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structural Geology Principles, Concepts, and Problems

Second Edition

CONTENTS

PREFACE TO THE SECOND EDITION mmBi

PREFACE TO THE FIRST EDITION ix

PART ONE INTRODUCTION 1

1 INTRODUCTION AND REVIEW 2 Fundamental Concepts 5 Plate Tectonics 10 Geochronology 12 Equilibrium 15 ESSAY Capability of Tectonic Structures 17 Geologic Cycles 20 Questions 21 Further Reading , . . n 22

2 NONTECTONIC STRUCTURES 23 Primary Sedimentary Structures 24 Sedimentary Facies 31 Unconformities 31 ESSAY Deciphering a Major Structure in the Southern Highlands of Scotland 33 Primary Igneous Structures 35 Gravity-Related Features v: 38 Impact Structures 43 Questions -^J y^a wrkio-mst^M hoc ,<r9j i- 45 Further Readi ng 46

PART TWO ROCK MECHANICS 47

3 S T R E S S _ 48 Definitions 49 Stress on a Plane , . Stress at a Point " " 54 Stress Ellipsoid ,,. 55 Mohr Construction 56 Amonton's Law and the Coulomb-Mohr Hypothesis 57 ESSAY Measuring Present-Day Stress in the Earth 59

Q^f'T • . O n ^ m r n A d J i o , Further Reading o**

65 66 66 69 70 71 73 74 75

5 STRAIN MEASUREMENT 76 Kinds of Strain 76 Strain Markers 76 Flinn Diagram 80 Strain-Measurement Techniques 82 Fibers as Strain Indicators 68 Determination of Pressure-Solution Strain 90 Questions 90 ESSAY PROBLEM Finite Strain from Deformed Pebbles 91 Further Reading 95

6 MECHANICAL BEHAVIOR OF ROCK MATERIALS 96 Definitions 97 Elastic (Hookean) Behavior rvn«t t . 98 Permanent Deformation—Ductility \ 100 Controlling Factors 103 Behavior of Crustal Rocks 103 Strain Partitioning 105 ESSAY Silly P u t t y a n d the Behavior of Mantle Rocks 107 Questions 108 Further Reading 109

7 MICROSTRUCTURES AND DEFORMATION MECHANISMS 111 Lattice Defects and Dislocations 112 Deformation Mechanisms 117 Unrecovered Strain, Recovery, and Recrystallization 125 Laboratory Models of Deformation Processes ^ 128 Discussion 129 ESSAY Cataclasites, Mylonites, and Metamorphic Rocks 131 Questions 134 Further Reading 134

PART THREE FRACTURES AND FAULTS 137

8 JOINTS AND SHEAR FRACTURES 138 Fracture Analysis 142 Formation of Fractures: Griffith Theory 145 Joints and Fracture Mechanics , , , _ 148 Joints in Plutons ' ' 154 Nontectonic and Quasitectonic Fractures 155 ESSAY Mesozoic Fracturing of Eastern North American Crust—Product of Extension or Shear? 158 Questions 160 Further Reading 161

4 STRAIN Definitions Measures of Strain Strain Ellipsoid Mohr Circles for Strain Simple and Pure Shear

ESSAY Daubree and Mead Experiment Questions Further Reading

9 FAULT CLASSIFICATION AND TERMINOLOGY PT 162 --atomy of Faults 163 --oersonian Classification 165 f-teria for Faulting 166

AY Existence and Displacement Sense of Large Faults 170 :-estions 174 .-ner Reading ^ 174

D FAULT MECHANICS 175 - - - - -son ' s Fundamental Assumptions , _ 176

- Vs Fault Types 177 - Fluids 178

: nal Sliding Mechanisms 180 vment Mechanisms 180 - Frictional) Heating in Fault Zones yitscinv : • MOitoS yd? T, . 183 r and Ductile Faults \ 184 • Zones \ 186

- • Artificial Earthquakes 188 -Sense Indicators 189 -Zone Kinematics 194

- • Differences in Behavior of Crustal Faults 198 "ons 198 er Reading 199

• * THRUST FAULTS ' 200 J T Thrust Faults 204

V : -ment Within a Sedimentary Sequence ' 207 --action (Wedge) and Extension Faults 212 agation and Termination of Thrusts " , 213

