Study on Paleomagnetism and Plate Tectonics of Indian Plate

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The aim of this survey is to clarify the paleogeographic position of the Indian subcontinent in the Gondwana super-continent, especially relative position to the Antarctica, and to trace its change of the position with time by the paleomagnetic studies of the eastern regions of the Indian Peninsula along the coast of the Bengal Bay.As a reconnaissance survey, the paleomagnetic and geophysical rock samples were obtained from various rock formations in the region of the Godavari and the Mahanadi Grabens in 1991. The preliminary paleomagnetic measurements of the samples show that most of the rocks of old ages such as Archean and Proterozoic have very complex multiple remanent components. So that, the paleomagnetic samplings were concentrated to the rocks of the trap basalt and the Gondwana sediments of the Paleozoic and Mesozoic in 1992 and 1993. Rock samples were collected from 35 sites in 1992 and from 24 sites in 1993 in the regions of Rajimahal hills, the Mahanadi Graben, the Godavari Graben and the Tamil-Nadu.Although the paleomagnetic and age dating studies are still on going, we got some preliminary results. 6 ages are determined by the Ar-Ar method. The ages obtained are 574 Ma for the Archean dike of Site 21, 520 Ma for the lower Proterozoic khondalite of Site 34, 510-520 Ma for the Proterozoic dolerite dike of Site 0, and 510 Ma for the Proterozoic gneissose granite of Site 1 in the Godavari graben, and 560 and 680 Ma for the Archean granitic gneiss of Site 38 and 59, in the Mahanadi Graben. And 6 reliable paleomagnetic remanent directions are obtained from the Archean granitic gneiss of Site 38, the Archean charnokite of Site 39, the Proterozoic dolerite dike of Site 0, and the Cretaceous Rajmahl trap basalt flows of Sites 80, 82 and 101.