Metamorphic characteristics and geotectonic implications of the high-pressure granulites from Namjagbarwa, eastern Tibet |
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| Authors: | Lin Ding Dalai Zhong |
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| Institution: | (1) Institute of Geology, Chinese Academy of Sciences, 100029 Beijing, China |
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| Abstract: | 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. Metamorphic 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 decompressure 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 than the widely accepted 45 Ma.
Project supported by the National Natural Science Foundation of China (Grant No. 49732100), the National Key Project for Basic
Research, and the Chinese Academy of Sciences Project for Tibetan Research Project (GrantNos. KZ951-A1-204, KZ95T-06). |
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| Keywords: | Tibetan Plateau Namjagbarwa HP granulite metamorphism |
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