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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS013 Oral Presentation 2228
Lithospheric structure and its relationship to diamond fertility of Dharwar
and Bastar cratons of the indian shield - a gravity perspective
Dr. Bijendra Singh
National Geophysical Research Institute, Hyderabad Scientist IASPEI
V. M. Tiwari, S. K. Verma
One of the unique features of the Indian shield is that it consists of number of Cratonic blocks bounded
by mobile belts. The lithospheric structures across these terrains are not well resolved due to scanty of
data. We have carried out gravity modeling along two long profiles cutting across the Indian shield to
understand the lithospheric configuration below the Dharwar and Bastar Cratons. Modeling is
constrained by the available geophysical results from deep seismic sounding, receiver function analysis,
seismic tomography and magnetotelluric methods. After accounting for the anomalies due to known
geological structures in the crust, long wavelength gravity response is interpreted in terms of variation
in the thickness of the lithosphere.Modeling results suggest that the lithosphere below the western
Dharwar Craton has got a maximum thickness of about 220-230 Km that reduces towards Eastern
Dharwar Craton to about 150 Km. Under the Godavari rift, it further reduces to about 100-120 Km.
North of Godavari in the Bastar Craton: the thickness again increases northward to about 200 Km.
Interestingly, the study of 1.1 Ga mantle xenoliths from kimberlite of Dharwar Craton also provide
similar depths. The lithospheric model thus obtained has significant implications on the geodynamic
evolution of Dharwar and Bastar Cratons and Diamond fertility of Kimberlite fields north and south
ofGodavari rift.It is suggested that the Godavari rift represents the zone of suturing between Dharwar
and Bastar Cratons during Archean period. The continent-continent collision of Dharwar and Bastar
Cratons along Godavari suture zone (GSZ) gave rise to number of parallel fracture zones both north and
south of the suture.The diamond fertility in Dharwar and Bastar Cratons are also governed by the GSZ
below which the two Cratonic blocks show minimum thickness that is not conducive for diamond
generation and stability. This is well reflected in the diamond barren kimberlite clusters belonging to
Tokapal kimberlite field lying in the north and Narayanpet kimberlite field (NKF) lying to the south of
GSZ. Kimberlite clusters further away from GZS are likely to be diamond fertile as they sample a thicker
lithosphere providing necessary conditions for diamond generation and stability. Geochemical studies of
mantle xenolith also reveal that these are derived from a 220-240 km thick lithosphere from less than
160 km lithosphere for the NKF. It is inferred that the Dharwar Craton in Peninsular India has not been
subjected to any major destabilization during the past one billion years.
Keywords: kimberlite, cratons, gravitymodeling