Passive source seismic imaging of the crust and upper mantle underlying the Archean Singhbhum Craton, Eastern India

Abstract

An improved image of crust-mantle structure has been obtained through the joint inversion of P-to-s receiver functions and fundamental mode group velocity data (7–70 s) of Rayleigh and Love waves at fifteen broadband stations in the Eastern Indian Craton. Our modelling reveals a marked crustal thinning of 5–10 km below the Singhbhum-Odisha-Craton (SOC) while the modelled Moho depths show a flat crust with a thickness of 42 km below the Chotanagpur Granitic Gneissic Terrain (CGGT). The modelled lithosphere is thin (∼90 km) beneath the SOC and deepens on both north and south sides to ∼100 km with a sharp drop of ∼4.4% in shear velocity across the lithosphere-asthenosphere boundary. The amount of melt required in the asthenosphere to account for this drop in shear velocity is ∼1%. The isotopic constituents of the Dalma volcanic rocks contains asthenospheric component. We suggest that the modeled crustal and lithospheric thinning might have been resulted from the earlier magmatism or plume episodes that led to lithospheric delamination below the SOC. Our modeling also detects a common elongated feature (extending between latitude 21–23°N and longitude 85–86.4°E), which is characterized by a marked crustal (5–10 km) as well as lithospheric (10–15 km) thinning and a significant drop in Vs (−2.1 to −4.4%) in the upper mantle, below the SOC. This mapped area coincides with the horse-shoe shaped broad Singhbhum synclinorium known as Iron Ore Group (IOG) basin that hosts huge iron ore and to some extent manganese deposits of Precambrian age. This lithospheric feature is inferred to have played a key role in forming the passage for melts to carry various iron rich minerals and metals to the uppermost oceanic crust during the Archean plume associated with magmatism episode.