C. W. Passchier · R. A. J. Trouw Microtectonics

Springer-Verlag Berlin Heidelberg GmbH

C. W. Passchier · R. A. J. Trouw

Microtectonics

With 254 Figures

Springer

PROF. DR. C. W. PASSCHIER

Universitat Mainz Institut fur Geowissenschaften 55099 Mainz Germany

PROF. DR. R. A. J. TROUW

Universidade Federal do Rio de Janeiro Depto. de Geologia CEP 21910-900 Rio de Janeiro Brazii

znd corrected reprint 1998

CIP data applied for.

Die Deutsche Bibliothek- CIP-Einheitsaufnahme

Passchier, Cornelis W.: Microtectonics 1 C. W. Passchier ; R. A. J. Trouw. - 2., corr. reprint.

ISBN 978-3-662-08736-7 ISBN 978-3-662-08734-3 (eBook)

DOI 10.1007/978-3-662-08734-3

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To HENK ZWART

To see a world in a grain of sand and a heaven in a wild flower hold infinity in the palm of your hand and eternity in an hour

Wiliam Blake

For his contribution to structural and metamorphic geology

Introduction

The origin of this book lies in a practical course in microtectonics started by Prof. Henk Zwart at Leiden University, the Netherlands, in the early 1960s. Both of us were students of Henk Zwart at the University of Leiden and later, as his assistants, charged with the organisation of this course. As such, we became enchanted by the many interesting thin sections of his collection which expanded over the years, as Henk extended his work from the Pyrenees to the Alps, the Scandinavian Caledonides and to many other places in the world. An explanatory text was elaborated and regularly updated by a number of assistants, including us, under Henk's supervision. This text, together with many thin sections of the collection, served as a core for the present book. In the early 1980s, the Geology Department of Leiden University was transferred to the University of Utrecht. The collection was transferred as well, and one of us (C.W.P) became responsible for its organisation and maintenance. A visit of R.A.J.T to Utrecht in 1991 with a number of didactic microstructures collected in South America triggered the final effort to build a manual for the study of micro tectonics. Because of his contributions to science and his enthusiasm for micro tectonics, we dedicate this book to Henk Zwart, who inspired us, taught us the principals of microtectonic analysis, and also furnished many crucial examples of microstructures.

Few geologists will be able to remember what their first impression was when they were confronted with a deformed rock under the microscope. That is unfortunate, because it inhibits experienced geologists from looking at geo­metries in thin section in an unbiased way. We commonly think that we 'see' dynamic recrystallisation, refolding and grain growth, while all we actually see are geometric patterns that may have formed in a number of different ways. In this book, we try to preserve some of the 'first encounter approach' with deformed rocks. Where possible, we present a description of the geometry of structures separately, followed by their state-of-the-art interpretation.

This book is meant for advanced undergraduate and graduate students, and is best used in combination with a practical course where thin sections can be studied and discussed. In our experience, a collection of 100-200 thin sec­tions with examples from structures treated in our Chapters 3-7 are sufficient for such a course.

In Chapter 1 the 'philosophy' of how we think that microstructures can be understood is discussed, including their usefulness in tectonic studies. Chapter 2 gives a simplified, non-mathematical background in kinematics and rheology, meant to explain the terminology used in the interpretation of microstructures. Deformation on the grain scale and deformation mechanisms are treated in Chapter 3· Chapters 4 to 7 form the core of the book and deal with the most commonly observed microstructures. In Chapter 8 a brief outline is given of a

VIII Introduction

new development in microtectonics which we called microgauges: structures that can be used to obtain quantitative data from deformed rocks. Chapter 9 describes a number of additional techniques other than optical microscopy. These techniques either use thin sections, or can be used in combination with optical microscopy to obtain additional data. The descriptions are short but should allow the reader to decide if his material can be studied using a techni­que with which he may not be familiar. Chapter 10 describes the problems involved with sampling and preparation of thin sections, including the pro­blems of the interpretation of three-dimensional structures using two-dimen­sional sections. Chapter 11 is a selection of photographs meant as examples of common problems in microtectonics; the reader may use them as an exercise trying to interpret the structure; our interpretation is given at the end of the chapter. A glossary of commonly used terminology in microtectonics is given at the end of the book; the definitions in this glossary reflect our opinion on the meaning of the terminology as used at present.

