东天山八大石早二叠世二长花岗岩中闪长质包体的特征、锆石定年及其地质意义  

Petrologic characteristics,zircon geochronology of dioritic enclaves in Early Permian Badashi monzogranite of East Tianshan Mountains and their geological implications

作　　者：汪传胜[1,2] 张遵忠[2] 吴昌志[1] 唐俊华[2] 邵毅[2] 刘四海[1] 冯慧[1] 雷如雄[1] 

机构地区：[1]南京大学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,江苏南京210093 [2]江苏省有色金属华东地质勘查局,江苏南京210007

出　　处：《岩石矿物学杂志》2009年第4期299-315,共17页Acta Petrologica et Mineralogica

基　　金：国家重点基础研究发展规划项目(2007CB411301-4;2001CB409802);国家自然科学基金资助项目(40472042;40672040;40603008)

摘　　要：东天山八大石黑云母二长花岗岩中广泛发育闪长质包体。闪长质包体与寄主花岗岩在矿物组合上不同,但两者中同类矿物的种属相似。与寄主花岗岩相比,闪长质包体的Fe、Mg、Ti、Ca含量较高,而Na、K、Si的含量较低;富HREE、Sr,贫Ba、Th、Hf、Zr。锆石LA-ICP-MS U-Pb年龄显示闪长质包体与寄主花岗岩在形成时间上非常接近(分别为301±1Ma和298±2Ma),表明两者均形成于早二叠世。闪长质包体和寄主花岗岩具有正的εNd(t)(+4.15和+3.06)、较低的(87Sr/86Sr)i(0.70412和0.70475)和相近的模式年龄tDM(812Ma和944Ma),暗示其母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。综合岩石学、地球化学和同位素等方面的对比研究,笔者认为八大石闪长质包体属于同源包体,为寄主花岗岩同源母岩浆经结晶分异作用形成的早期产物。Dioritic enclaves are widely distributed in Badashi biotite-monzogranite of the East Tianshan Mountains. These dioritic enclaves and their host granite are different in mineral association, but species of the same mineral within them are similar to each other. In comparison with the host granite, the dioritic enclaves are higher in Fe, Mg, Ti, Ca and richer in HREE, Sr, but lower in Na, K, Si and poorer in Ba, Th, Hf, Zr. Zircon LA-ICP-MS U-Pb dating gave ages of 301 ± 1 Ma and 298 ± 2 Ma for the dioritic enclaves and their host granite, respectively, indicating their Early Permian emplacement. The dioritic enclaves and their host granite have positive in ENd（t） （ ＋ 4.15 and ＋ 3.06） values and relatively low （873r/86Sr）i（0.704 12 and 0.704 75） with fairly similar model ages （tDM） （812 Ma and 944 Ma, resl：ectively）. It is suggested that the dioritic enclaves and their host granite were derived from the same parental magma that resulted from partial melting of the Neoproterozoic depleted-mantle-sourced juvenile crust. Petrologic, geochemical and isotopic studies prove that the Badashi dioritic enclaves are autoliths and the earlier products generated by crystal fractionation of the host granite parental magma.

关 键 词：闪长质包体 同源包体 二长花岗岩 结晶分异 东天山 

分 类 号：P588.121[天文地球—岩石学] P597[天文地球—地质学]