Metamorphic Evolution of Charnockites and Felsic Gneisses from the Schirmacher Region, East Antarctica

The structural and petrographic studies of the metamorphic rocks of the Schirmacher region, East Antarctica, indicate polyphase metamorphism, dominantly of an early granulite and later amphibolite facies metamorphism. In order to understand the metamorphic evolution of the region, the temperature and pressure of metamorphism has been estimated for felsic gneisses and charnockites using conventional models of geothermometry and geobarometry. The studies showed that, the early granulite facies metamorphism and charnockitization took place around 827±29°C at 7.3±0.3 kbar, while the later amphibolite facies metamorphism and granitization took place around 654±27°C at 5.4±0.4 kbar. The pressure and temperature recorded in these rocks suggest that metamorphism was initiated at 20 to 27 km depth, with a geothermal gradient of around 32°C/km. The P-T conditions reflect isobaric cooling path, with a gentle dP/dT slope (∼10±1 bar/°C). The isobaric cooling path owes its origin to the underplating of crust by mantle derived magmas.