Collision Tectonics THIS VOLUME IS DEDICATED TO THE WORK OF ROBERT M. SHACKLETON F.R.S. GEOLOGICAL SOCIETY SPECIAL PUBLICATION NO. 19 Collision Tectonics EDITED BY M. P. COWARD & ALISON C. RIES* Department of Geology, Imperial College, London, UK and *Earth Resources Institute, University College of Swansea, Swansea, UK 1986 Published for the Geological Society by Blackwell Scientific Publications Oxford • London • Edinburgh • Boston Palo Alto • Melbourne Published by DISTRIBUTORS Blackwell Scientific Publications USA and Canada Osney Mead, Oxford OX2 0EL Blackwell Scientific Publications Inc. 8 John Street, London WC1N 2ES PO Box 50009, Palo Alto 23 Ainslie Place, Edinburgh EH3 6AJ California 94303 52 Beacon Street, Boston, Massachusetts 02108, USA Australia 667 Lytton Avenue, Palo Alto, California 94301, USA Blackwell Scientific Publications 107 Barry Street, Carlton, Victoria 3053, Australia (Australia) Pty Ltd 107 Barry Street, Carlton, Victoria 3053 First published 1986 British Library Cataloguing in Publication Data © 1986 The Geological Society. Authorization to Collision tectonics. -- (Geological Society special photocopy items for internal or personal use, or publication, ISSN 0305-8719; no. 19) the internal or personal use of specific clients, 1. Plate tectonics is granted by The Geological Society for libraries I. Coward, M.P. II. Ries, Alison C. and other users registered with the Copyright III. Geological Society of London IV. Series Clearance Center (CCC) Transactional Reporting 551.1'36 QE511.4 Service, provided that a base fee of $02.00 per copy is paid directly to CCC, 27 Congress Street, Salem, MA 01970, USA. ISBN 0-632-01211-0 0305-8719/86 $02.00. Printed in Great Britain by the Alden Press Ltd, Oxford Contents Preface I: WATSON,J. V ......................................................... vii Preface II: DEWEY, J. F ......................................................... ix Introduction: COWARD, M. P. & RIES, A. C ........................................ xi PROCESSES OF COLLISION OROGENY DEWEY, J. F., HEMPTON, M. R., KIDD, W. S. F., SAROGLU, F. & ~ENGt)R, A. M. C. Shortening of continental 'lithosphere: the neotectonics of Eastern Anatolia -- a young collision zone ........................................................ 3 MATTAUER, M. Intracontinental subduction, crust-mantle d6collement and crustal-stacking wedge in the Himalayas and other collision belts ................. 37 KNIPE, R. J. & NEEDHAM, D. T. Deformation processes in accretionary wedges -- examples from the SW margin of the Southern Uplands, Scotland ................ 51 HARRIS, N. B. W., PEARCE, J. A. & TINDLE, A. G. Geochemical characteristics of collision-zone magmatism ................................................... 67 ENGLAND, P. C. & THOMPSON, A. Some thermal and tectonic models for crustal melting in continental collision zones ................................................ 83 MURRELL, S. A. F. Mechanics of tectogenesis in plate collision zones .................. 95 CONTINENT- CONTINENT COLLISION Himalayan-Alpine Belt TAPPONNIER, P., PELTZER, G. & ARMIJO, R. On the mechanics of the collision between India and Asia ............................................................. 115 LE FORT, P. Metamorphism and magmatism during the Himalayan collision ............ 159 COLCHEN, M., MASCLE, G. & VAN HAVER, T. Some aspects of collision tectonics in the Indus Suture Zone, Ladakh ................................................. 173 SEARLE, M. P. & FRYER, B. J. Garnet, tourmaline and muscovite-bearing leucogranites, gneisses and migmatites of the Higher Himalayas from Zanskar, Kulu, Lahoul and Kashmir .................................................................. 185 COWARD, M. P., WINDLEY, B. F., BROUGHTON, R. D., LUFF, I. W., PETTERSON, M. G., PUDSEY, C. J., REX, D. C. & ASlF KHAN, M. Collision tectonics in the NW Himalayas ................................................................ 203 HUNZII,:ER, J. C. The Alps: a case of multiple collision .............................. 221 RIcov, L. E. & SIDDANS, A. W. B. Collision tectonics in the Western Alps ............ 229 BUTLER, R. W. H., MA~HEWS, S. J. & PARISH, M. The NW external Alpine Thrust Belt and its implications for the geometry of the Western Alpine Orogen .............. 245 CHANNELL, J. E. T. Palaeomagnetism and continental collision in the Alpine Belt and the formation of late-tectonic extensional basins ................................... 261 Older collision belts HOSSACK, J. R. & COOPER, M. A. Collision tectonics in the Scandinavian Caledonides ... 287 HAWKESWORTH, C. J., MENZIES, M. A. & VAN CALSTEREN, P. Geochemical and tectonic evolution of the Damara Belt, Namibia .............................. : ........ 