3-D STRUCTURE AND GEODYNAMIC EVOLUTION OF ACCRETED IGNEOUS LAYER IN THE NARMADA-TAPTI REGION (INDIA)

The Narmada-Tapti rift system is an unusual feature crossing the west coast of India. A recent 2-D analysis of Bouguer gravity anomaly combi ned with four deep seismic sounding profiles in the region has reveale d a 15-20 km thick high-density (3.02 g cm(-3)) accreted igneous layer at the base of the crust. For a more realistic approximation a 3-D de nsity model of the proposed underplated layer is obtained. The thickne ss of the lower crustal accreted igneous layer varies from 8 km beneat h the eastern part to about 16 km beneath the central part and about 2 4 km beneath Navsari in the westernmost part of the region. The greate r thickness of the magmatic body beneath the Navsari gravity high pres ents itself as one of the potential feeder channels for the Deccan flo od basalts. The study further deciphers a normal Moho located at a dep th of about 38 km in the southwestern part of the region. The geotherm al signatures show an upwarped asthenosphere indicating the existence of partial melting conditions at very shallow depths. It is suggested that the massive eruption of the Deccan flood basalt on the west coast of India has modified the deep crustal structure of the Narmada-Tapti region in agreement with rheological boundary conditions. (C) 1997 El sevier Science Ltd.