Petrology of Lamproites Petrology of Lamproites
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PETROLOGY OF LAMPROITES PETROLOGY OF LAMPROITES Roger H. Mitchell Lakehead University Thunder Bay, Ontario Canada and Steven C. Bergman ARCO Oi! and Gas Company Plano, Texas SPRINGER SCIENCE+BUSINESS MEDIA, UC Llbrary of Congress Cataloglng-ln-Publlcation Data Mitchell, Roger H. Petrology of lamproites I Roger H. Mitehell and Steven C. Bergman. p. em. Ineludes bibliographieal referenees and index. ISBN 978-1-4613-6688-1 ISBN 978-1-4615-3788-5 (eBook) DOI 10.1007/978-1-4615-3788-5 1. Lamproite. 2. Petrology. 3. Geoehemistry. 4. Rocks, Igneous. I. Bergman, Steven C. 11. Tit18. QE462.L35M57 1991 552' .3--de20 90-25226 CIP ISBN 978-1-4613-6688-1 © 1991 Springer Science+ Business Media New York Origioallypublished by Plenum Press, New York in 1991 Spftcover reprint of the hardcover 1st edition 1991 All rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher This work is dedicated to REX T. PRIDER Emeritus Professor of Geology University of Western Australia in recognition of his pioneering studies of the mineralogy and petrology of lamproites. Preface In this book, the first dedicated entirely to the petrology of lamproites and their relationships to other potassium-rich rocks, the objective of the authors is to provide a comprehensive critical review of the occurrence, mineralogy, geochemistry, and petrogenesis of the clan. Although lamproites represent one of the rarest of all rock types, they are both economically and scientifically important and we believe the time is ripe for a review of the advances made in their petrology over the past two decades. Many of these advances stem from the recognition of diamond-bearing lamproites in Western Australia and the reclassification of several anomalous diamond-bearing kim berlites as lamproites. Consequently lamproites, previously of interest only to a small number of mineralogists specializing in exotica outside the mainstream of igneous petrol ogy, have become prime targets for diamond exploration on a worldwide basis. Contemporaneously with these developments, petrologists realized that lamproites possess isotopic signatures complementary to those of midoceanic ridge basalts, alkali basalts, kimberlites, and other mantle-derived melts. These isotopic studies provided new insights into the long-term development of the mantle by suggesting that the source regions of lamproites were metasomatically enriched in light rare earth and other incompatible elements up to 1-2 Ga prior to the melting events leading to generation of the magma. We believe that an understanding of the nature of lamproites is essential for geologists concerned with exploration for diamond, and petrologists and geochemists interested in continental alkaline magmatism and mantle evolution. In the book we present new inter pretations of various aspects of lamproite petrology. Hence, the work is not simply a summary of existing information and accepted concepts; rather it proposes hypotheses that it is hoped, will serve to stimulate further studies of these unusual rocks. The book is the work of two authors, and although in overall agreement regarding the content and philosophy of the text, each assumes primary responsibility for any errors or omissions to be found in his particular contributions. In addition to the style and overall editing of the work, Roger Mitchell was responsible for Chapters 1, 2, 6-8, and 10 and Steven Bergman was responsible for Chapters 3-5 and 9. Alan Edgar and Henry Meyer are thanked for reviewing initial drafts of many of the chapters. Valerie Dennison is especially thanked for proofreading the entire work. Many people have contributed to the production of this book. We are particularly appreciative of preprints, thin sections, and rock samples provided by and discussions with vii viii PREFACE Lynton Jaques, Barbara Scott Smith, Alan Edgar, Danielle Velde, Henry Meyer, Bram Janse, Leendert Krol, Peter Berendsen, John Lewis, Steve Foley, Gino Venturelli, Mike Roden, Peter Nixon, Carter Hearn, Ted Scamboz, Howard Coopersmith, Hugh O'Brien, Tony Irving, Ken Collerson, Tony Erlank, Nick Rock, and Dave Nelson. Special thanks go to Henry Meyer for providing many hours of microprobe time at Purdue University, Barbara Scott Smith for photographic work, and Ken Foland for geochronological data. 1. Toney, D. 1. Henry, and L. Liang assisted with some of the microprobe analyses in Dallas. We thank P. A. Sheahan, K. Weissman, P. A. Carper, L. Batzle, and 1. M. Prokesh for literature searches and the acquisition of citations. Technical assistance at ARCO in Dallas was provided by 1. Talbot, V. Mount, S. R. Yang, F. Stiff, and E. Kinsel, and at Lakehead University by A. MacKenzie, M. Downey, A. Hammond, R. Viitala, W. Bons, and