Geothermobarometry of the Central Crystallines from the Garhwal Himalaya

Pelitic schists, gneisses and amphibolites from the Central Crystallines of the Garhwal Himalaya display evidence of multiple deformation (D₁, D₂ and D₃) and polymetamorphism (M₁, M₂ and M₃)' During the M₁ episode of regional metamorphism which represents a thermal peak, the pelitic schists and gneisses developed the assemblage: sillimanite-kyanite-garnet- biotite-plagioclase-K-feldspar-quartz±garnet. Widespread development of garnet and sillimanite (locally kyanite) in muscovite-bearing schists and gneisses, hornblende in amphibolites, and diopside in calcschists indicate prograde metamorphism in the sillimanite-muscovite zone of the amphibolite facies. During the M₂ and M₃ episodes the higher grade rocks of the M₁episode retrograded under PT conditions of greenschist facies.

The electron microprobe analyses of coexisting minerals from the schists. gneisses and amphibolites have been used to estimate the PT conditions of metamorphism during the Ml episode through the pertinent models of geothermobarometry. These models of geothermobarometry suggest temperatures of 645°C±50°C and pressures of 7.5±0.5 kb during the thermal peak of metamorphism (M₁ episode).