Pn tomography and anisotropic study of the Indian shield and the adjacent regions

High-resolution P-wave velocity and anisotropy structure of the uppermost mantle beneath the Indian shield and its surrounding regions are presented to unravel the tectonic imprints in the lithosphere. We inverted high quality 19,500 regional Pn phases from 172 seismological stations for 4780 earthquakes at a distance range of 2◦ to 15◦ with a mean apparent Pn velocity of 8.22 km/s. The results suggest that the Pn velocity anomalies with fast anisotropic directions are consistent with the collision environments in the Himalaya, Tibetan Plateau, Tarim Basin, and Burmese arc regions. The higher Pn anomalies along the Himalayan arc explicate the subducting cold Indian lithosphere. The cratonic upper mantle of the Indian shield is characterized by Pn velocity of 8.12–8.42 km/s, while the large part of the central Indian shield has higher mantle-lid velocity of ~8.42 km/s with dominant anisotropic value of 0.2–0.3 km/s (~7.5%) suggesting the presence of mafic ‘lava pillow’ related to the Deccan volcanism. The impressions of the rifts and the mobile belts are conspicuous in the velocity anomaly image indicating their deep seated origin. The Pn anisotropy in the Indian shield exhibits a complex pattern and deviates from the absolute plate motion directions derived from the SKS study, demon- strating the presence of frozen anisotropy in the Indian lithospheric uppermost mantle, due to the large scale tectonic deformation after its breakup from the Gondwanaland.

Anisotropy Pn results with magnitudes superimposed on the Pn velocity solution to illustrate the correspondence between anisotropy patterns and the major velocity anomalies for the grid of cell size 1 × 1 deg.

Citation: Bhaskar Illa, K.S. Reshma, Prakash Kumar *, D. Srinagesh, C. Haldar, Sanjay Kumar, Prantik Mandal, 2021. Tectonophysics 813 (2021) 228932, external link