IGNEOUS PETROGENESIS

IGNEOUS PETROGENESIS

Marjorie Wilson Department of Earch Sciences, University of Leeds

~ Springer

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ISBN 978-0-412-75080-9 ISBN 978-94-010-9388-0 (eBook) DOI 10.1007/978-94-010-9388-0

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Originally published by Chapman & Hall

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© 1989 Marjorie Wilson

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This work is dedicated to my mother) Blanche Pearce) for a lifetime of love

and understanding) and to

Mary and Andrew

My main objective in writing this book has been to review the processes involved in present-day mag­ma generation and their relationship to global tectonic processes. Clearly, these are fundamental to our understanding of the petrogenesis of ancient volcanic and plutonic sequences, the original tec­tonic setting of which may have been obscured by subsequent deformation and metamorphism.

Until fairly recently, undergraduate courses in igneous petrology tended to follow rather classical lines, based on the classification of igneous rocks, descriptive petrography, volcanic landforms, types of igneous intrusions and regional petrology . However, the geologist of the late 1980s requires, in addition, an insight into the fundamental processes which operate within the Earth, and are responsible for the diversity of igneous rocks presently ex­posed. Unfortunately, attempts to make petrology

PREFACE

courses more petrogenesis-orientated are im­mediately confronted with a basic problem; the average student does not have a strong enough background in geochemistry to understand the finer points of most of the relevant publications in scientific journals. It is virtually impossible to fmd suitable reading material for such students, as most authors of igneous petrology textbooks have de­liberately steered clear of potentially controversial petrogenetic models. Even the most recent texts place very little emphasis on the geochemistry of magmas erupted in different tectonic settings, despite extensive discussions of the processes re­sponsible for the chemical diversity of magmas. Perhaps even more surprisingly, few texts have attempted to relate igneous activity to global tectonic processes, except at the most elementary levels.

Vlll PREFACE

This book has arisen out of ten years of teaching igneous petrology to undergraduate and graduate students in the Department of Earth Sciences, University of Leeds, UK, and the resultant frustra­tion at having no appropriate text which discusses the geochemical characteristics of magmas in rela­tionship to their tectonic setting. It should appeal to the more advanced undergraduate and beginning postgraduate students, and their teachers, who already have a basic foundation in petrological principles, including elementary geochemistry, phase diagrams, mineralogy, regional geology and global tectonics. The text has been deliberately put together in such a way that certain sections can be omitted at first reading if the background of the student is not appropriate. Thus, for example, a beginning student could omit the more detailed sections on the trace element and isotope geo­chemistry of magmas generated in a particular tectonic setting. As far as possible, continuity in the presentation of data for individual provinces has been maintained for ease of inter-province com pari­sions. Thus, in each chapter, sections will be found covering, for example, major element, trace ele­ment and radiogenic isotope geochemistry.

Clearly, a text of this length cannot hope to cover all examples of a particular type of igneous activity. Consequently, I have tended to focus on volcanic rocks from those recently active provinces for which we have the most comprehensive geochemi­cal data sets. Obviously, new data are appearing all the time and therefore the shape of many of the fields depicted in the geochemical variation dia­grams may change with time. Nevertheless, I believe that we have reached a stage in our understanding of the petrogenesis of igneous rocks at which most of the fundamental principles are well established. Consequently, the time is right for a text ofthis nature. I have deliberately not devoted

much space to the discussion oftopics such as phase diagrams and the fluid properties of magmas, as these have been extensively covered in several recent texts.

I would like to thank the following for their help and encouragement throughout the completion of this project: K. G. Cox for his much valued comments on the original manuscript; P.J. Wyllie and J.B. Gill for useful discussion of the format of the book and the early chapters; my colleagues in the Department of Earth Sciences, G.R. Davies, P.H. Nixon, E.H. Francis and R.A. Cliff, for their enthusiastic approach to all aspects of igneous petrology which has led to many fruitful discus­sions; S. Caunt for word processing the large number of references, and for much needed moral support during the final stages.

