祁漫塔格山阿格腾地区晚三叠世火成岩LA-MC-ICP-MS锆石U-Pb年龄、地球化学特征及构造意义

LA-MC-ICP-MS Zircon U-Pb ages,geochemical characteristics and tectonic significance of the Late Triassic igneous rocks in Ageteng area,Qimantage Mountains

阿格腾地区位于东昆仑西段,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。研究区内流纹岩及花岗岩的锆石U-Pb测年结果分别为215.3±0.5 Ma、220.7±0.5 Ma、220.7±0.4 Ma、220.6±1.4 Ma,为晚三叠世岩浆活动的产物。全岩地球化学分析结果显示,阿格腾地区晚三叠世火成岩属于高钾钙碱性系列,铝饱和指数显示为准铝到弱过铝质,富集轻稀土和大离子亲石元素(Rb、Th、K等),不同程度亏损Nb、Ta、P、Ti等高场强元素,负Eu异常明显(δEu=0.23～0.76),具有板块俯冲阶段的特征。结合区域资料和本文研究,初步分析认为阿格腾地区火成岩形成于活动大陆边缘弧环境,为古特提斯洋俯冲背景下造山作用的产物。该时期该地区陆壳没有明显的增厚,古特提斯洋尚未完全闭合。

Objectives: The Ageteng area 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 eastern 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 syenogranite,and whole rock geochemical analysis of igneous rocks in Ageteng area.Results: The zircon U-Pb datings of the rhyolite and granite in the study area are 215.37±0.56 Ma,220.75±0.57 Ma,220.71±0.47 Ma and 220.6±1.4 Ma,which are the product of Late Triassic magmatic activity. The wholerock geochemical analyses show that the igneous rocks in the Ageteng lie in high K calc-alkaline fields,the aluminium saturation index show the metalumininous and weak peraluminous features,integrated with enrichments of LREE and LILE( Rb,Th,K,et al),depletions of Nb,Ta,P and Ti( HFSE) and obvious Eu negative anomaly(δEu = 0.23~0.76),suggesting plate subduction-related geochemical affinities.Conclusions: Combining achievements of predecessors with this study,it’s believed that igneous rock in Ageteng area generated from an active continental margin arc environment,and it was a product of orogeny during Paleo-Tethys Ocean subduction. The continental crust was not obvious increased in this area,and the Paleo-Tethys Ocean was not completely closed in that period.