西秦岭天水地区志留纪利桥花岗岩的岩石成因——来自地球化学和锆石U-Pb年代学与Hf同位素的约束
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P588.12+1;P597

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中国地质调查局地质调查项目(DD20221649);国家自然科学基金项目(42072237)


Petrogenesis of the Silurian Liqiao granites in the Tianshui area, West Qinling: Constraints from geochemistry, zircon U-Pb geochronology and Hf isotope
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    摘要:

    花岗岩在探讨大陆地壳生长与演化、造山带的形成及地球动力学演化等方面具有重要的意义。西秦岭天水地区利桥花岗岩主要由斜长石、石英、钾长石和黑云母等矿物组成,锆石U-Pb年代学表明岩体结晶年龄为439±3 Ma。利桥花岗岩具有高硅、富碱的特征,其铝饱和指数A/CNK值介于1.01~1.16之间,属于弱过铝质高钾钙碱性-钙碱性花岗岩。利桥花岗岩富集K、Ba等大离子亲石元素和La、Ce等轻稀土元素,亏损Nb、Ta和Ti等高场强元素,显示具有俯冲带岛弧岩浆岩的地球化学特征。利桥花岗岩具有较低的Mg#值(25~41),且La/Yb-La、La/Sm-La图解显示该花岗岩在形成明显与部分熔融作用相关,此外岩体中的镁铁质微粒包体和正的锆石εHf(t)值,表明这些花岗岩在形成过程中有幔源物质的贡献。结合区域地质背景,我们认为利桥花岗岩是弧-陆碰撞前俯冲洋壳中先存的基性岩或新生地壳发生部分熔融所致,当然也不排除其为大陆边缘弧增厚下地壳部分熔融的产物。

    Abstract:

    Granite plays an important role in exploring the growth and evolution of continental crust as well as the geodynamics of orogenic belts. The Liqiao granite in the Tianshui area, West Qinling Orogen, is mainly composed of plagioclase, quartz, K-feldspar, and biotite. Zircon U-Pb dating shows that the crystallization age of the granite is 439 ±3 Ma. Geochemistry suggests that the granite contains high silicon and alkali, and it belongs to the peraluminous to high potassium calc-alkaline series. The granite is rich in large ion lithophilic elements (e.g. K and Ba), light rare earth elements (e.g. La and Ce), and depleted in high field strength elements such as Nb, Ta, and Ti, which shows the geochemical characteristics of island arc magmatic rocks. Furthermore, the granite in the Liqiao area shows low Mg# values (25~41), and the La/Yb-La and La/Sm-La diagrams show that the formation of the granite is related to partial melting. In addition, the existence of microgranular enclaves in the host rock mass and the positive εHf(t) values of zircons indicate that the formation of these granites is influenced by mantle-derived materials. Combined with the regional geological background and the results in this study, we believe that the Liqiao granite was formed by partial melting of the juvenile basaltic lower crust before the arc-continental collision. Certainly, it cannot be ruled out that it was the product of partial melting of the thickened of the continental marginal arc.

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李国倩,周开,李云帅,张建新,武亚威,郭祺,毛小红,2024,西秦岭天水地区志留纪利桥花岗岩的岩石成因——来自地球化学和锆石U-Pb年代学与Hf同位素的约束[J].岩石矿物学杂志,43(2):330~343. LI Guo-qian, ZHOU Kai, LI Yun-shuai, ZHANG Jian-xin, WU Ya-wei, GUO Qi, MAO Xiao-hong,2024,Petrogenesis of the Silurian Liqiao granites in the Tianshui area, West Qinling: Constraints from geochemistry, zircon U-Pb geochronology and Hf isotope[J]. Acta Petrologica et Mineralogica,43(2):330~343.

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  • 收稿日期:2023-12-17
  • 最后修改日期:2024-01-30
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  • 在线发布日期: 2024-03-16
  • 出版日期: 2024-03-25