitic Granitoids and Charnockite409
References and Further Reading411
Appendix: Symbols for rock forming minerals415
Index419

9.7 Blueschist Facies Metamorphism ............ ...................... 374 10.2.2 Metamorphism of Metagraywacke (Metaspammitic) 10.2.4 Contact Metamorphism of Metagraywackes xii Contents

Part I

Introduction and General Aspects of Metamorphism

Kyanite-eclogite from Verpeneset, Nordfjord, Norway. Omphacite (green), garnet (red brown, zoned) are the main minerals, additional minerals include kyanite, zoisite and phengite. The rock formed by Caledonian high-pressure metamorphism

Chapter 1 Definition, Conditions and Types of Metamorphism

Rock metamorphism is a geological process that changes the mineralogical and chemical composition, as well as the structure of rocks. Metamorphism is typically associated with elevated temperature and pressure, thus it affects rocks within the earth’s crust and mantle. The process is driven by changing physical and/or chemical conditions in response to large-scale geological dynamics. Consequently, it is inherent in the term, that metamorphism always is related to a precursor state where the rocks had other mineralogical and structural attributes. Metamorphism, metamorphic processes and mineral transformations in rocks at elevated temperatures and pressures are fundamentally associated with chemical reactions in rocks. Metamorphism does not include, by definition, similar processes that occur near the earth’s surface such as weathering, cementation and diagenesis. The transition to igneous processes is gradual, and metamorphism may include partial melting. The term metasomatism is used if modification of the rocks bulk composition is the dominant metamorphic process. Metamorphic rocks are rocks that have developed their mineralogical and structural characteristics by metamorphic processes.

The most typical metamorphism transforms sedimentary rocks to metamorphic rocks by addition of heat during mountain building or by a large volume of magma in the crust. For example, Upper Ordovician shales and nodular limestone (Fig. 1.1) in the Permian Oslo rift were heated to about 420 C by syenite plutons. The gray fissile shales composed predominantly of diagenetic clay minerals and quartz were transformed to dark splintery rocks called hornfels, which contain metamorphic minerals such as biotite, cordierite, K-feldspar and sillimanite. The limestone nodules consist of pure CaCO3 in the unmetamorphic sedimentary rock (Fig. 1.1a). At the temperature of metamorphism calcite reacted with the minerals of the shale. The reaction produced concentrically zoned nodules consisting of the Ca-silicates anorthite, wollastonite and diopside, so-called calcsilicate rocks

(Fig. 1.1b). All calcite has been used up in the reaction and all CO2 once present has left the rock together with H2O produced by the dehydration of the clay minerals. The example shows all characteristic features of metamorphism: The nodular limestone and shale were the precursor rocks (so-called protolith) of the newly formed metamorphic hornfels. A set of new minerals formed on the expense of previous minerals by chemical reactions in the rocks. The reactions were driven by heat added to the rock. The structure of the original rock was modified as

K. Bucher and R. Grapes, Petrogenesis of Metamorphic Rocks, DOI 10.1007/978-3-540-74169-5_1, # Springer-Verlag Berlin Heidelberg 2011 3

expressed by new ultrafine grainsize in the hornfels and by the concentric arrangement of chemically distinct reaction zones in the calcsilicate nodules as a result of small scale redistribution of chemical constituents in the rock. Obviously also the chemical composition of the rocks were changed on a local scale because the volume once occupied by carbonate (limestone nodule) was replaced by silicates during the metamorphic process and the rock is devoid of CO2 and H2O.

1.1 Conditions of Metamorphism

Large scale geologic events such as global lithospheric plate movements, subduction of oceanic lithosphere, continent–continent collision and ocean floor spreading all have the consequence of moving rocks and transporting heat. Consequently, changes in pressure (depth) and temperature are the most important variables in rock metamorphism. As an example, consider a layer of sediment on the ocean floor that is covered with more sediment layers through geologic time and finally subducted at a destructive plate margin. The mineral, chemical and structural transformations experienced by the sediment can be related to a gradually increasing temperature with time. The question may be asked: at what temperature does metamorphism begin?

1.1.1 Low-Temperature Limit of Metamorphism

Temperatures at which metamorphism sets in are strongly dependent on the material under investigation. Transformation of evaporites, of vitreous material and of shale (pelite) limestone nodule calcsilicate hornfels metapelitic hornfels zoned calcsilicate nodule

Fig. 1.1 Metamorphic transformation of sedimentary rocks (a) to metamorphic hornfels (b)i n a contact aureole of Permian plutons in the Oslo rift, Norway: (a) Upper Ordovician shale with fossiliferous limestone nodules. (b) Same rock as (a) but heated to about 430 C by a nearby pluton. Shale transformed to hornfels and limestone nodules reacted to zoned calcsilicate rock with anorthite and diopside as main minerals

4 1 Definition, Conditions and Types of Metamorphism organic material, for example, begins to take place at considerably lower temperatures than chemical reactions in most silicate and carbonate rocks. This book is not concerned with the metamorphism of organic material, i.e. coalification (maturation). For a review on this subject the reader is referred to Teichm€uller (1987) (see also Ruppert et al. 2010). Correlation between the rank of coalification and mineralogical changes in slightly metamorphosed sediments and volcanic rocks are reviewed by Kisch (1987).

