We have delineated a pseudo 3-D configuration (Fig.1) of the West Bengal sedimentary basin from first arrival seismic traveltime tomography, which shows south-easterly dip of the basin. The model is assessed through chi-squares estimates, rms residual, traveltime fit, rays traced and resolution by checkerboard tests, and depicts smooth velocity variations of Recent, Quaternary and Tertiary sediments of velocity 1.8–4.3 km s−1 deposited over the Rajmahal trap of 4.8 km s−1 velocity and the basement (5.9 km s−1) down to a maximum depth of 16 km. The study identifies a regional feature, known as the Hinge zone, where stable Indian shield ends and a sharp increase in sediment thickness occurs. The Hinge zone may represent the relict of continental and proto-oceanic crustal boundary formed during the rifting of India from Antarctica. The regional gravity map of the Bengal basin clearly brings out the Hinge zone with a linear gravity high that is compatible with the seismic data. Presence of Hinge zone and Rajmahal volcanism in the basin suggests the influence of rifting of India from the combined Antarctica–Australia at∼130 Ma due to mantle plume activity on the structure and tectonics of the West Bengal basin.
Fig.1: Pseudo 3-D velocity structure of the West Bengal sedimentary basin. RT represents the subsurface Rajmahal traps.
For Further Details:
N. Damodara, V. Vijaya Rao, Kalachand Sain, A.S.S.S.R.S. Prasad and A.S.N. Murty, 2017, Geophys. J. Int. (2017) 208, 1490–1507. doi: 10.1093/gji/ggw461.