Andean Magmatism: Chemical and Isotopic Constraints PDF
Preview Andean Magmatism: Chemical and Isotopic Constraints
ANDEAN MAGMATISM CHEMICAL AND ISOTOPIC CONSTRAINTS ANDEAN MAGMATISM CHEMICAL AND ISOTOPIC CONSTRAINTS R.S. Harmon and B.A. Barreiro (Editors) Southern Methodist University, Dallas and Dartmouth College, Hannover College of St. Paul & St Mary Francis Close Hall Library Shiva Publishing Limited SHIVA PUBLISHING LIMITED 4 Church Lane, Nantwich. Cheshire CWS SRQ. UK Available in North America from: BIRKHAUSER BOSTON, INC. P.O. Box 2007, Cambridge, MA 02139, USA British Library Cataloguing in Publication Data Andean magmatism.-(Shiva geology series) 1. Magmatism-Andes I. Hannon, R.S.-Barreiro, B.A. 552'.1 QE461 ISBN-13: 978-1-4684-7337-7 e-ISBN-13: 978-1-4684-7335-3 001: 10.10071978-1-4684-7335-3 CI R.S. Harmon and B.A. Barreiro, 1984 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording and/or otherwise, without the prior written permission of the Publishers. Typeset by Gilbert Composing Services, Leighton Buzzard Contents List of Contributors vii Preface Section 1: Volcanic Andes The tectonic setting of active Andean volcanism R. S. Thorpe 4 Oxygen isotope ratios in Late Cenozoic Andean volcanics R. S. Harmon and J. Hoefs 9 Lead isotopes and Andean magmagenesis B.A. Barreiro 21 Isotope and trace element data for orogenic andesites from the Austral Andes C.R. Stern. K. Futa and K. Muehlenbachs 31 Petrology and chemistry of volcanic rocks of the Southern Andes L. Lopez-Escobar 47 Geochemical variations in volcanic rocks from central-south Chile (33-42°S) R.L. Hickey. D. C. Gerlach and F.A. Frey 72 Sr, Nd, Pb and 0 isotope composition of Late Cenozoic volcanics, northernmost SVZ (33-34°S) C.R. Stern. K. Futa. K. Muehlenbachs. F.M. Dobbs. 1. Munoz. E. Godoy and R. Charrier 96 The Cerro Purico shield complex, north Chile p. W. Francis. w.F. McDonough. M. Hammill. L.1. O' Callaghan and R. S. Thorpe 106 Quantitative models for crustal contamination in the central and northern Andes D.E. James 124 v vi Contents Correlated Sr isotope and geochemical variations in basalts and basaltic andesites from Guatemala N.K. Grant, W.l. Rose, Jr and L.A. Fultz 139 Section 2: Plutonic Andes Phanerozoic plutonism in the Peruvian Andes W. S. Pitcher 152 The Coastal Batholith of Peru M.P. Atherton 168 Lead isotope systematics in batholithic rocks of the Western and Coastal Cordilleras, Peru S.B. Mukasa and G.R. Tilton 180 Geochemical characteristics of the Late Mesozoic Andean volcanics M. Boily, C. BrooksandD.E. James 190 The magmatic evolution of the Cordillera Oriental, southeastern Peru D.J. Kontak, A.M. Clark and E. Farrar 203 Geochemical characteristics of magmatism in the Southern Andes (45-46°S) D. s. Bartholomew and 1. Tarney 220 References. 231 Contributors M.P. Atherton Department of Geology, University of Liverpool, P.O. Box 147, Liverpool L69 3BX, UK B.A. Barreiro Department of Earth Sciences, Dartmouth College, Hannover, New Hampshire 03755, USA D. S. Bartholomew Department of Geology, University of Leicester, Leicester LEI 7RH, UK M. Boily Departement de Geologie, Universite de Montreal, CP 6128, Succ. 'A', Montreal, Quebec H3C 3J7, Canada C. Brooks Departement de Geologie, Universite de Montreal, CP 6128, Succ. 'A', Montreal, Quebec H3C 3J7, Canada R. Charrier Departamento de Geologia y Geofisica, Universidad de Chile, Casilla 13518, Santiago, Chile A.H. Clark Department of Geological Sciences, Queen's University, Kingston, Ontario K7L 3N6, Canada F.M. Dobbs Departamento de Minas, Universidad de Santiago, Casilla 10233, Santiago, Chile E. Farrar Department of Geological Sciences, Queen's University, Kingston, Ontario K7L 3N6, Canada P. W. Francis Lunar and Planetary Institute, 3303 NASA Road 1, Houston, Texas 77058, USA vii viii Contributors F.A. Frey Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA LA. Fultz Museum of Natural History, University of Nevada, Las Vegas, Reno, Nevada 89503, USA K. Futa USGS, MS963 Denver Federal Center, Denver, Colorado 80225, USA D. C. Gerlach Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA E. Godoy Departamento de Geologia y Geofisica, Universidad de Chile, Casilla 13518, Santiago, Chile N.K. Grant Department of Geology, Miami University, Oxford, Ohio 45056, USA M. Hammill Lunar and Planetary Institute, 3303 NASA Road 1, Houston, Texas 77058, USA; Now at The Open University, Milton Keynes, UK R.S. Harmon Department of Geological Sciences, Southern Methodist University, Dallas, Texas 75275, USA R.L. Hickey Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA 1. Hoefs Geochemisches Institut der Universitat Gottingen, D-3400 Gottingeri, West Germany D.E. James carnegie Institution of Washington, Department of Terrestrial Magnetism, 5241 Broad Branch Road, NW Washington DC 20015, USA D.l. Kontak Department of Geological Sciences, Queen's University, Kingston, Ontario K7L 3N6, Canada Contributors ix L. Lopez-Escobar Departamento de Geologia y Geofisica, Universidad de Chile, Casilla 13518, Santiago, Chile W.F. McDonough Lunar and Planetary Institute, 3303 NASA Road 1, Houston, Texas 77058, USA; Now at The Open University, Milton Keynes, UK Jr. Muehlenbachs Department of Geology, University