Since this book mainly deals with interpretation of geometries, a large number of drawings and photographs are included. We decided to use only black and white photographs in order to obtain maximum contrast and to keep costs of the book down. In the figure captions, PPL and CPL mean plane pola­rised and crossed polarised light, respectively. Provenance of the photographed thin sections is given where known. For some thin sections in the old collection from Leiden, the provenance is unknown and these were marked as 'Leiden Collection'. The scale of the photographs is given as a width of view.

The following critical readers of the original manuscript helped consider­ably to improve the book with useful suggestions: Hans de Bresser, Bas den Brok, Paul Dirks, David Grey, Monica Heilbron, Renee Heilbronner, Ralph Het­zel, Kyu-ichi Kanagawa, Win Means, Uwe Ring, Herman van Roermund, Luiz Sergio Simoes, Carol Simpson, Ron Vernon and Janos Urai. Bas den Brok provi­ded data for Chapter 3.12 and drew the original of Fig. 3.32. Their help is grate­fully acknowledged. Preparation of the manuscript was assisted by Anja Bohm, Magda Martens, Susanne Laws, Regina Summerer, Kerstin Thiel and Robert Bolhar, who are thanked for their efforts. Some of the photographs, samples and thin sections were kindly provided by Ralph Hetzel (Figs. 5.14, 7-45, 11.15), Paul Dirks (Figs. 7.51-54), Domingo Aerden (Fig. 11.10), Michel Arthaud (Fig. 6.23), Coen ten Brink (Fig. 9.11), Hanna Jordt-Evangelista (Fig. 7.21), Reinhardt Fuck (Fig. 11.14), Leo Kriegsman (Fig. 7.52), Gordon Lister (Fig. 4.24), Leo Minnigh (Fig. 6.24), Jin-Han Ree (Fig. 9.10), Andre Ribeiro (Fig. 11.2), Chris Schoneveld (Figs. 7.37, 11.16, and cover), Janos Urai (Fig. 6.2), Simon Wallis (Figs. 4.35, 7.35), Klaus Weber (Fig. 9.3) and Dirk Wiersma (Fig. 6.14a). Many other persons helped in one way or the other, either by furnishing samples with interesting microstructures that were integrated in our collections but not shown, or by discussing the meaning of microstructures. Their help is also gratefully acknowledged.

The Volkswagen Stiftung, the German Science Foundation (DFG), the Schil.rmann Fund, the Dutch Royal Academy of Sciences and the Brasilian Research Council ( CNPq) provided funding for our research, the results of which have been used in this book; this support is gratefully acknowledged. R.A.J.T thanks the Brasilian Research Council (CNPq) for financing his stay at Utrecht University and the Department of Geology in Utrecht for its hospitality.

C. W. Passchier R. A. J. Trouw

Contents

1 A Framework of Micro tectonic Studies . . . . . . 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . 1.2 Establishing and Interpreting Deformation Phases 1.3 Deformation Phases and Metamorphic Events

2 Flow and Deformation

1 1 3 5

7 2.1 Introduction 7 2.2 Terminology 7 2.3 Description and Reconstruction of Deformation 7 2.4 Reference Frames . . . . . . . . . . . . . . . . . . 8 2.5 Homogeneous and Inhomogeneous Flow and Deformation 11

2.5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . 11 2.5.2 Numerical Description of Homogeneous Flow and Deformation 13

2.6 Deformation and Strain . . . . . . . . . . . . 17 2.7 Progressive and Finite Deformation . . . . . 18 2.8 Flow and Deformation in Three Dimensions 19 2.9 Fabric Attractor . . . . . . 19 2.10 Application to Rocks . . 20 2.11 Stress and Deformation 20 2.12 Rheology . . . . . . . . . 21

3 Deformation Mechanisms 25 3.1 Introduction 25 3.2 Cataclastic Flow 25 3.3 Pressure Solution 26 3.4 Intracrystalline Deformation 29 3.5 Twinning 31 3.6 Recovery . . . . . . . . . . . 32 3.7 Recrystallisation . . . . . . . 36

3.7.1 Grain Boundary Migration Recrystallisation 36 3.7.2 Subgrain Rotation Recrystallisation . . . . 36 3.7.3 Competing Processes During Deformation 40

