Gravity field over Singhbhum, its relationship to geology and tectonic history

The gravity field over Singhbhum and adjoining areas lying between latitude 21° to 23°15′N and longitude 84° to 87°30′E has been analysed. The region has a very complex Precambrian history dating as far back as 3200 m.y. and extending up to 850 m.y., during which time it experienced a number of orogenic cycles. The activity has left an imprint on the gravity field which is marked by prominent gravity highs and lows. The highs are invariably surrounding the Singhbhum granite batholith, whereas the lows are conspicuous over the granites and their margins. The regional gravity field has been removed using a 4th order polynomial surface. The residual anomalies over prominent highs and lows have been interpreted using two-dimensional and three-dimensional models for underlying rock formations. It is inferred that the gravity highs are generally related to synclinal structures filled with sedimentary or metasedimentary formations and volcanics, such as the Iron Ore Group, the Singhbhum group, Dhanjori and Simlipal basins. The gravity lows can be attributed to a considerable thickness of granites of varying density, which could have been formed during different metamorphic/orogenic cycles by melting of a preexisting sialic crust.