Regional Appraisal from Gravity Investigations in the Dharwar Craton: Jadcharla-Goa Transect

Regional gravity investigations were carried out in the northern part of Dharwar craton along a 600 km long Jadcharla-Raichur-Gadag-Hubli-Dharwar-Goa transect to obtain a clearer perception of the deep geological structure and to throw light on some of the debatable aspects such as the contact between the eastern and western Dharwar cratons From qualitative analysis of the horizontal and vertical gradients and analytical signal amplitude computed from the Bouguer gravity, the boundaries of the supracrustals were delineated

The polynomial fitting technique was used to obtain the regional (long wavelength component of Bouguer gravity) to infer deep-seated features The 5^th order polynomial fit of the anomaly curve was modeled wlth GM-SYS software to obtain the crustal structure along the transect From the crustal upwelling/downwarps as indicated by modeling and the first horizontal gradient of regional Bouguer gravity the locations of four deep seated faults were determined Running west to east, the first of these, the west coast fault,is located near Ponda at station 34 The second, third and fourth faults, situated at stations 198, 307 and 530, correspond to the Bababudan-Nallur shear, the western margin of the Closepet batholith and the Makthal schist belt, respectively The structural configuration so obtained, contrary to established hypotheses of the geological classification of the craton into the eastern and western blocks, prompted to a modified tectonic classification of the craton into the western, an upthrust intervening, and eastern Dharwar blocks, whlch provided a new insight in to the structural configuration of the area While the average crustal thickness obtained for the western and eastern Dharwar blocks are 39 Km and 37 km respectively, the crustal thickness beneath the Chitradurga thrust fault, which lies in the middle of the intervening block IS 34 5 km.