Petrogenesis of Metabasites from the Schist Belts of the Dharwar Craton: Implications to Archaean Mafic Magmatism

The supracrustal belts of the Dharwar Supergroup in the Dharwar Craton include variably metamorphosed komatiitic and tholeiitic volcanics. Komatiites in general occur only in minor amounts. Available geochemical data of these rocks from the Holenarasipur ? Kudremukh, Bababudan and the Kolar schist belts were quantitatively modelled to infer that (1) Komatiitic magmas originated from deeper mantle sources at depths > 100 km., (2) tholeiitic magmas formed at depths < 50 km from sources different from those of komatiites and with much higher Fe/Mg ratios compared to normal mantle, (3) the two magma types are not genetically related either to one common parental magma or to one common source, (4) Dharwar magmatism could be related to rift related volcanism perhaps associated with one or more mantle plumes. High quality geochemical, including isotopic, data on a large number of samples is required to test this model of Dharwar magmatism.