Metamorphic characteristics and geotectonic implications of the high-pressure granulites from Namjagbarwa, eastern Tibet

<正> A large area of high-pressure garnet-kyanite granulite is exhumed in the Namjagbarwa area, which provides a window for observing the deep crust rocks and structures of the Tibetan Plateau. Three mineral assemblages can have been distinguished in the garnet-kyanite HP granulites by petrography, i.e. M1. Mus+Bi+P1+Q, M2. Gt+Ky +perphite/antiperphite+Rt+Q, M3. Gt+Sill+Cord+Sp+Ilm±Opx. Metanmrphic conditions of the peak granulite assemblages （M2） formatted by thickening of crusts, with available isotopic ages of 45-69 Ma, are at 1.4-1.8 Gpa and 750--850℃ . Their retrograde assemblages overprinted by deconpressure during the uplift, with available isotopic ages of 18-23 Ma, were formed at 0.60-0.70 Gpa, 621-726℃ . The thermobarometric evaluation, petrogenetic grid and corresponding isotopic ages indicate a clockwise isothermal decompression metamorphic path. The HP granulite metamorphic history indicates that the collision of the Indian Plate with the Eurasian Plate had begun at 70 Ma, far earlier tha