Description
This book explores the geotectonic evolution of the lithosphere beneath the Indian Shield, which comprises a collage of cratons variously bounded by mobile belts and palaeo-rifts. The lithosphere beneath these is fairly thin compared to other cratons worldwide, petrologically varied and shows considerable variation in thickness with depth both intra-craton and among cratons. Moreover, it has been subjected to the influence of repeated magmatic episodes from Proterozoic to Palaeocene, which have variously impacted different parts of the shield. The thermotectonic influence on constituent cratons is variable depending on the evolutionary history. This book discusses the impact of successive tectonomagmatic events on the evolution of the deep crust and shallow mantle, and their Phanerozoic modification as gleaned through the xenolith window. The book provides a petrotectonic perspective on the deep crust and shallow mantle from direct samples brought up as xenoliths of deep lithologies, and offers a comprehensive overview for students, researchers, academics and professionals, integrating the results of petrological studies of deep lithologies and geophysical investigations to (i) shed light on the physico-chemical and thermal structure of the lithosphere from an array of geotectonic settings and (ii) gain insights into the spatio-temporal evolution of the Indian Shield. An in-depth guide critical thinking on the complex issue of mantle differentiation, magmatism, lithosphere modification and crustal growth over time, the book allows readers to gain a better understanding of the processes that affect the lithosphere and shape the crust on which we live. Prof. Dr. Ashoka Dessai has over 39 years of teaching and research experience at post-graduate level, initially at S. P. Pune University, and later at Goa University. He has conducted research in India and abroad, published over 50 research papers in peer-reviewed national and international journals and has been a reviewer for international journals published by Springer and other publishers. Prof. Dr. Dessai has authored two books: (i) Geology and Mineral Resources of Goa, New Delhi Publishers, and (ii) Goa: Geology, Industry and Environment (in press), Publisher: Directorate of Art and Culture, Govt. of Goa. He has also delivered lectures at several universities and professional organisations and research institutes in India and abroad. He has worked in wide variety of terrains, such as ophiolites of Ladakh Himalaya, Precambrian layered complexes and komatiitic ultramafites of South India, Deccan Traps of western India, including Precambrian iron and manganese ores, chromites, and laterites and bauxites. He has participated in an Indian Ocean expedition for prospecting of polymetallic nodules. Prof. Dr. Dessai has served as the Dean of the Faculty of Pure Sciences and Registrar of Goa University. Chapter 1: Continental lithosphere Introduction Studies in India Methods and Techniques Seismic Surveys Electromagnetic and Magnetotelluric Techniques Xenolith Studies Relevance of Xenolith Studies Limitations of Xenolith Studies Thermal Structure of the Crust Thermobarometry Limitations Heat Flow Studies Heat Generation Mechanism of Heat Transfer Heat Flow Measurements Constraints Reduced Heat Flow Magnetic Studies Curie Point Isotherm Gravity Methods Primary Geochemical Differentiation Bimodality of the Crust Continental Crust Seismic Structure Types of Continental Crust Shield Craton Platform Oceanic Crust The Deep Crust Inferences from Receiver Function Studies Earth’s Mantle Mantle Composition Lithospheric Mantle: Seismic Structure Petrologic Lithosphere Thermal Lithosphere Chapter 2: Indian Shield Introduction Geotectonic Framework Geology of Peninsular Block Aravalli Craton Bundelkhand Craton Singhbhum Craton Bastar Craton Dharwar Craton Western Dharwar Craton Eastern Dharwar Craton Granulite Terrain Chotanagpur Gneiss-Granulite Terrain Eastern Ghat Mobile Belt Southern Granulite Terrain Granulite Types in South India Igneous vs Metasomatic Origin Nilgiri Domain Madurai Domain Offshore Region: Western Margin Eastern Margin Offshore Geophysical Studies in South India Crustal Structure from Magsat and Gravity Data Seismic Structure of WDC Structure of the Crust beneath EDC Crust beneath Southern Granulite Terrain Comparative Assessment of Indian Shield with Other Shields Xenolith Host Rocks CITZ Dyke Swarm Western Continental Margin Dyke Swarm Duration of Deccan Magmatism Chapter 3: Petrology Introduction Xenolith Occurrences in India Radiometric Ages of Host Rocks Petrology of Xenoliths Xenoliths from Deccan Traps (WDC) Mantle Xenolith: Lherzolites Crustal Xenoliths: Granulites Mineral Chemistry Xenoliths from Kutch (Aravalli Craton) Xenoliths in Kimberlites Xenoliths from Bundelkhand Craton Lherzolite Xenoliths from EDC Eclogite Xenoliths from EDC Xenolith from Bastar Craton Dyke Boudins from Pericratonic Terrain Chapter 4: Lithosphere structure Introduction Crustal Structure: Gravity and Seismic Studies Bundelkhand Region North of CITZ Northern Region of WDC Central Region of WDC Structure from S wave velocity Function Eastern Region beneath EDC Pericratonic Domain: Southern Granulite Terrain Offshore Crust of Arabian Sea Laxmi Ridge Section Chagos-Maldive Ridge Section Offshore Crust of Bay of Bengal Nature of Sub-continental Moho Characteristics of Shallow Mantle Nature of Crust-Mantle Boundary Seismic Interpretation Chapter 5: Geothermal structure Introduction Thermal Structure of the Shield Bundelkhand and WDC: Thermal structure Thermal Regime of the EDC and Bastar Cratons Southern Granulite Terrain: Thermal Characteristics Xenolith vis-a-vis Heat Flow Geotherms Comparison with Cratons Globally Inferences from Geotherms in Other Cratons Estimates of Thermal Boundary Layer Thermal Evolution of South Indian Cratons Thermal Peculiarities of the WDC Thermal Characteristice of EDC Temporal Variation in Thermal Structure Surface Heat Flow of the South Indian Shield Heat Flow Variation among South Indian Cratons Global Heat Flow Observations Heat Flow along Craton Margins Influence of Composition on Heat Generation Thermal Equilibration over Time Contribution to Heat Flow: Xenolith Guestimates Inferences from Other Parts of the World Thermal Perturbation: An Effect of Crustal Thickening Causes of Excess Heat and Estimation of Crustal Accretion Overall Heat Production of the Crust Chapter 6: Integration of insights Introduction Crustal Structure Parameters Western Dharwar Craton: A Synthesis Eastern Dharwar Craton Pericratonic Belt and Offshore Crust Nature of Sub-continental Moho Thermal Perspective: Indian Shield Western Dharwar and Bundelkhand Cratons Eastern Dharwar Craton and Pericratonic Region Tectonomagmatic Accretions Western Dharwar Craton Composition of the Lower Crust: Xenolith Assessment Inferences from Geophysical Estimates Lower Crust of Eastern Dharwar Craton Lower Crust of Pericratonic Terrain Origin of the Lower Crustal Granulites Exhumation of SGT Evolution of Lower Crust Formation of Felsic Crust: Recycling Mechanism Nature and Composition of the Lithospheric Mantle Archaean vs Proterozoic Mantle SCLM beneath Western India SCLM beneath EDC Metasomatic Modification of the Lithospheric Mantle Thickness of SCLM and its Evolution Contribution of Continental Margin to Lithospheric Growth Offshore Evidences of de-roofing of Continental Lithosphere Crustal Growth Processes: A Synoptic Overview Nature of Pristine Crust Secular Changes in Crustal Composition Generation of Primitive Crust Greenstone Belts Komatiites Layered Complexes Dyke Swarms Anorthosite Complexes Concluding Remarks Selected bibliography
