新疆南天山景汗花岗质岩体年代学、地球化学特征及其构造意义  

Geochronology and geochemistry of the Jinghan granitic pluton in South Tianshan,Xinjiang and their tectonic significance

作　　者：陈士海 钟文[2] 张健仁[2] CHEN Shi-hai;ZHONG Wen;ZHANG Jian-ren(School of Earth Sciences and Engineering,Nanjing University,Nanjing 210093,China;Jiangxi Institute of Geological Survey,Nanchang 330030,China)

机构地区：[1]南京大学地球科学与工程学院,南京210093 [2]江西省地质调查研究院,南昌330030

出　　处：《华东地质》2020年第2期128-141,共14页East China Geology

基　　金：新疆地勘基金中心“新疆西天山克尔古提一带1∶5万三幅区域地质调查(编号:T14-1-LQ07)”项目资助。

摘　　要：位于新疆南天山和硕县北部的景汗花岗质岩体,为研究南天山造山带构造演化提供了重要信息。岩体岩性以二长花岗岩为主,石英二长闪长岩和二云母花岗岩次之。LA-ICP-MS锆石U-Pb定年结果表明,岩体成岩年龄为(311.3±4.4)Ma^(297.2±4.2)Ma,属晚石炭世岩浆活动的产物。岩体SiO 2含量为54.20%~74.22%,全碱(ALK)为5.12%~9.25%,具有高钾钙碱性系列岩石的特征。A/CNK值为0.77~1.07,属于准铝质-弱过铝质花岗岩类。∑REE为(44~288)×10^-6,(La/Yb)N值为1.83~44.75,表明轻稀土元素富集较为明显。δEu值为0.54~0.93,整体表现为弱亏损特征。花岗质岩浆可能是地壳的部分熔融的产物,并与幔源基性岩浆发生过混合作用。该岩体形成于塔里木板块与伊犁—哈萨克斯坦板块碰撞造山作用晚期阶段,属于碰撞-后碰撞构造环境,南天山晚古生代残余海盆在晚石炭世最终闭合。The Jinghan granitic pluton,located in the north of Heshuo County,Xinjiang Autonomous Region,bears important information for studying the tectonic evolution of the South Tianshan orogenic belt.This pluton consists mainly of monzonitic granite and less amounts of quartz monzodiorite and two-mica granite.LA-ICP-MS zircon U-Pb dating yields ages of(316.1±3.9)Ma^(298±4)Ma,indicating that the pluton was emplaced in Late Carboniferous.Geochemically,this pluton shows wide variation of chemical compositions,with SiO 2 contents ranging from 54.20%to 74.22%,and total alkali values(ALK)from 5.12%to 9.25%,and show characteristics for rocks of high-K calc-alkaline series.Granitic rocks from this pluton have A/CNK values of 0.77~1.07,thus can be grouped into metaluminous-weakly peraluminous granitoids.Total REE contents of 29.65×10^-6 to 298.50×10^-6 and(La/Yb)N ratios of 1.83 to 29.16 show an obvious enrichment of light rare earth elements.Weakly negative Eu anomalies withδEu values of 0.54 to 1.04 display characteristic of weak depletion.Geochemical characteristics suggest that the granitic magmas likely originated from partial melting of crust materials,and also underwent magma mixing with mantle-derived mafic magmas during the formation process.Combined with the regional tectonic settings and the discrimination results of trace elements,it is concluded that the Jinghan pluton was generated during the late stage of the collision between the Tarim Plate and the Yili-Kazakhstan Plate under a collisional to post-collisional tectonic setting.These results also imply that the late Paleozoic residual oceanic basin in the South Tianshan Belt was finally closed in late Carboniferous.

关 键 词：构造环境 高钾钙碱性系列 锆石U-PB定年 新疆南天山 

分 类 号：P588.12[天文地球—岩石学]