Platinum-group element and Au geochemistry of an ultramafic intrusion from the Sonakhan greenstone belt, Bastar craton, Central India: Tectono-magmatic implications

The Sonakhan greenstone belt (SGB), located in the north-eastern Bastar craton of the Indian shield, comprises mafic-ultramafic and volcanic-intrusive sequences in the lower stratigraphic units. We investigate the Platinum-group element (PGE) relations of Boradih intrusion of the SGB to evaluate its tectono-magmatic evolution. The chondrite-normalized PGE patterns of boninitic cumulate rocks exhibit higher abundance of Palladium group PGEs (sigma PPGE = 292-496 ppb) relative to the Iridium group PGEs (sigma IPGE = 32-52 ppb) along with variable Au concentrations (51.34-718.05 ppb). The PGE concentrations are attributed to a boninitic parental melt, where the IPGEs in the source possibly partitioned into a monosulphide solid solution. The Cu (22-80 ppm), elevated Pt (22-238 ppb), and Pd (31-377 ppb) concentrations indicate Pt and Pd have partitioned into a semi-metal rich melt during the later stages of crystallization. The geochemical characteristics of the basalts and ultramafic cumulates of the SGB indicate a supra-subduction zone tectonic setting for its formation. Similar geochemical and litho-tectonic correlations are also noticed between the SGB of Bastar craton and greenstone belts of the Eastern Dharwar craton of south India. The SGB (V/Yb =146 +/- 25) and greenstone belts of Eastern Dharwar craton (V/Yb = 134 +/- 52) record similar oxidation conditions of Phanerozoic subduction zones. Accordingly, we propose magmatic as well as tectonic correlations are possible for the Archean-Palaeoproterozoic Bastar and Eastern Dharwar cratons.