中祁连苏里地区新元古代辉绿岩墙群LA-ICP-MS锆石U-Pb年龄及其地质意义
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P588.12+4;P597+.3

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青海学者专项(QHS201802);国家自然科学基金资助项目(41762006)


The zircon LA-ICP-MS U-Pb age of the Late Proterozoic diabase dyke in the Suli area of middle Qilian and its geological significance
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    摘要:

    中祁连西段苏里地区有大量北东和近东西向延伸的辉绿岩、辉长岩呈岩墙状侵入到元古宙地质体中。基性岩墙的SiO2含量为46.77%~52.37%,Al2O3含量为12.82%~15.86%,TiO2含量为1.16%~3.14%,MgO含量为3.84%~7.98%,FeOT含量为10.42%~15.53%,以贫K2O (0.10%~1.60%)、Na2O>K2O为特征,里特曼指数σ=0.67~2.96,岩石主量元素地球化学成分与大洋拉斑玄武岩一致;全岩稀土元素总量较低(51.28×10-6~165.11×10-6),轻重稀土元素之比为2.67~4.90,(La/Yb)N值为2.04~5.03,属轻稀土元素富集型,δEu=0.93~1.12,无明显的Eu异常;富集Rb、Ba、Th、U,亏损Nb和K,大离子亲石元素丰度变化范围相对较宽,高场强元素富集程度不强,微量元素蛛网图上具有左侧隆起、右侧相对平坦的分布型式。基性岩墙LA-ICP-MS锆石U-Pb年龄为819.5±5.2 Ma,形成时代与全球性Rodinia超级大陆裂解时代高度一致。岩石地球化学分析结果显示岩浆起源于亏损地幔源区,是尖晶石地幔橄榄岩部分熔融的产物,岩浆形成于陆内裂谷环境,表明其可能为Rodinia超级大陆裂解的产物。

    Abstract:

    Lots of diabase and gabbro in the Suli area of the west segment of middle Qilian invaded into the Proterozoic geological bodies in the form of dykes. The previous studies of the basic magmatic rocks in this area were relatively insufficient and hence there are rare relevant reports. The content of SiO2, Al2O3 and TiO2 in the basic dyke are 46.77%~52.37%, 12.82%~15.86% and 1.16%~3.14%, respectively, characterized by high MgO (3.84%~7.98%) and FeOT(10.42%~15.53%), and poor K2O (0.10%~1.60%) and P2O5 with Na2O higher than K2O. The total rare earth content of the whole rock is low (51.28×10-6~165.11×10-6), the ratio of light rare earth to heavy rare earth is between 2.67 and 4.90, and the (La/Yb)N ratio is between 2.04 and 5.03. The rocks are of light rare earth enrichment type, Eu=0.93~1.12, without obvious Eu anomaly. They are characterized by enrichment of Rb, Ba, Th and U and depletion of Nb and K; in addition, large ionic lithophile element abundance range is relatively wide, high field strength element enrichment degree is not strong, and trace element ratio on the cobweb diagram exhibits the pattern of an uplift on the left and relatively flat on the right, with the geochemical performance exhibiting the obvious characteristics of intraplate basalt. The LA-ICP-MS zircon U-Pb age is 819.5±5.2 Ma, and its formation age is older than that of the global Rodinia supercontinent. The results of rock geochemical analysis show that the magma originated from depleted mantle source area, probably being the product of partial melting of spinel mantle peridotite. The magma was formed in an intracontinental rift environment, indicating that it may have been the product of the breakup of Rodinia supercontinent.

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张金明,才航加,陈光庭,田成秀,雷晓清,2020,中祁连苏里地区新元古代辉绿岩墙群LA-ICP-MS锆石U-Pb年龄及其地质意义[J].岩石矿物学杂志,39(6):769~779.

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  • 收稿日期:2020-05-11
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  • 在线发布日期: 2020-11-13
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