EXPLORING. liarxh # AN INTRODUCTION TO PHYSICAL GEOLOGY JON P. DAVIDSON UNIVERSITY OF CALIFORNIA, LOS ANGELES WALTER E. REED

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1 EXPLORING liarxh # AN INTRODUCTION TO PHYSICAL GEOLOGY JON P. DAVIDSON UNIVERSITY OF CALIFORNIA, LOS ANGELES WALTER E. REED UNIVERSITY OF CALIFORNIA, LOS ANGELES PAUL M. DAVIS UNIVERSITY OF CALIFORNIA, LOS ANGELES Prentice Hall Upper Saddle River, NJ 07458

2 Preface About the Authors xv xviii CHAPTER 1 The Changing Planet 1 An Introduction to Plate Tectonics 3 / Climate and the Hydrologic Cycle 5 Understanding Earth: The Question of Scale 7 Geologic Time: An Important Perspective 11 Measuring Geologic Time 12 / The Present is the Key to the Past 14 A Process Approach to Physical Geology 16 FOCUS 1.1 A Matter of Perspective: Big and Small Numbers 12 FOCUS 1.2 The Philosophy of Science 18 CHAPTER 2 Earth: Origin and Composition 20 The Composition of the Universe 21 The Building Blocks of the Universe 24 Formation of the Elements 24 Our Solar System 27 Composition of the Solar System 27 I The Age and Origin of the Solar System 28 / The Planets 28 / Comets 29 / Asteroids and Meteorites 30 The Planet Earth, 31 Determining Earth's Composition 31 / Differentiation of Earth 34 I Earth's Core: Is it Iron? 37 / How Earth Works 39 The Future of Earth and Our Solar System 42 The Big Crunch 42 / The End of the Sun and Earth 42 FOCUS 2.1 The Doppler Shift: Evidence for the Expanding Universe 25 FOCUS 2.2 Impacts and Their Effects on Earth 32 FOCUS 2.3 ^Calculation of Density 35 FOCUS 2.4 The Moon 38 CHAPTER 3 Minerals: The Building Blocks of Rocks 46 What is a Mineral? 47 Atoms: The Building Blocks of Minerals 48 Building Minerals from Atoms 49 / Mineral Formation: Chemical Bonding 49 Crystals 51 Crystal Structures 51 / Controls on Crystal Structure 52 A Survey of Mineral Properties 55 vii

3 Mineral Groups 56 Silicate Minerals 56 / Nonsilicate Minerals 66 Distribution of Elements and Minerals in Earth 67 Compositional Layering within Earth 67 FOCUS 3.1 The Periodic Table 50 FOCUS 3.2 Determining Crystal Structures by X-ray Diffraction 53 FOCUS 3.3 Crystal Symmetry 54 FOCUS 3.4 Phase Diagrams 57 FOCUS 3.5 Solid Solutions 64 CHAPTER 4 The Cornerstones of Geology: Rocks! 71 Igneous Rocks 72 Intrusive and Extrusive Rocks 72 I Types of Intrusions 77 I Types of Volcanoes 80 / Melting and Magmatism 83 Sedimentary Rocks 86 Sedimentary Systems 86 / Types of Sediments 86 / Sedimentary Structures 92 / Lithification and Diagenesis 94 Metamorphic Rocks 95 Metamorphic Grade 96 / Types of Metamorphism 99 The Rock Cycle 102 FOCUS 4.1 Thin Sections 75 FOCUS 4.2 Crystallization of Lava: The Hawaiian Lava Lake 78 FOCUS 4.3 Simulating Earth's Interior 87 FOCUS 4.4 Determining Metamorphic Pressures and Temperatures 98 FOCUS 4^5 Getting Information from Rocks: Observation and Interpretation 104 CHAPTER 5 Earth Processes: Physical Principles 108 Seismic Waves 109 Density 109 / Elasticity 110 / Seismic P and S Waves 111 Velocity Variations Within Earth 112 Travel-Time Curves 112 / Travel Times within Earth 116 / Normal Modes 117 I Velocity Variations in the Crust 117 I Velocity Variations in the Mantle 118 / Seismic Velocity Variations in the Core 118 I Seismic Tomography 119 Gravity and Isostasy 121 Gravity 121 I Free-Air Gravity 122 / Bouguer Gravity 123 I Gravity Anomalies 124 I Isostasy 124 Geomagnetism 127 The Geodynamo 130 / Changes in Earth's Magnetic Field 131 I Paleomagnetism 132

