| 冈底斯南缘拉隆地区变形花岗岩地质特征及其构造意义 |
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| 作者姓名： | 唐华 陈永东 魏龙 李宁 |
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| 作者单位： | 1.四川省地质矿产勘查开发局川西北地质队,绵阳 621000; 2.成都理工大学沉积地质研究院,成都 610000 |
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| 基金项目： | 中国地质调查局“西藏尼木地区1:5万区域地质调查(编号: 121201010000150014-07)”项目资助 |
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| 摘 要： | 冈底斯岩浆弧中发育了1条重要的韧性剪切带,为深入了解该韧性剪切带上变形花岗岩的成因、变形作用及其性质,对冈底斯南缘拉隆地区变形花岗岩开展了地球化学、变形构造和锆石U-Pb同位素年代学研究。通过对冈底斯南缘拉隆地区出露的变形花岗岩进行实测地质剖面测制及野外地质填图,发现变形花岗岩呈近EW向展布,北侧与中生代麻木下组呈断层接触,其余被第四系覆盖。岩石类型主要为英云闪长岩,属于高硅钙碱性系列岩石。SiO2含量为66.2%~71.0%,平均值为68.3%,全碱(Na2O+K2O)含量、Al2O3含量和MgO含量均较高,轻稀土元素总量(∑LREE)大于重稀土元素总量(∑HREE),Rb、Th等大离子亲石元素富集,Ta、Zr、Nb等高场强元素亏损,Sr含量高,Y含量低,Sr/Y为73.02~99.05,整体显示具有埃达克质岩石的特征属性。变形花岗岩LA-ICP-MS锆石U-Pb年龄为(83.56±0.83) Ma,为晚白垩世,代表了其岩浆结晶形成的年龄。变形花岗岩主要为新特提斯洋壳向北俯冲削减背景下,增厚的下地壳部分熔融形成的产物,在中新世28~13 Ma遭受了近EW向左旋剪切、向北滑覆的韧性剪切变形作用。
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| 关 键 词： | 变形花岗岩 埃达克质岩石 锆石U-Pb年龄 剪切变形作用 新特提斯洋 |
| 收稿时间： | 2019-06-23 |
Geological characteristics and tectonic implications of the deformed granite in Lalong area in the southern margin of Gangdise |
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| Authors: | TANG Hua CHEN Yongdong WEI Long LI Ning |
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| Institution: | 1. Northwestern Sichuan Geological Team, Bureau of Geology and Mineral Resources Exploration and Development of Sichuan Province,Mianyang 621000, China; 2. Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu 610000, China |
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| Abstract: | In the Gangdise magmatic arc develops an important ductile shear zone. In order to peer deeper into the genesis of the deformed granite and its deformation and properties, the authors studied the whole rock geochemistry, deformation structure and zircon U-Pb geochronology of the deformed granite in Lalong area in the southern margin of Gangdise. It is found that the deformed granite is distributed in nearly EW direction, the north side contacts with Mesozoic Mamuxia Formation along a fault,and the rest is covered by Quaternary system,after the geological profile measurement and field geological mapping of the deformed granite exposed in Lalong area in the southern margin of Gangdise.The main rock type is tonalite, belonging to high silica calc alkaline series. SiO2 content ranges from 66.2% to 71.0%, with an average of 68.3%. The content of total alkali (Na2O + K2O) is higher,so is the content of Al2O3 and MgO.The content of light rare earth elements (∑LREE) is higher than that of heavy rare earth elements (∑HREE). Rb, Th and other large ion lithophile elements are enriched, while Ta, Zr, Nb and other high field-strength elements are depleted. Sr content is high, Y content is low, and Sr/Y value is 73.02~99.05. All shows that the rock has the adakitic rock characteristics. The LA-ICP-MS zircon U-Pb age of the deformed granite is (83.56±0.83) Ma, which is the late Cretaceous and represents the magmatic crystallization age.The deformed granite was mainly formed by partial melting of the thickened lower crust under the background of northward subduction and reduction of Neo-Tethys Ocean. During Miocene 28~13 Ma, the deformed granite underwent nearly EW trending left-lateral shear and northward slip ductile shear deformation. |
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| Keywords: | deformed granite Adakitic rock Ziron U-Pb shear deformation Neo-Tethys Ocean |
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