Deep electrical signatures across the Achankovil shear zone, Southern Granulite Terrain inferred from magnetotellurics

Two parallel magnetotelluric (MT) traverses across the Achankovil shear zone (AKSZ) in southern India using a wide band (1 kHz-1 ks) data acquisition system, reveal the regional geo-electric average strike direction of N 40 degrees W, consistent with the geological strike direction of the AKSZ. The derived model shows distinct high electrical resistivity (> 1000 Omega m) for the upper crust below the Madurai Granulite Block (MGB) with a gentle dip towards south and a northerly dip below the Kerala Khondalite Block (KKB). The lower crust is resistive below both MGB and KKB while it is moderately conductive (< 500 Omega m) below AKSZ. Our study shows that the AKSZ is a tectonic divide between the MGB to the north and KKB to the south. The results together with an integration of seismic, gravity and heat flow data suggest a high dense and moderately conductive mantle material brought up to the mid-lower crust, and a thermally eroded crust with a flower structure at depth, in conformity with the model of AKSZ as the trace of a collisional suture. (C) 2010 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.