of Alberta, Edmonton, Alberta T6G 2E3, Canada S.B. Mukasa Department of Geological Sciences, University of California, Santa Barbara, California 93106, USA J. Munoz Servicio Nacional de Geologia y Mineria, Casilla 10465, Santiago, Chile L.J. 0' Callaghan Lunar and Planetary Institute, 3303 NASA Road 1, Houston, Texas 77058, USA; Now at The Open University, Milton Keynes, UK W. S. Pitcher The Jane Herdman Laboratories of Geology, University of Liverpool, Brownlow Street, P.O. Box 147, Liverpool L69 3BX, UK w.I. Rose. Jr Department of Geology and Geological Engineering, Michigan Technologi cal University, Houghton, Michigan 49931, USA C.R. Stern Department of Geological Sciences, University of Colorado, Boulder, Colorado 80309, USA J. Tarney Department of Geology, University of Leicester, Leicester LEI 7RH, UK R.S. Thorpe Department of Earth Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK G.R. Tilton Department of Geological Sciences, University of California, Santa Barbara, California 93106, USA Preface Destructive plate margin magmagenesis is one of the most intensely studied and widely debated topics in the earth sciences at present. Calc-alkaline volcanic and plutonic rocks in orogenic settings exhibit such a diversity of composition and character that the subducted oceanic lithosphere, the overlying 'enriched' lithospheric mantle and the lower continental crust all have been advocated recently as the primary source region for island-arc and continental-margin basaltic to andesitic magmas. The role of the upper continental crust is also a matter of continuing controversy. It is clear that crustal contamination is a common, but not universal, feature of destructive plate margin magmatism. Whether this contamination is introduced at source by subduction-related processes or occurs during magma transit by bulk anatexis and magma mixing, selective contamination or coupled fractional crystallization-assimilation mechanisms is central to most current discussions of andesite petrogenesis. This book presents a series of papers which directly address these and other important geological and geochemical problems within the context of the Mesozoic-Cenozoic calc-alkaline magmatism characteristic of the Andean Cordillera of western South America. Although it is aimed primarily at postgraduate students and researchers familiar with the Andes, it is also a useful general reference for workers in other fields who wish to gain an insight into current thoughts, ideas and speculations on 'andesitic' magmatism at destructive plate margins. The 16 papers contained in the book were presented as part of a special symposium of the American Geophysical Union held in Baltimore, Maryland (USA) in June 1983. The contributors include geologists, petrologists and geochemists of various specializations who each bring their own varied perspectives to bear on a problem of common interest-Andean calc-alkaline magmatism. The individual papers in the volume are divided into two groups, those dealing with aspects of the Late Cenozoic 'andesitic' volcanism (of which the Andes is the type locality) and those considering primarily Mesozoic-Tertiary plutonism. Within each group the ordering of papers represents an evolution in scale from regional reconnaissance studies to detailed case studies of individual volcanic centres or intrusive complexes. The last paper in the volcanic section provides a useful comparison between Late Cenozoic 'andesitic' volcanism in central America with that in the Andes. The geochemical and isotopic data presented in the book do indeed provide some constraints on the origin and pre-eruption evolutionary history of Andean 1 2 Preface magmas. It is important to note at the outset, however, that the papers contained in the book do not arrive at a concensus regarding the questions addressed. The reader will find real differences in interpretation and opinion as well as a wide range of hypotheses advocated to explain the different aspects of Andean magmatism addressed by the various authors. The debate is by no means over and many of the problems discussed here will be a focus of continuing controversy for some time to come. Nevertheless, we hope that this volume points out the utility and importance of multi isotope and combined chemical-isotope approaches when undertaken within a framework of detailed field and petrographic studies. Our thanks are extended to the authors who contributed to the book. Their enthusiasm and timely preparation of the manuscripts after the Baltimore meeting made it possible to get the book completed without significant delay. Also, we would like to thank the symposium participants who did not contribute to the book for providing a stimulating forum for discussion and, in particular, P. J. Patchett who was instrumental in planting the seed of an idea that eventually blossomed into the symposium. We are very grateful to J. L. Atkinson for her assistance with reading the proofs. Finally our collective thanks are due to the staff of Shiva Publishing. R.S. HARMON, Southern Methodist University, Dallas November 1983 B.A. BARREIRO, Dartmouth College, Hannover
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