Global Tectonics

495 Pages·2009·63.5 MB·English

by  Philip Kearey

Global Tectonics

iii
Global Tectonic s
T H E L A T E P H I L I P K E A R E Y
Formerly of the Department of Geology
University of Bristol
UK
K E I T H A . K L E P E I S
Department of Geology
University of Vermont
Burlington, Vermont, USA
F R E D E R I C K J . V I N E
School of Environmental Sciences
University of East Anglia
Norwich, UK
T H I R D E D I T I O N
A John Wiley & Sons, Ltd., Publication
This edition fi rst published 2009, © 2009 by Philip Kearey, Keith A. Klepeis, Frederick J. Vine
Blackwell Publishing was acquired by John Wiley & Sons in February 2007. Blackwell’s publishing program
has been merged with Wiley’s global Scientifi c, Technical and Medical business to form Wiley-Blackwell.
Registered offi ce: John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ,
UK
Editorial offi ces: 9600 Garsington Road, Oxford, OX4 2DQ, UK
The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK
111 River Street, Hoboken, NJ 07030-5774, USA
For details of our global editorial offi ces, for customer services and for information about how to apply for
permission to reuse the copyright material in this book please see our website at www.wiley.com/wiley-
blackwell
The right of the author to be identifi ed as the author of this work has been asserted in accordance with the
Copyright, Designs and Patents Act 1988.
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or trans-
mitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except
as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior permission of the
publisher.
Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not
be available in electronic books.
Designations used by companies to distinguish their products are often claimed as trademarks. All brand
names and product names used in this book are trade names, service marks, trademarks or registered trade-
marks of their respective owners. The publisher is not associated with any product or vendor mentioned in
this book. This publication is designed to provide accurate and authoritative information in regard to the
subject matter covered. It is sold on the understanding that the publisher is not engaged in rendering profes-
sional services. If professional advice or other expert assistance is required, the services of a competent
professional should be sought.
Library of Congress Cataloguing-in-Publication Data
Kearey, P.
Global tectonics. – 3rd ed. / Philip Kearey, Keith A. Klepeis, Frederick J. Vine
p. cm.
Includes bibliographical references and index.
ISBN 978-1-4051-0777-8 (pbk. : alk. paper) 1. Plate tectonics–Textbooks. I. Klepeis, Keith A. II. Vine,
F. J. III. Title.
QE511.4.K43 2008
551.1'36–dc22
2007020963
A catalogue record for this book is available from the British Library.
Set in 9.5 on 11.5 pt Dante by SNP Best-set Typesetters Ltd., Hong Kong
Printed and bound in Singapore by Markono Print Media Pte Ltd
01 2009
Contents
Preface ix 2.8 The mantle 30
Acknowledgments x 2.8.1 Introduction 30
The geologic timescale and stratigraphic column xi 2.8.2 Seismic structure of the
mantle 30
2.8.3 Mantle composition 31
2.8.4 The mantle low velocity
1 Historical perspective
1 zone 31
2.8.5 The mantle transition zone 32
1.1 Continental drift 2 2.8.6 The lower mantle 32
1.2 Sea fl oor spreading and the birth 2.9 The core 33
of plate tectonics 6 2.10 Rheology of the crust
1.3 Geosynclinal theory 7 and mantle 33
1.4 Impact of plate tectonics 8 2.10.1 Introduction 33
2.10.2 Brittle deformation 34
2.10.3 Ductile deformation 36
2 The interior of 2.10.4 Lithospheric strength profi les 37
2.10.5 Measuring continental
the Earth deformation 39
9
2.10.6 Deformation in the mantle 41
2.1 Earthquake seismology 10 2.11 Isostasy 42
2.1.1 Introduction 10 2.11.1 Introduction 42
2.1.2 Earthquake descriptors 10 2.11.2 Airy’s hypothesis 43
2.1.3 Seismic waves 10 2.11.3 Pratt’s hypothesis 43
2.1.4 Earthquake location 11 2.11.4 Flexure of the lithosphere 44
2.1.5 Mechanism of earthquakes 12 2.11.5 Isostatic rebound 45
2.1.6 Focal mechanism solutions 2.11.6 Tests of isostasy 46
of earthquakes 12 2.12 Lithosphere and asthenosphere 48
2.1.7 Ambiguity in focal 2.13 Terrestrial heat fl ow 51
