Archaean granulite facies metamorphism at the Singhbhum Craton-Eastern Ghats Mobile Belt interface: implication for the Ur supercontinent assembly

Abstract

In this study, we investigate the geological significance and the antiquity of lower crustal granulite facies metamorphism from the Rengali Domain, which lies in between the Singhbhum Craton in the north and the Eastern Ghats Mobile Belt in the south. Petrographic, mineral compositional, metamorphic reaction history and geothermobarometric studies of two representative metapelite granulite samples reveal widespread biotite melting at peak granulite facies metamorphic conditions of 7.8 ± 0.13 kbar, 849 ± 31 °C and subsequent melt extraction, producing a mixture of residual granulites and melts in the Rengali Province. Depending on local bulk rock compositional variations, biotite melting produced peak metamorphic assemblages of garnet + cordierite in the more aluminous compositional domain, while garnet + orthopyroxene + cordierite resulted in domains of intermediate alumina. During post-peak cooling, there were localized developments of biotite + sillimanite + quartz symplectites replacing garnet and cordierite and biotite + quartz intergrowths after orthopyroxene. Application of garnet-orthopyroxene and garnet-biotite Fe–Mg exchange thermometers to co-existing garnet rim and symplectitic biotite show the extent of cooling to 610–660 °C. Electron microprobe geochronology of texturally well constrained monazites indicates the timing of peak granulite metamorphism at 3057 ± 17 Ma and its metamorphic reheating at 2781 ± 16 Ma. The present findings when collated with available geological and geophysical data appear to indicate that the studied granulites and the associated granite gneisses, charnockite and enderbite suite of rocks of the Rengali Domain are part of the exhumed lower continental crust of the Singhbhum Craton. The significance of this Neoarchaean orogenesis in the ‘Ur’ supercontinent assembly is discussed.