东天山伊吾二叠纪花岗质杂岩体的锆石定年、地球化学及其构造意义  

Zircon geochronology and geochemical characteristics of the Permian granitic complex at Yiwu,eastern Tianshan:Their tectonic significance

作　　者：汪传胜[1,2,3] 张遵忠[1] 顾连兴[1,2] 吴昌志[2] 唐俊华[1] 李中华[1,2] 冯慧[2] 雷如雄[2] 

机构地区：[1]江苏省有色金属华东地质勘查局,南京210007 [2]内生金属矿床成矿机制研究国家重点实验室,南京大学地球科学系,南京210093 [3]西北大学大陆动力学国家重点实验室,西安710069

出　　处：《岩石学报》2010年第4期1045-1058,共14页Acta Petrologica Sinica

基　　金："国土资源部百名优秀青年科技人才计划";国家重点基础研究发展规划项目(2007CB411301-4;2001CB409802);国家自然科学基金项目(40472042;40672040;40603008);西北大学大陆动力学国家重点实验室开放课题基金(06LCD02)联合资助

摘　　要：伊吾花岗质杂岩体主要由二长花岗岩和碱长花岗岩构成。锆石LA-ICP-MS U-Pb定年分析得到二长花岗岩和碱长花岗岩的侵位年龄分别为284.6±1.4Ma和284.0±1.1Ma。结合地质证据,此年龄表明该杂岩体形成于碰撞之后的二叠纪早期挤压-伸展转折阶段。岩石学、地球化学和同位素等方面的对比研究表明这两种岩石为同一岩浆演化的产物。与二长花岗岩相比,碱长花岗岩表现为硅、碱的含量较高,而铝的含量较低;富Th、U、Nb、Ta,贫Sr、P、Ti、Sm;DI和Rb/Sr升高,Nb/Ta和Zr/Hf下降,从二长花岗岩到碱长花岗岩表现出连续分异演化的趋势。计算得到二长花岗岩和碱长花岗岩的模式年龄(t_(DM))分别为693Ma和763Ma,ε_(Nd)(t)分别为+4.53和+4.64,(^(87)Sr/^(86)Sr)_i分别为0.703858和0.703855,表现出高ε_(Nd)(t)低(^(87)Sr/^(86)Sr)_i的特征。这些特征表明,伊吾岩体的岩浆来自新元古代时从亏损地幔分离出来的初生地壳源区。二长花岗岩岩浆是这种初生地壳岩浆演化的产物,而碱长花岗岩形成于二长花岗岩母岩浆经斜长石、磷灰石、钛铁氧化物、榍石、独居石、褐帘石和锆石等矿物分离结晶后的残留岩浆。The Yiwu granitic complex is mainly composed of a monzogranite and an alkali-feldspar granite phases.Zircon LA-ICPMS U-Pb dating gave ages of 284.6±1.4Ma and 284.0±1.1Ma for the monzogranite and alkali-feldspar granite,respectively, indicating their Early-Permian emplacement in accompany with post-collisional compression-extension transition.Petrological, geochemical and isotopic studies suggest that these rocks were evolution products from the same magma.In comparison with the monzogranite,the alkali-feldspar granite is higher in Si,alkai,DI and Rb/Sr,and richer in Th,U,Nb and Ta,but lower in Al,Sr, P,Ti,Sm,Nb/Ta and Zr/Hf.A continuous differentiation trend is exhibited from monzogranite to alkali-feldspar granite.Model ages (t_(DM)) are calculated to be 693Ma and 763Ma for the monzogranite and alkali-feldspar granite,respectively.Both rock types are higher inε_(Nd(t))(+4.53 and +4.64,respectively) and lower in(^(87)Sr/^(86)Sr)_i(0.703858 and 0.703855,respectively).It is suggested that the magma for the Yiwu granitic complex was produced by partial melting of a Neoproterozoic depleted-mantle-sourced juvenile mafic crust,and the alkali-feldspar granite represents the residue of the monzogranite parental magma after fractionation of plagioclase, apatite,Ti-Fe-oxides,sphene,monazite,allanite,zircon etc.

关 键 词：花岗质杂岩体 分离结晶 残留岩浆 后碰撞 东天山 

分 类 号：P588.121[天文地球—岩石学]