mechanism solutions 14
2.1.8 Seismic tomography 17
2.2 Velocity structure of the Earth 19
2.3 Composition of the Earth 21 3 Continental drift
54
2.4 The crust 22
2.4.1 The continental crust 22 3.1 Introduction 55
2.4.2 Upper continental crust 23 3.2 Continental reconstructions 55
2.4.3 Middle and lower continental 3.2.1 Euler’s theorem 55
crust 23 3.2.2 Geometric reconstructions
2.4.4 The oceanic crust 24 of continents 55
2.4.5 Oceanic layer 1 24 3.2.3 The reconstruction of
2.4.6 Oceanic layer 2 25 continents around the
2.4.7 Oceanic layer 3 26 Atlantic 56
2.5 Ophiolites 27 3.2.4 The reconstruction of
2.6 Metamorphism of oceanic Gondwana 57
crust 28 3.3 Geologic evidence for
2.7 Differences between continental and continental drift 58
oceanic crust 29 3.4 Paleoclimatology 60
v
vi CONTENTS
3.5 Paleontologic evidence for 6 Ocean ridges
121
continental drift 61
3.6 Paleomagnetism 64 6.1 Ocean ridge topography 122
3.6.1 Introduction 64 6.2 Broad structure of the upper
3.6.2 Rock magnetism 64 mantle below ridges 125
3.6.3 Natural remanent 6.3 Origin of anomalous upper mantle
magnetization 65 beneath ridges 127
3.6.4 The past and present
6.4 Depth–age relationship of
geomagnetic fi eld 66
oceanic lithosphere 128
3.6.5 Apparent polar wander
6.5 Heat fl ow and hydrothermal
curves 67
circulation 129
3.6.6 Paleogeographic reconstructions
6.6 Seismic evidence for an axial
based on paleomagnetism 68
magma chamber 131
6.7 Along-axis segmentation of
4 Sea fl oor spreading and oceanic ridges 133
6.8 Petrology of ocean ridges 140
transform faults 6.9 Shallow structure of the
72
axial region 141
4.1 Sea fl oor spreading 73 6.10 Origin of the oceanic crust 142
4.1.1 Introduction 73
6.11 Propagating rifts and
4.1.2 Marine magnetic
microplates 145
anomalies 73
6.12 Oceanic fracture zones 148
4.1.3 Geomagnetic reversals 74
4.1.4 Sea fl oor spreading 77
4.1.5 The Vine–Matthews
hypothesis 78
7 Continental rifts and
4.1.6 Magnetostratigraphy 79
4.1.7 Dating the ocean fl oor 84
rifted margins
4.2 Transform faults 84 152
4.2.1 Introduction 84
7.1 Introduction 153
4.2.2 Ridge–ridge transform
7.2 General characteristics of
faults 88
narrow rifts 155
4.2.3 Ridge jumps and transform
7.3 General characteristics of
fault offsets 89
wide rifts 162
7.4 Volcanic activity 169
7.4.1 Large igneous provinces 169
5 The framework of
7.4.2 Petrogenesis of
plate tectonics rift rocks 172
91
7.4.3 Mantle upwelling
5.1 Plates and plate margins 92 beneath rifts 175
5.2 Distribution of earthquakes 92 7.5 Rift initiation 176
5.3 Relative plate motions 94 7.6 Strain localization and
5.4 Absolute plate motions 97 delocalization processes 178
7.6.1 Introduction 178
5.5 Hotspots 99
7.6.2 Lithospheric stretching 179
5.6 True polar wander 103
7.6.3 Buoyancy forces and lower
5.7 Cretaceous superplume 106
crustal fl ow 181
5.8 Direct measurement of relative
7.6.4 Lithospheric fl exure 183
plate motions 107 7.6.5 Strain-induced weakening 184
5.9 Finite plate motions 110 7.6.6 Rheological stratifi cation
5.10 Stability of triple junctions 113 of the lithosphere 188
5.11 Present day triple junctions 120 7.6.7 Magma-assisted rifting 192
CONTENTS vii
7.7 Rifted continental margins 193 9.5 Thermal structure of the
7.7.1 Volcanic margins 193 downgoing slab 259
7.7.2 Nonvolcanic margins 196 9.6 Variations in subduction zone
7.7.3 The evolution of rifted characteristics 262
margins 198
9.7 Accretionary prisms 264
7.8 Case studies: the transition from
9.8 Volcanic and plutonic activity 271
rift to rifted margin 202
9.9 Metamorphism at convergent
7.8.1 The East African Rift
margins 275
system 202
9.10 Backarc basins 279
7.8.2 The Woodlark Rift 204
7.9 The Wilson cycle 208
10 Orogenic belts
286
8 Continental transforms
10.1 Introduction 287
and strike-slip faults 210 10.2 Ocean–continent convergence 287
10.2.1 Introduction 287
8.1 Introduction 211 10.2.2 Seismicity, plate motions, and
8.2 Fault styles and physiography 211 subduction geometry 289
8.3 The deep structure of 10.2.3 General geology of
continental transforms 224 the central and southern
8.3.1 The Dead Sea Andes 291
Transform 224 10.2.4 Deep structure of the
8.3.2 The San Andreas Fault 224 central Andes 294
8.3.3 The Alpine Fault 228 10.2.5 Mechanisms of noncollisional
