Detection of a collision zone in south Indian shield region from magnetotelluric studies

Magnetotelluric (NIT) investigations were carried out along a profile in the greenschist-granulite transition zone within the south Indian shield region (SISR). The profile runs over a length of 110 km from Kuppam in the north to Bommidi in the south. It covers the transition zone with 12 NIT stations using a wide-band (1 kHz-1 ks) data acquisition system. The Mertur shear zone (MTSZ) forms the NE extension of Moyar-Bhavani shear zone that traverses along the transition zone. The regional geoelectric strike direction of N40 degrees E identified from the present study is consistent with the strike direction of the MTSZ in the center of the profile. The 2-D conductivity model derived from the data display distinct high electrical resistivity character (10,000 Omega m) below the Archaean Dharwar craton and less resistive (< 3000 Omega m) under the southern granulite terrain located south of the MTSZ. The MTSZ separating the two regions is characterized by steep anomalous high conductive feature at lower crustal depths. The deep seismic sounding (DSS) study carried out along the profile shows dipping signatures on either side of the shear zone. The variation of deep electrical resistivity together with the dipping signature of reflectors indicate two distinct terrains, namely, the Archaean Dharwar Craton in the north and the Proterozoic granulite terrain towards south. They got accreted along the MTSZ, which could represent a possible collision boundary. (C) 2006 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.