Inversion of regional gravity anomalies and main features of the deep crustal geology of India

Abstract

Long-wavelength gravity field variations provide an important geophysical tool for delineating structural features of the deeper parts of the Earth's interior. Continuous developments in data-processing and inversion techniques have led to refinements in regional- as well as planetary-scale structural models. The present work uses the free-air gravity data of the Indian subcontinent to derive causative density contrast structures. The model obtained by assuming the point mass sources at a constant depth of 40 km (based on Deep Seismic Sounding Studies) reflects the known tectonic and geological provinces of the Indian subcontinent well. Interestingly, more than two-thirds of India exhibits “low”-density contrast values, with the lowest point occurring in the vicinity of the Sarda depression (which possibly hides a broken part of the Tethys trench). In general, the plateaus and uplifts are depicted as density contrast “highs”, while basins and depressions are associated with “lows”. An S-N traverse close to 78° E longitude confirms these findings. Further, the study confirms the postulated Burrard's hidden trough (Belgaum-Nellore) and additionally identifies 1. (1) a new hidden structural ridge running along the Ahmednagar-Hyderabad line, and 2. (2) a trough with an axis along the Mandya-Salem-Tanjavur line. All of these deformations exhibit connections with the seafloor spreading process, as they parallel the Carlsberg ridge in the Indian ocean in the south, and the Himalayan fold axis in the collision zone of the Indian and Eurasian plates.