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

Abstract

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 (∑PPGE = 292–496 ppb) relative to the Iridium group PGEs (∑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.