阿拉善雅布赖山二叠纪中酸性岩浆岩年代学、地球化学、锆石Hf同位素特征及构造意义  

Geochronology, geochemistry and zircon Hf isotope of the Permian intermediateacid igneous rocks from the Yabulai Mountain in western Alxa, Inner Mongolia, and their tectonic implications

作　　者：叶珂[1,2] 张磊[2] 王涛[2] 史兴俊[2,3] 张建军[1,2] 刘超[1,2] YE Ke ZHANG Lei WANG Tao SHI Xing-jun ZHANG Jian-jun LIU Chao(China University of Geosciences, Beijing 100083, China Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China Faculty of City and Environmental Science, Xinyang Normal University, Xinyang 464000, China)

机构地区：[1]中国地质大学,北京100083 [2]中国地质科学院地质研究所,北京100037 [3]信阳师范学院城市与环境科学学院,河南信阳464000

出　　处：《岩石矿物学杂志》2016年第6期901-928,共28页Acta Petrologica et Mineralogica

基　　金：中国地质调查局资助项目(DD20160123;12120113094000;1212011120115)~~

摘　　要：雅布赖山位于内蒙古自治区阿拉善盟西部,该地区广泛出露中酸性岩浆岩。锆石LA-ICP-MS U-Pb测年显示,雅布赖山花岗质岩石形成于早中二叠世,其中花岗闪长岩年龄为280±1 Ma,正长花岗岩年龄为286±1 Ma,英安岩年龄为275±2 Ma,英云闪长岩年龄为272±1 Ma。正长花岗岩个别锆石的εHf(t)值为正值,大多数低于0[εHf(t)=-5.8^+1.8],暗示其可能起源于新生地壳物质或形成过程中有亏损地幔物质的加入,而花岗闪长岩[εHf(t)=-13.0^-8.1]、英云闪长岩[εHf(t)=-10.1^-3.3]和英安岩[εHf(t)=-15.2^-4.9]中锆石的εHf(t)值均低于0,表明这些岩浆岩的源区主要为古老的地壳物质,这与典型的古老陆块上发育的酸性岩浆岩一致。地球化学分析结果表明,该地区花岗闪长岩和正长花岗岩具有相似的微量和稀土元素组成,都显示出轻稀土元素相对富集和重稀土元素相对亏损的特征,并具有微弱-中等的Eu负异常;而英云闪长岩则具有一定程度的Eu正异常,且相比前两者具有较高的Sr/Y值(>300)。排除岩浆在侵位过程中围岩同化混染作用的影响,中上地壳酸性侵入岩的结晶分异作用难以形成如此高的Sr/Y值,因而英云闪长岩高Sr/Y值特征可能是源区特征的反映。因斜长石、角闪石和黑云母均不能显著影响Sr/Y值,所以造成英云闪长岩与花岗闪长岩和正长花岗岩地球化学差异的原因可能是其源区较深而存在石榴子石残留。结合前人研究,雅布赖山地区及其以东的诺尔公-狼山一带以及华北克拉通北缘广泛分布的晚古生代岩浆岩形成了一条近东西向展布的岩浆岩带。其中,雅布赖山二叠纪岩浆岩可能形成于宗乃山-沙拉扎山构造带和雅布赖-诺尔公-红古尔玉林构造带拼合的碰撞或碰撞后环境。Located in the western part of Inner Mongolia, the Yabulai Mountain possesses extensively exposed intermediate-felsic plutons and some felsic volcanic rocks. Zircon U-Pb dating indicates that the granitic rocks from the Yabulai Mountain were formed in the Early to Middle Permian, as evidenced by the data from granodiorite （280±1 Ma）, K-feldspar granite （286±1 Ma）, tonalite （272±1 Ma）, and dacite （275±2 Ma）. In the K-feldspar granite, only a few zircon grains show positive εHf（t）, and εHf（t） of most zircons is below 0, implying that some juvenile crustal materials or depleted mantle materials were involved in the generation of the rocks. In granodiorite, tonalite and dacite, zircons are all characterized by εHf（t） lower than 0. Zircon Hf isotope indicates that the sources of these igneous rocks were mainly old crustal materials, and this feature is similar to that of felsic igneous rocks from cratons. The Early Permian granodiorite and the Early Permian K-feldspar granite share similar major and trace element compositions, and REE patterns of granodiorite and K-feldspar granite are high in LREEs and low in HREEs, with weak to moderate Eu negative anomalies. The Middle Permian tonalite exhibits positive Eu anomaly and higher Sr/Y ratios （〉300） than the granodiorite and the K-feldspar granite. The high Sr/Y ratio feature of the tonalite suggests that the tonalite might have been generated in the lower crust, with no assimilation/contamination of country rocks or fractionation of felsic magma in the upper crust. Because the presence of plagioclase, amphibole and biotite cannot significantly affect the Sr/Y ratio of the equilibrium melt, the differences of geochemistry between the granodiorite, K-feldspar granite and the tonalite may be attributed to the fact that the source of the tonalite was deeper and the garnet was present in the source. Combined with previous studies, the authors hold that the Permian magmatism probably formed a nearly EW-trending magmatic rock belt along

关 键 词：岩浆岩 锆石U-Pb年龄 HF同位素 地球化学 雅布赖山 阿拉善 

分 类 号：P588.12[天文地球—岩石学] P597[天文地球—地质学]