Indian Shield: Insight into the pristine size, shape and tectonic framework

摘要

Indian Shield which receives wide reference in literature occupied much wider area than the exposed Precambrian terrane of Peninsular India prior to its decimation during successive Phanerozoic events that started with the Jurassic break-up of Gondwanaland. Relying on the information from the Peninsular India, it is possible to trace out not only the history of destruction, but also the clue to divide this Precambrian crustal block into two major tectonic blocks: Precambrian continental core or Proto-India, and the accreted charnockitic terranes. Proto-India, belonging to two major domains: Aravalli-Bundelkhand and the Gondwana, can be further subdivided into six smaller units which are described as the fundamental nuclei or Protocontinents. These are: (1) Dharwar, (2) Bastar, (3) Singhbhum, (4) Rajmahal, (5) Bundelkhand and (6) Aravalli. The two accreted terranes which were added subsequently to the Proto-India include the Eastern Ghats Belt and the Southern Granulite Belts. The combined Precambrian crustal blocks of Proto-India and the accreted terranes constituted the Indian Shield. The Joins that separate or suture the Protocontinents as well as the 'accreted' terranes, are marked by different features, such as fault trace (as between the Aravalli and the Bundelkhand), thrust or ductile shear zone (as between Eastern Ghats Belt and the Dharwar, Bastar and Singhbhum to its west, and between Dharwar and Southern Granulite Belt), or Lineaments like Narmada-Son, Godavari or Mahanadi which follow coal-bearing Gondwana rift basins. It is suggested that the invariable occurrence of Gondwana rift basins along some Joins resulted at the time of Gondwana break-up when there was an abortive attempt to fragment the Indian Shield, resulting in the opening of intracratonic continental basins along pre-exiting weak zones marked by Joins.