Geosystems and Geoenvironment (Nov 2022)
India-Antarctica collisional ridge structure below Nellore Schist and Eastern Ghats Belts as revealed by seismic studies
Abstract
In Columbia, Rodinia and Gondwana supercontinental assembly periods, eastern margin of India lay quite close to the east Antarctica. During these periods, this region underwent prolonged sedimentation, magmatism, oceanic subduction, multiple accretion and continent-continent collision which have left their imprints in the geological and geophysical observations. In the present study, we have analyzed crustal seismic velocity structure along the DSS profiles located in the eastern part of the Indian shield that cuts across the Proterozoic Cuddapah Basin, Godavari and Mahanadi Gondwana grabens. The study revealed presence of a prominent high velocity (6.2–6.5 km/s) hidden ridge structure, which is 30 to 50 km wide and located at a shallow subsurface depth beneath the Nellore Schist Belt and Eastern Ghats Belt. It underlies below Kaligiri-Duttaluru along the Kavali-Parnapalle profile, Darsi-Addanki along the Alampur-Koniki-Ganapeswaram profile and Sattupalli-Ashwaraopet in Kallur-Polavaram profile. This ridge structure is conspicuously characterized by high gravity anomaly gradients from -90 to -15 mGal. Gravity patterns over these regions further indicate that this ridge which appears to continue from the north of Chennai to Bhavanipatna region in Bastar Craton, may have been formed due to the collision of East Antarctic terrain with eastern Indian Shield after the cessation of supra-subduction at the end of Mesoproterozoic. Further, this ridge structure is flanked by Proterozoic sediments on either side; in Cuddapah Basin on its western side and East Coast Sedimentary Basin on its eastern side, which together with the possible occurrence of Proterozoic sediments in other basins, would indicate that the extent of Proterozoic sedimentation was much larger than hitherto known. We suggest that this region was rifting during Paleo-Mesoproterozoic period and possibly a shallow marine basin existed, when it was an integral part of the Columbia supercontinent assembly. It underwent another rifting phase and denudation during the Gondwana period as indicated by thin patches of Gondwana sediments which are lined up all along the east coast. Quite likely, the rifting between India and Antarctica during the Gondwana super assembly period initiated in the Permo-Triassic Gondwana period itself, with final separation taking place much later during early Cretaceous period.
