中祁连东段乐都地区中酸性侵入岩LA-ICP-MS锆石U-Pb年龄及其构造意义  

THE ACID-INTERMEDIATE INTRUSIVE ROCKS IN THE EAST SECTION OF MIDDLE QILIAN OROGENIC BELT:LA-ICP-MS Zircon U-Pb Age and Tectonic Implications

作　　者：曹锦山 李五福[1] 王国良[1] 张新远[1] CAO Jin-shan;LI Wu-fu;WANG Guo-liang;ZHANG Xin-yuan(Key Laboratory of Geological Process and Mineral Resources in Northern Qinhai-Tibet Plateau/Qinghai Institute of Geological Survey,Xining 810012,China)

机构地区：[1]青海省青藏高原北部地质过程与矿产资源重点实验室/青海省地质调查院

出　　处：《地质与资源》2019年第5期423-433,共11页Geology and Resources

基　　金：中国地质调查局“青海区域地质调查片区总结与服务产品开发”项目（12120114079701）;中国地质调查局地质大调查“青海省民和县西沟地区三幅1∶5万区域地质矿产调查”项目（12120114041301）

摘　　要：青海省中祁连东段乐都沈家峡-碱沟一带发育有中酸性侵入体.野外地质调查和和岩相学等研究表明,侵入体呈岩株状,主要由二长花岗岩和花岗闪长岩组成,两者间呈脉动接触.对2件二长花岗岩样品进行LA-ICP-MS锆石U-Pb同位素测年,获得的加权平均年龄分别为465.7±2.2 Ma(n=24,MSWD=0.031)、459±2 Ma(n=21,MSWD=0.76),表明侵入体时代为中奥陶世.岩石地球化学特征表明,该期侵入体属准铝质-过铝质中高钾钙碱性系列岩石,岩石(La/Yb)N为10.57~23.126,δEu为0.47~0.69,稀土配分曲线具“V”型右倾特征;大离子亲石元素Rb、Ba、Th、K、La、Ce、Sm、Nd强富集,Zr、Hf弱富集,高场强元素Nb、Ta、P、Ti强亏损;岩石具有岛弧型岩浆岩特征,其形成可能与北祁连洋向南俯冲有关.The acid-intermediate intrusions are developed in Shenjiaxia-Jiangou area in the east section of Middle Qilian Mountains,Qinghai Province.The field geological survey and petrographic study show that the intrusions occur in stock,mainly consisting of monzogranite and granodiorite which are in pulsation contact with each other.The LA-ICP-MS zircon U-Pb isotopic dating of 2 monzogranite samples gains the weighted average ages of 465.7±2.2 Ma(n=24,MSWD=0.031)and 459±2 Ma(n=21,MSWD=0.76)respectively,indicating that the intrusions were formed in Middle Ordovician.The lithogeochemical characteristics reveal that the intrusions belong to quasialuminous-peraluminous medium-high K calc-alkaline series with the(La/Yb)N of 10.57-23.126 and δEu of 0.47-0.69.The REE patterns show right-dipping“V”shaped curves.The LILEs such as Rb,Ba,Th,K,La,Ce,Sm and Nd are strongly enriched,Zr and Hf weakly enriched,while the HSFEs(Nb,Ta,P and Ti)are strongly depleted.The rocks are characterized by island arc magmatite,which may be related to the southward subduction of North Qilian Ocean.

关 键 词：二长花岗岩 花岗闪长岩 LA-ICP-MS锆石U-PB年龄 岛弧 北祁连洋 青海省 

分 类 号：P597[天文地球—地球化学] P588.12[天文地球—地质学]