A plume - mantle interaction model for the petrogenesis of komatiite - komatiitic basalt - basalt - basaltic andesite volcanism from the Paleoarchean (3.57–3.31 Ga) Iron Ore Group greenstone belts, Singhbhum craton, India: Constraints from trace element geochemistry and Sm[sbnd]Nd geochronology

Abstract

The Paleoarchean Singhbhum craton greenstone belts comprise basalt, interbedded minor komatiite (both alumina depleted and undepleted, ADK and AUK, respectively), komatiitc basalt, dacite and chert grouped as (~3.57 Ga) southern Iron Ore Group (S-IOG, Daitari samples) and ~ 3.31 Ga eastern Iron Ore Group (E-IOG, Dabanki samples). Considering the importance of metabasalt in formation of TTG batholiths, modeling their petrogenesis from mantle sources and SmNd geochronology was conducted. The rocks resemble Archean non-arc greenstone basalt (Nb/Th = 3.61–10.3) with tholeiitic affinity. The ADK of S-IOG was modeled by 37% partial melting of garnet lherzolite, komatiitic basalt was derived from ADK magma by ~25% assimilation fractional crystallization (AFC) and ~ 16% AFC of this magma formed tholeiitic basalt. Derived from depleted parental magmas they yield an isochron age of 3573 ± 63 Ma (2SD), Ndi = 0.50810 ± 0.00008, MSWD = 0.59 (n = 10) and εNd (3573 Ma) = +2.03 ± 0.03. Dacite formation, modeled by mixing of melts between Eoarchean felsic crust and metabasalt, yielded an isochron age of 3507 ± 180 Ma (2SD), Ndi = 0.50800 ± 0.00015, MSWD = 0.15 (n = 11), εNd (3507 Ma) = −1.46 ± 1.71; ca. 3.8–3.9 Ga Nd TDM model ages indicate vestiges of Eoarchean crust. The AUK of E-IOG was modeled by ~45% partial melting and ADK by ~33% melting of garnet lherzolite mantle. About 32% AFC of primary ADK magma formed the komatiitic basalt that evolved to tholeiitc basalt magma (~24%) which on ~15% AFC evolved to basaltic andesite - andesite magma. Derived from depleted parental magmas, the E-IOG rocks yielded an isochron age of 3313 ± 110 Ma (2SD), Ndi = 0.50847 ± 0.00013, MSWD = 0.06 (n = 10), εNd (3313 Ma) = +2.62 ± 0.28. Petrogenesis of Paleoarchean greenstone non-arc basaltic volcanism and associated komatiite can be best explained by plume-mantle interaction and partial melting of ambient mantle followed by assimilation fractional crystallization of parental magmas, and does not preclude recycling of pre-existing crust.