Redefining Dharwar Craton-Southern granulite terrain boundary in south India from new seismological constraints

Abstract

The southern part of the Dharwar craton is an Archean granulite terrain that continues further south and joins with the Proterozoic Southern Granulite Terrain (SGT). The linkage and the boundary between the Dharwar craton and the SGT has been a subject of debate over the last 75 years. Based on adequate coverage of broadband seismological stations(80) over south India, we generated3-D shear velocity image of the crust through joint inversion of the P- receiver function and Rayleigh wave group velocity dispersions derived from the cross correlation of ambient noise time series analysis. The most significant finding is an unusually thick (15–28 km) high-velocity layer (HVL) with Vs > 4.0 km/sin the lowermost crust beneath the south Dharwar craton that continues southward in a most coherent fashion well beyond the southern limb of Palghat- Cauvery shear zone (PCSZ) widely considered to be the contact zone of the Dharwar and SGT. Elsewhere in south India the high-velocity layer is about 4–8 km thick similar to the global average. We interpret this HVL as a mafic magmatic underplate of Archean ancestry formed during granulite metamorphism. The study suggests that the Dharwar craton continues further south of the mapped orthopyroxene boundary to the Palghat shear zone in a continuous manner.