Lithosphere of the Dharwar craton by joint inversion ofPandSreceiver functions

Abstract

S U M M A R YThe 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 azimuthdependent 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.

Long wavelength gravity anomalies over India: Crustal and lithospheric structures and its flexure

“…The other sources are located at average depths of 43-45, 19 and 10-11 km representing Moho, lower crust and upper crustal sources, respectively. It is interesting to observe that the spectral depth to Moho (43-45 km), and the lower crust (19 km) is almost same as that inferred from various seismic studies (Kiselev et al, 2008;Reddy, 2010;Gupta et al, 2003). These seismic studies suggested crustal thickness largely varying from 34 to 55 km in different parts of the Indian shield.…”

“…Seismic results indicate that crustal thickness varies considerably, from 32 km under the EDC up to 55 km under the Western Dharwar Craton (WDC, Fig. 1) (Kiselev et al, 2008;Gupta et al, 2003). Deep seismic soundings have also suggested crustal thickness varying from 34 km under the EDC to 45-50 km under the SGT, the WDC and along the Himalayan front (Reddy, 2010).…”

Mantle dynamics, isostasy, and the support of high terrain

“…Crustal thicknesses beneath stable cratons vary by more than 10-15 km, for instance beneath India [Gupta et al, 2003;Kiselev et al, 2008;Rai et al, 2005], Canada [e.g., Perry et al, 2002], and the Great Plains of the USA [Gilbert, 2012;Sheehan et al, 1995], as well as beneath Tibet [e.g., Tseng et al, 2009]. Again from (2), if uncompensated, such differences in crustal thickness would generate free-air and isostatic gravity anomalies approaching 200-300 mGal.…”

Complex shallow mantle beneath the Dharwar Craton inferred from Rayleigh wave inversion

“…They infer a ∼200-km-thick lithosphere beneath the Dharwar Craton and a mid-lithospheric low velocity region at a depth of ∼100 km. Kiselev et al (2008) jointly inverted both P and S receiver functions and teleseismic P and S traveltime residuals to resolve the lithosphere-asthenosphere boundary (LAB) of the Dharwar Craton at 10 seismograph stations. The most conspicuous feature of their study is the absence of a high velocity mantle keel (Vs ∼ 4.7 km s -1 ), typically observed in other Archean cratons.…”