【摘要】 延边地区五道沟群变质英安岩中的锆石呈自形-半自形晶,具有较高的Th/U比值(0.28～0.81),表明为岩浆成因。定年结果表明,变质英安岩中锆石具有两组年龄。其中,10个测点的206Pb/238U年龄为(265±5)～(291±5)Ma,其加权平均年龄为(274±7)Ma(MSWD=3.4);另一组3颗锆石的206Pb/238U的加权平均年龄为(323±37)Ma(MSWD=3.6)。前者应代表变质英安岩原岩的形成时代,即早二叠世;后者应代表捕获锆石的年龄。结合最新定年结果,可以认为延边地区五道沟群的形成时代为早二叠世,它们与青龙村群一起,共同构成了晚古生代大陆边缘火山-沉积建造。更多还原

【Abstract】 Zircons from the metamorphic dacite of the Wudaogou Group in Yanbian area have euhedral-subhedral shapes and high Th/U ratios(0.28-0.81),implying their magmatic origin.The dating of these zircons indicates that they can be divided into two groups according to their ages.One group,206Pb/238U ages of 10 spots ranging from(265±5)Ma to(291±5)Ma,the weighted mean age of(274±7)Ma(MSWD= 3.4),represents the formation time of the metamorphic dacite(the Early Permian),the other include three zircon grains,and its weighted mean 206Pb/238U age of is(323±37)Ma(MSWD = 3.6),should be interpreted as the captured zircon ages.Combining with the recently dating data,it is suggested that the Wudaogou Group formed in the Early Permian.Together with the Qinglongcun Group,it constitutes a volcanic-sedimentary formation in the Late Paleozoic continental margin.更多还原