Thermal and baric evolution of garnet granulites from the Kharta region of S Tibet, E Himalaya .

Granulite-facies garnet-bearing metapelites, metabasics and calc-silicate rocks from the lower metamorphic complex (Kharta Gneiss) of the Greater Himalayan Sequence (GHS) in the Kharta region of S Tibet, E Himalaya, preserve textural and chemical evidence for prograde equilibration at temperatures of at least 700-720°C and pressures in the vicinity of 8 kbar during the main Himalayan metamorphism. Post-deformational reaction textures including clinopyroxene (± orthopyroxene) - plagioclase symplectites after garnet in calcsilicate rocks, and cordierite ± spinel coronas on sillimanite and garnet in metapelite granulites indicate a decompressional pressure-temperature evolution which is confirmed by geo-thermobarometry of zoned and symplectite minerals, and by modeled phase equilibria. A pervasive decompression through c. 3 kbar occurred at temperatures of about 700°C, and was followed by static recrystallization at temperatures of c. 650°C and low metamorphic pressures (~ 2.5 kbar).This type of trajectory, with most of the exhumation occurring at relatively constant metamorphic temperatures, requires a high-exhumation rate and/or a high heat flow, both typical conditions of post-collisional exhumation of thickened continental crust, with exhumation rates controlled by tectonic processes which operate on shorter time scales than erosion.