中祁连西段东干沟闪长岩地质地球化学特征及构造意义  

Zircon U-Pb Ages of the Late Jurassic Diorite from the Central Qilian Mountains of Suliarea and Its Geological Significance

作　　者：张金明[1] 付彦文 田成秀[1] ZHANG Jinming;FU Yanwen;TIAN Chengxiu(Qinghai Province Key Laboratory of Geological Process and Mineral Resources of Northern Qinghai-Tibet Plateau, Qinghai Institute of Geological Survey, Xining 810012, Qinghai, China)

机构地区：[1]青海省地质调查院青海省青藏高原北部地质过程与矿产资源重点实验室,青海西宁810012

出　　处：《西北地质》2018年第2期18-25,共8页Northwestern Geology

基　　金：青海省科技厅"柴达木盆地南北缘成矿系统与勘查开发示范"(2016-SF-A3);青海省天峻县苏里地区1:5万五幅区调(1212011140088)

摘　　要：对中祁连西段苏里地区的闪长岩所进行的时代及地球化学研究发现,该闪长岩形成时代为(155.1±1.4)Ma。岩石地球化学分析结果显示,常量元素Al_2O_3含量为13.37%~13.55%;Fe_2O_3含量为5.37%~5.90%;FeO含量为5.64%~6.20%;MnO含量为0.11%~0.16%;MgO含量为1.85%~2.16%,CaO含量为5.15%~5.67%,Na_2O含量为3.13%~3.58%,K_2O含量为1.39%~1.54%。具富铁富钙贫硅贫铝的特点,A/CNK=0.75~0.83,σ=1.32~1.41,为准铝质钙碱性系列,稀土总量较高,ΣREE=291.44×10^(-6)~319.87×10^(-6),明显具有壳源岩浆岩特征。LREE/HREE=5.06~6.11表现为轻稀土强烈富集的特点,δEu=0.86,(La/Yb)_N值大于1,为5.33~7.2。微量元素表现出明显的Ba、K、Sr、Ti等元素的负异常,而Rb、Th、Ce、Nd等元素相对富集的特点。综合岩石地球化学特征和构造环境判别图解可以确定闪长岩体发生在碰撞后的张弛阶段,为板块拉伸环境下的产物。The formation age and geochemistry of the diorite,was firstly found in Suli area of western section of Central Qilian by 1∶50000 regional geological survey,have been studied and analyzed in this paper.The zircon U-Pb dating shows that this diorite was formed in Late Jurassic,with an age of（155.1＋1.4）Ma.The geochemical data suggests that Al2O3,Fe2O3,FeO,MnO,MgO,CaO,Na2O and K2O contents are 13.37%-13.55%,5.37%-5.90%,5.64%-6.20%,0.11%-0.16%,1.85% -2.16%,5.15% -5.67%,3.13% -3.58% and 1.39% -1.54%,respectively,with a geochemical characteristics of rich Fe and Ca,but poor Si and Al.Itsσvalue and A/CNK ratio range from 1.32 to 1.41 and from 0.75 to 0.83,respectively,showing the feature of quasi-aluminum cal-alkaline series.ItsΣREE value,LREE/HREE ratio andδEu content vary from 291.44×10^-6 to 319.87×10^-6,from 4.93 to 5.06 and from 0.79 to 0.86,respectively,having obvious characteristics of crust source magmatic rocks.Its trace elements have obvious negative anomalies of Ba,K,Sr,and Ti,while Rb,Th,Ce and Nd are relatively enriched.Combined with the lithogeochemical characteristics and the discrimination diagrams of tectonic setting,the results can determine that this diorite was formed in the relaxation phase after the collision,serving as the product of plate tensional environment.The determination of zircon U-Pb age and genesis of this diorite provide an important geological information for the further study of the tectonic evolution of the Qilian orogenic belt.

关 键 词：成岩时代 闪长岩 构造环境 中祁连西段 东干沟 

分 类 号：P591[天文地球—地球化学]