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    吴建亮, 尹显科, 刘文, 雷传扬, 王波, 李威, 裴亚伦, 张伟. 2019: 西藏班公湖-怒江缝合带西段野马去申拉组富Nb火山岩的发现及其指示意义. 地质通报, 38(4): 471-483.
    引用本文: 吴建亮, 尹显科, 刘文, 雷传扬, 王波, 李威, 裴亚伦, 张伟. 2019: 西藏班公湖-怒江缝合带西段野马去申拉组富Nb火山岩的发现及其指示意义. 地质通报, 38(4): 471-483.
    shu
    WU Jianliang, YIN Xianke, LIU Wen, LEI Chuanyang, WANG Bo, LI Wei, PEI Yalun, ZHANG Wei. 2019: The discovery of Nb-rich volcanic rock of the Qushenla Formation in Yema area of the western segment of Bangong Co-Nujiang suture in Tibet and its implications. Geological Bulletin of China, 38(4): 471-483.
    Citation: WU Jianliang, YIN Xianke, LIU Wen, LEI Chuanyang, WANG Bo, LI Wei, PEI Yalun, ZHANG Wei. 2019: The discovery of Nb-rich volcanic rock of the Qushenla Formation in Yema area of the western segment of Bangong Co-Nujiang suture in Tibet and its implications. Geological Bulletin of China, 38(4): 471-483.
    shu

    西藏班公湖-怒江缝合带西段野马去申拉组富Nb火山岩的发现及其指示意义

    The discovery of Nb-rich volcanic rock of the Qushenla Formation in Yema area of the western segment of Bangong Co-Nujiang suture in Tibet and its implications

      摘要
    • 摘要: 以班公湖-怒江缝合带西段的去申拉组玄武岩和安山岩为研究对象，进行了岩石锆石测年和地球化学研究。测年结果显示，安山岩形成于108.5±1.5Ma，属于早白垩世晚期。岩石地球化学特征表明，野马去申拉组玄武岩Nb含量为10.5×10-6~11.1×10-6，Al2O3含量为17.63%~17.96%(平均值17.74%)，属于富Nb高铝玄武岩，为中钾钙碱性系列；安山岩属于高钾钙碱性系列岩石。野马火山岩轻、重稀土元素分异明显，其中玄武岩稀土元素总量为119.20×10-6~120.49×10-6，(La/Yb)N值为5.17~5.53；安山岩稀土元素总量为179.97×10-6~184.75×10-6，(La/Yb)N值为13.83~15.12；二者在微量元素上表现出不同程度的富集轻稀土元素和大离子亲石元素，Nb、Ta、Ti等高场强元素相对亏损，具低Cr、Ni，高Sr、Nb、Zr含量，发育岛弧火山岩相关特征。其岩浆源区受俯冲流体的影响较大，后经历了不同程度的铁镁矿物的结晶分离作用。综合分析认为，野马去申拉组火山岩可能形成于弧后盆地构造环境下，是班公湖-怒江特提斯洋岩石圈南向俯冲过程中板片断离导致软流圈地幔上涌，诱发弧后拉张背景下的直接岩浆响应。

       

      Abstract: The volcanic rocks from Qushenla Formation in Yema area is located in the west segment of Bangong Co-Nujiang suture zone, in reverse fault contact with the diabase slice of Bangong Co-Nujiang opiolite melange belt in the north. In this paper, detailed LA-ICP-MS zircon U-Pb dating geochronological and element geochemical studies were carried out for the basalt and andesite in the Qushenla Formation. The U-Pb dating of zircon from andesite yielded a weighted average age of 108.5±1.5Ma, indicating that the andesites were formed at the middle-late stages of Early Cretaceous. Lithogeochemical characteristics show that the Nb-rich basalts in Yema area are characterized by obvious enrichment of Nb and Al2O3, with the values of Nb being 10.5×10-6~11.1×10-6 and Al2O3 being 17.63%~17.96%, averaging 17.74%, suggesting Nb-rich, high-alumina basalt of calc alkaline series. The andesites belong to high-K calc alkaline series. All the volcanic rocks in Yama area are characterized by enriched LREE and relatively depleted HREE. The total REE of basalts are 119.20×10-6~120.49×10-6, with (La/Yb)N from 5.17 to 5.53, and the ∑REE of andesites are 179.97×10-6~184.75×10-6 and their (La/Yb)N range from 13.83 to 15.12. On primitive mantle-normalized trace element diagrams, the basalts and andesite display different degrees of enrichment of LIFEs (e.g., Rb, U, K), relative depletion of HFSE (Nb, Ta, Ti) with high content of Sr, Nb, Zr but low content of Cr, Ni, similar to features of island arc rocks. The magma source region was mainly influenced by the subduction fluid and underwent different degrees of fractionation crystallization of femic minerals with uplifting. A comprehensive study shows that the basalt and andesite of Qushenla Formation in Yema area were probably formed in the backarc tectonic rocks, which might have been the direct magma response to slab break-off caused by asthenosphere upwelling back-arcextension during the southward subduction of Bangong Co-Nujiang Tethyan Ocean at the late stage of Early Cretaceous.

       

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