I have been fortunate to have had a particularly lively group of research students over the past ten years, including I. Luff, Z. Palacz, H. Downes, J.P. Davidson, I. Wilson, D. Chaffey, S. Amini and S. Caunt, who have kept me on my toes. Many people, including the above, have contributed to my ideas on igneous petrogenesis over the years, in particular R. Powell, J.D. Bell, S.W. Richardson, K.G. Cox, M.J. O'Hara, P.E. Baker, C.J. Hawkes­worth, M.J. Norry, the late P.J. Betton, I.S.E. Carmichael, A. Ewart, W. Hildreth, B.D. Marsh, C. Bacon, H. Helgeson, G.M. Brown and C.H. Emeleus.

Thanks must go finally to my family and friends for putting up with my reclusive habits over the past few months, especially to my mother, my sister Mary and her husband Andrew, my step-children Jane and Gary (and step son-in-law David), the latest addition to the family, my step-grandson Anthony, and to Anne and Brian Frost. Thanks also to Roger Jones of Unwin Hyman for being such an understanding editor.

Marjorie Wilson Leeds

ACKNOWLEDGEMENTS

We are grateful to the following individuals and organizations who have kindly given permission for the reproduction of copyright material (figure numbers in parentheses): K. G. Cox (1.2, 3.23, 4.8, 4.9); G. Faure and by permission of John Wiley & Sons (2.13); J. H. Pearce and Elsevier (2.14); Elsevier (2.15, 2.16, 3.12, 5.26, 6.19, 8.7, 12.5); D.A. Wood and Elsevier (2.17); P. J. Wyllie (3.5, 3.14, 3.19, 6.10); A. A. Finnerty and by permission of John Wiley & Sons Ltd (3.9); B. Harte (3.10); Lunar and Planet­ary Institute (3.13,5.31,6.15,9.10); A. Zindler and by permission from Nature 298, Copyright © 1982 McMillan Magazines Ltd (3.16,3.17); G. C. Brown (3.18, 5.1, 5.3, 5.4, 5.8); H. S. Yoder Jr and National Academy of Sciences (3.22); D. S. Barker (3.20); D. Green and by permission of the Director, Bureau of Mineral Resources, Geology and Geo­physics, Canberra; Springer-Verlag (3.26, 3.27, 3.29); Figure 3.28 Copyright Mineralogical Society of America; R. N. Thompson and Carnegie Institu­tion of Washington (4.2); Z. A. Palacz and Elsevier (4.4,4.6); Figures 5.5 and 5.13 adapted from Earth (F. Press and R. Siever) by permission of W. H. Freeman and Company, © 1974, 1978, 1982 W. H. Freeman and Company; M. G. Best (5.7, 5.24); R. D. Ballard and Elsevier (5.9,5.12); R. Hekinian and Elsevier (5.10,5.21,5.30); R. S. White and by permission of the Geological Society (5.14); J. M. Sinton and Elsevier (5.16); S. Le Douaran and Elsevier (5.17, 5.46); P. Thy and Springer-Verlag

(5.18); J. -G. Schilling and by pernusslOn from Nature 313, Copyright © 1985 McMillan Maga­zines Ltd (5.19,5.49); J.M. Edmond and Copy­right © 1983 Scientific American, Inc. (5.23); Figure 5.25 adapted by permission from Ito et al., Acta 47, Copyright © 1983 Pergamon Journals Ltd; J. R. Cann and Elsevier (5.27); E. G. Nisbet and Royal Astronomical Society (5.28); J. F. G. Wilkin­son (5.33); H. Staudigel and Elsevier (5.43, 5.44, 5.45); A. Zindler and Elsevier (5.47); ]. C. Allegre and Elsevier (5.48); P. J. Wyllie and by permission from Geological Society of America Bulletin 93 (6.3, 6.11); J.B. Gill (6.4, 6.5, 6.9, 6.12, 7.6); H.K. Acharya (6.6); R. N. Anderson and The Journal of Geology 88, Copyright © 1980, by permission of the University of Chicago Press (6.7, 6.8); V. Renard and Elsevier (6.11); A. Ewart and by permission of John Wiley & Sons Ltd (6.28, 6.30, 6.31); C. J. Hughes and Elsevier (6.39); R. J. Arculus (6.40); C. J. Allegre and by permission from Nature 299, Copyright © 1982 McMillan Magazines Ltd (6.46); Figures 6.47 and 6.48 reproduced with permission from Annual Review of Earth and Planetary Sciences 9, © 1981 Annual Reviews Inc; R. H. Pilger and by permission from Geological Society of America Bulletin 93 (7.3); C. Condie and Copyright © 1982 Pergamon Books Ltd (7.8); P. J. Wyllie and The Royal Society (7.9, 7.10, 7.11); W. S. Pitcher and Blackie & Son (7.12); R. D. Beckinsale and Blackie & Son (7.13); W. S. Pitcher (7.14); R. S. Harmon and by permission of the Geological Society (7.19,

