Fossil earthquakes : the formation and preservation of Pseudotachylytes

This book focuses on the earthquake source materials produced or deformed by both seismic faulting and aseismic creep within seismogenic fault zones at different levels of the crust. In particular, the mechanisms and processes involved in the formation of earthquake materials are covered. The book is intended to help bridge the gap between seismology and geology and to encourage further studies of earthquake mechanisms and seismic faulting processes.

1 Introduction	p. 1
2 Terminology and Origin of Pseudotachylyte	p. 5
2.1 Terminology	p. 5
2.2 Controversy Regarding the Physical Origin of Pseudotachylyte	p. 8
3 Pseudotachylyte-Related Fault Rocks and Conceptual Fault Models	p. 17
3.1 Introduction	p. 17
3.2 Fault Rocks	p. 18
3.2.1 Classification of Fault Rocks	p. 18
3.2.2 Mylonitic Rocks	p. 23
3.2.3 Cataclastic Rocks	p. 25
3.2.4 Formation of S-C Fabrics	p. 39
3.3 Fault Zone Strength and Fault Model	p. 40
3.3.1 Seismogenic Fault Zone Strength	p. 40
3.3.2 Conceptual Fault Zone Model	p. 43
4 Tectonic Environment and Structure of Pseudotachylyte Veins	p. 47
4.1 Tectonic Environment and Field Occurrence of Pseudotachylyte	p. 47
4.1.1 Tectonic Environment	p. 47
4.1.2 Field Occurrence	p. 48
4.1.3 Chilling-margin and Crack Textures	p. 55
4.2 Classification of Pseudotachylyte Veins	p. 60
4.2.1 Fault Veins and Injection Veins	p. 60
4.2.2 Pseudotachylyte Generation Zones	p. 64
4.3 Relation Between Fault Vein Thickness and Slip Amount	p. 70
5 Pseudotachylyte Matrix	p. 75
5.1 Introduction	p. 75
5.2 Microstructural Characteristics	p. 76
5.2.1 Textural Classification of Pseudotachylyte Matrix	p. 76
5.2.2 Flow Structures	p. 81
5.2.3 Vesicles and Amygdules	p. 84
5.3 Powder X-Ray Diffraction Analysis	p. 90
5.3.1 X-Ray Diffraction Patterns for Pseudotachylyte	p. 90
5.3.2 Quantitative Analysis of Glass and the Crystalline Fraction	p. 93
5.3.3 Quantitative Analysis of Crystalline Material	p. 95
5.4 Discussion	p. 96
5.4.1 Properties of Glass and Glassy Matrix	p. 96
5.4.2 Effect of Frictional Melt on Fault Strength	p. 97
5.4.3 Estimation of the Formation Depth of Pseudotachylyte	p. 98
6 Microlites	p. 105
6.1 Introduction	p. 105
6.2 Texture and Morphology of Microlite	p. 106
6.2.1 Texture	p. 106
6.2.2 Morphology	p. 106
6.3 Microlite Chemistry and Magnetic Properties	p. 118
6.3.1 Microlite Chemistry	p. 118
6.3.2 Magnetic Properties	p. 128
6.4 Discussion of the Mechanism of Microlite Formation	p. 132
7 Fragments Within Pseudotachylyte Veins	p. 139
7.1 Terminology	p. 139
7.2 Fragments that Resemble Conglomerate Clasts	p. 139
7.3 Grain-size Analysis	p. 143
7.3.1 Grain-size Distribution Within Melt-origin Pseudotachylyte	p. 143
7.3.2 Grain-size Distribution: A Discussion	p. 148
7.4 Fabrics of Fragments and Degree of Rounding	p. 151
7.4.1 Fabrics	p. 151
7.4.2 Degree of Rounding of Fragments	p. 151
7.5 Formation of Rounded Fragments: A Discussion	p. 155
8 Chemical Composition and Melting Processes of Pseudotachylyte	p. 159
8.1 Introduction	p. 159
8.2 Bulk-Vein and Matrix Compositions	p. 160
8.2.1 Bulk Composition of Pseudotachylyte Veins	p. 160
8.2.2 Chemical Composition of Pseudotachylyte Matrix	p. 162
8.2.3 Water Contents of Pseudotachylyte Veins	p. 168
8.3 Discussion	p. 169
8.3.1 Melting Processes	p. 169
8.3.2 Melt Temperature	p. 171
8.3.3 Role of Water During Frictional Melting	p. 173
