Metamorphic evolution of the Chotanagpur Granite Gneiss Complex of the East Indian Shield: current status
Geological information on the Chotanagpur Granite Gneiss Complex (CGGC) has been reviewed with a view to: (a) identifying the different metamorphic episodes; (b) developing an event stratigraphy in the high-grade blocks; and (c) correlating the different metamorphic episodes with the globally extensive orogenic processes. Integrating the existing geological information, the geological evolution of the high-grade block of the CGGC has been divided into four stages associated with four distinct metamorphic events (MI−MIV). The earliest metamorphic event (MI) that is recorded in granulite enclaves in the regionally extensive felsic gneisses culminated in ultrahigh temperatures (>900 °C at c. 5–8 kbar) at around 1.87 Ga. In the second stage, voluminous felsic magmas were intruded – the MI granulites – and were metamorphosed to form migmatitic felsic gneisses (MII) within about 1.66–1.55 Ga. The third stage witnessed intrusions of a suite of anorthosite and porphyritic granitoids (c. 1.55–1.51 Ga), followed by high-grade metamorphism (700±50 °C, 6.5±1 kbar, MIII) during approximately 1.2–0.93 Ga. The fourth stage (MIV) is marked by the intrusion of a suite of mafic dykes, followed by infiltration-driven metamorphism (600–750 °C at 7±1) during 0.87–0.78 Ga. The proposed metamorphic events have been correlated with the supercontinental cycles in the Proterozoic time.
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Palaeoproterozoic of India
The Indian shield represents a vast repository of the Palaeoproterozoic geological record. Built over the four large amalgamated Archaean nuclei (Dharwar, Bastar, Singhbhum and Aravalli–Bundelkhand) the major and minor Palaeoproterozoic sedimentary basins and supracrustal sequences in India are comparable in scale, and perhaps also in development, to those of North America, Africa, Australia and Brazil. The deformation of these supracrustal sequences, attendant metamorphism and emplacement of plutonic bodies hold important clues to their connection with major orogenies. Research in these areas has led to investigations into global correlation, which in turn has had a direct bearing on refining models of Palaeoproterozoic supercontinent assembly and break-up. This book covers various aspects of regional geology as well as broader issues of the Indian Palaeoproterozoic geology and its global context. It is an outcome of the UNESCO-IGCP 509 Palaeoproterozoic Supercontinents and Global Evolution research project.