ISSN 1009-6248CN 61-1149/P 双月刊

主管单位:中国地质调查局

主办单位:中国地质调查局西安地质调查中心
中国地质学会

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    川陕交界地区刘家坪花岗岩年代学、地球化学特征及构造意义

    Geochronological and Geochemical Study on Liujiaping Granite in the Border Area between Sichuan and Shaanxi Province and Its Tectonic Significance

    • 摘要: 对川陕交界地区刘家坪花岗岩岩体进行了系统的锆石U-Pb年代学和地球化学研究,重点讨论了岩体的成因及其构造意义。测试结果显示,刘家坪花岗岩加权平均年龄值为825.9±7.8 Ma,属新元古代中期;岩石低K富Na,显示硅过饱和,w(SiO2)%平均为75.32,并伴有过Al质特征;稀土元素丰度较低,∑REE为(182.13~243.76)×10-6,平均为197.29×10-6,显示LREE富集、HREE相对亏损的特征,稀土元素球粒陨石配分模式图表现为右倾“海鸥”型,并且具有明显的Eu负异常(δEu平均为0.57);微量元素中Nb/Ta、Rb/Sr的结果及Mg#值综合显示岩浆来源主要为下地壳物质的部分熔融。岩石具有A型花岗岩特征,形成于碰撞期后的伸展构造背景,据此推测碧口地块与扬子地块在825 Ma之前曾发生碰撞造山作用。两者的拼合模式为从北东到南西的剪刀式拼合。

       

      Abstract: The Liujiaping granite intrusion is located in Sichuan-Shaanxi border area. The study of the zircon U-Pb geochronology and the geochemistry of the granite aim at discussing its formation and tectonic significance. The results show that the crystallization age of the granite is 825.9±7.8 Ma, which belongs to the mid-Neoproterozoic. The geochemistry analysis shows that the intrusion is low in potassium and rich in sodium and silica (with the average SiO2 being 75.32%), with peraluminous characteristics. The abundance of the ∑REE varies in the range of (182.13-243.76)×10-6, with 197.29×10-6 on average, which shows an enrichment of the LREE and a depletion of the HREE. Chondrite-normalized REE patterns are of the right sea-gull oblique type with the δEu being 0.57, showing a significant negative Eu anomaly. The results of the Nb/Ta, Rb/Sr and Mg# show that the magmatic rocks of this region originated from the partial melting of the lower crust. With the characteristics of A type granites, the rock formed in the post-collision extensional tectonic setting, which indicates a collision had occurred between the Eastern Bikou terrane and the Yangtze block before 825Ma. The jointing mode of the two blocks is scissors joint from northeast to southwest.

       

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