摘要
Two generations of monazite were identified in one mica schist sample from the central zone of the eastern Kunlun Orogen at the northern margin of the Qinghai-Tibet Plateau. The first generation was found in the cores of garnet porphyroblasts with relatively high Y2O3 contents (averaging 1.012±0.088 wt%). The second generation occurs either as inclusions in the rims of garnet porphyroblasts,matrix kyanite,plagioclase and quartz,or as separate crystals associated with matrix biotite and muscovite mostly having a relatively low Y2O3 content (averaging 0.479±0.100 wt%). Electron microprobe (EMP) Th-U-Pbtotal chemical dating for two grains of the first generation monazite yields average ages of 455 ± 18 Ma and 420 ± 20 Ma,respectively; six grains of the second generation gave an average age of 246.1 ± 3.8 Ma. These ages suggest that the core and rim of the garnet porphyroblasts and their associated assemblages record two events of significant tectonometamorphism. The formation of the Ordovician monazite is related to the tectonometamorphic event responsible for continuous amalgamation of the Gondwanaland in the Late Pan-African period or for consumption of the Proto-Tethys,whereas the development of the Triassic monazite is related to the tectonometamorphic event for consumption of the Paleo-Tethys.
Two generations of monazite were identified in one mica schist sample from the central zone of the eastern Kunlun Orogen at the northern margin of the Qinghai-Tibet Plateau. The first generation was found in the cores of garnet porphyroblasts with relatively high Y203 contents (averaging 1.012±0.088 wt%). The second generation occurs either as inclusions in the rims of garnet porphyroblasts, matrix kyanite, plagioclase and quartz, or as separate crystals associated with matrix biotite and muscovite mostly having a relatively low Y203 content (averaging 0.479±0.100 wt%). Electron microprobe (EMP) Th-U-Pbtototal chemical dating for two grains of the first generation monazite yields average ages of 455 ± 18 Ma and 420 ± 20 Ma, respectively; six grains of the second generation gave an average age of 246.1±3.8 Ma. These ages suggest that the core and rim of the garnet porphyroblasts and their associated assemblages record two events of significant tectonometamorphism. The formation of the Ordovician monazite is related to the tectonometamorphic event responsible for continuous amalgamation of the Gondwanaland in the Late Pan-African period or for consumption of the Proto-Tethys, whereas the development of the Triassic monazite is related to the tectonometamorphic event for consumption of the Paleo-Tethys.
基金
Supported by the National Natural Science Foundation of China (Grant Nos. 40272030 and 49972023)
Outstanding Research Award of HK
关键词
独居石
昆仑造山带
变质岩
电子探针测年
石榴石
monazite, electron microprobe Th-U-Pbtotal age, zoned garnet, converge of the Gondwanaland, Tethys evolution, eastern Kunlun Orogen,northern Qinghai-Tibet Plateau