9 Formation of Pseudotachylyte in the Brittle and Plastic Regimes	p. 177
9.1 Introduction	p. 177
9.2 Woodroffe Pseudotachylytes	p. 179
9.2.1 Tectonic Setting of the Woodroffe Thrust	p. 179
9.2.2 Field Occurrences of the Woodroffe Pseudotachylytes	p. 181
9.2.3 Microstructures	p. 187
9.3 Dahezhen Pseudotachylytes	p. 197
9.3.1 Tectonic Setting of the Dahezhen Shear Zone	p. 197
9.3.2 Field Occurrence of the Dahezhen Pseudotachylytes	p. 198
9.3.3 Microscopy and Chemical Composition	p. 204
9.4 Discussion	p. 212
9.4.1 Formation Mechanisms of Large Volumes of Pseudotachylytes	p. 212
9.4.2 Conditions of Formation of the Dahezhen and Woodroffe M-Pt Veins	p. 216
10 Crushing-Origin Pseudotachylyte and Veinlet Cataclastic Rocks	p. 225
10.1 Introduction	p. 225
10.2 Occurrence of Crushing-Origin Pseudotachylyte and Cataclastic Veins	p. 226
10.2.1 Crushing-Origin Pseudotachylyte	p. 226
10.2.2 Fault-Gouge Injection Veins	p. 230
10.2.3 Layered Fault Gouge and Pseudotachylyte Veins	p. 232
10.2.4 Crack-Fill Veins	p. 234
10.3 Petrologic Characteristics of Veinlet Cataclastic Rocks	p. 237
10.3.1 Microstructures of Veinlet Cataclastic Rocks	p. 237
10.3.2 Powder X-ray Diffraction Analysis of Veinlet Material	p. 244
10.3.3 Chemical Composition Data and Isotope Analyses	p. 250
10.3.4 Age Data for Crack-fill Veins	p. 252
10.4 Discussion on the Formation Mechanisms of Veinlet Cataclastic Rocks	p. 253
10.4.1 Formation Mechanism of Amorphous Material Within Veinlet Cataclastic Rocks	p. 253
10.4.2 Coseismic Fluidization of Fine-grained Material Within Fault Zones	p. 254
10.4.3 Repeated Events of Seismic Slip	p. 256
10.4.4 Repeated Coseismic Infiltration of Surface Water into Deep Fault Zones	p. 257
11 Landslide-related Pseudotachylyte	p. 265
11.1 Introduction	p. 265
11.2 Occurrences of Landslides and Related Pseudotachylytes	p. 266
11.2.1 Langtang Himalaya Landslide and Related Pseudotachylyte	p. 266
11.2.2 Chiufener-Shan Landslide and Related Pseudotachylyte	p. 269
11.3 Petrographic Characteristics of Landslide-related Pseudotachylytes	p. 274
11.3.1 Petrography of the Langtang Himalaya Pseudotachylyte	p. 274
11.3.2 Petrography of the Chiufener-Shan Pseudotachylyte	p. 277
11.3.3 Glass Contents of the Observed Pseudotachylytes	p. 279
11.4 Discussion of the P-T Conditions during the Formation of Landslide-related Pseudotachylyte	p. 280
12 Experimentally Generated Pseudotachylyte	p. 283
12.1 Introduction	p. 283
12.2 High-Velocity Frictional Experiments	p. 284
12.2.1 Test Equipment and Experimental Conditions	p. 284
12.2.2 Experiment Samples and Procedures	p. 290
12.2.3 High-Velocity Frictional Properties	p. 292
12.3 Microstructures of Experimentally Generated Pseudotachylyte	p. 293
12.3.1 Textures of the Fault Shear Plane	p. 293
12.3.2 Vein Geometry and Texture of Molten Material	p. 294
12.4 Powder X-ray Diffraction Analysis of Run Products	p. 300
12.4.1 Diffraction Patterns of Run Products	p. 300
12.4.2 Quantitative Analysis	p. 301
12.5 Chemical Composition Data	p. 304
12.5.1 Gabbro Samples	p. 304
12.5.2 Granite Samples	p. 307
12.5.3 Albitite-Quartz and Anorthosite-Anorthosite Pairs	p. 308
12.6 Discussion	p. 315
12.6.1 Vein Geometry	p. 315
12.6.2 Melting Textures	p. 315
12.6.3 Non-equilibrium Melting Processes	p. 316
12.6.4 Melting Temperature	p. 318
12.6.5 High-Velocity Slip Weakening	p. 319
References	p. 321
Index	p. 341

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