Crustal structure of Peninsular Shield, India from DSS studies

Deep Seismic Sounding (DSS) investigations have been carried out in the Ind ian Peninsula, mainly using the refraction and wide-angle reflection techni ques. Since 1972, about 22 DSS profiles totalling more than 5000 km in leng th have been covered. Contours prepared for depth to Moho boundary, show la rge variations in the depth to the Moho surface emphasizing conspicuous lat eral variations of the structure. The Moho boundary is deep (44 km) in the north-western part of the country especially in the region of Aravalli Fold Belt, Similarly, except for the coastal regions, the crust is also thick i n the southern parts of the Peninsular Shield (37-45 km), The crust seems t o become thinner (24 km) towards the northern parts of the west coast. Comp ared to the west, the crust towards the east coast seems to be either norma l or thicker except for the prominent doming-up at the eastern flank of the West Bengal basin. However, it is relevant to state that absence of deep c rustal information of the southern parts of the east and west coasts restri cts the above statement to the region north of 15 degrees N latitude. The a verage crustal thickness in the Dharwar Craton is 35 km, whereas the crusta l thickness in the Proterozoic Cuddapah basin is about 40-43 km, with the m aximum at its eastern margin. The large thickness of the Tertiary sediments in the Cambay Basin and relatively thin crust in the region suggest furthe r rifting during the Tertiary. The region on the west coast is also charact erized by an upwarp in the Moho during the Late Cretaceous period, probably representing a transitional crust and a major source for the Deccan Trap f lows. Interpretation of the crustal structure in terms of geological and ge ochronogical setting and the inferred crustal composition, deep depressions in this prominent boundary associated with faults/fracture zones are prese nted along with the variations in the velocity structure; an input that can help in better understanding of the structure and tectonics.