Occurrence of Ultramafic-Mafic Rocks of Komatiitic Affinity in the Abujhrnar Basin of Bastar Craton (ME), India

Ultramafic-mafic rocks of komatiitic affinity are reported from the Kerali area of Abujhmar basin in Bastar Craton, Madhya Pradesh. These rocks, occurring below the Gundul sandstone member of the Middle Proterozoic Abujhmar group, are composed of peridotitic komatiites, pyroxenitic komatiites and basaltic komatiites, besides tholeiites and microgabbro emplaced into them as dykes. Petrographically, olivine and pyroxene occur both as major phenocrysts, and as microphenocrysts, with the groundmass made up of interstitial glass. Normatively, these rocks are both olivine and hypersthene normative. Petrochemical data plots on discriminant ternary diagrams such as AFM, Jensen Cation plot, MgO-CaO-AI 2 O 3 diagram, indicate their close similarity to the komatiitic trends shown by the type area rocks from the Munro Township area, Canada and Yilgarn Block of West Australia very much paralleling the trend of Barbertonland komatiites. Trace element data involving Ti, Y, Zr and V plots also points out that these rocks fall in the kornatiitic field as against the tholeiitic field. Tectonic environment discriminant diagram involving the plots of these ultramafic-mafic rocks indicates the possibility of deep passive or 'failed' (?) rift in the region through which these ultramatic-mafic rocks of komatiitic affinity might have been emplaced.