Petrology and Geochemistry of Precambrian Mafic and Ultramafic Rocks from North Devanahalli, Bangalore Rural, Karnataka, Southern India

Abstract

The Archaean crust of the eastern Dharwar Craton preserves important records of early mantle-derived magmatism and crustal evolution. Mafic and ultramafic rocks occurring in the Precambrian terrain of North Devanahalli Taluk, Bangalore Rural District, southern India, form a significant component in this regard. These rocks occur as enclaves, lenses, and intrusive bodies within the Peninsular Gneissic Complex and are spatially associated with high-grade metamorphic lithologies. The present study integrates field observations, petrographic investigations, and whole-rock geochemical analyses of representative mafic and ultramafic samples to constrain their petrogenesis and tectonic affinity. Petrographic characteristics reveal relict magmatic textures such as gabbroic and poikilitic fabrics, overprinted by granoblastic textures developed during amphibolite to lower granulite facies metamorphism. Geochemical data indicate tholeiitic to komatiitic affinity, marked by enrichment of compatible elements (Ni, Cr, Co, V) and weakly fractionated rare earth element patterns. These features suggest derivation from mantle-derived magmas followed by limited fractional crystallization and minor crustal interaction. The mafic-ultramafic rocks of the study area represent remnants of Archaean magmatic activity associated with early crust-mantle differentiation processes in the eastern Dharwar Craton.