Petrological and Geochemical Studies of Felsites around Mandya District, Western Dharwar Craton, South India, Karnataka

The Dharwar Craton in south India offers unique opportunity to study the natural cross-section of late Archaean continental crust. A preliminary attempt has been made in this study to understand the petrological and geochemical aspects of felsite dykes that are spread around Mandya district in south India. Geologically investigated area is made up of varied assemblages of rock types ranging from gneiss, ancient supracrustals of Sargur group, Peninsular gneiss, ultramafics, meta-ultramafites, amygdaloidal metabasalt and pillowed/BIF, granodorite, amphibolite and to younger intrusives of Neo-proterozoic age. Felsites in alternation with pegmatites are also exposed. Quartzo-feldspathic veins traverses the felsites at places and felsite with large phenocryst of feldspar are also found. At places felsites are highly jointed and the joint plane trend in E-W direction. Petrographic study shows that felsites are aphanitic and porphyritc in texture. The field and petrographic studies coupled with chemistry data suggest that the felsites dykes of the study area have evolved from a complex crystallization history and are formed in a volcanic arc granitic environment. The concentration of uranium up to 7.1 ppm indicates the potentiality of felsites for the occurrence of radioactive elements.