Crustal velocity structure of western Dharwar Craton, South India

Abstract

A deep seismic sounding (DSS) experiment was carried out across the Indian shield in 1972–1975. Kaila et al. (Kaila, K.L., Roy Chowdhury, K., Reddy, P.R., Krishna, V.G., Hari Narain, Subbotin, S.I., Sollogub, V.B., Chekunov, A.V., Kharetchko, G.E., Lazarenko, M.A., Ilchenko T.V., 1979. Crustal structure along Kavali-Udipi profile in the Indian peninsular shield from deep seismic sounding. J. Geol. Soc. of Ind., 20, 307–333) presented a crustal depth section based on the interpretation of the analog seismic data. In this paper, we re-examine the crustal structure of the Western Dharwar Craton (WDC) by reprocessing the data of three major shot points. Kinematic 1-D inversion, followed by 2-D forward modeling of the first arrival refraction and a few persistent wide-angle reflection phases, was carried out to build, a first order two-dimensional velocity model of this segment of the profile. This model brings out a simple crustal velocity structure consisting of an upper and lower crust. The upper crust (velocity 6.0–6.2 km/s) is on average 23 km thick, which is underlain by a lower crust of velocity 6.8–7.0 km/s. The average Moho depth in this part is about 37–40 km, with higher-than-normal Pn velocity of 8.4 km/s. A relatively deep Moho in this part of the Archean peninsular shield is associated with relatively low velocities in the lower crust, perhaps indicating absence of underplating in this region. Present results bring out the fact that the crust of WDC is not so typical as many other Archean crusts, in terms of both thickness and velocities.