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Early Precambrian Processes Geological Society Special Publications Series Editor A. J. FLEET Professor John Sutton FRS GEOLOGICAL SOCIETY SPECIAL PUBLICATION NO. 95 Early Precambrian Processes EDITED BY M. E COWARD Geology Department Imperial College London, UK and A. C. RIES Ries-Coward Associates Ltd Reading, UK 1995 Published by The Geological Society London THE GEOLOGICAL SOCIETY The Society was founded in 1807 as the Geological Society of London and is the oldest geological society in the world. It received its Royal Charter in 1825 for the purpose of 'investigating the mineral structure of the Earth'. The Society is Britain's national society for geology with a membership of around 7500. It has countrywide coverage and approximately 1000 members reside overseas. The Society is responsible for all aspects of the geological sciences including professional matters. The Society has its own publishing house, which produces the Society's international journals, books and maps, and which acts as the European distributor for publications of the American Association of Petroleum Geologists, SEPM and the Geological Society of America. Fellowship is open to those holding a recognized honours degree in geology or cognate subject and who have at least two years' relevant postgraduate experience, or who have not less than six years' experience in geology or a cognate subject. A Fellow who has not less than five years' relevant postgraduate experience in the practice of geology may apply for validation and, subject to approval, may be able to use the designatory letters C Geol (Chartered Geologist). Further information about the Society is available from the Membership Manager, The Geological Society, Burlington House, Piccadilly, London W1V 0JU, UK. The Society is a Registered Charity, No. 210161 Published by the Geological Society fi'om: The Geological Society Publishing House Unit 7 Brassmill Enterprise Centre Brassmill Lane Bath BA1 3JN UK (Orders: Tel 01225 445046 Fax 01225 442836) First published 1995 The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility for any errors or omissions that may be made. 9 The Geological Society 1995. All rights reserved. No reproduction, copy or transmission of this publication may be made without written permission. No paragraph of this publication may be reproduced, copied or transmitted save with the provisions of the Copyright Licensing Agency, 90 Tottenham Court Road, London W1P 9HE. Users registered with the Copyright Clearance Center, 27 Congress Street, Salem, MA 01970, USA: the item-fee code for this publication is 0305-8719/95/$07.00. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library. ISBN 1-897799-36-5 Typeset by EJS Chemical Composition, Midsomer Norton, Bath, Avon Printed by The Alden Press, Osney Mead, Oxford, UK. Distributors USA AAPG Bookstore PO Box 979 Tulsa OK 74101-0979 USA (Orders: Tel (918) 584-2555 Fax (918) 548-0469) Australia Australian Mineral Foundation 63 Conyngham Street Glenside South Australia 5075 Australia (Orders: Tel (08) 379-0444 Fax (08) 379-4634) India Affiliated East-West Press PVT Ltd G-1/16 Ansari Road New Delhi 110 002 India (Orders: Tel (11) 327-9113 Fax (11) 326-0538 Japan Kanda Book Trading Co. Tanikawa Building 3-2 Kanda Surugadai Chiyoda-Ku Tokyo 101 Japan (Orders: Tel (03) 3255-3497 Fax (03) 3255-3495) Preface The papers in this volume are grouped together, following particular themes or models of Early Precambrian processes. In the first paper Maarten de Wit & Andrew I-lynes discuss the onset of interaction between the hydrosphere and oceanic crust. According to these authors the