东昆仑造山带波洛斯太地区晚三叠世中酸性火山岩锆石U-Pb年代学、地球化学及地质意义  

Zircon U-Pb Chronology, Geochemistry and Geological Significance of Late Triassic Intermediate-Acid Volcanic Rocks in Boluositai Area, East Kunlun Orogenic Belt

作　　者：封铿 李瑞保[1,2] 裴先治[1,2] 李佐臣[1] 刘成军[1] 裴磊[1] 陈有炘[1] 陈国超[1] 杨再兵 Feng Keng;Li Ruibao;Pei Xianzhi;Li Zuochen;Liu Chengjun;Pei Lei;Chen Youxin;Chen Guochao;Yang Zaibing(Faculty of Earth Science and Resources,Chang’an University,Xi’an 710054,China;Key Laboratory of Western China’s Mineral Resources and Geological Engineering,Ministry of Education,Xi’an 710054,China)

机构地区：[1]长安大学地球科学与资源学院,陕西西安710054 [2]西部矿产资源与地质工程教育部重点实验室,陕西西安710054

出　　处：《地球科学》2022年第4期1194-1216,共23页Earth Science

基　　金：国家自然科学基金项目(Nos.41502191,41472191,41172186);中央高校基本科研业务费专项资金项目(Nos.310827161002,310827161006,310827173702);陕西省自然科学基础研究计划(No.2020JM-229);青海省国土资源厅—中国铝业公司公益性区域地质矿产调查基金项目(No.200801)。

摘　　要：东昆仑造山带东段波洛斯太地区出露一套晚三叠世中酸性火山岩,对研究古特提斯洋关闭及碰撞造山过程具有重要意义.通过对该火山岩进行详细的锆石U-Pb年代学、地球化学和Hf同位素研究来确定其形成时代、岩石成因和构造环境.研究结果表明,英安岩加权平均年龄为233.4±1.3 Ma和234.7±1.5 Ma,形成时代为晚三叠世.火山岩SiO_(2)含量为64.57%~71.27%,全碱含量(ALK)为7.53%~8.07%,Na_(2)O/K_(2)O值为0.84~1.01,Mg^(#)值为35.66~45.39,A/CNK为1.0~1.1之间,表现为弱过铝高钾钙碱性系列.岩石轻、重稀土元素分馏明显,表现为轻稀土富集、重稀土亏损的特征,具有弱的负Eu异常.英安岩的锆石ε_(Hf)(t=235)为-4.81~+0.09,对应的二阶段模式年龄为1059~1309 Ma,岩石成因研究表明英安岩为陆壳富长石杂砂岩和少量基性岩部分熔融的产物.综合区域地质资料认为该英安岩形成于后碰撞构造环境,进一步说明东昆仑造山带于晚三叠世早期古特提斯洋已关闭,并转化到后碰撞构造演化阶段.Late Triassic intermediate-acid volcanic rocks exposed in the Boluositai area,East Kunlun orogenic belt are of great significance for studying the closure of the Paleo-Tethys ocean and subsequent collision orogenic processes.It conducted detailed zircon U-Pb chronology,geochemistry and Hf isotopic studies of the volcanic rock to determine its formation age,petrogenesis and tectonic environment.The results show that the zircon weighted average ages of dacites are 233.4±1.3 Ma and 234.7±1.5 Ma respectively,suggesting the Late Triassic.The whole-rock geochemical results show that the SiO_(2) contents range from 64.57%to 71.27%,with the total alkali contents(ALK)from 7.53%to 8.07%,the Na_(2)O/K_(2)O ratios from 0.84 to 1.01,the Mg^(#)values from 35.66 to 45.39,and the A/CNK from 1.0 to 1.1.These features show weak peraluminous,high-potassium calcium alkaline series.The light and heavy rare earth elements of the rocks are obviously fractionated,which is characterized by the enrichment of light rare earth elements and the depletion of heavy rare earth elements,with a weak negative Eu anomaly.The zirconε_(Hf)(t=235)of dacites ranges from-4.81 to+0.09,and the two-stage model age is 1059-1309 Ma.The petrogenesis research indicates that the dacites were derived from feldspar-rich sandstone and basalts in the continental crust.Based on regional geological data,it is suggested that the dacites were formed in a post-collision setting and that the Paleo-Tethys Ocean had been closed in the early Late Triassic and the East Kunlun orogen transformed into a post-collision stage.

关 键 词：东昆仑 印支期 火山岩 地球化学 后碰撞 岩石学 

分 类 号：P548[天文地球—构造地质学]