Geochemistry and Petrogenesis of Perinthatta Anorthosite, Northern Kerala
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GEOCHEMISTRY AND PETROGENESIS OF PERINTHATTA ANORTHOSITE, NORTHERN KERALA THESIS SUBMITTED TO THE COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN THE FACULTY OF MARINE SCIENCE BY P. SONEY KURIEN DEPARTMENT OF MARINE GEOLOGY AND GEOPHYSICS SCHOOL OF MARINE SCIENCES COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY LAKESIDE CAMPUS, COCHIN — 682 016 MAY 2000 Dedicated to my family DECLARATION I, P. Soney Kurien, do hereby declare that the thesis entitled “Geochemistry and Petrogenesis of Perinthatta Anorthosite, Northern Kerala" is a genuine record of research work done by me under the supervision of Dr. C.G. Nambiar, Reader, Department of Marine Geology and Geophysics, School of Marine Sciences, Cochin University of Science and Technology, Lakeside Campus, Cochin — 682 016. This work has not been previously formed the basis for the award of any degree or diploma of this or any other University or other institute of learning. CochinMay 2, 2000 P. SONEY -16 KURIEN W CERTIFICATE I certify that this thesis, "Geochemistry and Petrogenesis of Perinthatta Anorthosite, Northern Kera|a" has been prepared by P. Soney Kurien under my supervision and guidance in partial fulfilment of the requirements for the degree of Doctor of Philosophy and no part thereof has been submitted for any other degree. MayCochin a,,2000 - 16.(Research .G. NambiarSupervisor) Dept. of Marine Geology and Geophysics School of ’Marine Sciences Cochin University of Science and Technology Cochin — 682 016. Preface This report deals essentially with the geochemistry and petrogenesis of Perinthatta anorthosite. The work also addresses the geological setting of the pluton in terms of its field relationships and petrography and the structure and metamorphism of the region and examines its relation with the associated plutons. For the sake of convenience, the thesis is divided into six chapters. The first chapter gives a general introduction to the topic in terms of regional geology, petrogenetic problem of anorthosites and the objectives and methodology adopted in the work. The second chapter deals with the structure of the region and the third chapter attempts a synthesis of metamorphism of the northern Kerala. Chapter IV describes the field aspects and petrography of anorthositic rocks. The fifth chapter deals with the geochemistry or anorthositic rocks and the petrogenetic interpretations based on this. It also incorporates the mineral chemistry of the anorthositic rocks and thermobarometric calculations and the results of preliminary isotope analysis on the pluton. The last chapter gives an account of the field, petrographic, geochemical and petrogenetic aspects of other plutonic rocks spatially associated with Perinthatta anorthosite and examines their genetic relationship with the anorthositic rocks. The summary of the work is given at the end which is followed by a bibliography of cited references and three appendices. ACKNOWLEDGEMENTS I wish to express my profound thanks and deepest sense of gratitude to Dr. C. G.Nambiar, Reader, Department of Marine Geology & Geophysics, Cochin University of Science & Technology, for unfailing guidance, invaluable suggestions, critical comments and constant encouragement throughout the course of this work. I express my heartfelt gratitude to Dr. M. Radhakrishna, Lecturer, Department of Marine Geology 8. Geophysics, Cochin University of Science & Technology for his valuable help and advice during the filed and laboratory studies. I place on record my sincere thanks to Prof. K. T. Damodaran, Head, Department of Marine Geology & Geophysics, for making the facilities available in the department and for his constant encouragement. I also express my thanks to Prof. N.R. Menon, Director, School of Marine Sciences, for making the common facilities of the school during the course of the study. I place on record my sincere thanks to the faculty members of the department like Prof. P.Seralathan, Dr. A.C. Narayana, Prof. K. Sajan, Dr. A.D. Singh, Dr. M. Ravishankar, and Dr. S. Rajendran for the help and encouragement rendered by them. I am thankful to the Department of Science and Technology. Government of Inida for the fellowship in a SERC project entitled “Nature and evolution of Precambrian lower crustal segments associated with Bavali lineament and Wynad Schist belt". A number of individuals have helped me in various ways in the course of this doctoral work while it is impossible to mention all of them, I note the following in particular with appreciation: Dr. M.K. Devarajan, Dr. S.N. Kumar, Dr. M. Satish Kumar, Dr. K. Sundar, Dr. T.M. Mahadevan, Dr. K. Gopalan, Dr. J.K. Zacharia and Dr. Anil