冀东青龙一带双山子与朱丈子群的时代归属问题

本文谁了各类变质岩的全岩Ｒｂ－Ｓｒ等时线所反映的岩石初始或叠加变质变形年龄。角闪岩相的锆石Ｕ－Ｐｂ一致线和Ｓｍ－Ｎｄ等时线则因原岩（火成或沉积成因）的差别分别反映生成年龄或变形年龄，实际是受原生水控制。Ｓｍ－Ｎｄ等时线年龄偏低，还与低温动力变质中水的加入有关。由于本区２４５０Ｍａ的数据出现频率很高，反映了太古宙与元古宙间的主要地质事件，结合双山子群、朱丈子群中发育可供洲际对比的绿岩带，故二者统归太

GEOCHRONOLOGY OF THE SHUANGSHANZI AND ZHUZHANGZI GROUPS,QINGLONG,EASTERN HEBEI

In isotopic dating this paper emphasizes the role of fluids in isotopic rehomo-genization during metamorphism.Sedimentary metamorphic rocks are abundant inconnate water and the dating of clastic zircon yields,in most cases,the age ofmetamorphism and deformation.In some cases the Sm-Nd isochron ages of igneousrocks are also relatively low.All this may be related to the incorporation of mixedwater during low-temperature diaphthoresis.It is concluded,based on the availableU-Pb ages,Rb-Sr isochron ages and Sm-Nd ages(including the whole-rock isochronand mortal ages)in conjunction of the geochronology data of global greenstones,thatthe Shuangshaazi and Zhuzhangzi groups should be Late Neoarchaean in age,rangingfrom 2450 to 2650 Ma.