Wet mantle transition zone beneath the Indian shield: Constraints from P-to-S receiver functions analysis

Abstract

Indian plate passed over four plumes on its way toward the Eurasian plate. These interactions with plumes certainly affected the upper mantle and crust of the Indian plate as manifested by its thinned lithosphere and relatively low shear velocities both in the crust and upper mantle, but the depth extent of these effects of plume-lithosphere interaction remains ambiguous. In this study, we investigate the mantle transition zone beneath the Indian shield using P receiver functions computed at 23 stations covering the entirety of the Indian shield to investigate the depth extent of the imprints of the plume-lithosphere interaction as well as to study the lateral variations of transition zone beneath a stable intraplate setting like the Indian shield. Our results show good agreement with the results of previous studies as well as with the tomographic models in terms of the average apparent depths of the 410 and 660 discontinuities and the transition zone thickness. However, unlike previous studies, we find compelling evidence of a persistent mid-transition zone discontinuity beneath all the stations and a low-velocity layer beneath some regions. We also investigated the frequency dependence of amplitudes of receiver functions and found that most of the stations showed a strong dependence of amplitudes on frequency. Based on the evidence from our investigation, we demarcate the regions potentially containing relatively more weight percentage of water inside the otherwise considered as a ‘dry’ mantle transition zone. These regions should be further investigated in detail by a dense seismic network and a realistic 3-D velocity model.