Archean granitoids at the contact of Eastern Ghat Granulite Belt and Singhbhum-Orissa craton, in Bhuban-Rengali sector, Orissa, India

The small granite plutons occurring at the contact of the Singhbhum-Orissa Iron Ore craton (IOC) to the north and the Eastern Ghat Granulite Belt (EGG B) to the south in eastern Indian shield are characterised by the presence of enclaves of the granulites of EGGB and the greenschist facies rocks of I OC. These granites also bear the imprints of later cataclastic deformation which is present at the contact of the IOC and the EGGB. In situ Pb-Pb zirc on dating of these granites gives minimum age of their formation similar to 2.80 Ga. A whole-rock three point Rb-Sr isochron age of this rock is found to be similar to 2.90 Ga. Therefore, the true age of formation of these gr anites will be around 2.90-2.80 Ga. These,granitic rocks also contain xenoc rystic zircon components of similar to 3.50 Ga and show a later metasomatic or metamorphic effect 2.48 Ga obtained from the analyses on overgrowths de veloped on 2.80 Ga old zircon cores. The presence of granulitic enclaves wi thin these contact zone granite indicates that the granulite facies metamor phism of the EGGB is similar to 2.80 Ca or still older in age. The cataclas tic deformations observed at the contact zone of the two adjacent cratons i s definitely younger than 2.80 Ga and possibly related to 2.48 Ga event obs erved from the overgrowths. As 2.80 Ga granite plutons of small dimensions are also observed at the western margin of the IOC; it can be concluded tha t a geologic event occurred similar to 2.80 Ga over the IOC when small gran ite bodies evolved at the marginal part of this craton after its stabilisat ion at similar to 3.09 Ga.