甘肃北山红石山地区晚石炭世英云闪长岩锆石U- Pb年龄、地球化学特征及构造意义
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本文为中国地质调查局“北山图拉尔根—辉铜山地区区域地质调查”项目(编号: DD20190812)的成果


Zircon U- Pb age, geochemical characteristics and tectonic significance of the Late Carboniferous tonalites from Hongshishan area, Beishan Mountains, Gansu
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    摘要:

    笔者等以出露于红石山—百合山蛇绿混杂岩带南侧的英云闪长岩体为研究对象,通过野外地质调查和岩石学、地球化学、锆石LA- ICP- MS U- Pb年代学研究,探讨其成因、构造环境及红石山洋俯冲消亡过程。岩石地球化学研究表明,红石山南英云闪长岩体富硅(SiO2=63. 95%~66. 22%)、高铝(Al2O3=15. 31%~16. 61%)、富钠(Na2O=3. 73%~4. 33%)、低钾(K2O=1. 00%~1. 85%),相对高锶(Sr=246. 0×10-6~417. 0×10-6)、低钇(Y=8. 83×10-6~11. 80×10-6),富集Rb、Sr等大离子亲石元素和LREE,亏损Nb、Ta、Ti、P等高场强元素,HREE相对亏损,无明显Eu异常。岩石学和岩石地球化学特征表明,为俯冲洋壳脱水熔融的产物。锆石LA- ICP- MS U- Pb测年表明,红石山南英云闪长岩体的形成年龄为306. 9~309. 9 Ma,表明该岩体侵位于晚石炭世,反映了红石山—百合山缝合带晚石炭世大洋俯冲带岩浆作用事件,进一步约束了红石山洋俯冲时限。结合红石山—百合山缝合带石炭纪蛇绿岩、石炭纪—二叠纪岛弧型岩浆岩和早二叠世末期(275 Ma)的辉长岩和花岗岩侵位及早—中二叠世双堡塘组下部的角度不整合均反映了红石山洋盆的闭合过程(辛后田等,2020),表明红石山洋盆在晚石炭世并未关闭,而是处于大洋俯冲消减和陆壳增生过程中。

    Abstract:

    We found Late Carboniferous tonalites in the south of Hongshishan SSZ- type ophiolitic melange. This paper discuss their geological characteristics, genesis and tectonic environment, combining with the relationship between spatiotemporal distribution and evolution of Late Paleozoic SSZ ophiolite, island- arc magmatic rocks in Hongshishan—Baiheshan suture zone. We summarize regional tectonic evolution, so as to provide some chronological constraints for subduction, extinction of Hongshishan ocean and continental crust accretion process. Methods: Based on field geological survey, petrology, geochemistry and LA- ICP- MS zircon U- Pb geochronology of the tonalites in the south of Hongshishan, this paper discusses the petrogenesis and tectonic setting of the tonalites, and the final closure time and subduction process of the Hongshishan Ocean. Results: The tonalites in the south of Hongshishan are characterized by high silicon w(SiO2)=63. 95%~66. 22%, rich aluminum w(Al2O3)=15. 31%~16. 61%, rich sodium and poor potassium, A/CNK=0. 98~1. 45. Zircon U- Pb dating shows that the tonalites in the south of Hongshishan were emplaced in Late Carboniferous, with age of 306. 9~309. 9 Ma, in the northern Beishan orogenic belt, which is the Late Carboniferous. Conclusions: The contents of Zr, Nb, Ce and Zr+Nb+Ce+Y of the rock samples in this paper are all lower than the lower limit of A- type granite, and the samples fall into the area of undifferentiated granite in the discriminant diagram of granitoid genetic type and show the characteristics of I- type granite. The rocks are enriched in Rb, Ba, Th and La, and depleted in high field strength elements such as Nb, Ta, P, Ti and Eu. In terms of chemical composition, the values of Mg# are relatively low (0. 42 ~ 0. 52), and the degrees of differentiation are relatively low (D.I.=64. 5 ~ 73. 5). They were formed in the island arc environment during the oceanic crust subduction period.

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郑小明,管诰,王宏伟,刘志强,袁鸣.2023.甘肃北山红石山地区晚石炭世英云闪长岩锆石U- Pb年龄、地球化学特征及构造意义[J].地质论评,69(1):219-233,[DOI].
ZHENG Xiaoming, GUAN Gao, WANG Hongwei, LIU Zhiqiang, YUAN Ming.2023. Zircon U- Pb age, geochemical characteristics and tectonic significance of the Late Carboniferous tonalites from Hongshishan area, Beishan Mountains, Gansu[J]. Geological Review,69(1):219-233.

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  • 收稿日期:2022-03-02
  • 最后修改日期:2022-11-14
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  • 在线发布日期: 2023-01-20
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