3.8 Solid-State Diffusion Creep . . . . . . . . . . 40 3.9 Grain Boundary Sliding and Superplasticity . 41 3.10 Grain Boundary Area Reduction (GBAR) . . 43 3.11 Static Recrystallisation . . . . . . . . . . . . 45 3.12 Deformation of Some Rock-Forming Minerals 48

3.12.1 Introduction . . . . . 48 3.12.2 Quartz . . . . . . . . 48 3.12.3 Calcite and Dolomite 48

X

3.12.4 Feldspars 3.12.5 Micas .. 3.12.6 Olivine . 3.12.7 Orthopyroxene 3.12.8 Clinopyroxene . 3.12.9 Amphiboles ..

3.13 Deformation of Polymineralic Rocks 3.13.1 Introduction . . . . . . . . . 3.13.2 Quartz-Feldspar Aggregates . 3.13.3 Deformed Ignimbrites ....

3.14 Flow Laws and Deformation Mechanism Maps

4 Foliations, Lineations and Lattice Preferred Orientation 4.1 Introduction 4.2 Foliations . . . . . . 4.3 Primary Foliation 4.4 Diagenetic Foliation 4.5 Secondary Foliations 4.6 Morphology of Foliations 4.7 Continuous Foliation . . . 4.8 Spaced Foliation 4.9 Mechanisms of Foliation Development

4.9.1 Introduction .......... . 4.9.2 Mechanical Rotation of Tabular or Elongate Grains. 4.9.3 Solution Transfer ...... . ... . ... . . . . 4.9.4 Crystalplastic Deformation .. .......... . 4.9.5 Dynamic Recrystallisation and Related Processes 4.9.6 Mimetic Growth . . . . . . . . . . . . . . . 4.9.7 Oriented Growth Defined by a Stress Field 4.9.8 Microfolding . . . . . . . . . . . . . . . .

4.10 Geological Context of Foliation Development . 4.10.1 Foliations and Folds .. ........ . 4.10.2 Foliations and The XY Plane of Tectonic Strain 4.1 0.3 Foliations, Strain and Volume Change 4.10.4 Foliations, Lithotype and Metamorphic Conditions

4.11 Practical Use of Foliations . . 4.11.1 Introduction . . . . . . . . . . 4.11.2 Overprinting Relations . . . .

4.12 Lattice-Preferred Orientation (LPO) 4.13 Origin of Lattice-Preferred Orientation 4.14 Presentation of LPO Data 4.15 LPO Patterns of Quartz ...... . . .

4.15.1 Introduction .......... . 4.15.2 The Effects of Strain and Recrystallisation 4.15.3 Shear Sense Determination Using Quartz Fabrics

4.16 LPO Patterns of Other Minerals ............. .

5 Shear Zones . . . . 5.1 Introduction 5.2 Brittle Fault Rocks

5.2.1 Incohesive Fault Rocks 5.2.2 Cohesive Fault Rocks 5.2.3 Pseudotachylyte . . ..

Contents

49 50 50 50 51 51 51 51 52 53 53

57 57 58 59 61 61 63 64 65 69 69 69 70 74 75 76 77 77 78 78 78 82 83 84 84 86 88 89 90 92 92 93 95 95

97 97 98 98 99 99

Contents

5.3 Mylonite . . . .. .. .. . ... . . . 5.3.1 Introduction . .. .. ... . . 5.3.2 Characteristic Fabric Elements 5.3.3 Mylonite Classification . . .. 5.3.4 Dynamics of Mylonite Development 5.3.5 Mylonite and Metamorphic Conditions

5.4 Complex Fault Rocks 5.5 Sense of Shear . . .. ... . .. ... ... .

5.5.1 Introduction . . . . . . . . . . . . . . . 5.5.2 Displacement and Deflection of Markers 5.5.3 Foliation Curvature . . . . . . . . . . . .

