Upper crust of the Archean Dharwar craton in southern India as revealed by seismic refraction tomography and its geotectonic implications

Abstract

Imaging shallow crustal structure is essential to extend the geological information from surface mapping to a depth and to develop tectonic models. We applied seismic tomography modelling to refraction data acquired along a 200-km-long line in the Dharwar craton of the Indian shield, and we derived a crustal velocity model that was evaluated with checkerboard tests to demonstrate the reliability of the model. We also tested the model for artefacts. Upper-crustal velocities vary between 5.7 and 6.4 km s–1 and are determined to 10 km depth, probably due to very low-velocity gradients in the upper crust. Undulating high and low velocities in the top layers of the crust are terminated at a depth of 7–8 km, consistent with a probable detachment. We interpret the undulating upper-crustal velocity layers to represent a fold-thrust belt structure that developed during a collision in a transpressional tectonic regime, consistent with the model of Chadwick et al., which suggests oblique convergence and accretion of two crustal blocks in the region. The velocity structure also correlates reasonably well with the distinct geological units. We interpret relatively low velocities between the undulating layers as representative of faults that bound various tectonic domains.