东昆仑祁漫塔格早奥陶世岛弧：中基性火成岩地球化学、Sm-Nd同位素及年代学证据  

Early Ordovician island arc of Qimantag Mountain,eastern Kunlun:Evidences from geochemistry,Sm-Nd isotope and geochronology of intermediate-basic igneous rocks

作　　者：崔美慧[1] 孟繁聪[1] 吴祥珂[1,2] 

机构地区：[1]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 [2]中国地质大学,北京100083

出　　处：《岩石学报》2011年第11期3365-3379,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：祁漫塔格山西段鸭子泉祁漫塔格群中发育有中基性火成岩,岩石类型主要为角闪辉长岩、闪长岩、玄武岩及安山岩。其主要地球化学及同位素特征为:(1)基性岩样品的SiO2含量为47.93%～50.54%,MgO为3.40%～6.24%,全铁FeOT为11.24%～14.10%,主要为拉斑玄武岩系列;中性岩样品的SiO2含量为51.5%～59.59%,MgO为2.05～6.42%,全铁FeOT含量为5.65%～9.38%,属于拉斑-钙碱性系列岩石组合;(2)基性及中性火成岩稀土配分型式均为LREE富集的右倾型,(La/Yb)N为1.44～11.69;(3)富集大离子亲石元素Sr、Ba、Th、U,而相对亏损高场强元素P、Zr、Ti等,Nb为明显的负异常,而Ta显示弱负异常;(4)εNd(t=480Ma)介于+1.1～+7.9之间,表明该中基性火成岩在形成过程中受到过俯冲地壳物质的混染。上述特征说明鸭子泉中基性火成岩可能形成于岛弧环境。对闪长岩样品中的锆石进行LA-ICP-MSU-Pb同位素分析,获得206Pb/238U加权平均年龄为480±3Ma,代表了闪长岩的形成时间,这表明在早奥陶世祁漫塔格洋已经存在并开始俯冲,形成鸭子泉岛弧火成岩。Intermediate-basic igneous rocks,including hornblende gabbros,basalts,diorites and andesites,were found in Qimantag Group of Yaziquan area,west of Qimantag Mountain.The main geochemistry and isotope characteristics are as follows：（1） basic igneous rocks show SiO2 47.93%～50.54%,MgO 3.40%～6.24% and total Fe（FeOT） 11.24%～14.10%,belonging to tholeiitic rocks;intermediate rocks are of SiO2 51.5%～59.59%,MgO 2.05～6.42%,total Fe（FeOT） 5.65%～9.38%,belonging to tholeiitic and calc-alkalic rocks;（2） REE patterns show that both basic and intermediate igneous rocks are enriched in LREEs,with（La/Yb）N=1.44～11.69;（3） Enriched in LILEs（like Sr,Ba,Th,U） and depleted in HFSEs（P,Zr,Ti）,especially Nb and Ta negative anomaly;（4） εNd（t=480Ma） is from ＋1.1 to ＋7.9,showing that they were contaminated with subducted crustal materials.The characteristics above show that these intermediate-basic igneous rocks formed in an island arc setting.Zircon U-Pb dating for a diorite sample yields ages of 480±3Ma,representing the rock forming age.Indicating that the Qimantag oceanic basin already exist in Early Ordovician and began subducting then,leading to the formation of island arc igneous rocks in Yaziquan.

关 键 词：地球化学 SM-ND同位素 锆石U-PB定年 中基性火成岩 鸭子泉 

分 类 号：P588.4[天文地球—岩石学]