x ACKNOWLEDGEMENTS

7.31); J. A. Pearce (7.25, 7.26); R. J. Stern and by permission from Geological Society of America Bulletin 93 (8.1); A. J. Crawford and Elsevier (8.2); Figure 8.11 adapted with permission from Woodhead and Fraser, Acta 49 Copyright © 1985 Pergamon Journals Ltd; K. C. Burke (9.1, 9.2, 9.4); E. M. Parmentier (9.6); A. B. Watts and by per­mission from Nature 315, Copyright © 1985 McMillan Magazines Ltd (9.7); M. P. Ryan (9.8); Figure 9.19 adapted with permission from Humphris et ai, Acta 49, Copyright © 1985 Per­gamon Journals Ltd; S. R. Hart and by permission from Nature 309, Copyright © 1984 McMillan Magazines Ltd (9.27); Figure 9.31 adapted with permission from Kurz et al. , Nature 297, Copyright © 1982 McMillan Magazines Ltd; K. G. Cox and by permission from Nature 272, Copyright © 1978 McMillan Magazines Ltd (10.1); M. A. Menzies and The Royal Society (10.3); K. G. Cox and Oxford University Press (10.4, 10.13); R. B. Smith

and National Academy Press (10.6); F. Barberi (11.2); C. E. Keen (11.4); J. D. Fairhead and Elsevier (11.5); R. E. Long (11.7a); R. W. Girdler and Elsevier (11. 7b); Y. A. Sinno (11. 8); W. Bosworth and by permission from Nature 316, Copyright © 1985 McMillan Magazines Ltd (11.11); Figure 11.33 adapted with permission from McDonough et ai., Acta 49, Copyright © Pergamon Journals Ltd; Plenum Press (12.3); C. B. Smith and the Geological Society of South Africa (12.14); S. C. Bergman and by permission of the Geological Society (12.15); R. N. Thompson and Springer-Verlag (12.18); A. LeRoex and by per­mission from Nature 324, Copyright © 1986 McMillan Magazines Ltd (12.19, 12.22); Figure 12.21 adapted with permission from Nelson et aI., Acta SO, Copyright © Pergamon Journals Ltd; G. Ferrara and Springer-Verlag (12.27); D. K. Bailey and the Geological Society of South Mrica (12.28, 12.29).

PREFACE

ACKNOWLEDGEMENTS

LIST OF TABLES

SOME COMMON ABBREVIATIONS USED IN THE TEXT

PART ONE

Magmatism and global tectonic processes

CHAPTER ONE

Relation of present-day magmatism to global tectonic processes

1.1 Introduction 1.2 Characteristic magma series associated

with specific tectonic settings Further reading

CHAPTER TWO

Geochemical characteristics of igneous rocks as petrogenetic indicators

2.1 Introduction 2.2 Chemical analysis of igneous rocks

CONTENTS

vu 2.3 Chemical variation diagrams 2.4 Geochemical characteristics of primary

tx magmas 2.5 Isotopes as petrogenetic indicators

xv 2.6 Geochemical criteria for the identification of the palaeotectonic setting of ancient volcanic sequences

