Tectonic Evolution of the Paleoarchean to Mesoarchean Badampahar-Gorumahisani Belt, Singhbhum Craton, India – Implications for Coexisting Arc and Plume Signatures in a Granite-Greenstone Terrain

An association of tonalite-trondhjemite-granodiorite (TTG), other granitoids and greenstones constitute the Paleoarchean-Mesoarchean Singhbhum craton in India. The deformed and metamorphosed greenstone succession of Badampahar-Gorumahisani belt (BGB) in eastern Singhbhum consists of mafic-ultramafic volcanics, intercalated chemical sediments in the lower part and clastic sediments in the upper part. Geology, structure and geochemistry of BGB mafic volcanics, contemporaneous TTG and slightly younger intrusive granite have been integrated to constrain the tectonic setting of Paleoarchean felsic crust generation and coupled deformation of granite-greenstone. Subalkaline, low-K BGB metabasalts show distinct tholeiitic trend of differentiation from komatiitic basalt parent magma. BGB metabasalts with LILE enrichment, negative Nb anomaly, and Ti/V ratio in the range 10-20, are comparable to island arc tholeiites, though the associated komatiites and high-Mg basalts suggest plume related origin. Limited crustal contamination of a komatiitic basalt magma cannot be ruled out altogether. Singhbhum granite batholith with older tonalite-trondhjemite and younger granite-granodiorite plutons were derived from low- to high-K mafic source, together with some TTG reworking for younger granites. With low HREE, higher primordial mantle normalized La/Yb ratio, insignificant Eu anomaly, and coupled depletion of Y and enrichment of Sr, older strongly deformed plutons compare well with the Archean TTG suite. The younger intrusive granites show weak positive Eu anomaly (Eu/Eu* similar to 1.3-1.7) and strongly positive Y anomaly. Geochemical discrimination (e.g. Rb vs Y + Nb) suggests comparison with volcanic arc granites, which is also supported by enrichment of LILE (K, Rb and Ba) and LREE, and relative depletion of HREE and HFSE. However, structural geometry of BGB and adjoining granitoid plutons, association with komatiite, absence of typical signatures of derivation from subduction wedge, and heterogeneity of source for the BGB mafic volcanics, suggest Paleoarchean crustal accretion by mantle plume activity as well as local shallow subduction or subcretion under a transitional tectonic regime.