Late Triassic crustal growth in southern Tibet: Evidence from the Gangdese magmatic belt
Late Triassic crustal growth in southern Tibet: Evidence from the Gangdese magmatic belt
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DOI：
10.1016/j.gr.2015.10.007
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发表时间：
2016-09
影响因子：
6.1
通讯作者：
Yuanku Meng;Zhiqin Xu;M. Santosh;Xuxuan Ma;Xijie Chen;G. Guo;Fei Liu
中科院分区：
文献类型：
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作者：
Yuanku Meng;Zhiqin Xu;M. Santosh;Xuxuan Ma;Xijie Chen;G. Guo;Fei Liu
冈底斯岩浆带位于拉萨造山带南缘，具有重要的铜、多金属成矿作用，保存了与印度-欧亚碰撞和藏南地壳生长有关的重要构造信息。本文对冈底斯岩浆带中部曲水岩基进行了研究，首次报道了角闪辉长岩的产出。本文提供了这些岩石的岩石学、锆石U-Pb-Hf同位素和岩石化学数据。角闪岩辉长岩显示亚碱性特征，与拉斑玄武岩成分相对应。它们还显示中等K钙碱性至低K亲和力。岩石富集大离子亲石元素和轻稀土元素，但亏损高场强元素，表明岩浆形成于与俯冲有关的活动大陆边缘环境。计算结果表明，辉长岩岩体侵位于约1000 m的中下地壳深度。十八公里。角闪辉长岩中的锆石结晶年龄约为0.0001。210 Ma，揭示了晚三叠世岩浆事件。结合冈底斯岩浆带的研究结果，我们认为新特提斯洋壳向北俯冲至拉萨造山带南缘之下的时间可能不晚于三叠纪诺利期。角闪岩辉长岩的锆石εHf（t）值为9.56 ~ 14.75（平均值12.44），对应于256 ~ 459 Ma的单阶段模式年龄（TDM 1），表明拉萨南缘的地壳生长与新特提斯洋壳俯冲有关。
The Gangdese magmatic belt, located in the southern margin of the Lhasa terrane and carrying significant copper and polymetallic mineralization, preserves important information relating to the tectonics associated with Indian–Eurasian collision and the crustal growth of southern Tibet. Here we investigate the Quxu batholith in the central domain of the Gangdese magmatic belt and report the occurrence of hornblende gabbros for the first time. We present petrologic, zircon U–Pb–Hf isotopic and bulk-rock chemistry data on these rocks. The hornblende gabbros display sub-alkaline features, and correspond to tholeiite composition. They also show medium K calc-alkaline to low K affinity. The rocks show enrichment in LILEs and LREEs, but are depleted in HFSEs, indicating a subduction-related active continental margin setting for the magma genesis. Our computations show that the gabbroic pluton was emplaced in the middle-lower crustal depth of ca. 18 km. Zircons from the hornblende gabbros yield crystallization age of ca. 210 Ma, revealing a late Triassic magmatic event. Combined with available data from the Gangdese magmatic belt, our study suggests that the northward subduction of the Neo-Tethys oceanic crust beneath the southern margin of the Lhasa terrane might have been initiated not later than the Norian period of Triassic. Zircons from the hornblende gabbro show positive εHf(t) values of 9.56 to 14.75 (mean value 12.44), corresponding to single stage model ages (TDM1) in the range of 256 Ma to 459 Ma, attesting to crustal growth in the southern Lhasa terrane associated with the subduction of the Neo-Tethys oceanic crust.