曾孝文, 王明, 李航, 曾先进, 申迪. 西藏中部狮泉河-纳木错蛇绿岩带的构造属性——来自阿索混杂岩带岛弧玄武岩的地球化学制约[J]. 地质通报, 2021, 40(8): 1291-1301.
    引用本文: 曾孝文, 王明, 李航, 曾先进, 申迪. 西藏中部狮泉河-纳木错蛇绿岩带的构造属性——来自阿索混杂岩带岛弧玄武岩的地球化学制约[J]. 地质通报, 2021, 40(8): 1291-1301.
    ZENG Xiaowen, WANG Ming, LI Hang, ZENG Xianjin, SHEN Di. Tectonic attribute of the Shiquanhe-Namco ophiolitic belt: Constraint from geochemistry of the island-arc basalts in the Asa mélange zone, central Tibet[J]. Geological Bulletin of China, 2021, 40(8): 1291-1301.
    Citation: ZENG Xiaowen, WANG Ming, LI Hang, ZENG Xianjin, SHEN Di. Tectonic attribute of the Shiquanhe-Namco ophiolitic belt: Constraint from geochemistry of the island-arc basalts in the Asa mélange zone, central Tibet[J]. Geological Bulletin of China, 2021, 40(8): 1291-1301.

    西藏中部狮泉河-纳木错蛇绿岩带的构造属性——来自阿索混杂岩带岛弧玄武岩的地球化学制约

    Tectonic attribute of the Shiquanhe-Namco ophiolitic belt: Constraint from geochemistry of the island-arc basalts in the Asa mélange zone, central Tibet

    • 摘要: 明确狮泉河-纳木错蛇绿岩带的构造属性是重建西藏中部中特提斯演化的关键之一。报道了西藏中部阿索地区蛇绿混杂岩带中岛弧玄武岩的岩石学、地球化学特征,并讨论了该岩石的构造意义。野外和镜下观察结果显示,该样品具有枕状构造并具有细碧岩的岩石特征,表示其形成于海底喷发环境。全岩地球化学分析结果显示,该样品属于亚碱性系列中的钙碱性玄武岩。该岩石富集轻稀土元素,具有平坦的重稀土元素分布特征,轻、重稀土元素分异较强。岩石富集Ba、Th、Pb等大离子亲石元素,亏损Nb、Ta等高场强元素。地球化学分析结果显示,岩石起源于被俯冲沉积物熔体交代的亏损地幔的部分熔融,形成于洋内岛弧环境之下。结合前人研究,发现狮泉河-纳木错蛇绿岩带并非仅存在洋壳成因的蛇绿岩,还保存了一些岛弧成因的岩浆岩。这些岛弧成因岩浆岩的存在表明,狮泉河-纳木错蛇绿岩带中的岩浆岩并非单一构造背景下形成的蛇绿岩,而是包含了多种构造背景之下的岩浆产物。研究表明,狮泉河-纳木错蛇绿岩带并非仅保留了弧后盆地的遗迹,其包含了洋内俯冲环境中多种成因的岩浆作用产物。

       

      Abstract: The tectonic setting of the Shiquanhe-Namco ophiolitic belt in central Tibet is a key to understanding the Mesozoic tectonic evolution of the Meso-Tethys Ocean.Based on the analysis of major and trace element compositions of island arc basalts in the Asa mélange zone, central Tibet, its tectonic significance was discussed.Field observation and microscopic study indicate that they were formed in submarine eruption environment.Whole-rock geochemical analyses suggest that these rocks belong to calc-alkaline rocks, rich in light rare earth and Ba, Th, Pb large-ion lithophile elements, and depleted in Nb and Ta, with clear differentiation of light and heavy rare earth elements and flat distribution of heavy rare earth elements.Geochemical analysis shows that the rocks were originated from partial melting of depleted mantle metasomatized by melt of subducting sediments and formed under the oceanic island arc environment.Combined with previous work, it is suggested that there are some island arc basalts widely preserved in the Shiquanhe-Namco ophiolitic belt.The existence of the island-arc magmatic rocks within the Shiquanhe-Namco ophiolitic belt reveals that the Shiquanhe-Namco ophiolitic belt cannot be interpreted as an ophiolite in a single back-arc setting but contains magmatic products under various tectonic settings.The results show that the Shiquanhe-Namco ophiolite belt does not only retain the remains of backarc basin, but also contains the magmatic products of various genesis in the subduction environment.

       

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