内蒙古巴林右旗巴彦查干岩体年代学与地球化学:对古亚洲洋闭合时间的限定

古亚洲洋闭合时限一直存在争议.对巴林右旗巴彦查干岩体进行了地球化学、锆石U-Pb测年和Lu-Hf同位素研究，确定其时代和成因，探讨区域构造背景.巴彦查干岩体岩性为二云母二长花岗岩.测年显示，花岗岩侵位于232.0~241.7 Ma，为中晚三叠世.花岗岩富硅和铝，贫镁和铁，属强过铝系列（A/CNK=1.10~1.25），富集轻稀土和大离子亲石元素，亏损重稀土和Nb、Ta等高场强元素，具S型花岗岩特征.锆石的ε_Hf（t）值为-1.8~+4.01，二阶段模式年龄（t_DM2）在1 006~1 380 Ma之间.上述研究表明，原始岩浆起源于加厚陆壳的部分熔融.结合内蒙古东南部蛇绿混杂岩、晚古生代岩浆岩带和沉积环境、三叠纪碰撞相关花岗岩带等研究，推测古亚洲洋东段的闭合发生在晚二叠世；三叠纪进入陆陆碰撞阶段. 

Geochronology and Geochemistry of Bayanchagan Pluton in Balinyouqi,Inner Mongolia: Implication for Timing of Closure of Paleo-Asian Ocean

It is a highly controversial topic about the closure of the Paleo-Asian Ocean. Based on the geochemistry, zircon U-Pb dating and Lu-Hf isotope studies of Bayanchagan pluton in Balinyouqi, in this paper, it discusses its formation age, petrogenesis and the regional tectonic setting. Bayanchagan pluton is two-mica monzogranites. LA-ICP-MS zircon U-Pb dating indicates the two-mica monzogranite formed in the Middle-Late Triassic(232.0-241.7 Ma). The two-mica monzogranite is high in SiO₂, Al₂O₃ and low in MgO, Fe₂O₃, belonging to strongly peraluminous series(A/CNK=1.10-1.25), enriched in light rare earth elements and large ion lithophile elements, and depleted in heavy rare earth elements and high field strength elements(Nb, Ta), showing that it is S-type granite. Hf isotopic analysis results show ε_Hf(t) values of -1.8 to +4.01, two-stage model ages ranging from 1 006 Ma to 1 380 Ma, respectively, indicating that the primary magma was derived from the partial melting of a thickened crust. Combined with the studies of the ophiolitic melange, magmatic belt and sedimentary environment of Late Paleozoic, collision related granites, and so on, it is suggested that the eastern segment of the Paleo-Asian Ocean closed in the Late Permian-Early Triassic, and was at the period of continental collision during Triassic.