Paleoproterozoic trench–distal back-arc setting origin of the Mahakoshal Basin, Central Indian Tectonic Zone (CITZ): Evidence from the geochemistry of the metabasalts

The present study of metabasalts was carried out to understand the mantle source and geodynamic setting of the Mahakoshal Group in the Central Indian Tectonic Zone. In this study, we present detailed field, petrography, and whole rock geochemistry of the Mahakoshal metabasalts. The Mahakoshal metabasalts are sub-alkaline in nature and belong to the tholeiitic series of rocks. The variation in rare-earth element patterns of metabasalts indicates the different degrees of partial melting at shallow as well as deeper depths. Further, Eu/Eu* varies from 0.8 to 1.1 (except sample KP-144=0.3), Ce/Ce* varies from 0.97 to 1.05, showing no cerium anomaly, and Nb/Nb* ranges from 0.7 to 1.3 (except KP-144=0.1). The magnesium number (Mg#) varies from 0.2 to 0.3, which is quite low, indicating the evolved nature of the metabasalts. The studied metabasalts show E-MORB to OIB-type affinities, which are placed in the trench-distal back-arc setting. The opening of the Mahakoshal Basin is due to retreating orogen in the accretionary orogen setting and is contemporaneous with the assembly of the Columbia Supercontinent (~2.1–1.8 Ga). Hence, field, petrographic, and geochemical signatures indicate that the Mahakoshal basin opened as a back-arc rift basin on the Bundelkhand Craton, and that metabasalts are derived from the mantle that underwent variable degrees of partial melting at different depths.