Lithosphere of the Dharwar craton by joint inversion of P and S receiver functions

Abstract

The Archean Dharwar craton in south India is known for long time to be different from most other cratons. Specifically, at station Hyderabad (HYB) the Ps converted phases from the 410- and 660-km mantle discontinuities arrive up to 2 s later than in other cratons of comparable age, which implies lower upper mantle velocities. To resolve the unique lithosphere-asthenosphere system of the Dharwar craton, we inverted jointly P and S receiver functions and teleseismic P and S traveltime residuals at 10 seismograph stations. This method operates in the same depth range as long-period surface waves but differs by much higher lateral and radial resolution. We observe striking differences in crustal structures between the eastern and western Dharwar craton (EDC and WDC, respectively): crustal thickness is of around 31 km, with predominantly felsic velocities, in the EDC and of around 55 km, with predominantly mafic velocities, in the WDC. In the mantle we observe significant variations in the P velocity with depth, practically without accompanying variations in the S velocity. In the mantle S velocity there are azimuth-dependent indications of the Hales discontinuity at a depth of ~100 km. The most conspicuous feature of our models is the lack of the high velocity mantle keel with the S velocity of ~4.7 km s^-1, typical of other Archean cratons. The S velocity in our models is close to 4.5 km s^-1 from the Moho to a depth of ~250 km. There are indications of a similar upper mantle structure in the northeast of the Indian craton and of a partial recovery of the normal shield structure in the northwest. A division between the high S-velocity western Tibet and low S-velocity eastern Tibet may be related to a similar division between the northeastern and northwestern Indian craton.