EMP chemical ages of monazites from Central Zone of the eastern Kunlun Orogen:Records of multi-tectonometamorphic events  

作　　者：CHEN NengSong SUN Min WANG QingYan ZHAO GuoChun CHEN Qiang SHU GuiMing 

机构地区：[1]Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China [2]Department of Earth Sciences, the University of Hong Kong, Poflam Road, Hong Kong, China [3]School of Earth and Space Sciences, Peking University, Beijing 100871, China

出　　处：《Chinese Science Bulletin》2007年第16期2252-2263,共12页

基　　金：Supported by the National Natural Science Foundation of China (Grant Nos. 40272030 and 49972023);Outstanding Research Award of HK

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.

关 键 词：独居石 昆仑造山带 变质岩 电子探针测年 石榴石 

分 类 号：P578[天文地球—矿物学]