- Produced by Erosion 215 -,e Thrusts ' 218

- : The Paradox of Large Overthrust Faults "' 220 - Mechanics 222

. ersus Compression 225 cs of Crystalline Thrusts 227

\atural Model Gravity Foldbelt 228 -1 Problem and Cross-Section Construction 230

n , 231 234

Feading 234

- 2 STRIKE-SLIP FAULTS 236 - es and Geometry 236

•ents of Strike-Slip Faulting r,- 237 - Fault Zones 237 ;5 of Strike-Slip Faulting ' , 239

r ? metry Related to Other Fault Types 240 : ons of Strike-Slip Faults 241

•op - : r y y , - 241 - gid Indenters and Escape Tectonics 246

248 . Feading 248

13 NORMAL FAULTS f0O 249 Properties and Geometry 250 Environments and Mechanics 252 ESSAY inverted Faults and Tectonic Inheritance 265 Questions , _ 269 Further Reading . 269

PART FOUR FOLDS AND FOLDING 271

14 FOLD GEOMETRY AND CLASSIFICATIONS ' 272 Descriptive Anatomy of Simple Folds 273 Map-Scale Parallel Folds and Similar Folds 283 Fold Classifications 286 ESSAY Folds in the Development of the Petroleum Industry 296 Questions - i s u j j j t^a: 297 Further Reading 298

15 FOLD MECHANICS 299 Fold Mechanisms and Accompanying Phenomena _ 300 Deformation Mechanisms and Strain • n n y 31g Discussion 317 ESSAY Fold Mechanisms, Space, Time, and Orogenic Belts S' 323 ESSAY Deciphering the Fold Mechanisms of Two Small Folds 327 Questions 330 Further Reading 330

16 COMPLEX FOLDS ; 332 Occurrence and Recognition •

Fold-Interference Patterns 333 Recognition of Multiple Fold Phases r l ' ! - 335 Noncylindrical and Sheath Folds , , , 335 Formation of Complex Folds ' ' ' ' 337 Mechanical Implications of Complex Folding 339 ESSAY The Value of Rosetta Stones ,,,, - 343 Questions , s T ^ ,t - ^. .-• ) .r^-« 346 Further Reading .

PART FIVE FABRICS, PLUTONS, AND STRUCTURAL ANALYSIS 349

17 C L E A V A G E AND FOLIATIONS ^ 350 Definitions 350 Cleavage-Bedding Relationships 355 Cleavage Refraction 355 Early Ideas on the Qrigin of Slaty Cleavage P : 359 Mechanics of Slaty Cleavage Formation -y i i f i i i H , ? 3g2 Crenulation Cleavage 369 Cleavage Fans and Transecting Cleavages 371 Transposition s.y;,. • ; •! 3 q t , j n r . .•-•?tnA>: 372

ESSAY Cleavage Formation and the Identification of Elephants 375 Questions T T 377 Further Reading y ; ^ ̂ .y v : , 377

— 5 - -

18 LINEAR STRUCTURES 379 ~^y-"»jons 379

• ons as Shear-Sense Indicators ~" 385 • _-.nd Lineations 385

ned Lineations 386 • --yyetation of Linear Structures 387

• Pitfalls in Interpreting Linear Structures 388 -•:ons 391

Reading 392

19 TECTONIC STRUCTURES IN PLUTONS 393 r -̂ nguishing Magmatic From Tectonic Structures 394

acement of Tabular Plutons 394 acement of Stocks and Batholiths 399

A T a l e o f Two Plutons 406 oions 411

- :aer Reading 412

20 STRUCTURAL ANALYSIS 413 - -itions 414

i ing Structures in Multiply Deformed Rocks 414 r jscopic Analysis 418

i»mmetry of Fabrics 420 Structural-Analysis Procedures 421 ESSAY Structural Analysis at Woodall Shoals 425 Questions 431 Further Reading 431

PART SIX GEOPHYSICAL TECHNIOUES IN STRUCTURAL GEOLOGY 433

21 GEOPHYSICAL TECHNIOUES 434 Potential Field Methods 434 Seismic Reflection 448 Seismic Refraction 453 Electrical Methods 453 ESSAY Enhancing Structural Interpretation with Geophysical Data 455 Questions 457 Further Reading 458

APPENDICES 459

APPENDIX 1 FABRIC DIAGRAMS 460 How to Begin 460 Planar Structures 460 Lines 461 Locating Fold Axes Using Equal-Area Plots: p and n Diagrams 463 Contouring Data 464

APPENDIX 2 STRUCTURAL MEASUREMENTS AND OBSERVATIONS Orientation of Planes: Strike and Dip Orientation of Lines: Trend and Plunge; Rake nosfeos'oni g^nsE-Shear-Sense Indicators -' Recording Data

APPENDIX 3 COMPUTER SOFTWARE FOR STRUCTURAL GEOLOGY

APPENDIX 4 WOODALL SHOALS FABRIC DATA

GLOSSARY

R E F E R E N C E S CITED

AUTHOR INDEX

S U B J E C T INDEX

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