柴达木盆地西北缘石英闪长岩的形成时代、岩石成因及地质意义  

The age,petrogenesis and geological significance of quartz diorite on the northwestern margin of Qaidam basin

作　　者：辜平阳[1,2] 陈锐明[2] 查显锋[2] 董增产[2] 庄玉军 查方勇[1] 李培庆[2] 

机构地区：[1]长安大学地球科学与资源学院西部矿产资源与地质工程教育部重点实验室,陕西西安710054 [2]中国地质调查局西安地质调查中心国土资源部岩浆作用成矿与找矿重点实验室,陕西西安710054

出　　处：《岩石矿物学杂志》2018年第1期19-33,共15页Acta Petrologica et Mineralogica

基　　金：陕西省自然科学基金项目(2017JM4001);中国地质调查局地质调查项目(1212011121193;DD20160014);国家自然科学基金项目(41002063)~~

摘　　要：柴达木盆地西北缘石英闪长岩Al2O3含量较高,全碱(Alk)含量较低,Na2O>K2O,铝饱和指数A/CNK为0.87~0.91,属钙碱性准铝质岩石系列。球粒陨石标准化的稀土元素配分曲线表现为轻稀土元素富集型,轻、重稀土元素分馏明显,Eu弱负异常;微量元素地球化学特征显示,岩石富集Rb、Th、U等大离子亲石元素,亏损Nb、Ta、P、Ti等高场强元素,Nb/La和Rb/Nb比值较低,具有I型花岗岩的特征。石英闪长岩Ca O/Na2O比值较高(2.32~2.64),结合源岩判别图解综合推断其源于变玄武岩的部分熔融。全岩Zr饱和温度计算结果显示初始岩浆温度>768℃;岩石地球化学特征表明岩浆源区压力>1.5 Ga,源岩部分熔融的残留相可能为石榴子石+角闪石+金红石。经过锆石阴极发光分析和MC-LA-ICP-MS锆石U-Pb测年,获得206Pb/238Pb加权平均年龄为252±1 Ma,代表了柴达木盆地西北缘石英闪长岩的成岩年龄。结合区域地质演化特征,认为该岩体形成于与板块俯冲有关的火山弧构造环境,是晚二叠世末期宗务隆洋壳向柴北缘欧龙布鲁克地块俯冲,变玄武岩在相对较高的温压条件下发生部分熔融形成的。The quartz diorite on the northwestern margin of Qaidam basin is characterized by high Al2O3, low Alk and Na2O〉 K2O, with alumina saturation index A/CNK being 0.87 -- 0.91. These features suggest that this quartz diorite belongs to calc-alkaline peraluminous and metaluminous rocks. The chondrite-norlnalized REE show right-inclined patterns with slightly negative Eu anomaly, and the primitive mantle normalized trace element spidergrams are characterized by enriched LILE（such as Rb, Th and U）, depleted HFSE（such as Nb, Ta, P and Ti）, low Nb/La and Rb/Nb ratios, which are comparable with the characteristics of I-type granites. High CaO/Na2O（2.32--2.64）ratios and diagrams show that the pluton was derived from remelting of the meta-morphic basalt in the lower crust. The initial temperature of magma was 〉768℃ by using whole rock Zr thermometer. Rock geochemical characteristics indicate that the pressure of the source region was probably 〉 1.5 Ca, and the residual facies was correspondingly garnet ＋ amphibole ＋ rutil. Combined with the cathodolumi- nescence （CL） images and element features of zircon, this study yielded an age of 252 ± 1 Ma for pluton using LA-ICP-MS zircon U-Pb dating. On the basis of regional geological evolution, the authors hold that Zongwulong oceanic crust subdueted toward Oulongbuluke block in Late Permian.

关 键 词：柴达木盆地西北缘 石英闪长岩 锆石U-PB测年 岩石成因 地质意义 

分 类 号：P588.122[天文地球—岩石学] P597.3[天文地球—地质学]