Mineral Chemistry of Mafic Chain Silicate Minerals in the Torappadi Layered Complex of the Southern Granulite Terrain

The chemistry of the mafic chain silicate minerals in the Torappadi layered ultramafic-mafic complex occurring in the southern granulite terrain of the Indian shield has been presented. The pyroxene compositions are found to be sympathetically related to the whole-rock chemistry; further the orthopyroxenes are discriminated to be metamorphic in terms of chemical parameter. All amphiboles of the complex are 'calcic' and their compositions spread from magnesio-hornblende to edenitic homblende/tschermakitic hornblende depending upon the rock-chemistry. Pyroxene geothermometry (assuming complete disordering) using different methods reveals a comparatively large range for a particular rock (up to 181°C). Amphibole geothermometry, on the other hand, gives consistent temperature values (716°-804°C) which has been taken as the range of temperature of equilibration of the whole complex. Estimation of pressure with amphibole-compositions yields a mean value of 4.16 kb. It has been suggested that Torappadi rocks correspond to shallow level - low pressure granulite equivalent to a depth of ca. 10- 17 km.