Three dimensional configuration of Moho discontinuity over some parts of India from gravity field data

Abstract

The Bouguer anomalies over the central Indian shield and the Aravalli regions have been subjected to spectral analyses. A plot of the logarithm of energy of the observed field against radial angular frequency exhibits several linear segments whose slopes and intercepts provide the ensemble average depths to various levels of the concentration of anomalous sources and their total masses respectively. These computed parameters are then used to design matched filters to deconvolve the gravity effects of sources at various depths. The gravity effect arising from the Moho is converted into a 3-D relief using (sinX/X).(sinY/Y) technique with standard density contrast of 0.4 gm/cc and mean depth from energy spectrum. The depths to the Moho discontinuity over the central Indian shield is 37 km and its relief exhibits depth variation from 32 to 42 km. These results are compared with the Deep Seismic Soundings along four profiles. A tectonic map of the central India has been prepared through the analyses of various processed maps, viz. Bouguer anomaly, low pass filtered, deconvolved effect and mass distribution to decipher the regional tectonic history. Similar analyses of the Bouguer anomaly over the Aravalli region have provided average depth to Moho as 35 km. On the basis of various processed maps, the existence of a locked zone between Bhilwara and Ajmer, controlling the geological settings, has been proposed. A conceptual geological model has been evolved by using several sets of filtered data coupled with analytic signal technique to compute depths and locations of the body corners. The derived model suggests underplating of the crust. Attempts have been made to map discontinuities in the astheno-sphere from the Bouguer anomaly under the International Lithosphere Program. Preliminary results along four profiles traversing the length and breadth of the Indian sub continent reveal the presence of a discontinuity at a depth of 250-350 km.