Xtx Further reading

CHAPTER THREE

Partial melting processes in the Earth's 1 upper mantle

3.1 Introduction 3.2 The physical state of the upper mantle 3.3 Chemical composition and mineralogy

of the upper mantle 3.4 Partial melting processes in the upper

3 mantle 3.5 The basaltic magma spectrum in relation

3 to partial melting processes 3.6 Segregation and ascent of magma

7 Further reading 11

CHAPTER FOUR

Processes which modify the composition of 13 primary magmas

4.1 Introduction 13 4.2 Convection and mixing in magma 14 chambers

14

21 22

32 34

37 37 38

44

58

67 70 72

73 73

78

xii

4.3 Fractional crystallization 82 processes 159 4.4 Crustal contamination 89 6.6 Segregation, ascent and storage of 4.5 Zone refining 96 magma 162 4.6 Liquid immiscibility 97 6.7 Characteristic magma series 164 4.7 Gaseous transfer processes 97 6.8 Spatial and temporal variations in Further reading 97 island-arc magmatism 167

6.9 Surface volcanic features 168 6.10 Petrography of island-arc volcanic

PART TWO rocks 169

Magmatism at constructive plate margins 99 6.11 Chemical composition of erupted

magmas 172 6.12 Detailed petrogenetic model 188 Further reading 190

CHAPTER FIVE

M id-ocean ridges 101

5.1 Introduction 101 CHAPTER SEVEN 5.2 Simplified petrogenetic model 104 5.3 Nature of the oceanic crust 106 Active continental margins 191 5.4 Structure of mid-ocean ridges 110 5.5 Heat flow and metamorphism 119 7.1 Introduction 191 5.6 Convection systems at constructive 7.2 Simplified petrogenetic model 196

plate margins 124 7.3 The structure of active continental 5.7 Partial melting processes 125 margins 198 5.8 Magma storage and release 126 7.4 Thermal structure and partial melting 5.9 Petrography of mid-ocean ridge processes 201

basalts 129 7.5 Magma storage in the crust 203 5.10 Chemical composition of erupted 7.6 Petrographic characteristics of the

magmas 132 volcanic and plutonic rocks 206 5.11 Detailed petrogenetic model 145 7.7 Chemical composition of the magmas 208 Further reading 149 7.8 Detailed petrogenetic model 223

Further reading 225

PART THREE

Magmatism at destructive plate margins 151

CHAPTER EIGHT

CHAPTER SIX Back-arc basins 227

Island arcs 153 8.1 Introduction 227 8.2 Simplified petrogenetic model 229

6.1 Introduction 153 8.3 Petrography of the volcanic rocks 231 6.2 Simplified petrogenetic model 154 8.4 Chemical composition of the erupted 6.3 Structure of island arcs IS7 magmas 231 6.4 Earthquakes and magma genesis 158 8.S Detailed petrogenetic model 239 6.S Thermal structure and partial melting Further reading 241

xm

PART FOUR CHAPTER ELEVEN

Magmatism within plates 243 Continental rift zone magmatism 325

11.1 Introduction 325 11.2 Simplified petrogenetic model 332 11.3 Crust and upper mantle structure 335

CHAPTER NINE 11.4 Petrography of the volcanic rocks 339 1l.5 Chemical composition of the erupted

Oceanic islands 245 magmas 342 11.6 Detailed petrogenetic model 371

9.1 Introduction 245 Further reading 374 9.2 Simplified petrogenetic model 250 9.3 Crustal structure of oceanic islands 253 9.4 Partial melting processes 255 CHAPTER TWELVE 9.5 High-level magma storage 256 9.6 Petrography of oceanic-island volcanic Potassic magmatism within continental plates 375

rocks 258 9.7 Chemical composition of erupted 12.1 Introduction 375

magmas 261 12.2 Simplified petrogenetic model 380 9.8 Detailed petrogenetic model 282 12.3 Partial melting processes in the upper Further reading 285 mantle 384

