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Magmatism in the Ocean Basins Geological Society Special Publications Series Editor K. COE GEOLOGICAL SOCIETY SPECIAL PUBLICATION NO 42

Magmatism in the Ocean Basins

EDITED BY A. D. SAUNDERS & M. J. NORRY Department of Geology The University Leicester LEI 7RH

1989

Published for The Geological Society by Blackwell Scientific Publications

OXFORD LONDON EDINBURGH

BOSTON MELBOURNE Published for DISTRIBUTORS The Geological Society by USA and Canada Blackwell Scientific Publications Publishers' Business Services Osney Mead, Oxford OX2 0EL PO Box 447 Tel. 0865-240201) (Orders: Brookline Village 8 John Street, London WC1N 2ES Massachusetts 02147 23 Ainslie Place, Edinburgh EH3 6AJ (Orders: Tel. (617) 524-7678) 3 Cambridge Center, Suite 208 Cambridge, Massachusetts 02142, USA Canada 107 Barry Street, Carlton, Victoria 3053 Oxford University Press Australia 70 Wynford Drive Don Mills First published 1989 Ontario M3C 1J9 (Orders: Tel. (416) 441-2941) 1989 The Geological Society. Authorization to Australia photocopy items for internal or personal use, or the Blackwell Scientific Publications internal or personal use of specific clients, is granted (Australia) Pty Ltd by The Geological Society for libraries and other 107 Barry Street, Carlton users registered with the Copyright Clearance Center Victoria 3053 (CCC) Transactional Reporting Service, providing (Orders: Tel. (03) 347-0300) that a base fee of $03.00 per copy is paid directly to CCC, 27 Congress Street, Salem, MA 01970, USA. British Library Cataloguing in Publication Data 0305-8719/89 $03.00 Magmatism in the ocean basins. Typeset by Setrite Ltd, Hong Kong 1. Oceans. Beds. Magmatism. Printed and bound at I. Saunders, A.D. II. Norry, M.J. Cambridge University Press III. Geological Society of London IV. Series 551.46'08 ISBN 0-632-02384-8

Library of Congress Cataloging-in-Publication Data Magmatism in the ocean basins. (Geological Society special publication; no. 42) Bibliography: p. Includes index. 1. Magmatism. 2. Ocean bottom. I. Saunders, A. D. II. Norry, M.J. III. Series. QE461.M23784 1989 551.46'08 88-16828 ISBN 0-632-02384-8 Contents

SAUNDERS, A. D. & NORRY, M. J. Introduction vii

GASS, I. G. Magmatic processes at and near constructive plate margins as deduced from the Troodos (Cyprus) and Semail Nappe (N Oman) ophiolites 1

WHITE, R. S. Asthenospheric control on magmatism in the ocean basins 17

SPRAY, J. G. Upper segregation processes: evidence from alpine-type peridotites 29

NATLAND, J. H. of a lithologically heterogeneous mantle: inferences from crystallization histories of magnesian abyssal tholeiites from the Siqueiros Fracture Zone 41

DICK, H. J. B. Abyssal peridotites, very slow spreading ridges and ocean ridge magmatism 71

BLOOMER, S. H., NATLAND, J. H. & FISHER, R. L. Mineral relationships in gabbroic rocks from fracture zones of Indian Ocean ridges: evidence for extensive fractionation, parental diversity, and boundary-layer recrystallization 107

ELTHON, D. Pressure of origin of primary mid-ocean ridge 125

FuJn, T. Genesis of mid-ocean ridge basalts 137

PALACZ, Z. A. • WOLFF, J. A. Strontium, neodymium and lead isotope characteristics of the Granadilla Pumice, Tenerife: a study of the causes of strontium isotope disequilibrium in felsic pyroclastic deposits 147

STOREY, M., WOLFF, J. A., NORRY, M. J. & MARRINER, G. F. Origin of hybrid from Agua de Pau volcano, Sao Miguel, Azores 161

THOMPSON, G., BRYAN, W. B. & HUMPHRIS, S. E. Axial on the East Pacific Rise, 10-12 ~ N 181

HELGASON, J. The Fjallgardar volcanic ridge in NE Iceland: an aborted early stage plate boundary or a volcanically dormant zone? 201

FLOYD, P. A. Geochemical features of intraplate oceanic plateau basalts 215

DAVIES, G. R., NORRY, M. J., GERLACH, D. C. & CLIFF, R. A. A combined chemical and Pb-Sr-Nd isotope study of the Azores and Cape Verde hotspots: the geodynamic implications 231

CHAFFEY, D. J., CLIFF, R. A. & WILSON, B. M. Characterization of the St Helena source 257

JORON, J.-L. & TREUIL, M. Hygromagmaphile element distributions in oceanic basalts as fingerprints of partial melting and mantle heterogeneities: a specific approach and proposal of an identification and modelling method 277

FISHER, D. E. Evaluation of rare gas data in relation to oceanic 301

SON, S.-s. & MCDONOUGH, W. F. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes 313

MURTON, B. J. Tectonic controls on boninite genesis 347

Index 379