4 FOCUS 5.1 The Velocities of Seismic Waves 114 FOCUS 5.2 Isostasy: Controls on Surface Elevation 128 FOCUS 5.3 Magnetic Fields in Space 132 CHAPTER 6 Plate Tectonics 136 Continental Drift: The Beginnings of the Idea 137 Wegener's Theory 139 / Problems with Continental Drift 139 I Geosynclines and Mountain Building 141 Plate Tectonics: A Unifying Theory 141 The Ocean Bottom and Sea-Floor Spreading 141 I Paleomagnetism and Polar Wandering 142 I Paleomagnetism and Sea-Floor Spreading 143 The Rock Record: Fossils, Climate, and Continents 144 Climate Dynamics 145 / The History of Earth's Climate 146 / Pangaea: Reconstruction of the Lost Continent 147 Plates and Plate Boundaries 151 Triple junctions 151 A Plate-Tectonic Link to Earthquakes and Volcanoes 152 Hot Spot Trails 154 Topography of the Lithosphere 155 What Drives Plate Motions? 156 Plate Motions Through Geologic Time 157 Uniformitarianism and Plate Tectonics 158 Living With Geology: Can Plate Tectonics Cause Ice Ages? FOCUS 6.1 The Nature of the Low-Velocity Zone 152 FOCUS 6.2 Vector Notation for Plate Motion 158 CHAPTER 7 Deformation, Earthquakes, and Formation of Geologic Structures 163.Crustal Deformation 164 Stress and Strain 164 I How Rocks Respond to Deformation 165 Geologic Structures 166 Joints 166 / Faults 167 / Folds 169 Earthquakes 172 Measuring Earthquakes 175 / Earthquake Locations 175 I Earthquake Sizes 175 I Foreshocks and Aftershocks 178 / Earthquake Motions 179 Plate Motions and Earthquakes 183 Measurement of Past Plate Motions 183 I Geodesy and Measurement of Present-Day Plate Motions 186 / Strain Measurement: Strainmeters and Tiltmeters 188 ix

5 Intraplate Deformation 188 Elastic Flexure of the Lithosphere 189 Volcano Deformation Cycle 189 FOCUS 7.1 Prediction of the Haicheng Earthquake of FOCUS 7.2 The Loma Prieta Earthquake 184 FOCUS 7.3 Volcanic Deformation in Hawaii 190 CHAPTER 8 Divergent Plate Margins and the Ocean Floor 194 Rifts: Windows to the Mantle 195 Continental Breakup and Plate Migration 195 / Oceans Subduct and Continents Rift 196 Oceanic Rifting 198 Mid-Ocean Ridges 198 / Oceanic Crust, Lithosphere, and Asthenosphere 198 / Anatomy of a Mid-Ocean Ridge 199 / Interaction of Mid-Ocean Ridge Basalts and Seawater 201 / Ocean- Ridge Uplift 202 I Central Grabens 206 I Propagating Rifts 206 I The Driving Mechanism for Sea-Floor Spreading 207 Continental Rifting 208 Structure of Continental Rifts 208 I Gravity 210 I Failed Rifts,*,. 211 I The Mechanisms for Continental Rifting 212 0' ''" FOCUS 8.1 The East Pacific Rise and Mid-Atlantic Ridge 204 FOCUS 8.2 Continental Rifting: The East African Rift 214 CHAPTER 9 Plates That Collide: Convergent Margins 221 The Action at Convergent Margins 224 Earthquakes at Convergent Margins 224 I Magmatism at Convergent Margins 227 Sedimentation in Arc Environments 237 Types of Sediment 237 I The Formation of an Accretionary Wedge 241 Continental Collisions: Plate Suturing 242 The Rise and Fall of Mountain Ranges 242 I Deformation and Metamorphism 244 Collage Tectonics and Exotic Terranes 248 Living With Geology 251 Explosive Volcanic Eruptions: A Hazard to Aircraft 251 FOCUS 9.1 The (Good Friday) Alaskan Earthquake 225 FOCUS 9.2 The Andes and the Lesser Antilles: A Continental Arc and an Oceanic Arc 228 FOCUS 9.3 The Eruption of Mount St. Helens 238 FOCUS 9.4 Estimation of the Crustal Root for Isostatic Equilibrium in the Himalayas 245

