Accretionary Evolution of the Ramagiri Schist Belt, Eastern Dharwar Craton

Abstract

The gold mineralized Ramagiri Schist Belt is a volcanic dominated, late Archaean belt in the eastern Dharwar Craton. Based on the lithological association, mode of occurrence of rocks, geochemical characteristics of mantle derived rocks and the metamorphic grade of rocks, the belt is divided into three blocks that are tectonically interleaved with and surrounded by granitic rocks of distinct histories. The eastern block has amphibolite facies rocks, dominantly basic metavolcanics having light rare earth element (LREE) depleted patterns with minor banded ferruginous quartzite (BFQ). The central block includes mafic and felsic volcanics, pyroclastics, gabbroic and felsic dykes, argillites and BFQ. The volcanic rocks as well as the intrusives have LREE enriched patterns. The central block has dominantly greenschist facies rocks. The western block is made up of fine grained metabasalts with well preserved pillow structures at places, and retrogressed chlorite-actinolite and chlorite-carbonate schists in shear zones, serpentinite and BFQ. These rocks have flat to moderately LREE depleted patterns. The associated serpentinite is of residual origin, probably representing obducted pieces of Archaean oceanic lithosphere. Available age information and required tectonic settings of the volcanics necessitate subduction related magmatism and corroborate the idea of crustal genesis by accretionary processes in the eastern Dharwar Craton during late Archaean.