Deep electrical imaging of the Narmada-Tapti region, central India from magnetotellurics

Next to Himalayas, the Narmada-Son Lineament (NSL) zone is characterized tectonically as a highly disturbed zone in Indian geology. Magnetotelluric (MT) study is carried out across NSL zone along a 190 km long N-S trending traverse. The present study region extends from Balapur (20°40′34″) in the South to Andharwadi (22°20′49″) in the North. The 2D modeling results for shallow crustal section has brought out a moderately resistive layer (50-200 Ω m) representing the exposed Deccan traps, overlying almost similar resistive layer (20-100 Ω m) inferred to be subtrappean sediments underlain by high resistive basement. The Deccan trap thickness varies from around a few tens of meters to a maximum of 1.5 km along the traverse. A subtrappean sedimentary basin like feature is delineated in the middle of the traverse with a thickness amounting to as much as 2 km. The resistive (>1000 Ω m) upper crust is relatively thin towards the southern and northern part of the traverse and tends to become thicker in the middle. A moderately conductive (50-500 Ω m) layer is traced from mid crust towards south and at lower crust-upper mantle towards north. It is characterized by enhanced heat flow, high density and high seismic velocity. This layer is interpreted as a mafic/intrusive layer presumably associated with magmatic underplating of the crust, perhaps due to reported asthenospheric upwelling due to tectonic activity.