In many rocks mineral transformations begin shortly after sedimentation and proceed continuously with increasing burial. Whether such reactions are called “diagenetic” or “metamorphic” is largely arbitrary. Further examples of processes that are intimately related to metamorphism include low temperature alteration of volcanic rocks, precipitation of mineral coatings in fractures and low-temperature rock–water reactions that produce mineral-filled veins and fissures. Hence, metamorphic processes occur in a temperature continuum from surface temperature upward. However, the low-temperature limit of metamorphism has been arbitrarily set to 150 C 50 C in this book and most of our phase-diagrams show phase equilibria above 200 C or 300 C.

Some minerals are considered distinctly metamorphic, that is they form at elevated temperature and are not found in diagenetically transformed sediments. In a regime of increasing temperature, the first occurrence of such minerals in sediments thus marks the onset of metamorphism. Indicators of beginning of metamorphism include: carpholite, pyrophyllite, Na-amphibole, lawsonite, paragonite, prehnite, pumpellyite, or stilpnomelane. Note, however, that these minerals may also be found as detrital grains in unmetamorphosed sediments. In this case, textural evidence from thin-sections will distinguish between a neoformation or a detrital origin. For a more detailed discussion of problems dealing with the lowtemperature limit of metamorphism and its delimitation from diagenesis the reader is referred to Frey and Kisch (1987) and Robinson and Merriman (1999).

1.1.2 High-Temperature Limit of Metamorphism

Ultimately, at high temperature, rocks will start to melt and dealing with silicate melts is the subject of igneous petrology. However, partial melting has always, both, a metamorphic and an igneous aspect. Crustal rocks that are characteristically produced by partial melting, so called migmatites, are made up of a residual metamorphic rock and an igneous rock component. Nevertheless, melting temperatures of rocks define the high-temperature limit of metamorphism. Melting temperatures are strongly dependent on pressure, rock composition and the amount of water present. For example, at 500 MPa and in the presence of an aqueous fluid, granitic rocks begin to melt at a temperature of about 660 C while basaltic rocks need a much higher temperature of about 800 C (Fig. 1.2). If H2O is absent, melting temperatures are much higher. Granitic gneisses will not melt below about 1,0 C, mafic rocks such as basalt require > 1,120 C to melt. The highest temperatures

1.1 Conditions of Metamorphism 5

reported from crustal metamorphic rocks are 1,0–1,150 C (e.g. Lamb et al. 1986; Ellis 1980; Harley and Motoyoshi 2000; Hokada 2001; Sajeev and Osanai 2004), determined by indirect methods of thermobarometry as explained in Sect. 4.7. Such rocks are termed ultra high temperature (UHT) metamorphic rocks and are typically magnesian- and aluminous-rich gneisses, e.g. Napier Complex (Antarctica), Scourian gneiss (Scotland), the Highland Complex (Sri Lanka). Temperatures in the lower continental crust of geologically active areas are inferred to be about 750–850 C and the rocks produced under these conditions are termed granulites. This is also the typical upper temperature limit of crustal metamorphism. However, pressure temperature conditions inside this shaded field are not verified within the planet earth

Pressure (GPa)

Depth (Km) 150

Dora Maira pyrope-coesite gneiss

NW Scotland Scourian gneisses sedimentarydiagenetic H

O-saturated melting of granite

N Kazakhstan diamond-bearing gneisses metamorphism Napier Antarctica granulites

Su-Lu China eclogites normal thickness of continents lower crust water-absent melting of granite upper crust double crust continent collision igneous processes

Fig. 1.2 The pressure temperature range of metamorphic processes. The P–T gradients of four typical geodynamic settings are shown. The boundary between diagenesis and metamorphism is gradational, but a T-value of ~150 C is shown for convenience. Note that the metamorphic field has no upper P–T limit on this diagram, and that there is a large overlap for metamorphic and magmatic conditions. Extreme P–T conditions are shown for the following areas: (1) Sapphirine quartzite from the Napier Complex, Antarctica (Harley and Motoyoshi 2000); (2) Scourian granulites from NW Scotland (Lamb et al. 1986, Fig. 3); (3) Pyrope-coesite rocks from Dora Maira, western Alps (Schertl et al. 1991); (4) diamond-bearing metamorphic rocks from the Kokchetav massif, northern Kazakhstan (Shatsky et al. 1995); (5) Garnet peridotite from the Su- Lu unit, east central China (Yang et al. 1993). The wet granite melting curve is after Stern and Wyllie (1981), and the dry granite melting curve is after Newton (1987, Fig. 1)

6 1 Definition, Conditions and Types of Metamorphism metamorphism is not restricted to the Earth’s crust. A given volume of rock in the convecting mantle continuously undergoes metamorphic processes such as recrystallization and various phase transformations in the solid state at temperatures in excess of 1,500 C.

(Parte 1 de 7)

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