Constraints on the Evolution of the Purana Basins of Peninsular India

The seven supracrustal, epicratonic Purana basins occupy more than a fifth of the area of Precambrian exposures in the Indian Shield. They are repositories of Proterozoic shallow marine sediments, resting unconformably on the eroded surfaces of the older rocks; and are preserved in an unmetamorphosed and marginally deformed state. These sequences have comparable characters though their mutual differences are quite significant, indicating that each one of the host basins had an independent evolutionary history.

The gross sedimentological contents, associated igneous rocks, structural and metamorphic features of the Purana basins and their geographical and temporal proximity with the Middle Proterozoic Mobile Belt are examined to evaluate the broad geotectonic framework within which they evolved. These "polyhistory, continental" basins are apparently analogous to the "Atlantic-type" passive continental margin systems associated with extensional tectonic regimes. The Bhima basin is an exceptional case of a "simple", transtensional, "pull-apart" type basin, while some of the others were probably initiated as "back-arc" basins.