Diversity in the peninsular Indian lithosphere revealed from ambient noise and earthquake tomography

Abstract

Significant diversity in the Indian lithosphere is seen in 3-D shear wave velocity images inverted from the dispersion of group velocities measured from ambient noise and earthquake waveforms along 21,600 paths. Velocity models constructed at 1° intervals to a depth of 200 km suggest a bipolar nature of the Indian lithosphere. We observe a two layer lithospheric mantle beneath the eastern Peninsular India, comprising the Archean cratons of eastern Dharwar, Bastar, Singhbhum, Chotanagpur, Bundelkhand and the Proterozoic Vindyhan basin. The intra-lithospheric mantle boundary is at a depth of ~90 km where Vs increases from 4.5 km/s to >4.7 km/s. The velocity increase continues to a depth of 140 to 180 km followed by its reversal with a minimum Vs of 4.3–4.4 km/s, possibly representing the lithosphere-asthenosphere boundary. Geologically, these regions correlate with the diamond bearing kimberlite fields. In contrast, the Precambrian terrains of western Dharwar, eastern Deccan Volcanic Province (DVP), southern Granulite terrane and the Marwar block in western India are characterized by an almost uniform lithosphere mantle with Vs of 4.4–4.55 km/s. Presence of lower than expected velocity in the lithosphere could be due to its fertile composition, such as clinopyroxene-rich cumulate or metasomatised peridotite. The imprint of Deccan volcanism is observed as the thinned lithosphere (100–120 km) restricted primarily to the westernmost part of DVP, defining the regional extent of Reunion plume-Indian lithosphere interaction. The seismic velocity image suggests evidence for segmentation of Indian lithosphere beneath the Ganga basin at 75° E and 84° E coinciding the Delhi-Haridwar and the Monghyr-Saharsa ridges. Subduction of such a heterogeneous lithosphere could have contributed to the varying style of deformation and subduction pattern in the Himalayan-Tibet region.