8.4 Transform continental margins 230 orogenesis 297
8.5 Continuous versus discontinuous 10.3 Compressional sedimentary
deformation 232 basins 302
8.5.1 Introduction 232 10.3.1 Introduction 302
8.5.2 Relative plate motions and 10.3.2 Foreland basins 302
surface velocity fi elds 233 10.3.3 Basin inversion 303
8.5.3 Model sensitivities 236 10.3.4 Modes of shortening in foreland
8.6 Strain localization and fold-thrust belts 304
delocalization mechanisms 239 10.4 Continent–continent collision 306
10.4.1 Introduction 306
8.6.1 Introduction 239
10.4.2 Relative plate motions and
8.6.2 Lithospheric heterogeneity 239
collisional history 306
8.6.3 Strain-softening
10.4.3 Surface velocity fi elds
feedbacks 242
and seismicity 309
8.7 Measuring the strength of
10.4.4 General geology of the
transforms 246
Himalaya and Tibetan
Plateau 312
10.4.5 Deep structure 316
10.4.6 Mechanisms of continental
9 Subduction zones
249 collision 318
10.5 Arc–continent collision 330
9.1 Ocean trenches 250
10.6 Terrane accretion and
9.2 General morphology of island
continental growth 332
arc systems 251
10.6.1 Terrane analysis 332
9.3 Gravity anomalies of subduction
10.6.2 Structure of accretionary
zones 252 orogens 336
9.4 Structure of subduction zones 10.6.3 Mechanisms of terrane
from earthquakes 252 accretion 342
viii CONTENTS
11 Precambrian tectonics 12.5.3 T he vertical extent of
convection 387
and the supercontinent
12.6 The forces acting on plates 388
cycle 12.7 D riving mechanism of
346
plate tectonics 390
11.1 Introduction 347 12.7.1 Mantle drag mechanism 391
11.2 Precambrian heat fl ow 347 12.7.2 Edge-force mechanism 391
12.8 E vidence for convection in
11.3 Archean tectonics 349
11.3.1 General characteristics of the mantle 393
cratonic mantle lithosphere 349 12.8.1 Introduction 393
11.3.2 General geology of 12.8.2 Seismic tomography 393
Archean cratons 350 12.8.3 Superswells 394
11.3.3 The formation of Archean 12.8.4 The D” layer 395
lithosphere 351 12.9 T he nature of convection in
11.3.4 Crustal structure 355 the mantle 396
11.3.5 Horizontal and vertical tectonics 358 12.10 Plumes 399
11.4 Proterozoic tectonics 361 12.11 T he mechanism of the
11.4.1 General geology of supercontinent cycle 401
Proterozoic crust 361
11.4.2 Continental growth and
craton stabilization 363
11.4.3 Proterozoic plate tectonics 364 13 Implications of
11.5 The supercontinent cycle 370
plate tectonics
11.5.1 Introduction 370 404
11.5.2 Pre-Mesozoic
reconstructions 370 13.1 Environmental change 405
11.5.3 A Late Proterozoic 13.1.1 C hanges in sea level and sea
supercontinent 370 water chemistry 405
11.5.4 Earlier supercontinents 373 13.1.2 C hanges in oceanic circulation
11.5.5 Gondwana–Pangea assembly and the Earth’s climate 406
and dispersal 374 13.1.3 Land areas and climate 411
13.2 Economic geology 412
13.2.1 Introduction 412
13.2.2 A utochthonous and
12 The mechanism of
allochthonous mineral
plate tectonics deposits 413
379 13.2.3 D eposits of sedimentary
12.1 Introduction 380 basins 420
13.2.4 Deposits related to climate 421
12.2 Contracting Earth hypothesis 380
13.2.5 Geothermal power 422
12.3 Expanding Earth hypothesis 380
13.3 Natural hazards 422
12.3.1 Calculation of the ancient moment
of inertia of the Earth 381
12.3.2 Calculation of the ancient
radius of the Earth 382 Review questions 424
12.4 Implications of heat fl ow 382 References 428
12.5 Convection in the mantle 384 Index 463
12.5.1 The convection process 384
12.5.2 F easibility of mantle convection 386 Color plates appear between pages 244 and 245
A companion resources website for this book is available at www.blackwellpublishing.com/kearey
The mechanism of plate tectonics ix
Preface
As is well known, the study of tectonics, the branch Thus one moves from consideration of the fundamentals
of geology dealing with large-scale Earth structures of plate tectonics, which are best illustrated with refer-
and their deformation, experienced a major break- ence to the ocean basins, to continental tectonics, culmi-
through in the 1960s with the formulation of plate nating in Precambrian tectonics, and a discussion of the
tectonics. The simultaneous confi rmation of sea fl oor possible nature of the implied convection in the mantle.
