邓明荣, 董永胜, 张修政, 张乐, 许王, 柳佳成. 藏北羌塘中西部红脊山地区晚古生代蛇绿岩地球化学特征及构造意义[J]. 地质通报, 2014, 33(11): 1740-1749.
    引用本文: 邓明荣, 董永胜, 张修政, 张乐, 许王, 柳佳成. 藏北羌塘中西部红脊山地区晚古生代蛇绿岩地球化学特征及构造意义[J]. 地质通报, 2014, 33(11): 1740-1749.
    DENG Ming-rong, DONG Yong-sheng, ZHANG Xiu-zheng, ZHANG Le, XU Wang, LIU Jia-cheng. Geochemical characteristics and tectonic implications of Hongjishan ophiolite in central and western part of Qiangtang, northern Tibetan Plateau[J]. Geological Bulletin of China, 2014, 33(11): 1740-1749.
    Citation: DENG Ming-rong, DONG Yong-sheng, ZHANG Xiu-zheng, ZHANG Le, XU Wang, LIU Jia-cheng. Geochemical characteristics and tectonic implications of Hongjishan ophiolite in central and western part of Qiangtang, northern Tibetan Plateau[J]. Geological Bulletin of China, 2014, 33(11): 1740-1749.

    藏北羌塘中西部红脊山地区晚古生代蛇绿岩地球化学特征及构造意义

    Geochemical characteristics and tectonic implications of Hongjishan ophiolite in central and western part of Qiangtang, northern Tibetan Plateau

    • 摘要: 以变质玄武岩为研究对象,对红脊山蛇绿岩进行了详细的岩石学和地球化学研究。结果表明,玄武岩主量元素含量与典型的N-MORB非常相似,稀土元素总量较低,具有轻稀土元素略亏损的近平坦左倾型配分型式,Eu异常不显著(δEu=1.05~1.16)。微量元素蛛网图总体也与N-MORB相似,表明变质基性岩源于N-MORB型亏损地幔源区。与典型的大洋中脊玄武岩相比,微量元素蛛网图显示出部分大离子亲石元素明显富集和部分高场强元素明显亏损的特征,尤其是Nb的亏损较为明显(Nb=1.67×10-6~2.26×10-6,平均值为1.97×10-6),表明本区玄武岩受俯冲带物质的影响,很可能形成于俯冲带之上的弧后盆地次级扩张的大地构造背景,属SSZ型蛇绿岩范畴,为特提斯大洋岩石圈在俯冲过程中引发弧后盆地次级扩张的产物。本研究为龙木错—双湖—澜沧江板块缝合带中西段的构造演化研究提供了重要依据。

       

      Abstract: Taking metamorphic basalt as the main research object, the authors conducted detailed studies of petrology and geochemistry of the Hongjishan ophiolite. The geochemical characteristics indicate that the content of major elements is quite similar to that of typical N-MORB, the Hongjishan ophiolite exhibits low ∑REE and light rare element depletion, and δEu is normal (δEu=1.05~1.16). These characteristics are quite similar to those of the typical N-MORB primitive mantle-normalized trace element patterns and also quite similar to features of typical N-MORB. These data indicate that the Hongjishan ophiolite originated from a depleted asthenosphere mantle with distinctive geochemical features of N-MORB. However, compared with the typical mature mid-ocean ridge basalt, this basalt exhibits the enrichment of some lithophile elements (Ra, Ba, U)and the depletion of Nb, Ta (especially Nb) on the curves of N-MORB normalized trace element distribution pattern (Nb=1.67×10-6~2.26×10-6, mean value of Nb is 1.97×10-6), quite different from features of both the typical mature mid-ocean ridge basalt and the typical island-arc basalt. These unique geochemical characteristics indicate the influence of subduction material and suggests that the Hongjishan ophiolite was formed in a marginal basin tectonic setting resulting from the back-arc mantle convection and back-arc oceanic crust formation which constituted a spreading center near the subduction zone. The results achieved by the authors provide important basis for the study of tectonic evolution of the middle-western part of the Lungmu Co-Shuanghu-Lancang River suture zone.

       

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