5.6 Microscopic Shear Sense Indicators in Mylonite 5.6.1 Introduction . . . . . 5.6.2 Foliation Orientation 5.6.3 Oblique Foliations . . 5.6.4 Shear Band Cleavages 5.6.5 Mantled Porphyroclasts 5.6.6 Development of Mantled Porphyroclasts 5.6.7 Mica Fish .. ..... .. . . 5.6.8 Quarter Structures . . . . . . . . . . . . 5.6.9 Lattice-Preferred Orientation . ... . . 5.6.10 Vergence of Asymmetric Fold Sections 5.6.11 Potential Shear Sense Markers

5.7 Shear Sense Indicators in the Brittle Regime 5.7.1 Introduction .. . .. . .. . . 5.7.2 Incohesive Brittle Fault Rocks 5.7.3 Cohesive Brittle Fault Rocks 5.7.4 Pseudotachylyte ... . . .. .

6 Dilatation Sites: Vibrous Veins, Strain Shadows, Strain Fringes and Boudins

6.1 Introduction 6.2 Fibrous Veins . . . . . . . .

6.2.1 Introduction 6.2.2 Curved Fibres and Fibre Growth Direction 6.2.3 Veins in Non-Coaxial Progressive Deformation

6.3 Strain Fringes . . . . . . . . . . . . . . . 6.3.1 Introduction . . . . . . . . . . . . 6.3.2 Fringes on Spherical Core Objects 6.3.3 Fringes on Angular Core Objects .

6.4 Fibres and the Deformation Path . . . . 6.5 Non-Fibrous Strain Shadows and Strain Caps 6.6 Microboudinage . . . . . . . . . . .

7 Porphyroblasts and Reaction Rims 7.1 Introduction ........ . ... . 7.2 Porphyroblast Nucleation and Growth 7.3 Inclusions .... . . . . . .. ... . . 7.4 Classification of Porphyroblast-Matrix Relations

7.4.1 Introduction ... . .. .. .. . . . 7 .4.2 Pretectonic Porphyroblast Growth . 7.4.3 Intertectonic Porphyroblast Growth 7.4.4 Syntectonic Porphyroblast Growth . 7.4.5 Post-Tectonic Porphyroblast Growth

XI

102 102 103 106 106 106 108 109 109 109 109 110 110 110 111 111 115 116 121 123 124 124 124 128 128 128 128 129

131 131 133 133 136 139 141 141 141 143 145 148 149

153 153 154 154 157 157 159 161 162 163

XII

7.4.6 Complex Porphyroblast Growth ..... 7.5 Millipede and Deflection-Fold Microstructures 7.6 Problematic Porphyroblast Microstructures ..

7.6.1 Inclusion-Free Porphyroblasts ..... . 7.6.2 Shape and Size of Inclusion and Matrix Grains 7.6.3 False Inclusion Patterns 7.6.4 Mimetic Growth ................ . 7.6.5 Deformed Porphyroblasts ........... . 7.6.6 Uncertain Age Relation of Host and Inclusions 7.6.7 Discontinuous Si and Se ............ . 7.6.8 Rotation of Porphyroblasts .......... .

7.7 Crystallographically Determined Inclusion Patterns 7.8 Reaction Rims ..... .

7.8.1 Introduction ... . 7.8.2 Coronas and Moats 7.8.3 Symplectites .... 7.8.4 Establishing the Nature of Reactions 7.8.5 Pseudomorphs ............ . 7.8.6 Relation with Deformation ..... .

7.9 Reconstruction of Tectono-Metamorphic Evolution

8 Natural Microgauges 8.1 Introduction 8.2 Strain Gauges . . . 8.3 Vorticity Gauges

8.3.1 Introduction 8.3.2 Deformed Sets of Veins

Contents

163 169 170 170 170 172 172 173 173 176 176 182 185 185 187 190 192 194 194 194

197 197 197 199 199 199

8.3.3 Lattice-Preferred Orientation 199 8.3.4 Mantled Porphyroclasts, Fibrous Veins and Fringes 200 8.3.5 Porphyroblasts . . . . . . . . . . . . . . . . . . 200 8.3.6 Tension Gashes and Foliations in Shear Zones 200 8.3.7 Oblique Foliations . . . 200 8.3.8 Al-Cr Zoning in Spinel 200 8.3.9 W k History . . . . . . . 200

8.4 The Concept of Palaeostress Gauges 201 8.5 Gauges for the Orientation of Palaeo stress Principal Axes 201

8.5.1 Calcite Twins . . . . . . . . . . . . . . . . . . . . . . 201 8.5.2 Deformation Lamellae ........................ 201

