Sub-continental lithospheric mantle discontinuity beneath northeast India

One of the prominent discontinuities in the Indian sub-continental lithospheric mantle (SCLM) is the Hales discontinuity (H-D). It has been seismologically modeled at depth of 100-110 km with 4-8% shear-wave velocity increase beneath the Eastern Dharwar Craton (EDC) and the Southern Granulite Terrain (SGT). The genesis of the H-D, beneath EDC and SGT, has been petrologically shown to be an interface between paleo-subducted slab eclogite, derived from oceanic crustal gabbro, and lithospheric mantle peridotite. Northeast (NE) India comprises Precambrian cratonic blocks of the Shillong Plateau-Mikir Hills (SP-MH), with similar crustal structure as the EDC. We use P-wave receiver function (P-RF) analysis to image the SCLM discontinuities beneath NE India and seek a unified genesis for the H-D. P-RFs have been computed for teleseismic data from 15 broadband stations in NE India at Gaussian width 2.5 ( f max ~0.46 Hz), using the iterative time domain deconvolution technique. These stations are sited on SP-MH and the Eastern Himalayan foreland basin (the Brahmaputra Valley - BV). The H-D P-to-S converted phase (P h s) is observed at all 15 stations between 10 and 11 s. Using published crustal models for these stations, we calculate arrival times of the crustal phases and show that all phases before 10 s are either crustal conversions or reverberations, therefore distinct from the P h s phase. We perform joint inversion of P-RFs with Rayleigh wave group velocity dispersion data for central SP station (SHLG) and BV station (TEZ). Our results show that the H-D is at depths of 98±5 km and 100±5 km beneath SHLG and TEZ, respectively. The H-D Vs increase beneath both stations is ~10%. P-RF data from all other stations will be analysed in the same manner and we will present a 3-D map of the H-D beneath NE India.