秦岭西段天水一带李子园群变质变形时代的~(40)Ar-~(39)Ar年代学证据

位于秦岭西段北侧天水市附近的李子园群系张维吉等建立，由遭受不同程度变质作用改造的新元古代至早古生代火山沉积岩系构成。对关子镇一带李子园群研究后，发现该群至少遭受了两期强烈变形。早期为伴生低绿片岩相变质作用的近东西向右行剪切，晚期为北西—南东向的左行剪切。通过对变质矿物黑云母的４０Ａｒ３９Ａｒ定年研究，确定早期变质变形事件发生在石炭纪初（３５５Ｍａ）

40

The Liziyuan Group exposed on the northern side of the western sector of the Qinling Mountains near Tianshui City was estimated by Zhang Weiji et al.It consists of Neoproterozoic to Early Paleozoic volcano sedimentary sequences that have undergone different degrees of metamorphism.Study of the Liziyuan Group in the vicinity of Guanzizhen has revealed that the group underwent at least two stages of strong destructural deformation. The early stage deformation was marked by nearly E W directed dextral shear accompanied by low greenschist facies metamorphism,while the late stage one by SE directed sinistral shear. 40 Ar 39 Ar dating of the metamorphic mineral biotite implies that the early event took place at the beginning of the Carboniferous(355 Ma B.P.).