Teleseismic delay-time tomography of the upper mantle beneath Southeastern India: imprint of Indo-Antarctica rifting

Abstract

A 3-D P-velocity map of the crust and upper mantle beneath the southeastern part of India has been reconstructed through the inversion of teleseismic traveltimes. Salient geological features in the study region include the Archean Dharwar Craton and Eastern Ghat metamorphic belt (EGMB), and the Proterozoic Cuddapah and Godavari basins. The Krishna-Godavari basin, on the eastern coastal margin, evolved in response to the Indo-Antarctica breakup. A 24-station temporary network provided 1161 traveltimes, which were used to model 3-D P-velocity variation. The velocity model accounts of 80 per cent of the observed data variance. The velocity picture to a depth of 120 km shows two patterns: a high velocity beneath the interior domain (Dharwar craton and Cuddapah basin), and a lower velocity beneath the eastern margin region (EGMB and coastal basin). Across the array velocity variations of 7-10 per cent in the crust (0-40 km) and 3-5 per cent in the uppermost mantle (40-120 km) are observed. At deeper levels (120-210 km) the upper-mantle velocity differences are insignificant among different geological units. The presence of such a low velocity along the eastern margin suggests significantly thin lithosphere (<100 km) beneath it compared to a thick lithosphere (>200 km) beneath the eastern Dharwar craton. Such lithospheric thinning could be a consequence of Indo-Antarctica break-up.