GEOCHEMISTRY AND TECTONIC SIGNIFICANCE OF LATE ARCHEAN EARLY PROTEROZOIC METABASALTS FROM BACHELI, BASTAR DISTRICT, MADHYA-PRADESH

The fine grained, massive metabasalts of Bacheli- Kirandul areas, Bast ar district, M.P., characterized by a greenschist facies mineral assem blage have been studied for their major, trace and REE geochemical dis tribution pattern. On Jensen's AFM Plot and diagrams of relatively imm obile elements, these metabasalts fall in the tholeiitic basalts to ba saltic andesite field. Large scatter in Na2O/K2O, K/Rb and Rb/Sr ratio s suggest to alteration effects, while high MgO content ascribes to th e oxidative diagenesis. Relatively immobile and HFSE element discrimin ant diagrams point to an island arc/convergent plate setting. The depl etion in Nb and Ta relative to Th and LREE in these samples may be rel ict from a previous tectonic event. Inferences drawn from geochemical tectonic discriminant diagrams have been evaluated in the light of add itional geological data, and an ensialic rift setting for these volcan ics is envisaged.