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STUDIES IN GEOPHYSICS . Continental Tectonics Geophysics Study Committee Geophysics Research Board Assembly of Mathematical and Physical Sciences National Research Council NATIONAL ACADEMY OF SCIENCES Washington, D.C. 1980

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Once: The project that is the subject of this report was approved by the Governing Board of the National Research Council. whose members are drawn from the Councils of the National Academy of Sciences. the National Academy of Engineering, and the Institute of Medicine. The members of the Committee responsible for this report were chosen for their special competences and with regard for appropriate balance. This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering. and the Institute of Medicine. The Geophysics Study Committee is pleased to acknowledge the support of the National Science Foundation, the U.S. Geological Survey, the Department of Energy, the National Oceanic and Aunosphenc Administration. the Defense Advanced Research Projects Agency, and the National Aeronautics and Space Administration for the conduct of this study. Library of Congress Cataloging in Publication Dam National Research Council. Geophysics Study Committee. Continental tectonics. (Studies in geophysics) Based on papers presented at the .Ame~ican Geophysical Union meeting in Miami in Apr. 1978. Includes bibliographies. 1. Plate tectonics. 2. Continents. I. Title. 1I. Senes. QE5 11.4.N37 1980 ISBN ~309 02928-7 Available from 5~1.'36 79-26942 Office of Publications National Academy of Sciences 2101 Constitution Avenue, N.W. Washington, D.C. 20418 Printed in the united States of America

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Geophysics Research Boarct PHIL~ H. NELSON, American Association for the Advancement of Science, Chairman EE~-~n Am, Massachusetts Institute of Technology JOHN D. BREDEHOEF7, U.S. Geological Survey MUSTER G. W. C - IERON, Harvard College Observatory RICHARD x. coo., National Bureau of Standards CHARLES L. Dot, Dartmouth College SIXTY ]. GWEN, University Research Park THOMAS 0. HUG, University of Wisconsin CECIL E. LEl~, JR., National Center for Atmospheric Research JOHN C. MAXWELL, University of Texas, Austin IVY I. FELLER, Ohio Sate University ANDREW F. NAGY, University of Michigan GORDON A. NEWIURE, JR., National Center for Atmospheric Research JOHN S. NISBET, Pennsylvania Sate University HUGH ODIS~w, University of Arizona JACK E. OLIVER, Comell University WILLIAM A. OLIVER, JR., U.S. Geological Survey RALPH O. SIMMONS, University of Illinois VERGER E. SLOW, University of Wisconsin .

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Geophysics Research Board 1V ROSEMARY VID=E, TAOS Ammos Scientific Laboratory A. L~COLN WASB~, University of Washington CHARLES A. WHrl1EN, Silver Spring, .\laryland WARREN S. WOOSTER, University of Washington En Officio D. =LAN BROMLEY, Yale University C. GORDON Li-~-~-~E, National Oceanic and Atmospheric Administration AR~UR E. ~XWELL, WOODS Hole Oceanographic Institution ELSKE V. P. SMITH, University of Maryland Assembly of Mathematical and Physical Sciences Liaison Representatives PRESTON CLOUD, U.S. Geological Survey; University of Califomia, Sand Barbara ROBERT G. FL=GLE, University of Washington CARL H. SAVIT, Western Geophysical Company of America

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Geophysics Study Committee lo, CHARLES L. Do, Dartmouth College, Chairman LO=S J. Bans, University of Arizona, Vice Chairman JO~ D. B~DEHOE=, U.S. Geological Survey ARYAN v. con, Stanforc} University FRANCIS S. JOLSON, Universes of Texas at Dally HUGH ODIS~W, University of Arizona CHARLES B. OFFICER Dartmouth College TREED H. Vie ~DEL, Sanford University ARC Staff THOMAS M. USSELMAN PETROL ]. HART DONALD C. SHAPERO Liaison Representatives JAMES R. BALSLEY, a. Geological Survey EUGENE w. BIERLY, National Science Foundation EDWARD A. FLINN, National Aeronautics and Space Administration

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Geophysics Study Committee Vl PEONS E. JOLSON, National Science Foundation GEORGE A. KOLST~, Depa~l~ent of Energy ~cxIlAQUE s. Soon, National Aeronautics and Space Administration CARL F. ROMNEY, Defense A3vancecl Research Projects Agency WALTER TELESETS=, National Oceanic an] A - ospheric Administration

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Pane} on Continental Tectonics B. CI^RE BURCHFIEL, Massachusetts Institute of Technology, Co-chai~an JACK E. OLI - ~ Comell University, Co-chai~an LEON T. SIL^R, Califomia Institute of Technology, Co-chai~an LAWRENCE W. BRMLE, Purdue University ICEVI}J C. BUR", State University of New York, Albany GREGORY A. DAVIS, University of Southern California GORDON P. EATON, U.S. Geological Survey WARREN HUTTON, U.S. Geological Survey GIBBET N. ~SON, Sate University of New York, Stony Brook WIL~ I. HAZE, Purdue University ROBERT W. "Y. Cornell University SUZANNE MAHLBURG I"Y, Cornell University G. RANDY tCELLER, University of Texas, E! Paso EDWARD G. LIDIU, University of Pittsburgh P--~-tR W. LIPS, U.S. Geological Survey WILLIAM R. MUEHLBERGER, University of Texas, Austin MARTIN A. SCHUEPBACH, Exxon Production Research Company PETER R. VME, Exxon Production Research Comply ISIS= ZlE=, U.S. Geological Survey With a contribution from T. K. HUNG, Chinese Academy of Geological Sciences V11

