Crust and Upper Mantle Structure across Dharwar Craton along a broadband seismological profile

We used multiple seismological approaches to investigate the deep structure along a profile from the west to the east coast of south India. This profile covers passive continental margin and the Western Ghat escarpment created during India Madagascar separation, Archean western and eastern Dharwar Craton, and Proterozoic basin. Earthquake waveforms recorded over 38 stations with an average spacing of 15-20 km, have been analysed using joint inversion of receiver function and surface wave, core refracted SK(K)S phases for anisotropy and mantle layering. We found that the Moho depth along the profile varies smoothly between 34 and 41 km, except beneath the Western Ghat and at the contact of east and west Dharwar Craton, where it is offset by up to 8 km. Additionally observe a thick high velocity layer (HVL, Vs > 4 km/s) beneath the west to east coast of India. The crustal images suggest (i) the deep crustal structure control on the location of Western Ghat escarpment, rather than the surface process, (ii) the Moho offset is possible and preserved in deep time possibly since Precambrian following stabilisation of the craton, and (iii) Unusually thick HVL beneath the west coast of India and the adjoining region may represent the underplated material formed by the rifting process of India-Madagascar separation, also supported by the presence of seaward dipping reflectors and 85-90 Ma mafic dyke in the western Dharwar and the adjoining island. Additionally, shear wave splitting measurements show the evidence of lateral variation of anisotropy. In the western part of the craton anisotropy is `frozen-in' within the lithosphere possibly linked to cratonization. In contrast, in the eastern part of the craton anisotropy seems to be related the plate motion and the continental rifting. Further, in the deep mantle we map sharp 410 and broad and complex 660 km discontinuities. This suggests that 660 is greatly influenced by the presence of non-olivine components such as garnet.