辽东地区什司县变质基性岩墙群的LA-ICP-MS锆石U-Pb测年及其意义

LA-ICP-MS Zircon U-Pb Age of Plagioclase Amphibolite from Shensixian Mafic Dyke Swarm in Liaodong Area, China and Its Significance

本文对辽东地区什司县变质基性岩墙群中的斜长角闪岩进行了锆石LA-ICP-MS年代学研究。锆石呈现不规则状、椭圆状、港湾状形态,显示遭受后期构造热事件的影响;CL图像显示扇形分带、杉叶形分带及无分带的特征,且Th/U值较低,为0.03~0.14,为典型的变质锆石;20粒锆石给出了1874±31 Ma的207Pb/206Pb加权平均年龄。1874±31 Ma的变质年龄代表华北板块东部辽吉古元古裂谷带闭合时的区域变质事件的时代。

This paper studies the chronology of plagioclase amphibolite from Shensixian mafic dyke swarms in Liaodong area, China by using LA-ICP-MS zircon U-Pb dating.Zircons show irregular, elliptical and harbor-like morphology, indicating that they suffered effect of late tectonothermal event. CL images indicate that the zircon is characterized by sector and cedar-leaf zoning or no zoning. The zircons have Th/U ratios varying from 0.03 to 0.14. The characteristics described above indicate that the zircons are of a typical metamorphic origin. Twenty analysis on the zircons gave a weighted mean 207Pb/206 Pb age of 1874±31 Ma, which is interpreted to be the metamorphic age of the dated amphibolite. This metamorphic age of 1874±31 Ma represents the time of regional metamorphism resulting from the closure of Liaoji Paleoproterozoic rift located in the eastern part of the North China Craton.