Petrography, Geochemistry and Tectonic Settings of Granitic Gneisses from Swarnagadde Plateau of Western Ghats, Karnataka

Abstract: The granitic gneisses of the Swarnagadde plateau located on the southwestern margin of Uttar Kannada district forming a basement complex of peninsular gneiss, have been examined in the field, mapped and interpreted on the basis of petrological and geochemical data. This was meant to categorize the rocks and to understand the tectonic setting in order to evaluate the crustal evolution. The chemical analyses were done using inductively-coupled plasma mass spectrometer. From the results obtained, the major element contents of granitic gneisses reflect their fairly homogeneous composition. Mineralogy of rock is dominated by plagioclase (49-62%), quartz (29-42%), K-feldspar (1-5%) and /or hornblende is in decreasing order. The granitic gneisses formed from medium to low grade metamorphism of granite and granodiorite witnessed at a late stage in the Precambrian records of the area. Tectonically most of the rock samples plotted in the field of volcanic arc granite+Syn-collisional granite rocks, which indicated that the protolith granite and granodiorite are volcanic arc magmas predominantly post orogenic development in island-arc to continental and collision zone.

Keywords: Granitic gneiss, Swarnagadde, tectonic setting, tonalitic, collision zone.