张正平, 辛后田, 程海峰, 张永, 梁国庆, 提振海, 朱炜, 苏朋涛, 杜金利, 王猛, 赵麒寓. 内蒙古北山造山带发现额勒根蛇绿岩——红石山-百合山蛇绿岩带东延的证据[J]. 地质通报, 2020, 39(9): 1389-1403.
    引用本文: 张正平, 辛后田, 程海峰, 张永, 梁国庆, 提振海, 朱炜, 苏朋涛, 杜金利, 王猛, 赵麒寓. 内蒙古北山造山带发现额勒根蛇绿岩——红石山-百合山蛇绿岩带东延的证据[J]. 地质通报, 2020, 39(9): 1389-1403.
    ZHANG Zhengping, XIN Houtian, CHENG Haifeng, ZHANG Yong, LIANG Guoqing, TI Zhenhai, ZHU Wei, SU Pengtao, DU Jinli, WANG Meng, ZHAO Qiyu. The discovery of the Elegen ophiolite in Beishan orogenic belt, Inner Mongolia: Evidence for the east extension of the Hongshishan-Baiheshan ophiolite belt[J]. Geological Bulletin of China, 2020, 39(9): 1389-1403.
    Citation: ZHANG Zhengping, XIN Houtian, CHENG Haifeng, ZHANG Yong, LIANG Guoqing, TI Zhenhai, ZHU Wei, SU Pengtao, DU Jinli, WANG Meng, ZHAO Qiyu. The discovery of the Elegen ophiolite in Beishan orogenic belt, Inner Mongolia: Evidence for the east extension of the Hongshishan-Baiheshan ophiolite belt[J]. Geological Bulletin of China, 2020, 39(9): 1389-1403.

    内蒙古北山造山带发现额勒根蛇绿岩——红石山-百合山蛇绿岩带东延的证据

    The discovery of the Elegen ophiolite in Beishan orogenic belt, Inner Mongolia: Evidence for the east extension of the Hongshishan-Baiheshan ophiolite belt

    • 摘要: 通过1:5万黑红山幅区调工作,在内蒙古北山造山带的额勒根地区新发现并详细填绘出一套由玄武岩、斜长花岗岩、硅质岩和砂板岩构成的蛇绿构造混杂岩组合,该蛇绿混杂岩带呈NWW向带状展布,宽2.5~8 km,延伸约25 km。其中,玄武岩具富Na2O(3.02%~6.04%)、MgO(4.29%~5.46%)而贫K2O(0.03%~0.23%)、TiO2(0.44%~0.59%),轻稀土元素球粒陨石标准化配分模式为平坦型;微量元素富集大离子亲石元素Ba、U,明显亏损高场强元素Nb、Ta、P、Ti,兼具洋中脊玄武岩和岛弧玄武岩特征。斜长花岗岩与蛇绿岩中的玄武岩具相似的岩石地球化学特征,形成于玄武质岩浆部分熔融,稀土元素配分模式显示弱负Eu异常的似平坦型曲线。在斜长花岗岩中获得LA-ICP-MS锆石U-Pb年龄为342±4.7 Ma,推测古洋壳形成于早石炭世。结合蛇绿岩两侧不同时代火山岩构造环境的分析,认为额勒根蛇绿混杂岩为古亚洲洋向南俯冲过程中弧后扩张形成的SSZ型蛇绿岩。晚中生代一系列北东向左行走滑断裂,使红石山-百合山蛇绿岩带向北错移至额勒根一带通过。该蛇绿岩带的发现,解决了区域上红石山-百合山蛇绿岩带的东延问题,为北山乃至中亚造山带古生代构造演化提供了重要信息。

       

      Abstract: There is a set of ophiolite tectonic melange belt composed of basalt, plagiogranite, siliceous rock and sand slate which was discovered in the Elegen area of the Beishan orogenic belt in Inner Mongolia, based on the project of 1: 50000 Heihongshan Sheet regional geological survey.The ophiolitic melange belt is in NWW stripe-shaped distribution, with a width of about 2.5 to 8 km and an extension of about 25 km.The basalts in the Elegen ophiolite are rich in Na2O(3.02%~6.04%), MgO(4.29%~5.46%)and poor in K2O(0.03%~0.23%)and TiO2(0.44%~0.59%), and chondrite-normalized LREE patterns are flat.The primitive mantle normalized trace element patterns are characterized by the enrichment of the LILE(Ba, U)and depletion of the HFSE(Nd, Ta, P, Ti), which also have the characteristics of MORB and IAB, showing the lava characteristics of the SSZ-type tectonic background.The trace elements are enriched in the large ion lithophile elements Ba and U, while the high field strength elements Nb, Ta, P and Ti are obviously depleted, and have the characteristics of MORB and IAB, showing the lava characteristics of the SSZ-type tectonic background.The basalts in the the ophiolite and plagiogranite have similar rock geochemical characteristics, suggesting that they were formed in the partial melting of the basaltic magma, and the REE patterns show a flat-like curve with weak negative Eu anomalies.The LA-ICP-MS zircon U-Pb age of 342±4.7 Ma was obtained in the plagiogranite, and it is determined that the Elegen ophiolite was formed in the Early Carboniferous.Through the analysis of the tectonic setting of the ophiolite and the volcanic rocks in different ages around this area, the authors believe that the Elegen ophiolite might have been formed in the expansion stage of the post-arc basin in the Hongshishan-Baiheshan area during the southward reduction of the Paleo-Asian Ocean.In the Late Mesozoic, a series of NE-striking sinistral strike-slip faults caused the Hongshishan-Baiheshan tectonic belt to move northward to the area of Elegen.The discovery of the ophiolite explains the east extension of the Hongshishan-Baiheshan ophiolite belt, thus providing important information for the Paleozoic tectonic evolution of the Beishan area and even the whole Central Asian Orogenic Belt(CAOB).

       

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