李瑞保, 裴先治, 王兴, 陈有炘, 李佐臣, 刘成军, 王盟, 裴磊, 张玉, 颜全治, 彭思钟, 胡晨光. 祁连造山带东段中寒武世深沟组中-基性火山岩锆石U-Pb年龄、地球化学特征及构造环境[J]. 地质通报, 2018, 37(4): 589-603.
    引用本文: 李瑞保, 裴先治, 王兴, 陈有炘, 李佐臣, 刘成军, 王盟, 裴磊, 张玉, 颜全治, 彭思钟, 胡晨光. 祁连造山带东段中寒武世深沟组中-基性火山岩锆石U-Pb年龄、地球化学特征及构造环境[J]. 地质通报, 2018, 37(4): 589-603.
    LI Ruibao, PEI Xianzhi, WANG Xing, CHEN Youxin, LI Zuochen, LIU Chengjun, WANG Meng, PEI Lei, ZHANG Yu, YAN Quanzhi, PENG Sizhong, HU Chenguang. Zircon U-Pb dating, geochemical characteristics and tectonic setting of intermediate-basic volcanic rocks from Middle Cambrian Shengou Formation, eastern Qilian orogen[J]. Geological Bulletin of China, 2018, 37(4): 589-603.
    Citation: LI Ruibao, PEI Xianzhi, WANG Xing, CHEN Youxin, LI Zuochen, LIU Chengjun, WANG Meng, PEI Lei, ZHANG Yu, YAN Quanzhi, PENG Sizhong, HU Chenguang. Zircon U-Pb dating, geochemical characteristics and tectonic setting of intermediate-basic volcanic rocks from Middle Cambrian Shengou Formation, eastern Qilian orogen[J]. Geological Bulletin of China, 2018, 37(4): 589-603.

    祁连造山带东段中寒武世深沟组中-基性火山岩锆石U-Pb年龄、地球化学特征及构造环境

    Zircon U-Pb dating, geochemical characteristics and tectonic setting of intermediate-basic volcanic rocks from Middle Cambrian Shengou Formation, eastern Qilian orogen

    • 摘要: 拉脊山构造带南东端磨沟地区出露一套变安山岩夹片理化变玄武岩组合,其原岩分别为亚碱性拉斑系列安山岩和玄武岩。研究表明,变安山岩锆石U-Pb年龄为503.1±6.6Ma,形成于中寒武世。玄武岩稀土元素总量为93.40×10-6~135.39×10-6,(La/Yb)N值为2.76~3.64,δEu为0.87~1.00,微量元素蛛网图具有不相容元素富集特征,没有明显的Nb、Ta负异常,与板内火山岩特征相似。安山岩稀土元素总量低于玄武岩,而微量元素蛛网图具有富集大离子亲石元素Cs、Rb、Ba等,亏损高场强元素Nb、Ta、Ti等特征。岩石成因研究表明,玄武岩没有经历显著的地壳混染,为软流圈地幔石榴子石+尖晶石二辉橄榄岩低程度部分熔融的产物,而安山岩为地壳部分熔融的产物。构造环境判别表明,深沟组火山岩形成于大陆裂谷环境,表明祁连地块中部的拉脊山构造带南东端可能没有发育成熟的洋盆系统,随后在南祁连洋早古生代俯冲消减过程中以裂谷型岩石圈碎片的方式构造侵位于中祁连地块南缘。

       

      Abstract: There are andesites intercalated with metabasalts in the Mogou area, southeastern Lajishan mélange. Their protoliths are an-desite and basalt belonging to the sub-alkaline tholeiite series. LA-ICP-MS zircon U-Pb dating of the andesite yielded an age of 503.1±6.6Ma, suggesting Middle Cambrian. ∑REE values of basalt are 93.40×10-6~135.39×10-6, (La/Yb)N=2.76~3.64, and δEu=0.87~1.00. The spider diagram of trace elements shows similar characteristics to OIB or continental rift volcanic rock, with no obviously anomaly of δEu and enrichment of incompatible elements. The andesites have lower REE content than basalt, and the negative Eu anomalies are not obvious.The spider diagram of trace elements of andesites show the enrichment of LILEs (Cs, Rb, Ba) and depletion of HFSE (Nb, Ta, Ti). The genetic analysis suggests that the basalt resulted from low degree partial melting of garnet+spinel lherzolites without obvious crustal contamination, and andesite was derived from partial melting of the crust. Tectonic environment discrimination shows that Shengou Formation was formed in a continental rift environment. These data further indicate that southeastern termination of Lajishan belt might not have had a mature system of ocean basin in the central part of Central Qilian block. With the South Qilian Ocean subdcution in the Early Paleozoic, the Shengou Formation was emplaced on the southern margin of central Qilian block as fragments of continental rift lithosphere.

       

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