青海祁漫塔格玛兴大坂晚三叠世花岗岩年代学、地球化学及Nd-Hf同位素组成  

Zircon U-Pb dating,geochemistry and Nd-Hf isotopic compositions of the Maxingdaban Late Triassic granitic pluton from Qimantag in the eastern Kunlun

作　　者：吴祥珂[1,2] 孟繁聪[2] 许虹[1] 崔美慧[2] 

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,大陆构造与动力学国家重点实验室,北京100037

出　　处：《岩石学报》2011年第11期3380-3394,共15页Acta Petrologica Sinica

基　　金：中国地质调查局项目(1212010918003);创新研究群体科学基金项目(40921001)联合资助

摘　　要：青海东昆仑祁漫塔格玛兴大坂岩体岩石类型为二长花岗岩,主要矿物组合为斜长石(30%～35%)+钾长石(25%～33%)+石英(23%～25%)+黑云母(3%～5%),全岩地球化学总体显示SiO2为68.61%～69.37%,K2O为3.95%～4.08%,P2O5为0.11%～0.12%,FeOT/MgO为4.02～4.21,A/CNK(0.96～0.99)<1,为高钾钙碱性系列准铝质花岗岩,具有I型花岗岩的特征。其稀土元素配分图和蛛网图显示具有大陆弧花岗岩特点,富集Rb、Th等大离子亲石元素,而相对亏损Sr、P、Ti、Nb和Ta等元素;玛兴大坂二长花岗岩的143Nd/144Nd比值为0.512326～0.512340、εNd(t)=-2.5～-3.2,指示该花岗岩具有壳幔混合I型花岗岩的特征;锆石LA-MC-ICP-MSU-Pb年龄数据显示玛兴大坂二长花岗岩体的侵位时代为218±2Ma;锆石176Hf/177Hf比值较低(0.28251～0.282623),εHf(t)值为-4.43～-0.62,可能为幔源物质(大的正εHf(t)值)与古老地壳物质(大的负εHf(t)值)混合后的结果。Nd同位素tDM2(1.20～1.25Ga)与Hf同位素tDM2(1.08～1.28Ga)基本一致,推测中元古代末期祁漫塔格地区存在壳幔分异作用,而玛兴大坂二长花岗岩的部分源岩为中元古代以前的物质。认为玛兴大坂二长花岗岩与祁漫塔格晚三叠世火山岩形成时代相近,响应于三叠纪末古特提斯洋的关闭。The main rock type of Maxingdaban granitic pluton from Qimantag of Qinghai in the eastern Kunlun is monzogranite.It consists of plagioclase（30%～35%）＋K-feldspar（25%～33%）＋quartz（23%～25%）＋biotite（3%～5%）.Whole-rock analysis shows SiO2 68.61%～69.37%,K2O 3.95%～4.08%,P2O5 0.11%～0.12%,FeOT/MgO 4.02～4.21,A/CNK（0.96～0.99）1,which must be high-K calc-alkaline series metaluminous granite.It represents the features of I-type granite.According to REE partition diagram and spider diagram,the granite shows a marked chemical resemblance to continental arc granite,exhibiting enrichment in LILEs such as Rb and Th,but depletion in HFSEs such as Sr,P,Ti,Nb and Ta.143Nd/144Nd（0.512326～0.512340） and εNd（t）（-2.5～-3.2） imply the monzogranite shares the characters of crust-mantle mixed I-type granite.Based on LA-MC-ICP-MS zircon U-Pb dating,the emplacement of Maxingdaban monzogranitic pluton occurred at 218±2Ma.Zircon 176Hf/177Hf ratio is low（0.282517～0.282623）,εHf（t） is-4.43～-0.62,which may indicate a mixture with mantle source（large positive εHf（t）） and ancient crust（large negative εHf（t））.The accordance of tDM2（1.20～1.25Ga） of Nd and tDM2（1.08～1.28Ga） of Hf leads to the conclusion that the crust-mantle differentiation occurred at Mesoproterozoic in Qimantag and indicates the source of the granite may be partly from the pre-Mesoproterozoic materials.It is suggested that the Maxingdaban monzogranitic pluton emplaced at the same time with the Qimantag Late Triassic volcanic rock,when the Paleo-Tethys Ocean closed.

关 键 词：U-PB年龄 地球化学 Nd-Hf同位素 二长花岗岩 玛兴大坂 祁漫塔格 

分 类 号：P588.121[天文地球—岩石学]