Petrology and U-Th-Pb chemical monazite dating of the low-P metapelitic granulites at the region of Muzhaerte River in southwestern Tianshan, NW China, and their geological implications.

作者：Gou LongLong^*; Zhang LiFei

来源：Acta Petrologica Sinica, 2009, 25(9): 2271-2280.

• Southwest Tianshan
• Monazite
• Low-P pelitic granulite
• paired metamorphic zone
• Isochron age
• South Tianshan Paleo-Ocean

During the closure of the South Tianshan Paleo-Ocean, a suite of low-pressure pelitic granulite-facies Crd-Grt-Sil-Bt gneiss was formed by the intrusion of are magma into the landward continental margin of Muzhaerte River in South Tianshan, Xinjiang. Using the thermodynamic software of Theriak-Domino, we performed the NCKFMASH phase equilibria calculation on the Crd-Grt-Sil-Bt gneiss (WQ003) and the sillimanite-bearing Crd-Grt-Bt gneiss ( WQ006), and gained that their peak metamorphic conditions are T = 630 similar to 674 degrees C, P 5.2 similar to 5.5kbar and T = 645 similar to 684 degrees C P = 5.4 similar to 5. 7kbar, respectively. Moreover, we carried out the geochronological research on three monazite grains in sample WQ006 with the technique of U-Th-pb chemical monazite dating by electron microprobe and got two characteristic isochron ages, 376 +/- 8Ma and 280 +/- 8 Ma (2 sigma). Based on the petrographic Study of monazite, 280 +/- 8Ma can be explained as the age of peak granulite-facies metamorphism, whereas 376 8 Ma (2 sigma) maybe represent the age of detrital or diagenesis, and we conclude that the subduction of South Tianshan oceanic crust began in Late paleozoic and confirm the opinion that the subduction-collision of Southwest Tianshan orogen occurred after Late-Permian.

• 出版日期2009-9
• 单位北京大学