三江造山带义敦岛弧中段格聂(南)花岗岩体地球化学特征及地质意义  

Geochemical Characteristics of Southern Genie Granite in the Eastern Tibet and Its Geological Significance

作　　者：马比阿伟 木合塔尔.扎日 文登奎 张明春[3] 

机构地区：[1]新疆大学地质与矿业工程学院,乌鲁木齐830002 [2]中亚造山带大陆动力学与成矿预测自治区重点实验室,乌鲁木齐830002 [3]四川省地质调查院,成都610000

出　　处：《地质学报》2015年第2期305-318,共14页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号:41162006);中国地质调查局大调查项目(编号:121201088408)联合资助

摘　　要：夹持于甘孜—理塘结合带与金沙江结合带之间的义敦弧岩浆岩带上发育了3条纵贯南北的造山花岗岩带,其中:中带形成了由20余个岩体组成的雀而山—格聂花岗岩带和相关的银、锌、铅-锌多金属矿床。本文对格聂(南)花岗岩体进行研究,发现其岩石类型为花岗闪长岩、二长花岗岩和钾长花岗岩三类,以二长花岗岩为主体。锆石LA-ICP-MS U-Pb定年结果表明格聂花岗岩的成岩年龄为89.9±3.6Ma。地球化学研究表明,岩石中主量元素化学成分具有富硅、富铝、低钠高钾的特征,为典型的S型花岗岩。铝饱和指数ASI>1,指示岩浆源自地壳;(CaO)%/(Na2O)%值等于0.1左右,表明源岩为大陆地壳沉积岩区的泥质岩。稀土总量均值228.83×10-6,稀土配分曲线呈略右倾近直线海鸥型,与地壳熔融型花岗岩形态一致。轻重稀土分馏不明显;铕出现明显负异常(δEu=0.13),显示岩浆分异结晶作用强烈。微量元素蛛网图上明显亏损大离子亲石元素Sr;富集高场强元素U。Rb/Sr平均比值14.97,表明格聂花岗岩的源岩为上部陆壳。结合Rb-(Y+Nb)图解、(Rb/30)-Hf-(Ta×3)图解、R1-R2变异图解,格聂南岩体形成于后碰撞造山环境,应是甘孜-理塘洋盆和金沙江洋盆闭合后,造山后伸展作用活动的产物。Three N-S-trending granite belts were developed within the Yidun arc magmatic zone,which is sandwiched between Garze-Litang and Jinsha River composite tectonic zones.The middle belt,i.e.the Yuershan-Genie granite belt,is composed of more than 20 granite intrusions and related Ag,Zn,Pb-Zn deposits.Our study shows that the batholith of Genie granite can be classified into granodiorite,adamellite and potassium-feldspar granite,with the adamellite dominant in this area.Zircon LA-ICP-MS U-Pb dating for the adamellite yields a weighted mean age of 89.9±3.6Ma.Geochemical analysis shows that the Genie granite is characterized with high contents of Si,Al,K and low Na,indicating a typical to S-type granite.ASI〉1and CaO/Na2 O ratio of about 0.1indicate that the magma was sourced from continental crust and likely mudstone.The Genie granite has a total REE amount of 228.83×10-6.REE distribution curve of Genie granite is near flat,and this is in accordance with that of remelted continental crust granite.Weak fractionation of LREE and HREE and strong negative Eu anomaly（δEu=0.13）demonstrates strong crystallization differentiation.Sr depletion,U enrichment and average Rb/Sr value（14.97）indicates that the magma of Genie granite was derived from upper continental crust.Diagrams of Rb vs（Y＋Nb）,（Rb/30）-Hf-（Ta×3）,and R1 vs R2 also suggest that the Genie granite was formed in a post-orogenic and extensional tectonic setting,following closing of the Garze-Litang and the Jinsha River oceanic basins.

关 键 词：格聂 花岗岩 地球化学 岩石成因 构造环境 

分 类 号：P588.121[天文地球—岩石学]