12.4 Petrographic characteristics of kimberlites and ultrapotassic rocks 388

12.5 Chemical composition ofkimberlites and ultrapotassic rocks 391

12.6 Detailed petrogenetic model 411 CHAPTER TEN Further reading 416

Continental tholeiitic flood basalt provinces 287 10.1 Introduction 287

APPENDIX 417 10.2 Simplified petrogenetic model 291 10.3 Crustal structure and magma storage Approximate ranges ofD values for the

reservoirs 294 partitioning of trace elements between the 10.4 Crustal contamination of magmas 295 common rock-forming minerals and liquids 10.5 Petrography of the volcanic rocks 296 of basic- intermediate composition 10.6 Chemical composition of the erupted

magmas 298 BIBLIOGRAPHY 423 10.7 Detailed petrogenetic model 321 Further reading 323 INDEX 457

LIST OF TABLES

1.1 Global rates of Cenozoic magmatism 5 1.2 Approximate equivalents of some K-rich and normal rock types 9 1.3 Characteristic magma series associated with specific tectonic settings 11 2.1 Summary of key trace element parameters useful in evaluating

petrogenetic models 17 3.1 Selected heat flow data for the Earth 41 3.2 Estimated radioactive contents and heat productivities 41 3.3 Mineral chemistry of the major phases in typical spinel and

garnet lherzolites 46 3.4 Major element compositional ranges for spinel and garnet Iherzolites 47 3.5 Comparison of bulk rock compositions of spinel lherzolite xenoliths 51 3.6 Calculated values of CdCo for modal and non-modal batch and

fractional melting of bulk composition X in the system forsterite-diopside-enstatite for the highly incompatible elements Ce and Yb 65

4.1 Major and trace element analyses of some typical continental crustal rocks 95

5.1 The layered structure of the oceanic crust 108 5.2 Classification of mid-oceanic ridges according to spreading rate 112 5.3 Comparison of the major element geochemistry of MORB with that

of a typical oceanic-island tholeiite, an island-arc tholeiite and a continental flood tholeiite 133

5.4 Major (a) and trace element (b) geochemistry of average primitive (M = 60-70) normal, plume and transitional type MORB from the Mid-Atlantic Ridge 135

5.5 Typical large cation abundances and ratios for oceanic tholeiites 138 5.6 Volatile contents in the glassy rims of basalts and andesites from the

Galapagos spreading centre 142 6.1 Classification of island arcs according to convergence rate, crustal

thickness and characteristic magma series 167 6.2 A comparison of the major element composition of basaltic rocks from

island arcs, mid-oceanic ridges and oceanic islands 174

XVl LIST OF TABLES

6.3 Major and trace element characteristics of the island-arc tholeiite series lavas from the South Sandwich arc 174

6.4 Major and trace element characteristics of the island-arc calc-alkaline series lavas from the South Sandwich arc 175

6.5 Major and trace element characteristics of the island-arc high-K calc-alkaline series lavas from the Sunda arc 176

6.6 Trace element concentrations in island-arc basalts, compared to other oceanic basalt magma types 176

7.1 Tectonic and geological characteristics of the late Cenozoic volcanic zones of the Andes 196

7.2 Average major and trace element compositions of Andean volcanic rocks, compared with those from the island arcs of the south-west Pacific 215

7.3 Major and trace element analyses of basaltic andesites from the northern, central and southern active volcanic zones of the Andes 216

7.4 Com parison of the geochemical characteristics of an alkali basalt erupted to the east of the volcanic front in the CVZ and a calc-alkaline basalt erupted in the SVZ 217

7.5 Analyses of plutonic rocks from the Lima segment of the Coastal Batholith of Peru 218

8.1 Duration of spreading and total opening rate for currently active back-arc basins 228

8.2 Major and trace element analyses of back-arc basin basalts from the East Scotia Sea, a typical tholeiitic basalt from the associated South Sandwich island arc, and depleted and enriched South Atlantic MORB compositions 232

8.3 Major and trace element abundances in boninite lavas from the Bonin islands, Japan 235

8.4 Trace element characteristics of East Scotia Sea back-arc basin basalts, compared to MORB and oceanic-island tholeiites 236

9.1 Summary of the petrographic differences between tholeiitic and alkali basalts 259

9.2 Pyroxene compositions in Hawaiian tholeiitic and alkalic basalts 260 9.3 Mineralogy of oceanic-island alkalic magma series: (a) phenocrysts;

