祁漫塔格东段晚三叠世花岗岩与流纹岩岩浆同源性:年代学、地球化学及Nd、Pb同位素制约  

Magmatic consanguinity of the Late Triassic granites and rhyolites in eastern Qimantage: Constraints from geochronology, geochemistry and Nd-Pb isotopes

作　　者：徐博 李玉龙 史连昌 张晖青 马德庆 任鑫 王成勇 XU Bo;LI Yulong;SHI Lianchang;ZHANG Huiqing;MA Deqing;REN Xin;WANG Chengyong(Qinghai Geological Survey Bureau,Xining,810000;College of Earth Sciences,Jilin University,Changchun,130061)

机构地区：[1]青海省地质调查局,西宁810000 [2]吉林大学地球科学学院,长春130061

出　　处：《地质论评》2020年第3期686-698,共13页Geological Review

基　　金：青海省祁漫塔格地区1∶5万多元地质信息集成与找矿预测项目(编号:12120114000201)的成果。

摘　　要：祁漫塔格位于东昆仑西段,对该地区晚三叠世火成岩的研究不仅有助于认识东昆仑造山带印支期构造-岩浆演化历史,而且为古特提斯洋俯冲时限及洋盆闭合时限提供约束。本次在克停哈尔南的二长花岗岩中获得了219.8±0.5 Ma的锆石U-Pb年龄,结合以往获得的年龄数据,可以确定该期火成岩为晚三叠世岩浆活动的产物。全岩地球化学分析结果显示,祁漫塔格东段晚三叠世火成岩为准铝到弱过铝质岩石,属高钾钙碱性系列,富集轻稀土和Rb、Th、K等大离子亲石元素,不同程度亏损Nb、Ta、P、Ti等高场强元素,具有明显的铕负异常,显示板块俯冲阶段的特征。花岗岩与流纹岩具有相似的Nd、Pb同位素组成,花岗岩εNd(t)值介于-4.66^-4.53之间,亏损地幔模式年龄TDM2为1363~1375 Ma,流纹岩εNd(t)值为-4.63,TDM2=1368 Ma。在n(143Nd)/n(144Nd)-n(206Pb)/n(204Pb)图解和Pb同位素组成图解中投影点均位于上地壳和EMII地幔端元附近。祁漫塔格东段晚三叠世花岗岩与流纹岩空间分布关系密切,形成时间相近,主、微量元素和Nd、Pb同位素特征方面都具有相似性或一致性,因此,笔者认为它们为同一时期、同一构造环境下的同源岩浆产物。结合区域资料和本文研究,初步分析认为东昆仑地区该时期处于板块俯冲阶段的活动大陆边缘弧环境,古特提斯洋尚未完全闭合。Objectives: Qimantage is located in the western part of the East Kunlun belt. The study of the Late Triassic igneous rocks in this area not only helps to understand of the Indosinian tectonic-magmatic evolution history of the East Kunlun orogenic belt,but also can provide constraints for the subduction and the closing time of the Paleo-Tethys Ocean.Methods: Detailed geological survey, LA-ICP-MS zircon U-Pb dating of monzogranite, whole rock geochemical and Nd-Pb isotopes analysis of igneous rocks in eastern Qimantage,East Kunlun orogenic belt.Results: The zircon U-Pb dating of the monzogranite in southern Ketinghaer is 219. 8 ±0. 5 Ma,combining previous ages it can be ascertained that the igneous rocks are the products of Late Triassic magmatic activities. The whole-rock geochemical analyses show that the Late Triassic igneous rocks in eastern Qimantage lie in high K calcalkaline fields, the Aluminium saturation index show the metalumininous and weak peraluminous features,integrated with enrichments of LREE and LILE( Rb,Th,K,etc.),depletions of Nb,Ta,P and Ti( HFSE) and obvious Eu negative anomaly,suggesting plate subduction-related geochemical affinities. Granites and rhyolites have similar Nd and Pb isotopic compositions. The εNd( t) of granites range from-4. 66 to-4. 53,the model age of depleted mantle range from 1363 Ma to 1375 Ma. The εNd( t) of rhyolite is-4. 63,and the TDM 2 is 1368 Ma.Projection points in n(143 Nd)/n(144 Nd) -n(206 Pb)/n(204 Pb) diagram and Pb isotopic compositions diagrams are located near the upper crust and EMII mantle regions.Conclusions: The Late Triassic granites and rhyolites in eastern Qimantage are closely related to their spatial distribution with similar formation time and similarity or consistency in major-trace elements and Nd-Pb isotopic compositions. Therefore,the authors believe that they are the products of homologous magma in the same period and tectonic environment. Combining achievements of predecessors with this study,it’s believed that the East Kunlun region was

关 键 词：晚三叠世 东昆仑造山带 祁漫塔格 地球化学 锆石U-Pb年龄 Nd-Pb同位素 同源岩浆 

分 类 号：P534.51[天文地球—古生物学与地层学] P588.1[天文地球—地质学] P597.3