Plate Tectonics Plate Tectonics Unraveling the Mysteries of the Earth Revised Edition Jon erickson Foreword by Ernest H. Muller, Ph.D. PLATE TECTONICS Unraveling the Mysteries of the Earth, Revised Edition Copyright © 2001, 1992 by Jon Erickson All rights reserved. No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval systems, without permission in writing from the publisher. For information contact: Checkmark Books An imprint of Facts On File, Inc. 11 Penn Plaza New York,NY 10001 Library of Congress Cataloging-in-Publication Data Erickson, Jon, 1948– Plate tectonics : unraveling the mysteries of the earth / Jon Erickson ; foreword Ernest H. Muller—Rev. ed. p. cm. — (The living earth) Includes bibliographical references and index. ISBN 0-8160-4327-2 (hardcover: alk. paper) ISBN 0-8160-4589-5 (pbk) 1. Plate tectonics. I.Title. QE511.4.E75 2001 551.1′36—dc21 00-049039 Checkmark Books are available at special discounts when purchased in bulk quantities for businesses, associations, institutions, or sales promotions. Please contact our Special Sales Department at 212/967-8800 or 800/322-8755. You can find Facts On File on the World Wide Web at http://www.factsonfile.com Text design by Cathy Rincon Cover design by Nora Wertz Illustrations by Jeremy Eagle and Dale Dyer, © Facts On File Printed in the United States of America MP Hermitage 10987654321 (pbk) 10987654321 This book is printed on acid-free paper. CONTENTS Tables vii Acknowledgments ix Foreword xi Introduction xiii 1 Continental Drift: Discovery Of Plate Tectonics The Birth of Geology I Matching Coastlines I Evidence for Drift I Continental Movements I Paleomagnetism I Lithospheric Plates 1 2 Historical Tectonics: An Overview of Earth History Archean Tectonics I Proterozoic Tectonics I Paleozoic Tectonics I Mesozoic Tectonics I Cenozoic Tectonics 27 3 CoNvection Currents: The Driving Force Heat Flow I The Core I The Mantle I Mantle Convection I The Rifting of Continents I Supercontinents 53 4 Crustal Plates: The Lithosphere in motion Continental Crust I Oceanic Crust I Terranes I Hot Spots I Plate Motions I Earthquakes I Fault Zones 78 5 Seafloor Spreading: The Midocean Ridges The Mysterious Ocean I The Mid-Atlantic Ridge I The Spreading Seafloor I Basaltic Magma I Magnetic Stripes I Seamounts and Guyots I Abyssal Red Clay 104 6 Subduction Zones: The Deep-Sea Trenches Oceanic Trenches I Seafloor Topography I Plate Subduction I Descending Plates I Island Arcs I The Ring of Fire I Volcanic Eruptions 130 7 Mountain Building: Crustal Uplift and Erosion Episodes of Orogeny I Plate Collisions I Uplift and Erosion I Igneous Activity I Mineral Deposits I Geothermal Energy 156 8 The Rock Cycle: The Balance of Nature The Atmosphere and Ocean I The Heat Budget I The Water Cycle I The Carbon Cycle I The Nitrogen Cycle I Carbonate Rocks I Volcanoes 181 9 Tectonics and Life: Making A Living Planet The Biosphere I The Geosphere I Tectonics and Evolution I Tectonics and Extinction I Tectonics and Climate I Tectonics of the Future 206 10 Tectonics In Space: Exploring The Solar System Lunar Tectonics I Mercurial Tectonics I Venusian Tectonics I Martian Tectonics I Jovian Tectonics I Saturnian Tectonics I Uranian Tectonics I Triton Tectonics 232 Conclusion 259 Glossary 260 Bibliography 271 Index 279 tableS 1 The Geologic Time Scale 10 2 The Drifting of the Continents 47 3 History of the Deep Circulation of the Ocean 50 4 Frequently Used Radioisotopes for Geologic Dating 58 5 Composition of the Earth’s Crust 79 6 Classification of the Earth’s Crust 82 7 Summary of Earthquake Parameters 102 8 Comparison of Magnetic Reversals with Other Phenomena 121 10 The World’s Ocean Trenches 132 11 The Tallest Mountain Peaks by State 158 12 Albedo of Various Surfaces 190 13 The Evolution of the Biosphere 209 14 Flood Basalt Volcanism and Mass Extinctions 216 15 The Major Ice Ages 230 16 Major Volcanoes of Mars 247 VII ACKNOWLEDGMENTS he author thanks the National Aeronautics and Space Administration T (NASA), the National Oceanic and Atmospheric Administration (NOAA), the U.S.Air Force, the U.S. Department of Agriculture–Forest Service, the U.S. Department of Energy, the U. S. Geological Survey (USGS), and the U.S. Navy for providing photographs for this book. The author also thanks Mr. Frank K. Darmstadt, Senior Editor, and Ms. Cynthia Yazbek,Associate Editor, and the rest of the staff at Facts On File for their invaluable assistance in the publication of this book. IX foreword rom time immemorial, people’s perceptions of Earth have been framed Flargely by personal experience and by conversation among neighbors, later by broader communication and across linguistic barriers. With modern advances in science and information technology,knowledge of Earth seems sometimes on the verge of bursting ahead of popular comprehension. Whereas Earth has been commonly conceived of as stable and unresponsive, science recognizes it as dynamic and responsive in degree far beyond general