The Singhbhum Craton from the Indian Shield is the only major archive of Palaeo–Mesoarchean geological processes. The Palaeoarchean granitoids from the Keonjhar area of Singhbhum Craton are potassic granites and granodiorites of calc-alkaline affinity. Their age and elemental concentrations resemble the low Al2O3 granites reported from the Eastern Pilbara Craton of Australia. The geochemical systematics of these granitoids suggests their derivation due to crus- tal reworking involving partial melting of a tonalitic source, possibly older metamorphic tonalitic gneiss (OMTG). The OMTG could have been derived due to the melting of an enriched basaltic source at the base of an oceanic plateau. In the second stage, the resul- tant underplating at crustal levels caused the reworking that led to intracrustal melting and differentiation of OMTG to form potassic granites, similar to that of Keonjhar pluton. Consolidating the evidences from the available geochemical and isotopic studies with our own data and correlating them with the geophysi- cal evidences, we interpret that the Keonjhar granito- ids are the product of intracrustal melting in an oceanic plateau setting.
Figure: Location and examples of Keonjhar granites
Ajay Dev Asokan, Kumar Krishna, R. Elangovan and M. Ram Mohan; Current Science, Vol. 118, No. 6 (2020). https:// doi: 10.18520/cs/v118/i6/910-919