滇西无量山群北段变质基性火山岩夹层年龄及其地质意义  

LA-ICP-MS Zircon U-Pb Age of Metamorphic Basic Volcanic Rocks in the Northern Segment of the Wuliangshan Group, Western Yunnan Province, and Its Geological Significance

作　　者：吴继文 林宇[1] 吕勇[1] 廖家飞[1] 吴亮君 孟庆鑫 WU Ji-wen;LIN Yu;LüYong;LIAO Jia-fei;WU Liang-jun;MENG Qing-xin(Key Laboratory of Karst Dynamics,Ministry of Natural Resources,Institute of Karst Geology,Chinese Academy of Geological Sciences,Guilin,Guangxi 541004)

机构地区：[1]中国地质科学院岩溶地质研究所自然资源部岩溶动力学重点实验室

出　　处：《地球学报》2019年第6期871-883,共13页Acta Geoscientica Sinica

基　　金：中国地质调查局地质调查项目(编号:DD20179247)资助~~

摘　　要：滇西无量山岩群为原1:100万下关幅(1975)命名,为一套浅变质砂岩和泥岩,形成于滨海相-浅海陆棚相,其时代一般认为属古生代,但一直缺乏化石依据或准确的年龄数据。本次1:5万区调在澜沧江西岸云龙县毛草坪村无量山岩群四段(PzW4)的下部和上部获得两层变质基性火山岩夹层,根据野外岩石产状、镜下薄片鉴定、岩石地球化学综合分析恢复其原岩为玄武岩,形成于大洋扩张环境。采用LA-ICP-MS技术,对下部和上部变质基性火山岩中的锆石进行了U-Pb同位素测定,分别获得206Pb/238U年龄为(327±11)Ma(N=14,MSWD=6.7)和(284±3.7)Ma(N=27,MSWD=4.9),为早石炭世晚期和早二叠世晚期,这为无量山岩群形成时代及其演化提供了重要的年龄依据,对于进一步深入研究古特提斯洋晚古生代的构造属性与演化历史具有重要意义。Wuliangshan Group,which was named by Xiaguan Geological Survey in 1975,is composed of epimetamorphic sandstone and mudstone representing a set of littoral facies-shallow sea shelf facies sediments.Its formation age has been generally considered to be Paleozoic,which,however,is not based on the evidence of fossils or accurate dating.In this study,the authors identified the stratigraphic sequence composed of two layers of metamorphic basic volcanic rock in the lower and upper member of Wuliangshan Group(PzW4)in Maocaopin village,Yunlong county.It is held that its original rock was basalt formed in an ocean spread environment,according to comprehensive analysis of the rock occurrence in the field,the thin section and rock geochemistry.The selected magmatic zircons 206Pb/238U isotopic ages of the lower and upper parts of the metamorphic basic volcanic rocks,measured by LA-ICP-MS,were(327±11)Ma and(284±3.7)Ma respectively,corresponding to the Late Early Carboniferous and Late Early Permian.These data provide an important chronological constraint for the formation and evolution of Wuliangshan Group.This achievement is very important for the further study of the tectonic characteristics and evolution history of the Paleo-Tethys Ocean in Late Paleozoic.

关 键 词：滇西澜沧江 无量山岩群 变质基性火山岩 LA-ICP-MS 锆石U-PB 古特提斯洋 

分 类 号：P575[天文地球—矿物学] P597[天文地球—地质学]