awareness.As an example, recent discovery of 10 new planetary bodies outside our solar system once again marks an advance of science ranging ahead of common experience. In language scientifically correct, yet designed for the typical inquiring mind, Jon Erickson seeks in Plate Tectonics to broaden popular awareness of the expanded temporal and spatial dimensions of geologic science. In sequence and informal manner, the opening chapter credits scientists who, in recent centuries, have recognized the relationships and formulated the principles upon which geology is based. The reader is introduced early to conjectural primitive Archean events that account for differentiation of Earth’s crust, man- tle, and lithosphere. Movement of crustal plate over semimolten mantle rock at a depth below Earth’s surface comprises the essence of plate tectonics.This accounts directly or indirectly for essentially all near-surface movement and deforma- tion as represented in the geologic record. On a major scale, these changes involve displacement of continents, changing of ocean basins, and building of XI Plate Tectonics mountains—subjects treated in successive chapters. On a more local scale, plate tectonics accounts for volcanism and earthquakes. Even more subtle and indirect consequences of plate tectonics are variations in ocean currents and atmospheric climates that have been made apparent in the distribution of marine fossils and archeological remains. Although geology literally refers to earth science, its scope is stretched in the last chapter as plate tectonics theo- ry is invoked for assessing the nature of neighboring planets. —Ernest H. Muller, Ph. D. XII INTRODUCTION ll aspects of the Earth’s history and structure, including its majestic Amountains, giant rift valleys, and deep ocean basins, were fashioned by mobile crustal plates.The Earth’s outer shell is made up of a dozen or so plates composed of the upper mantle, or lithosphere, and the overlying conti- nental and oceanic crust.The plates ride on the semimolten rocks of the upper mantle and carry the continents along with them.The movement of the plates accounts for all geologic activity taking place on the planet’s surface. In this man- ner, plate tectonics is continously changing and rearranging the face of the Earth. The interaction of lithospheric plates plays a fundamental role in global tectonics and accounts for many geologic processes that shape the surface of the planet. The theory of plate tectonics clearly explains how these changes take place.When two plates collide, they create mountain ranges on the con- tinents and volcanic islands on the ocean floor.When an oceanic plate slides beneath a continental plate, it produces sinuous mountain chains.The breakup of a plate creates new continents and oceans.The rifting and patching of the continents have been ongoing processes practically since the very beginning. The text begins with the discoveries leading to the theory of plate tec- tonics. It follows the evolution of the planet from the earliest construction of the crust to the present, defines the force that drives the continents around the surface of the Earth, and examines the mobile crustal plates, their interactions, and their effects on the planet. It reveals how the best evidence for plate tec- tonics was found lying on the bottom of the ocean and how new oceanic crust is created at midocean ridges. XIII Plate Tectonics The discussion continues with an exploration of the ocean floor for evi- dence of plate subduction, the counterpart of seafloor spreading. After explaining the basics of plate tectonics, it applies that knowledge to the sub- ject of mountain building, the most visible manifestations of the powerful tec- tonic forces that shape the Earth. After seeing how plate tectonics has played a fundamental role in shaping the Earth, the text explains how it has made our world a living planet and examines the critical cycles that are important to life on Earth. This revised and updated edition is a much expanded examination of plate tectonics.The book makes a difficult-to-understand and sometimes con- troversial theory easily comprehensible to the lay reader. Science enthusiasts will particularly enjoy this fascinating subject and gain a better understanding of how the forces of nature have shaped the Earth. Students of geology and earth science will find this a valuable reference book to further their studies. Readers will enjoy this clear and easily readable text that is well illustrated with fascinating photographs, detailed illustrations, and helpful tables.A com- prehensive glossary is provided to define difficult terms, and a bibliography lists references for further reading. Perhaps no other theory has changed the fundamental thinking about our living Earth as has plate tectonics. XIV 1 CONTINENTAL DRIFT DISCOVERY OF PLATE TECTONICS hen early cartographers drew the first world maps, they noticed W something very peculiar.