6 CHAPTER 10 The Conservative Boundary: Transform Plate Margins 253 The Nature of Transform Margins 254 Continental Transforms 258 I Mechanics of Strike-Slip Faulting 259 I Fault-Bend Geometries 262 Oceanic Transform Faults 269 Transform Faults and Fracture Zones 269 Living With Geology 271 Can Earthquakes Be Controlled? 271 FOCUS 10.1 The Alpine Fault, New Zealand 256 FOCUS 10.2 The San Andreas Fault, California 260 FOCUS 10.3 The Salton Trough of California: A Pull-Apart Basin 268 FOCUS 10.4 The Beginning of California's Transform Margin 270 CHAPTER 11 Plate Interiors 274 The Structure of Plates 275 Oceanic Lithosphere 275 / Continental Lithosphere 276 I Shields and Platforms 277 I The Origin of the Continental Lithosphere 278 I Passive Continental Margins: Junctures between Oceanic and Oontinental Lithosphere 279 i""" Sedimentation in Plate Interiors 281 Changes in Sea Level 281 I Sedimentary Successions at Passive Margins 284 Seismicity and Earthquakes in Plate Interiors 285 Intraplate Magmatism 287 Distribution 287 / Hot Spots, Plumes, and Plate Tectonics 289 / Hot Spots, Continental Flood Basalts, and Rifting 294 FOCUS The Atlantic Continental Margin of North America 280 FOCUS The New Madrid Earthquakes of 1811 and FOCUS 11.3 Hawaii: An Example of Intraplate Magmatism 290 CHAPTER 12 The Formation of Sediment: Weathering 299 Physical Weathering: The Disaggregation of Rocks into Sediment 301 Effects of Joints and Fractures on Massive Rocks 301 I Mechanical Disintegration of Solid Rock into Grains 302 Chemical Weathering: Oxidation, Hydration, and Hydrolysis of Minerals 302 How Water Reacts with Silicate Minerals 303 / How Water Reacts xi

7 with Carbonate Minerals 304 I Weathering Products and Solubility 306 / Development of Soils 306 / Chemical Separation During Weathering 310 I Effect of Lithology on Weathering 313 Weathering and Plate-Tectonic Setting 313 The Role of Climate in Weathering 316 Arid Environments 316 / Temperate Environments 319 I Tropical Environments 320 Living With Geology 321 Acid Rain 321 FOCUS 12.1 Acids and Minerals 306 FOCUS Why is the Ocean Salty? 310 CHAPTER 13 Sedimentary Systems: Transportation and Deposition of Sediments 324 Transportation of Sediments 325 Sediment Transport in Air and Water 326 / Sediment Transport in Mud and Ice 327 I Sedimentary Structures Formed During Transportation 328 I Grain Sorting 330 I Flow and Sediment Transport in Natural Rivers 331 Deposition of Sediments 334 River Environments 335 / Lake Environments 337 I Desert Environments 339 / Shorelines 341 I Shallow Marine Environments 344 I Deep Marine Environments 347 Tectonic Control on Sedimentary Processes and Depositional Environments 350 Living With Geology 350 Damming a Wild River 350 FOCUS 13.1 Controls on Settling Velocities of Grains 328 FOCUS 13.2 The Great Pleistocene Floods of Western North America 333 CHAPTER 14 Geomorphology: The Study of Landforms 353 Mass Wasting 356 The Importance of Water in Mass Wasting 356 / Falls 356 / Slides and Slumps 358 / Flows 359 / Soil Creep 360 Shaping the Surface: The Hydrologic Cycle 360 Fluvial Geomorphology 362 Geomorphic Age 363 / Effects of Climate 363 / Drainage Patterns 363 Glaciers 365 What is a Glacier? 366 / Glacial Erosion and Deposition 374

