藏东吉塘地区吉塘岩群斜长角闪岩的时间序列:来自锆石LA-ICP-MS U-Pb年龄的证据  

Time Sequence of Plagioclase Amphibolites of Jitang Group in Jitang Area,Eastern Tibet:Evidence from Zircon LA-ICP-MS U-Pb Dating

作　　者：于涛[1] 周新 樊炳良 YU Tao;ZHOU Xin;FAN Bingliang(School of Science,Tibet University,Lhasa 850000,China;Geothermal Geological Survey Party,Tibet Bureau of Geology and Mineral Exploration and Development,Lhasa 850000,China)

机构地区：[1]西藏大学理学院,西藏拉萨850000 [2]西藏自治区地质矿产勘查开发局地热地质大队,西藏拉萨850000

出　　处：《高原科学研究》2021年第2期13-26,共14页Plateau Science Research

基　　金：西藏卡贡地区1:5万四幅区域地质调查(DD20160016-21)。

摘　　要：文章对藏东吉塘地区以残留体形式留存于中酸性岩体中的斜长角闪岩进行了岩石学、岩石地球化学和年代学研究,探讨其时代演化序列。地球化学研究表明:吉塘地区吉塘岩群中斜长角闪岩原岩是亚碱性拉斑玄武岩,斜长角闪岩SiO_(2)含量为47.43%~49.0%,K_(2)O/Na_(2)O比值为157.3~327.6,属富钾系列;稀土元素和微量元素结果表明其具有E-MORB的地球化学特征。锆石LA-ICP-MS年代学研究表明,斜长角闪岩原岩形成于晚寒武世-早奥陶世(509~454 Ma),受澜沧江闭合的影响,于早二叠世((273±32)Ma)经历了区域变质作用,在印支期先后两次遭受岩浆热事件((250.3±5.0)Ma、(224.6±2.7)Ma)的改造,最终呈残留体产出于吉塘岩体中。藏东吉塘地区斜长角闪岩演化时间序列的确定,对于认识北澜沧江结合带的构造演化历史具有重要意义。Petrology,petrogeochemistry and chronology studies of amphibolites found in intermediate-acid rock bodies in Jitang area,eastern Tibet,were conducted and their time sequence of evolution was discussed in this paper.Geochemical studies of plagioclase amphibolites of Jitang group show that they are subalkaline tholeiite and their content of SiO_(2)and ratio of K_(2)O/Na_(2)O are 47.43%~49.0%and 157.3~327.6,respectively.Further⁃more,they are belong to the potassium-rich series.The results of rare earth elements and trace elements studies of the plagioclase amphibolites show that they have the geochemical characteristics of E-MORB.Zircon LA ICP-MS geochronology study of the plagioclase amphibolites shows that they were formed in the Early Ordovi⁃cian((472±68)Ma).They underwent regional metamorphism in the Early Permian((273±32)Ma)due to the im⁃pact of the closure of the Lancang River,and were transformed twice by magmatic thermal events((250.3±5.0)Ma and(224.6±2.7)Ma)during the Indosinian period.Finally,they were produced in the Jitang pluton as residu⁃al body.The determination of the time sequence of plagioclase amphibolites evolution in Jitang area is of great significance for understanding the tectonic evolution history of the North Lancang River junction belt.

关 键 词：斜长角闪岩 地球化学 锆石U-PB LA-ICP-MS 时间序列 吉塘 

分 类 号：P597.3[天文地球—地球化学]