Paleomagnetism: Continents And Oceans

PALEOMAGNETISM PALEOMAGNETISM This is Volume 73 in the INTERNATIONAL GEOPHYSICS SERIES A series of monographs and textbooks Edited by RENATA DMOWSKA, JAMES R. HOLTON, and H. THOMAS ROSSBY A complete list of books in this series appears at the end of this volume. PALEOMAGNETISM Continents and Oceans MICHAEL W.McELHINNY Gondwana Consultants Hat Head, New South Wales, 2440 Australia PHILLIP L McFADDEN Australian Geological Survey Organisation Canberra, 2601 Australia ACADEMIC PRESS A Harcourt Science and Technology Company San Diego San Francisco N e w York Boston London Sydney Tokyo Front cover photograph: A depiction of a dipole field. Courtesy of Michael W. McElhinny and Phillip L. McFadden. Back cover photograph: Global paleogeographic map for Late Permian. (See Figure 7.11 for more details.) This book is printed on acid-free paper. Copyright © 2000 by ACADEMIC PRESS All Rights Reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the pubUsher. Requests for permission to make copies of any part of the work should be mailed to: Permissions Department, Harcourt, Inc., 6277 Sea Harbor Drive, Orlando, Florida 32887-6777 Academic Press A Harcourt Science and Technology Company 525 B Street, Suite 1900, San Diego, California 92101-4495, U.S.A. http \ll^^^. apnet. com Academic Press 24-28 Oval Road, London NWl 7DX, UK http://www.hbuk.co.uk/ap/ Harcourt/Academic Press A Harcourt Science and Technology Company 200 Wheeler Road, Burhngton, Massachusetts 01803 http://www.harcourt-ap.com Library of Congress Catalog Card Number: 99-65104 International Standard Book Number: 0-12-483355-1 International Standard Serial Number: 0074-6142 PRINTED IN THE UNITED STATES OF AMERICA 99 00 01 02 03 04 MM 9 8 7 6 5 4 3 2 1 Contents Preface xi Chapter 1 Geomagnetism and Paleomagnetism 1.1 Geomagnetism 1.1.1 Historical 1.1.2 Main Features of the Geomagnetic Field 1.1.3 Origin of the Main Field 1.1.4 Variations of the Dipole Field with Time 1 1 3 7 12 1.2 Paleomagnetism 1.2.1 Early Work in Paleomagnetism 1.2.2 Magnetism in Rocks 1.2.3 Geocentric Axial Dipole Hypothesis 1.2.4 Archeomagnetism 1.2.5 Paleointensity over Geological Times 1.2.6 Paleosecular Variation 14 14 16 18 22 25 26 Chapter 2 Rock Magnetism 2.1 Basic Principles of Magnetism 2.1.1 Magnetic Fields, Remanent and Induced Magnetism 2.1.2 Diamagnetism and Paramagnetism 2.1.3 Ferro-, Antiferro-, and Ferrimagnetism 2.1.4 Hysteresis 31 31 34 35 37 2.2 Magnetic Minerals in Rocks 2.2.1 Mineralogy 2.2.2 Titanomagnetites 2.2.3 Titanohematites 38 38 40 45 vi Contents 2.2.4 Iron Sulfides and Oxyhydroxides 2.3 Physical Theory of Rock Magnetism 2.3.1 Magnetic Domains 2.3.2 Theory for Single-Domain Grains 2.3.3 Magnetic Viscosity 2.3.4 Critical Size for Single-Domain Grains 2.3.5 Thermoremanent Magnetization 2.3.6 Crystallization (or Chemical) Remanent Magnetization 2.3.7 Detrital and Post-Depositional Remanent Magnetization 2.3.8 Viscous and Thermo viscous Remanent Magnetization 2.3.9 Stress Effects and Anisotropy 46 48 48 51 54 56 60 64 68 71 74 Chapter 3 Methods and Techniques 3.1 Sampling and Measurement 3.1.1 Sample Collection in the Field 3.1.2 Sample Measurement 79 79 82 3.2 Statistical Methods 3.2.1 Some Statistical Concepts 3.2.2 The Fisher Distribution 3.2.3 Statistical Tests 3.2.4 Calculating Paleomagnetic Poles and Their Errors 3.2.5 Other Statistical Distributions<