8 Deserts 376 Distribution and Origin of Deserts 376 / Erosion and Deposition in Deserts: Effects of Water and Wind 376 Coasts 378 Waves and Tides 378 I Coastal Erosion and Deposition 378 I Emergent and Submergent Coasts 381 Controls on Geomorphology at Passive and Active Continental Margins 381 FOCUS 14.1 Fractals and Scale lnvariance in Geology 354 FOCUS 14.2 The Physics of Mass Wasting 357 FOCUS 14.3 Ice Ages 370 CHAPTER 15 Geologic Hazards and the Environment 384 Earthquakes 385 Building Failure in Earthquakes ' 385 / Effects of Geology on Building Survival 386 / Liquefaction 386 / Effects of Construction Techniques and Materials on Building Survival 387 I Tsunamis 388 I Earthquake Strength 388 Volcanic Hazards 389 Types of Hazards 390 / Volcanic Hazards in the United States 392 Flooding 393 Incidental Pollution and Flood Runoff 394 I Stream Channelization 395 I Building Design and Floodplains 395 Landslides 396 Geology of Landslide Damage 396 I Causes of Landslides 396 Coastal Erosion Problems 397 Surface Subsidence 397 Subsidence Due to Fluid Withdrawal 397 / Subsidence Due to Dissolution of Underlying Rocks 398 Pollution 398 Petroleum in the Marine Environment 399 / Natural Petroleum Degradation 399 / Spills in the Open Ocean 400 I Oil Washed Onshore 400 The Greenhouse Effect and Global Warming 400 How the Greenhouse Effect Works 401 / Evidence for Greenhouse Effects 404 I Geologic Feedback 405 The Ozone Hole 405 Volcanoes and Atmospheric Pollution 406 Volcanoes and Climate 407 FOCUS 15.1 Calculation of Moment Magnitude 390 xiii

9 FOCUS 15.2 Electromagnetic Radiation 403 FOCUS 15.3 The Antarctic Ozone Hole 408 CHAPTER 16 Earth's Resources 410 Mineral Resources 411 Minerals and Society 411 Mineral Deposits 411 Magmatic Processes 412 / Hydrothermal Processes 415 I Sedimentary Processes 416 I Weathering Processes 417 I Prospecting for Mineral Deposits 418 / Nonmetallic Economic Deposits 418 / Minerals and Plate Tectonics 420 Fossil Fuels 421 Peat 421 / Coal 422 / Petroleum 424 I Oil Exploration 426 I Oil Recovery 430 Water 431 Exploring for Water 437 I Superheated Water and Geothermal Energy 439 FOCUS 16.1 Uranium Ore and Nuclear Energy 419 FOCUS 16.2 How Plate Tectonics Redistributes Mineral and Organic Resources 432 FOCUS 16.3 Earth's Water: Where Did It Come From? 435 FOCUS 16.4 Resources from Space 438 Appendix I: Conversion Table 442 Appendix U: Geologic Time Scale 444 Appendix III: The Periodic Table of the Elements 445 Appendix IV: Common Minerals and Their Properties 446 Appendix V: Earth Statistics 448 Glossary 449 Photo Credits 459 Index 46J