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

Abstract

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.