藏东吉塘群黑云二长片麻岩锆石U-Pb年龄及其变质时代的厘定  

Zircon U-Pb age and metamorphic age of biotite monzogneiss from the Jitang Group,eastern Tibet

作　　者：张力文 罗拉次旺 樊炳良 布嘎次仁 周新 冯德新 郭伟康 ZHANG Liwen;LUOLA Ciwang;FAN Bingliang;BUGa Ciren;ZHOU Xin;FENG Dexin;GUO Weikang(Geothermal Geological Survey Party,Tibet Bureau of Geology and Mineral Exploration and Development,Lhasa 850000,Tibet,China;Faculty of Geosciences and Environmental Engineering,Southwest Jiaotong University,Chengdu 610031,Sichuan,China;Chengdu Institute of Geology and Mineral Resources,Chengdu 610081,Sichuan,China)

机构地区：[1]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 [2]西南交通大学地球科学与环境工程学院,四川成都610031 [3]成都地质矿产研究所,四川成都610081

出　　处：《地质通报》2022年第11期1927-1941,共15页Geological Bulletin of China

基　　金：中国地质调查局项目《西藏吉塘地区15万四幅区域地质调查》(编号:DD20160016-21);《雅鲁藏布江缝合带(喜马拉雅东构造结段)三维结构厘定及其对川藏铁路的影响》(编号:XZ202001ZY0011G)。

摘　　要：藏东吉塘群变质基底时代归属一直以来存在较大争议,至今未形成统一认识。对藏东察雅县吉塘镇多穷沟吉塘群黑云二长片麻岩进行了碎屑锆石U-Pb定年,同时与西北部的类乌齐地区吉塘群进行了对比研究。碎屑锆石U-Pb年龄结果表明:吉塘群黑云二长片麻岩最大沉积时限不早于566±9.5 Ma,时代为新元古代晚期;吉塘群黑云二长片麻岩原岩为副片麻岩,推测其碎屑物质多来源于太古宙、新元古代的花岗质岩石、长英质火山岩等。对比研究发现,吉塘地区吉塘群与类乌齐地区吉塘群在物质组成上具有一定的相似性,后者的正片麻岩单元属于华力西期—印支期岩浆作用的产物,不属于吉塘群结晶基底物质。结合已有的研究成果,认为吉塘群原岩成岩后经历了5期构造热事件改造,变质年龄峰值分别为427 Ma、377~359 Ma、308~273 Ma、255~252 Ma、226~203 Ma,其中226~203 Ma的岩浆活动可能导致了吉塘群的重融。The attribution of the metamorphic basement age of the Jitang Group in eastern Tibet has been controversial.Here we report the results of detrital zircon U-Pb dating for the Duoqionggou biotite monzogneiss in the Jitang Group from the Jitang area,Chaya County,eastern Tibet,and compared with the northwest Jitang Group in the Leiwuqi area.LA-ICP-MS zircon U-Pb dating results indicate that the maximum depositional time of biotite monzogneiss in the Jitang Group is no earlier than 566±9.5 Ma and is of the Late Neoproterozoic.The protolith of biotite monzogneiss is paragneiss,and the detrital materials are probably derived from the Archean to Neoproterozoic granitic rocks and felsic volcanic rocks.By comparison,the Jitang Group in the Jitang area is similar to the Jitang Group in the Leiwuqi area in material composition.The orthogneiss unit of the latter belongs to a product of magmatism of the Variscan-Indosinian period,and instead of being part of the crystalline basement of the Jitang Group.Combined with existing data,we propose that the protoliths of the Jitang Group underwent five periods of tectono-thermal events after diagenesis,with peak metamorphic ages of ca.427 Ma,ca.377~359 Ma,ca.308~273 Ma,ca.255~252 Ma,and ca.226~203 Ma,respectively,of which the magmatic activity at ca.226~203 Ma may have resulted in the remelting of the Jitang Group.

关 键 词：吉塘群 沉积时限 碎屑锆石 黑云二长片麻岩 变质年龄 地质调查工程 西藏 

分 类 号：P588.34[天文地球—岩石学] P5973[天文地球—地质学]