spreading and continental drift, together with the recog- The book is aimed at senior undergraduate students
nition of transform faults and subduction zones, derived in the geological sciences and postgraduate students and
from the interpretation of new and improved data from other geoscientists who wish to gain an insight into the
the fi elds of marine geology and geophysics, and subject. We assume a basic knowledge of geology, and
earthquake seismology. By 1970 the essentials of plate that for a full description of geophysical and geochemi-
tectonics – the extent of plates, the nature of the plate cal methodology it will be necessary to refer to other
boundaries, and the geometry and kinematics of their texts. We have attempted to provide insights into the
relative and fi nite motions – were well documented. trends of modern research and the problems still out-
As further details emerged, it soon became apparent standing, and have supplied a comprehensive list of ref-
that plates and plate boundaries are well-defi ned in erences so that the reader can follow up any item of
oceanic areas, where the plates are young, relatively thin, particular interest. We have included a list of questions
but rigid, and structurally rather uniform, but that this is for the use of tutors in assessing the achievement of
not true for continental areas. Where plates have conti- their students in courses based on the book. These are
nental crust embedded in them they are generally thicker, mainly designed to probe the students’ integrative
older and structurally more complex than oceanic plates. powers, but we hope that in their answers students will
Moreover the continental crust itself is relatively weak make use of the references given in the text and material
and deforms more readily by fracture and even by fl ow. on relevant websites listed on the book’s website at:
Thus the nature of continental tectonics is more complex http://www.blackwellpublishing.com/kearey
than a simple application of plate tectonic theory would The initial impact of the plate tectonic concept, in the
predict and it has taken much longer to document and fi elds of marine geology and geophysics and seismology,
interpret. An important element in this has been the was quickly followed by the realization of its relevance
advent of Global Positioning data that have revealed to igneous and metamorphic petrology, paleontology,
details of the deformation fi eld in complex areas. sedimentary and economic geology, and all branches of
The other major aspect of plate tectonics in which goescience. More recently its potential relevance to the
progress initially was slow is the driving mechanism Earth system as a whole has been recognized. In the past,
for plate motions. Signifi cant progress here had to await processes associated with plate tectonics may have pro-
the development of new seismologic techniques and duced changes in seawater and atmospheric chemistry,
advances in laboratory and computer modeling of con- in sea level and ocean currents, and in the Earth’s climate.
vection in the Earth’s mantle. These ideas are briefl y reviewed in an extended fi nal
Since 1990, when the fi rst edition of Global Tectonics chapter on the implications of plate tectonics. This
appeared, there have been many developments in our extension of the relevance of plate tectonics to the
understanding of Earth structure and its formation, par- atmosphere and oceans, to the evolution of life, and pos-
ticularly in relation to continental tectonics and mantle sibly even the origin of life on Earth is particularly grat-
convection. As a consequence, approximately two-thirds ifying in that it emphasizes the way in which the
of the fi gures and two-thirds of the text in this third biosphere, atmosphere, hydrosphere, and solid Earth are
edition are new. The structure of the book is largely interrelated in a single, dynamic Earth system.
unchanged. The order in which data and ideas are pre-
K.A. KLEPEIS
sented is in part historical, which may be of some interest
F.J. VINE
in itself, but it has the advantage of moving from simple
to more complex concepts, from the recent to the distant A companion resources website for this book is avail-
past, and from the oceanic to the continental realms. able at http://www.blackwellpublishing.com/kearey
ix