Deccan Magma Accretion at the Base of the Crust Beneath the Narmada-Tapti Region: A Geophysical Analysis

81-87The Narmada-Tapti region is an unusual feature crossing the west coast of India. The region is covered by a thick pile of Deccan lava and is characterized by several hidden tectonic structures and complex geophysical signatures. Though deep seismic sounding (DSS) studies have provided some vital information about its crustal configuration, the extremely complex structure and evolution is still a subject of debate. Unified seismic/density modelling has revealed a 10-20 km thick high density (3.02 g/cm3) accreted igneous layer at the base of the crust. Thickness of this layer decreases gradually towards east. It varies from 8 km beneath the eastern part to about 16 km beneath the central part and about 24 km beneath Navsari in the western most part of the region. The greater thickness of the magmatic body beneath the Navsari gravity high presents itself as one of the potential feeder channels for the Deccan flood basalts. Contrary to seismic observations, the unified investigation further deciphers a normal Moho located at a depth of about 38 km in the southwestern part of the region. The geothermal signatures show an upward asthenosphere indicating the existence of partial melting conditions at very shallow depths. The inferred high density accreted igneous layer at the base of the crust, in the realm of geodynamic/rheological boundary conditions, is interpreted as the imprint of the Deccan magmatism