Wet Mantle Transition Zone beneath the Indian shield? Constraints from
P-to-S Receiver Functions Analysis
Abstract
Indian plate passed over four plumes during its way towards Eurasian
plate. These interactions with plumes certainly affected the upper
mantle and crust of Indian plate as manifested by its thinned
lithosphere and relatively low shear velocities both in 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 Indian shield using P-to-S receiver functions
computed at 24 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 a 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 most
of the stations showed 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 ‘dry’ mantle transition zone. These regions
should be further investigated in detail by a dense seismic network and
a realistic 3-D velocity model.