Tectonic framework of geomorphic evolution of the Deccan Volcanic Province, India

Abstract

The geomorphology of the Deccan Volcanic Province (DVP) has its foundation in the eruption of flood basalts that covered nearly half of the Indian Peninsula during the Cretaceous – Paleogene transition and the asymmetric eastward tilt of the Peninsula. The northward trajectory of the Indian plate through the tropics leading to its collision with the Asian plate and the emergence of the Himalayan ranges are known to have resulted in significant climate changes through the Cenozoic. The DVP terrain preserves an imperfect, patchy record of these events and their impact on Cenozoic landscape evolution within an emergent continental block.The subhorizontal disposition of the stacks of lava flows in the DVP was interpreted to manifest the post-eruptive tectonic stability of this terrain. Earlier interpretations of the geomorphic characters of this terrain, with its step-like slope-profiles were consequently attributed to dominant climatic control. We review the regional topographic framework with additional inputs from the structural framework of the Deccan flood basalts, characters of the major rivers draining the province largely based on their high scale longitudinal profiles and Quaternary hinterland sedimentary basins within the DVP. It is evident that the erstwhile interpretation of the DVP as a singular morphotectonic unit where the antecedent drainage responded to Cenozoic tropical climate change with subsidiary tectonic controls requires re-examination.The component blocks of the DVP have differing morphotectonic characters because of the subtle diversity in their relative uplift / sag trajectories and structural characters. The influence of the monsoon climate (with alternating stronger and weaker phases) on landscape evolution in the subprovinces of the DVP is likely to be less significant than was earlier believed. The Deccan landscape reflects the Cenozoic reactivation of ancient tectonic zones that bound the constituent blocks of the province. Its landscape is carved by an antecedent tropical drainage, that was modified by Paleogene and Neogene intracontinental block movements driven by far-field stresses derived from the ridge-push of the Indian Ocean in the south and slab-pull of the subducting Indian Plate in the north. The Deccan landscape provides an example of how lithological and climatic controls on drainage evolution are overprinted by weak midcontinental tectonics.