藏南程巴岩体副矿物研究:岩浆源区的指示  

Study on accessory minerals in Yaja granite,northern Tibet:Indicator of the magma source

作　　者：周利敏[1] 侯增谦[1] 郑远川[1] 李为[2] 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]中国地质大学地球科学与资源学院,北京100083

出　　处：《岩石学报》2011年第9期2786-2794,共9页Acta Petrologica Sinica

基　　金：国家重点基础研究发展计划项目(2009CB421008;2011CB403100)资助

摘　　要：藏南程巴岩体具有埃达克岩的地球化学性质,但其形成年代、产出位置和成矿组合不同于冈底斯带成矿斑岩。利用背反射图像和电子探针成分分析发现其具有钙碱性花岗岩不常见的副矿物组合:Fe-Ti氧化物+锆石+磷灰石+榍石+独居石+钍石+氟碳铈矿+晶质铀矿+水氟碳钙钍矿,其中独居石富Th,钍石富U,独居石和钍石经富F、CO2流体交代形成氟碳铈矿和水氟碳钙钍矿。在(87Sr/86Sr)i和Th含量图解中,冈底斯带含矿斑岩与程巴岩体落在一条混合线线上,程巴岩体位于已证明受到上地壳物质或其他富集组分混染的甲马含矿斑岩和其他冈底斯含矿斑岩之间,表明程巴岩体在其源区或演化过程中也受到了富集端元的混染,但加入量少于甲马斑岩。Yaja granite occurring in southern Tibet has the geochemical characteristics of adakite,however,it is different from typical Gangdese porphyries in age,location and mineralization assemblage.Backscatter images and EPMA was conducted on Yajia granite,and results indicate an accessory mineral assemblage consisting of Fe-Ti oxide＋zircon＋apatite＋sphene＋monazite＋thorite＋bastnaesite＋uraninite＋thorbastnsite which is rare in calc-alkali granites.The apatite is rich in Th,and the thorite is rich in U.In presence of fluid enriched in F and CO2,they are altered into bastnaesite and thorbastnsite,respectively.Both accessory mineral assemblage and geochemical data suggest that Yaja granite is significantly enriched in Th and LREE.In the plot of（87Sr/86Sr）i vs.Th content,the data of Gangdese porphyries and Yaja granite form a mixing line between a depleted and an enriched end members.Jama porphyry contaminated by upper crust component is closed the enriched end member,while Yaja granite is between Jama porphyry and other Gangdese porphyries,which demonstrates that in the source or the evolution,Yaja granite was also contaminated by enriched component,but the contamination level was less than Jama porphyry.

关 键 词：独居石 钍石 混染 埃达克岩 程巴岩体 

分 类 号：P578.92[天文地球—矿物学] P588.1[天文地球—地质学]