Thinning of granitic-gneissic crust below uplifting hyderabad granitic region of the eastern Dharwar craton (south Indian shield): Evidence from AMT/CSAMT experiment

Hyderabad granitic region (HGR) forms one of the most unusual geotectonic segment of the south Indian shield. Analysis of multiparametric geological, geophysical and IGS-GPS studies have earlier suggested that this region is neotectonically uplifting at a rapid rate. We propose that consequent to such uplift, only a thin veneer of surface granitic layer now remains. In order to quantitatively examine the thickness of highly resistive granitic-gneissic crust below HGR, a audio-magnetotelluric (AMT) / controlled source AMT (CSAMT) experiment was conducted at three separate locations, situated about 50 km east of Hyderabad. The study reveals a maximum thickness of 5.5 to 6.0 km for the granitic — gneissic crust beneath HGR, which is underlain by thick low resistive exhumed intermediate (granulitic ?) crust. This finding is in sharp contrast to that of a thick granitic-gneissic crust (15–20 km) usually found in comparable late Archaean terrains elsewhere.