Elemental Mobility and Crustal Contamination of Metabasalts Around Bisnal Area, Karnataka, India with Emphasis on Trace Element Geochemistry

The present work includes the study of the metabasalt samples collected from Bisnal village of Bagalkot District, Karnataka which forms the northwest extension of the Hungund Kushtagi (H-K) schist belt, belonging to the Eastern Dharwar Craton (EDC), indicate supper green schist to epidote amphibolites facies of metamorphism. These rocks have also undergone the process of hydrothermal alteration, which is evidenced by the occurrence of pyrite and chalcopyrite in the quartz carbonate veins. These metabasalts show compositional variation from basalts to andesite which is determined by the ratios of Nb/Y vs Zr/Ti and Nb/Y vs Zr/TiO2. The slight enrichment of the LILE and LREE elements with the LREE/HREE ratio (1.70-2.17), the HREE ratio (1.09- 1.13) and the negative Eu/Eu* ratio for all samples with a range of 0.89-0.93 indicates that these rocks have undergone low to moderate fractionation process during crystallization. Elements such as Na, K, Ca and the HFSE elements such as Nb,Th,Zr,Hf, and Ta show slight deviation from their normal values, and the variation in the Ce/Ce* ratios, indicates the elemental mobility and the magma crust interaction process. The Lower values of Ni, Cr and higher ratios of Th/La, than that of the primitive mantle and the Nb/Y ratios to that of the lower crust indicates that these metabasalts have undergone the crustal contamination processes. Keywords: Metabasalt, Amphibolite, Trace Elements, REE, Geochemistry