305 DALY, M. C. The intracratonic Irumide Belt of Zambia and its bearing on collision orogeny during the Proterozoic of Africa ...................................... 321 SHACKLETON, R. M. Precambrian collision tectonics in Africa ........................ 329 CONTINENT- ARC COLLISION MILSOM, J. & AUDLEY-Cr~ARLES, M. G. Post-collision isostatic readjustment in the Southern Banda Arc ....................................................... 353 vi Contents CORDILLERAN COLLISION JONES, D. L., SILBERLING,N. J. & CONEY, P. J. Collision tectonics in the Cordillera of western N America: examples from Alaska .................................... 367 DALZIEL, I. W. D. Collision and Cordilleran orogenesis: an Andean perspective ........ 389 INDEX ........................................................................ 405 Preface I The orogenic belts that result from the collision of crustal plates form a worldwide system whose origins go back for several hundred million years. The spectacular topographical forms of these belts were familiar to man long before the emergence of geology as an independent science. The geologists of the eighteenth and early nineteenth century felt no doubts about the need to examine fundamental structures such as mountain belts on a global scale. More than a quarter of the 180 papers published in the first three volumes of the Quarterly Journal of the Geological Society of London (1845-7) were concerned with overseas terranes; and the same volumes included a substantial paper by R. I. Murchison on the relationships of the Lower Palaeozoic of Scandinavia and the Baltic area and another, even more comprehensive, on the structure of the Alps, Apennines and Carpathians. The relevance of direct observation in the field was equally well understood; in volume 3 of the Quarterly Journal, Daniel Sharpe demonstrated the implications of rock cleavage with respect to the effects of compression and Henry de la Beche included in his Presidential Address an interesting analysis of Appalachian folds as indicators of crustal shortening. At the present day, the range of phenomena to be accounted for in the development of collisional orogenic belts and the diversity of scales on which they must be examined, continue to challenge the ingenuity of earth scientists. The massive build-up of factual data and the advent of many specialized techniques make it increasingly hard for an individual geologist to master any major topic as a whole and discussion meetings involving a number of contributors have, to a large extent, replaced the single authoritative review as a means of arriving at a general picture. The William Smith Lectures of the Geological Society, established in 1944 to provide annual occasions for reviews of topics of current interest, have accordingly evolved into William Smith Meetings built around the principal lecture but providing ample scope for contributions from other specialists. The William Smith Meeting of April 1983, of which the present volume is the outcome, touched on many aspects of the collision process, clarified many new fields of investigation and highlighted some of the problems that remain to be solved. Many of those who took part are former students or colleagues of Professor R. M. Shackleton, the William Smith Lecturer, whose address formed the culmination of the meeting. This special volume therefore stands not only as a record of the progress of research in an important branch of earth science but also as a personal tribute to an outstanding field geologist, whose experience and acumen have become legendary. JANET WATSON t (President 1982-4) * Deceased 1985. Preface II Robert Shackleton stands almost alone in the earth sciences as a field observer of unrivalled ability. He has a most acute geometric sense and a talent for quickly unravelling complex structures and reducing them to their fundamental essentials. These abilities, coupled with more than half a century of field experience in, among other places, Africa, Arabia, the British Caledonides, S America and Fiji, make Robert a most perceptive and formidable field-based generalist of the kind that is tragically becoming a rare species in modern earth science. Field observation has been central to his life's work and is mostly encapsulated in a set of field notebooks numbering some 150. A man of enormous energy and fitness, his interests have centred principally around structural geology and tectonics at all scales. Robert's career began in Liverpool where he gained his Ph.D in 1932 on the geology of Moel Hebog, at which time began his lifetime love of North Wales geology. Between 1932 and 1934 he was Beit Research Fellow at Imperial College and also worked for Whitehall Securities in Fiji. From 1934 to 1940 and from 1945 to 1948, Robert lectured at Imperial College and began