Late Neoarchean crust generation and final cratonisation of the Bastar Craton: Insights from granitoids petrology, zircon U-Pb and Lu-Hf systematics

The end of Neoarchean (⁓2.5 Ga) is characterized by the emplacement of diverse granitoid groups, final cratonisation of different Archean blocks, and the onset of mobile lid tectonics/modern style plate tectonics associated with the cooling of the mantle. The southeastern margin of the Bastar Craton, Central India, contains well-developed exposures of granitoids of this period. We for the first time report field, petrographic, whole-rock geochemical, zircon U-Pb and Hf isotope studies on these poorly documented granitoids. These ⁓2.47–2.48 Ga granitoids are deformed, silicic, potassic, ferroan, LILE, and HFSE enriched, showing characteristics similar to A-type granites. They show a low Sr/Y ratio (<25), moderate to high Y and Yb contents, distinct negative Eu and Sr anomalies, and moderately fractionated to nearly flat HREE patterns. These granitoids yielded distinct sub-chondritic initial εHf signatures (εHf_t: –3.8 to –14.1). All these features indicate the formation of these granitoids due to the high-temperature reworking of older felsic crust at a shallow depth, leaving behind a plagioclase-bearing residue without significant garnet. By synthesizing craton-wide information on rock association, we suggest the operation of subduction and accretion of various arc-related terrains at ~2.5 Ga within the Bastar Craton. We further propose that the ~2.48 Ga high LILE-HFSE, ferroan potassic granitoids are formed in an extensional geodynamic setting associated with post-orogenic uplift. This marks the termination of the compressive forces of the subduction, leading to the final cratonisation.