S. Millar. Sam Spivak drafted all of the original diagrams. Mitchell's work on lamproites is supported by the Natural Sciences and Engineering Research Council of Canada and Lakehead University. Much of Bergman's contribution was supported by the Anaconda Minerals Company (Industrial Minerals Group) and the ARCO Oil and Gas Company Exploration and Production Research Laboratory, in conjunction with their (presently expired) diamond exploration and minerals research programs. Roger Mitchell wishes to thank Valerie Dennison for her continued encouragement of his studies of lamproites and maintenance of an environment favorable to the preparation of this book. Steve Bergman acknowledges the support and consideration provided by Mary, Allison, Everett, Louise, and Maggie Bergman. Roger Mitchell Thunder Bay Steven Bergman Dallas Contents Chapter 1. The Lamproite Clan-Etymology and Historical Perspective 1 1. 1. Introduction 1 1.2. Initial Discoveries-1870-1906 1 1.3. Etymology of Lamproite 2 1.4. Western Australian Discoveries-The Legitimization of Lamproites 3 1.5. Johannsen and Modal Classifications of Rocks 4 1.6. Further Developments, New Occurrences, and Diamond- Bearing Lamproites 5 1.7. Reclassification of Anomalous Kimberlites 6 1. 8 . Recent Developments 7 Chapter 2. Potassic Rocks and the Lamproite Clan 9 2.1. Alkalinity, Sodic, Potassic, and Ultrapotassic Rocks 9 2.2. Alkali-Alumina Relationships 10 2.3. Potassic Rocks-General Petrographic Characteristics and Terminology 11 2.3.1. Lamproites 11 2.3.2. Roman Province Leucitites 12 2.3.3. Ultrapotassic Leucitites 13 2.3.4. Kalsilite-Bearing Lavas (Kamafugitic Rocks) 14 2.3.5. Potassic Lamprophyres 15 2.3.6. Kimberlite and Micaceous Kimberlites 15 2.3.7. The Shoshonite Association 16 2.3.8. Potassic Intrusive Rocks 17 2.4. Petrochemical Classifications of Potassic Rocks 17 2.4.1. Niggli Parameters 18 2.4.2. K20-Na20 Diagrams 19 2.4.3. Total Alkali-Silica Classifications 19 2.4.4. Sahama (1974) 21 2.4.5. Barton (1979) 23 ix x CONTENTS 2.4.6. Bogatikov et al. (1985) 26 2.4.7. Foley et al. (1987) 29 2.5. Petrographic and Mineralogical Classifications 31 2.5.1. Petrographic Classifications 31 2.5.2. Mineralogical Classifications 32 2.6. The Lamproite Clan 35 2.6.1. Geochemical Criteria for Lamproite Recognition 37 2.6.2. Mineralogical Criteria for Lamproite Recognition 37 Chapter 3. Description of Lamproite Occurrences-Distribution, Age, Characteristics, and Geological Framework 39 3.1. Introduction 39 3.2. North American and Greenland Lamproites 40 3.2.1. Group Name: Prairie Creek 43 3.2.2. Group Name: Leucite Hills 46 3.2.3. Group Name: Smoky Butte 50 3.2.4. Group Name: Francis 52 3.2.5. Group Name: Hills Pond 55 3.2.6. Group Name: Sisimiut 57 3.2.7. Group Name: Yellow Water Butte 59 3.2.8. Group Name: Froze-to-Death Butte 61 3.3. European Lamproites 63 3.3.1. Group Name: Murcia-Almeria 65 3.3.2. Group Name: Sisco 69 3.3.3. Group Name: Sesia-Lanzo and Combin 70 3.4. African Lamproites 72 3.4.1. Group Name: Kapamba 73 3.4.2. Group Name: Pneil, Postmasburg, Swartruggens 75 3.4.3. Group Name: Bobi 76 3.5. Australian Lamproites 79 3.5.1. Group Name: Argyle 80 3.5.2. Group Name: West Kimberley 83 3.6. Antarctic Lamproites 86 3.6.1. Group Name: Gaussberg 86 3.6.2. Group Names: Mount Bayliss and Priestley Peak 87 3.7. Asian Lamproites 89 3.7.1. Group Name: Chelima 90 3.7.2. Group Name: Majhgawan 93 3.7.3. Group Name: Barakar 96 3.7.4. Group Name: Murun 97 3.8. South American Lamproites 98 3.8.1. Group Name: Coromandel 98 3.9. Conclusions 101 CONTENTS xi Chapter 4. Tectonic Framework of Lamproite Genesis 103 4.1. Age and Temporal Relations of Lamproite Magmatism 104 4.2. Regional Geological and Tectonic Setting Generalizations 107 4.2.1. Lamproites and Plate Tectonics 108 4.2.2. Lamproites and Contemporaneous Subduction Zones 108 4.2.3. Fracture Zones, Transform Faults, and Continental Lineaments 110 4.2.4. Mantle Plumes, Hot Spots, and Hot Regions 111 4.2.5. Continental Rift Zones and Aulacogens 114 4.2.6. Orogeny and Postorogenic Relaxation 115 4.3. Lithospheric History of Lamproite Settings 116 4.3.1. Regional Structure 116 4.3.2. Basement Age, Composition, and Evolution 117 4.3.3. Contemporaneous, Previous, and Subsequent Magmatism 117 4.3.4. Importance of Paleosubduction and Fossil Benioff Zones 119 4.3.5. Mantle Metasomatism-Another Necessary Condition 120 4.3.6. Comparison with Kimberlites, Alkali Basalts, Lamprophyres, and Potassium-Rich Rocks 121 4.4. Tectonic Framework of Four Mesozoic-to-Cenozoic Lamproite Type-Locality Magmatic Fields 122 4.4.1. Leucite Hills 122 4.4.2. West Kimberley 122 4.4.3. Murcia-Almeria 123 4.4.4. Prairie Creek 123 4.5. Conclusions and Preferred Model 123 Chapter 5. Petrological Facies and Igneous Forms of the Lamproite Clan 125 5.1.