Kumar. I express my thanks to Prof. Thrivikramaji, Department of Geology. University of Kerala for providing the facilities for preparing the photomicrographs. I express my appreciation to Dr. Sabu Joseph, Research Assistant, Department of Geology, University of Kerala for helping me to prepare the photomicrographs. This work would not have been accomplished without the tremendous help rendered by my colleagues Mr.John Kurian, P, Dr. Manoj Kumar. P, Mr. G.N. Hariharan, Mr. Reji Srinivas, Mr. Arts K.P, Mr. Ajayakumar. P, Mr. Priju, Mr. Anandraj. Ms. Nisha, Mr. Sunil Kumar. G..and Mr. Joseph George. I owe my parents and brothers for the inspiration and support extended to me for the completion of this task. Contents PREFACE Chapter I. INTRODUCTION Regional geology General introduction to anorthosite Indian anorthosites Previousworks on Perinthatta anorthosite 11 Objectives of the present study 12 Study Area 12 _L—l—|—L—L—Lfi xiouo-:.r=.c.o'r\>'—x Methodology 13 1.7.1 Field study 13 1.7.2 Petrography 13 1.7.3 Chemical analysis of rocks 13 1.7.4 Chemical analysis of minerals 14 1.7.5 X-ray studies 14 1.7.6 Geochronological studies 14 1.7.7 Data processing and computations 14 Chapter II. STRUCTURE Introduction 15 Previous work 15 Structural data from the present work 16 2.3.1 Eastern sector 16 2.3.2 Central sector 18 2.3.3 Western sector 21 2.3.4 Mylonite 23 2.4 Geometrical analysis of folds 24 2.5 Discussion 25 Chapter III. METAMORPHISM Introduction 30 Metamorphic provinces 30 Petrography of northern granulite province 32 3.3.1 Mafic granulites 32 3.3.2 Charnockite 35 Mineral chemistry 38 3.4.1 Clinopyroxenes 38 3.4.2 Orthopyroxenes 39 3.4.3 Garnet 39 3.4.4 Plagioclase 40 3.4.5 Hornblende 40 3.4.6 llmenite 41 3.4.7 Magnetite 41 3.5 Geothermobarometry 41 3.5.1 Results of geothermobarometry 43 3.6 Discussion and conclusion 48 Chapter IV. Field relationships and petrography 4.1 Introduction 51 4.2 Field relationships 51 4.3 Rock nomenclature 57 4.4 Megascopic petrography 58 4.4.1 Anorthosite 58 4.4.2 Dioritic anorthosite 58 4.4.3 Anorthositic diorite 59 4.5 Microscopic petrography 59 4.5.1 Anorthosite 59 4.5.2 Dioritic anorthosite 62 4.5.3 Anorthositic diorite 63 4.6 Discussion 65 Chapter V. GEOCHEMISTRY AND PETROGENESIS 5.1 Introduction 67 5.2 Rock types 67 5.3 Major elements 68 5.3.1 Anorthosite 68 5.3.2 Dioritic anorthosite 69 5.3.3 Anorthositic diorite 70 5.3.4 Variation in major element chemistry 70 5.4 Trace elements 71 5.4.1 Trace element variations 72 5.5 Rare earth elements 73 5.6 Petrogenesis 76 5.6.1 Petrogenesis of massif-type anorthosite 76 5.6.2 Petrogenesis of Perinthatta anorthositic rocks 78 5.6.3 Rare earth element based modelling of parent melt 83 5.7 Mineral chemistry 85 5.7.1 Plagioclase 85 5.7.2 XRD analysis of plagioclase 86 5.7.3 Pyroxenes 87 5.7.4 Fe-Ti oxides 88 5.8 Geothermobarometry of anorthosites 88 5.8.1 Barometry 88 5.8.2 Thermometry 89 5.105.9 Isotope Discussion analysis 9190 Chapter VI. ASSOCIATED PLUTONS 6.26.1 Ezhimala Introduction gabbro-granophyre complex 93 93 6.2.26.2.1 Ezhimala Ezhimala granitoids gabbro 100 94 6.36.3.1 Peralimala Field relationships syenite 109 110 6.3.2 Megascopic petrography 110 6.3.3 Microscopic petrography 111 6.3.4 Majorelementgeochemistry 112 6.3.5 Trace element geochemistry 113 6.46.3.76.3.6 Chemical Diorites Petrogenesis grouping and tectonic discrimination 116 115 114 6.4.26.4.1 Majorelementgeochemistry Petrography 116 117 6.56.4.46.4.3 Discussion Trace Petrogenesis element geochemistry 120 119 118 SUMMARY BIBLIOGRAPHY Appendix I Appendix II Appendix III iii List of Figures 1.1 Map of South India showing major shear zones and granulite blocks. 1.2 Geological map of South India. 1.3 Geological map of northern Kerala. 1.4 Map of Northern Kerala showing the study area. 2.1 Foliation map of the study area. 2.2 (a) Field sketch of minor ductile shear (b) Field sketch of conjugate set of minor brittle shear. 2.3 (a) & (b) Field photographs showing F1 folds. 2.4 (a) & (b) Field photographs showing F2 and F3 folds. 2.5 (a), (b) & (c) Field photographs showing hook shaped, double zig-zag and dome and basin type interference patterns. 2.6 Field photographs showing pinch and swell structure. 2.7 Field sketches of shear sense indicators in mylonite. 2.8 (a), (b) & (c) Photomicrographs of oriented thin sections of mylonites showing shear sense indicators. 2.9 (a), (b) 8. (c) Pi-pole diagrams of foliation planes for the three sectors. 3.1 Map of northen Kerala showing the different metamorphic provinces 3.2 Photomicrograph of mafic granulite showing the alteration of clinopyroxene to hornblende. 3.3 Photomicrograph of mafic granulite showing the alteration of orthopyroxene to hornblende. 3.4 Photomicrograph of mafic granulite showing the alteration of garnet to hornblende.