Unusual lithospheric structure beneath the Hyderabad granitic region, eastern Dharwar craton, south India

Using multiparametric geological and geophysical data, the evolutionary history of the lithosphere beneath the Late Archean—early Proterozoic Hyderabad granitic region (HGR) of the eastern Dharwar craton of south Indian shield has been attempted. Our study reveals that the entire granitic region and the surroundings (∼200 km×200 km) is being neotectonically uplifted possibly due to a major intrusive body situated at sub-crustal depth, leading to changes in river courses and also erosion of several kilometers (∼10 km) from its upper crustal column. Beneath this region, the Moho is elevated (32–33 km), the reduced heat flow is of the order of 28 mW/m2 and the asthenosphere is located at shallow depths of about 124 km, i.e. far less than 200–400 km depth found in Precambrian shield areas of the globe. The cratonic mantle lithosphere beneath HGR contains a highly conductive (15 Ωm) hydrous and seismically anisotropic metasomatic zone between depth of 90 and 100 km, where the estimated temperatures could be in the range of 900–1000 °C. The surface granitic layer, containing unusually high radioactivity (5.25 μW/m3), appears very thin probably a kilometer or so, beneath which the entire crustal column seems to be differentiated and made up of low radioactive granulite facies (?) rocks of acid to intermediate composition. Persistent episodic thermal reactivations during the last 2.6 gega years and continuous uplifting seems to have played a major role towards making its crustal column unusual.