Published:January 01, 2015
The Older Metamorphic Group and the Older Metamorphic Tonalite Gneiss are classic examples of Palaeaoarchaean high-grade metamorphic rocks of the Singhbhum Craton of India. The Older Metamorphic Group is a supracrustal assemblage that was probably deposited as a greenstone belt-type succession before c. 3.32 Ga, the low-grade equivalents of which are found in parts of the Iron Ore Group. The Older Metamorphic Tonalite Gneiss represents a suite of granitoids that are tectonically interleaved with the supracrustal gneisses and that formed over an extended period of time, 3.53–3.45 Ga and possibly later, by processes of Archaean crustal growth.
Archaean to Palaeoproterozoic metasediments overlie the Archaean granitoid pluton of the Singhbhum Craton in east India. Relatively little is known about the Archaean metasediments, but they comprise several conglomerates in the state of Jharkhand. Their age is most probably Mesoarchaean, possibly earliest Neoarchaean. They occur at separate localities and their exposures commonly consist of scattered patches with a limited extent. Their interrelationships are consequently poorly known. Sedimentological analysis of their structure, architecture and clast composition suggests that most of them represent individual occurrences that partly have been largely eroded away. Other occurrences must have had a limited extent from the very beginning. The various conglomerates were deposited in different environments. Some represent braided or meandering fluvial environments, whereas others seem to have been deposited by mass flows with different degrees of viscosity, possibly mainly on alluvial fans.
Figures & Tables
Precambrian Basins of India: Stratigraphic and Tectonic Context
This Memoir provides a comprehensive review of the Precambrian basins of the four Archaean nuclei of India (Dharwar, Bastar, Singhbhum and Aravalli-Bundelkhand), encompassing descriptions of the time–space distribution of sedimentary–volcanic successions, the interrelationship between tectonics and sedimentation, and basin histories. Studies of 22 basins within the framework of an international basin classification scheme deepen an understanding of the basin architecture especially for cratonic basins. Most Indian sedimentary successions formed as cratonic to extensional-margin rift and thermal-sag basins, some reflecting mantle plume movement, subcrustal heating or far-field stress. This Memoir shows that Phanerozoic plate-tectonic and sequence stratigraphic principles can be applied to the Precambrian basins of large Archaean provinces. The differences between the stratigraphic architecture of the Indian Precambrian and examples of Phanerozoic basin-fill successions elsewhere are ascribed to variable rates and intensities of the controls on accommodation and sediment supply, and changes inherent in the evolution of the hydrosphere–atmosphere and biosphere systems.