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Studies in Geophysics* ENERGY AND CLIMATE Roger R. Revelle, panel chairman, July 1977, 158 pp. CLIMATE, CLIMATIC CHANGE, AND WATER SUPPLY James R. Wallis, panel chairman, August 1977, 132 pp. ESTUARIES, GEOPHYSICS, AND THE E.NVIRO.~ME`NT Charles B. Officer, panel chairman, August 1977, 127 pp. THE UPPER ATMOSPHERE AND MAG.NtEI~OS PHE RE Francis S. Johnson, panel chairman, October 1977, 169 pp. GEOPHYSICAL PREDICTIONS Helmut E. Landsberg, panel chairman, .\Iay 1978, 215 pp. IMPACT OF TECHNOLOGY ON GEOPHYSICS Homer E. Newell, panel chairman, September 1979, 121 pp. CO~N'TINE.bJTAL TECTONICS B. Clark Burchfiel, Jack E. Oliver, and Leon T. Silver, panel co-chairmen. February 1980, 197 pp. Published to date. . V'111

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Preface In 1974 the Geophysics Research Board completed a plan, subsequently am proved by the Committee on Science ant! Public Policy of the National Academy of Sciences, for a series of studies to be canker} out on various subjects relatecI to geophysics. The Geophysics Study Committee was established to provide guid- ance in the conduct of the studies. One purpose of the studies is to provide assessments trom the sclentItic com- munity to aid policymakers in decisions on societal problems that involve geo- physics. An important part of such an assessment is an evaluation of the adequacy of present geophysical knowledge and the appropriateness of present research programs to provide information required for those decisions. This study on Continental Tectonics was motivated by a combination of scien- tific and societal problems. Among societal problems related to the solid earth ~ .. . .. lo. that have taken on urgency in recent years are those involving natural hazards- including questions of siting of darns, power plants, and other facilities and the isolation of toxic and radioactive wastes. The thesis of this report is that more reliable scientific input to the decisions conceiving these problems can be provided only with a much improved basic understanding of continental tec- tonics. This basic understanding has been stressed in a broader context by the U.S. Geodynamics Committee, which is placing greater emphasis on the conti- nents in its program planning for geodynamics in the 1980's. 1X

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Preface The study was developed through meetings of the panel and presentation of papers in preliminary form at the American Geophysical Union meeting in Miami in April 1978. They provide examples of our current basic geophysical knowledge of the architecture and processes on the continents. They also pose many of the fundamental questions and uncertainties that require additional research. The essays allude to several practical applications for which an im- proved understanding of the continents is needed. In completing their papers, the authors had the benefit of discussion at this symposium as well as the com- ments of several scientific referees. Responsibility for the individual essays rests with the corresponding authors. The overview of the study summarizes the highlights of the essays and for- mulates conclusions and recommendations. In preparing it, the pane] chairmen had the benefit of meetings and discussion that took place at the symposium and the comments ofthe pane] of authors and selected referees. Responsibility for its content rests with the Geophysics Study Committee and the chairmen of the panel. x

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Contents OVERVIEW AND RECOMMENDATIONS I. SUMMARY 1. Plate Tectonics and the Continents: A Review B. Clark Burchfiel 2. Problems of Pre-~\Iesozoic Continental Evolution Leon T. Silver It. PLATE-BOUNDARY TECTONICS 3. Complexities of Modern and Ancient Subduction Systems Warren B. Hamilton 4. Intracontinental Rifts and Aulacogens Kevin Burke S. Evolution of Outer Highs on Divergent Continental Margins Martin A. Schuepbach and Peter R. Vail X1 3 13 lo ~6 31 33 ~2 ~0

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Contents III. I1N'T~P~TE TECTONICS 6. Tectonics of Noncollisional Regimes The Modem Andes and the Mesozoic Cordi]leran Orogen of the Western Uniter! States B. Clark Burchfie! .Moclels for Midcontinent Tectonism William J. Hinge, Lau;rence W. Braite, G. Randy KeIZer, and Edward G. Lidiak i. S. Problems of Intraplate Extensional Tectonics, Western United States Gregory A. Davis 9. Geophysical ant! Geological Characteristics of the Crust of the Basin and Range Province Cordon P. Eaton IV. CHARACTERIZATION OF CONTINENTAL CRUST 10. Seismic Exploration of the Continental Basement: Trends for the 1980's Jack E. Oliver 63 65 _^ ( .' 84 96 115 11, 11. Exploration of the Continental Crust Using Aeromagnetic Data 127 lsidore Z'etz 12. Chemistry of the Lower Crust: Inferences from Magmas and Xenoliths Robert W. Kay and Suzanne Mahiburg My 13. Geochemical Evolution of the Continental Crust Gilbert N. Hanson V. CONTINENTAL EVOLUTION 14. Cenozoic Volcanism in the Western United States: Implications for Continental Tectonics Peter W. L`ipman 15. The Shape of North America during the Precambrian William R. `~uehiberger 16. An Outline of the Tectonic Characteristics of China T. K. Huang . .Y11 ~ ~ lo, 151 1~9 161 184