Significance of the Archaean bimodal volcanics from the Ramagiri schist belt in the formation of Eastern Dharwar craton

The central arm of the trident shaped Ramagiri schist belt includes a centr al block which consists predominantly of bimodal (mafic-felsic) volcanics, apart from minor metasedimentary units. The geological set up of the variou s rock types suggests that the central block could be a tectonic melange. T he metatholeiites and the felsic volcanics of the central block show simila r LREE - enriched and fractionated REE patterns; the metatholeiites however , show a much larger variation in abundances. It has been suggested that th e protoliths to the Ramagiri central mafic suite of bimodal volcanics were formed by different extents of melting of the metasomatically enriched mant le sources and were emplaced in an island are setting. We suggest here that partial melting of similar metatholeiites, constituting an are crust, at s imilar to 8 kbar pressures and at similar to 1000 degrees C temperatures, p roduced magmas to the associated felsic volcanics. The geochemical characte ristics of the mafic and felsic volcanic rocks in the Ramagiri belt, as wel l as the adjoining Sandur belt, have many similarities to those of the mode m day island are volcanic suites. The idea that the Phanerozoic style magma tic and accretionary tectonic processes operated during the Late Archaean s uggested from the studies of granitic rocks in the Eastern Dharwar craton i s corroborated by the metavolcanics of the Ramagiri schist belt.