Mineral Chemistry of mafic chain silicate minerals in the Torappadi layered complex of the Southern Granulite Terrain

摘要

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 onhopyroxenes are discriminated to be metamorphic in terms of chemical parameter. All amphiboies of the corriplex are 'calcic' and their compositions spread from riagnesio-homblende to edenitic hornblende/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℃). Amphibole geothermometry, on the other hand, gives consistent temperature values (716° - 804℃) 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 pnmulite equivalent to a depth of ca. 10- 17km.