Genetic relationship among komatiites and associated basalts in the Badampahar greenstone belt (3.25–3.10 Ga), Singhbhum Craton, Eastern India

Abstract

The ultramafic–mafic volcanic rocks of Archean greenstone belts are important archives for lithospheric and asthenospheric processes of the early Earth. Despite decades of research on this context, many issues still remain unsolved. For example, the process of komatiite magma genesis and the genetic relationship among komatiites, komatiitic basalts and tholeiitic basalts in Archean greenstone belts are not clearly understood. The metavolcanic rocks of the Badampahar greenstone belt (BGB), Singhbhum Craton are studied by major–trace element geochemistry to address the said problems and better understand the evolution of melts in Archean lithosphere. Our research suggests that the protoliths of the metavolcanic rocks were komatiites (both Al –depleted and –undepleted), komatiitic basalts and tholeiitic basalts. The Al–heavy rare earth element (HREE) depleted komatiites were formed by moderate degree mantle melting at a higher depth and the Al–HREE undepleted komatiites are products of moderate to high degree mantle melting at a shallower depth. The melting–assimilation–fractional crystallization modelling result shows that komatiitic basalts were generated from Al–undepleted komatiites, and tholeiitic basalts were generated from evolved komatiitic basalts by assimilation and fractional crystallization processes. The older age limit of the BGB is determined to be 3.25 Ga. and the basement of sedimentation and volcanism was composed of plutonic felsic rocks.