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现代地质 ›› 2018, Vol. 32 ›› Issue (02): 316-328.DOI: 10.19657/j.geoscience.1000-8527.2018.02.10

• 岩石学 • 上一篇    下一篇

西秦岭西段共和盆地周缘西功卡花岗闪长岩体锆石U-Pb年龄、地球化学特征及其构造意义

杨瀚文1,2(), 申俊峰2(), 魏立勇1, 张振1, 刘满年1, 冯博鑫1, 张洛宁3   

  1. 1.中国人民武装警察部队黄金第五支队,陕西 西安 710100
    2.中国地质大学(北京) 地球科学与资源学院,北京 100083
    3.河北省地质调查院,河北 石家庄 050081
  • 收稿日期:2017-11-25 修回日期:2018-02-11 出版日期:2018-04-10 发布日期:2018-05-07
  • 通讯作者: 申俊峰,男,教授,博士生导师,1962年出生,矿物学、岩石学、矿床学专业,主要从事成因矿物学与找矿矿物学方面的研究工作。Email:shenjf@cugb.edu.cn
  • 作者简介:杨瀚文,男,助理工程师,1992年出生,矿物学、岩石学、矿床学专业,主要从事环境与生命矿物学方面的研究工作。Email:306134832@qq.com
  • 基金资助:
    中国地质调查局地质矿产调查项目(1212011220660)

Zircon U-Pb Ages, Geochemical Characteristics and Tectonic Implications of Xigongka Granodiorite Around Gonghe Basin, West of Western Qinling Mountains

YANG Hanwen1,2(), SHEN Junfeng2(), WEI Liyong1, ZHANG Zhen1, LIU Mannian1, FENG Boxin1, ZHANG Luoning3   

  1. 1. No.5 Gold Geological Party of PAP, Xi’an, Shaanxi 710100,China
    2. School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China
    3. Hebei Geological Survey Institute, Shijiazhuang, Hebei 050081, China
  • Received:2017-11-25 Revised:2018-02-11 Online:2018-04-10 Published:2018-05-07

摘要:

西功卡花岗闪长岩体位于西秦岭西段的共和盆地周缘。对该岩体进行了系统的岩相学、锆石U-Pb年代学和岩石地球化学研究。锆石LA-ICP-MS U-Pb年龄为(227.2±7.3) Ma(MSWD=2.0),代表岩体侵位时间。西功卡岩体具有高硅(SiO2=69.86%~70.94%)、富钾(K2O= 3.20%~4.08%)、富碱(K2O+Na2O=5.61%~7.03%)、弱过铝质(A/CNK=0.99~1.20)特征,属于高钾钙碱性Ⅰ型花岗岩。西功卡岩体富集K、Rb、Ba、Th、U等大离子亲石元素,亏损Nb、Ta、Ti、P等高场强元素,轻重稀土元素分馏较明显(LREE/HREE=11.04~13.13),具有中等Eu负异常(δEu=0.72~ 0.84)。岩石地球化学特征表明,西功卡花岗闪长岩主要由壳源物质熔融形成,结合前人研究成果,笔者认为,西功卡岩体形成于晚三叠世,与区域其他岩体年龄基本一致,均形成于后碰撞构造环境,为同一构造-岩浆事件的产物。研究表明,西秦岭造山带西段共和盆地周缘于晚三叠世进入后碰撞构造演化阶段,该认识对西秦岭造山带构造-岩浆事件演化过程提供了新的约束。

关键词: 锆石U-Pb年龄, 地球化学, 构造环境, 西功卡花岗闪长岩, 共和盆地, 西秦岭

Abstract:

Xigongka granodiorite is located in Gonghe Basin, west of the Western Qinling mountains Orogenic Belt, and the main composition of rock is gray, fine-grained, block granodiorite. In this paper,we carried out the petrography, zircon U-Pb geochronology and geochemistry of Xigongka granodiorite. Zircon LA-ICP-MS U-Pb dating yielded a weighted mean age of (227.2±7.3) Ma, which is interpreted as the emplacement age of the Xikongka intrusion.The Xigongka intrusion is weakly peraluminous and high-K calc-alkaline with A/CNK values of 0.99-1.20 and high contents of SiO2(69.86%-70.94%),K2O(3.20%-4.08%),K2O+Na2O(5.61%-7.03%), and belongs to I-type granite. It is characterized by enrichment in LILE(such as K, Rb, Ba, Th, U), and by depletion in HFSE(such as Nb, Ta, Ti, P) with high LREE/HREE ratios of 11.04-13.13 and moderate negative Eu anomalies (δEu=0.72-0.84). The geochemical characteristics of the Xigongka granodiorite suggested that it was partial melting of crustal components. In combination with previous studies, the Xigongka intrusion was formed in the Late Triassic,which is consistent with the ages of other intrusions in the region. Therefore, they were all formed in the same tectonic environment of post-collision. This finding indicated that the west part of Western Qinling Orogen turned into the tectonic environment of post-collision in the Late Triassic and it also provided new constraints on the tectono-magmatic evolution of Gonghe Basin in Western Qinling Orogen.

Key words: zircon U-Pb geochronology, geochemistry, tectonic setting, Xigongka granodiorite, Gonghe Basin, western Qinling mountains

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