8.6 Differential Stress Gauges (Palaeopiezometers) 202 8.6.1 Dynamically Recrystallised Grain Size 202 8.6.2 Twins in Calcite and Dolomite 203 8.6.3 Microboudins 203 8.6.4 Deformation Lamellae 203

8.7 Pressure Gauges 8.8 Strain Rate Gauges . 8.9 Temperature Gauges 8.10 Rheology Gauges .

8.10.1 Introduction 8.10.2 Folding and Boudinage 8.10.3 Mantled Objects

9 Special Techniques . . 9.1 Introduction 9.2 Cathodoluminescence

203 204 204 206 206 207 207

209 209 209

Contents

9.3 Fluid Inclusion Studies 9.4 Electron Microscopy . . ... . ... . 9.5 Scanning Electron Microscope (SEM)

9.5.1 Introduction ..... .. .. . . 9.5.2 Secondary and Backscatter Electrons 9.5.3 Problems with Orientation .. . . . 9.5.4 Sample Preparation ........ .

9.6 Transmission Electron Microscope (TEM) 9.6.1 Introduction .... 9.6.2 Sample Preparation

9.7 Image Analysis ..... . 9.7.1 Introduction . . . . 9.7.2 Heilbronner Method

9.8 Lattice-Preferred Orientation 9.8.1 Introduction . . ... . 9.8.2 U-Stage Measurements 9.8.3 Sample Selection and Preparation for Measurement 9.8.4 Optical Bulk Analysis- Price Method 9.8.5 CIP Method 9.8.6 Texture Goniometers 9.8.7 Channelling

9.9 Analogue Modelling 9.9.1 Introduction 9.9.2 Linear Rig 9.9.3 Torsion Rig . 9.9.4 Triaxial Rig . 9.9.5 Marker Particles 9.9.6 Analogue Experiments

9.10 Use of the U-Stage 9.10.1 Introduction .. . . . 9.10.2 Preparation of the Stage for Measurement 9.10.3 Measurement of c-Axes of Quartz 9.10.4 Notation of Measurements

10 From Sample to Section 10.1 Introduction . . . . . . . 10.2 Sampling . . . . . . . . . 10.3 Orientation of Hand Specimens 10.4 Where to Sample in Outcrop 10.5 Cutting Samples . .. .. . .. . 10.6 Types of Thin Sections . .. . . 10.7 Geometries in Thin Section- a Problem of Dimensions 10.8 Choosing the Orientation of Thin Sections

11 Exercises . . . . 11.1 Introduction . . 11.2 Problem Section 11.3 Interpretations

Glossary .

References

Index .. .

XIII

210 211 211 211 212 213 213 216 216 217 217 217 218 218 218 218 219 219 219 220 220 220 220 220 223 223 223 224 225 225 225 228 230

231 231 231 231 231 233 233 234 236

239 239 239 250

255

267

283

Abbreviations and Principal Symbols

Ak AVA diagram CCC CIP CISH CPL CRSS £ £ EDAX FA GBAR GBM recrystallisation ISA Lr LPO OCP ODF diagram PPL P-T diagram PTt path R/<p

(JI, (J2' (J3

(Jn

s sl, s2, s3

sr sbc SR recrystallisation 't

TTT diagram wk (0

X, Y,Z axes

kinematic dilatancy number Achsenverteilungsanalyse-Diagram compressional crenulation cleavage computer-integrated polarisation microscopy cumulative incremental strain history crossed polarised light critical resolved shear stress ( 't c) strain strain rate energy dispersive X-ray analysis fabric attractor grain boundary area reduction grain boundary migration recrystallisation instantaneous stretching axis reference lineation lattice-preferred orientation octachloropropane orientation distribution function diagram plane polarised light pressure temperature diagram pressure temperature time path Rf: elliptic ratio of objects; <p angle of longest axis of elliptical shape with reference direction stress principal stress values normal stress stretch in Chapter 2: principal stretches or principal strain values (length of principal strain axes). In other chapters and in the literature also used as abbreviation for foliations stretching rate internal foliation in a porphyroblast with inclusions external foliation with respect to a porphyroblast with inclusions reference foliation shear band cleavage subgrain rotation recrystallisation shear stress time-temperature-transformation diagram kinematic vorticity number angular velocity of material lines principal axes of strain