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.
出处
《岩石矿物学杂志》
CAS
CSCD
北大核心
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)~~