(b) groundmass 261-2 9.4 Representative analyses of volcanic rocks from Ascension Island 264 9.5 Representative analyses of volcanic rocks from Tristan da Cunha 264 9.6 Major and trace element geochemistry of typical tholeiitic and alkalic

basalts from Hawaii, compared to N-type MORB 266 9.7 Comparison of selected trace element abundances in MORB,

oceanic-island tholeiites and oceanic-island alkali basalts 269 10.1 Ages and dimensions of the major continental flood-basalt provinces 288 10.2 Major and trace element data for basalts from the Columbia

River Province 299 10.3 Major and trace element data for continental flood basalts, compared

to a typical oceanic-island tholeiite and normal and enriched MORB 300 10.4 Major and trace element data for the (a) HPT and (b) LPT series

LIST OF TABLES XVll

volcanics from the Parana province 301 11.1 Major and trace element analyses of ultra potassic lavas from the

western branch of the East African Rift 344 11.2 Major and trace element analyses of members ofthe basanite-phonolite

suite from Mt Kenya 345 11.3 Major and trace element analyses of an alkali basalt-trachyte suite

from the southern Gregory (Kenya) Rift 346 11.4 Major and trace element analyses of a transitional basalt-rhyolite suite

from the Boina centre, Afar Rift, Ethiopia 347 1l.5 Major and trace element analyses of a bimodal transitional

basalt-rhyolite suite from the Naivasha volcanic field, Kenya Rift 348 12.1 Mineralogical classification of lamproites 390 12.2 Major and trace element analyses of some typical Group I ultrapotassic

rocks (lamproites) 392 12.3 Major and trace element analyses of some Group II ultrapotassic

rocks from the western branch of the East African Rift 393 12.4 Major and trace element analyses of Group III ultra potassic

lavas from Vulsini, Roman Province 394 12.5 Average major and trace element analyses ofkimberlites 395 12.6 Average major and trace element analyses of kimberlite, lamproite and

lamprophyre 396 12.7 Subdivision of the lamprophyre clan of rocks 399 12.8 Characteristic features of Group I and II southern African kimberlites 406

SOME COMMON ABBREVIATIONS USED IN THE TEXT

A alkalic Elements Mn manganese AFM the variation diagram of F (FeO + Fe203) -M (MgO) - A (Na20 + K2O) Nd neodymium

BABI Basaltic Achondrite Best Initial; the best Al aluminium Ni nickel estimate ofthe initial 87Srf!6Sr ratio of Ar argon Nb niobium basaltic achondrite meteorites, assumed to Ba barium N nitrogen be similar to the primordial isotopic Be beryllium 0 oxygen composition of Sr in the Eanh

CA calc-alkaline Ca calcium P phosphorus CFB continental flood basalt C carbon K potassium CHUR chondritic uniform reservoir Ce cerium Pr praesodymium CMAS the system Cao-MgO-Al20 3 - Si02 CI chlorine Rb rubidium D the distribution or partition coefficient for Cr chromium Sm samarium the partitioning of a trace element between a

Co cobalt Sc scandium mineral and a silicate melt (see Appendix) DM depleted mantle Cu copper Si silicon DSDP Deep Sea Drilling Project Dy dysprosium Ag silver EM enriched mantle Er erbium Na sodium EPR East Pacific Rise Eu europium Sr strontium 102 fugacity of oxygen Ga thousand million years F fluorine S sulphur lAB island-arc basalt Gd gadolinium Ta tantalum Ma million years Au gold Tb terbium MAR Mid-Atlantic Ridge Hf hafnium Th thorium MORB mid-ocean ridge basalt He helium Tm thulium OIB ocean-island basalt P pressure (kbar) Ho holmium Ti titanium REE rare eanh element (LREE = light REE, H hydrogen U uranium

HREE = heavy REE) Fe iron V vanadium SMOW standard mean ocean water La lanthanum Yb ytterbium T Temperature ("C) Pb lead Y yttrium TH tholeiitic Vp seismic velocity of P waves Li lithium Zn zinc Vs seismic velocity of S waves Lu lutetium Zr zirconium p density (g em -3) Mg magnesium