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多种同位素年代学方法综合研究表明，扬子克拉通北缘中段基底岩系后河群和西乡群变质地层的原岩形成时代并非早期推测或报道的新元古代．后河群斜长角闪岩原岩的形成时代应为古元古代，并有太古宙岩石存在的可能．后河群混合岩化变质作用发生于２１４１Ｍａ．西乡群底部白勉峡组属古元古代，而中上部孙家河组为中元古代末期．普遍存在的７００～８００Ｍａ的Ｋ－Ａｒ和Ｒｂ－Ｓｒ年龄反映了区内于晋宁期发生了一次大规模的构造热事件
A comprehensive study of various isotopic geochronological methods shows that the protolith formation age of the Houhe Group and the Xixiang Group metamorphic strata in the middle margin of the northern margin of the Yangtze Craton is not an early Neoproterozoic or previously reported Neoproterozoic. The formation age of the Houhe Group plagioclase amphibole should be Paleoproterozoic, and the Archean rocks may exist. The latter metamorphism occurred at 2141Ma. The White Mianxia Formation at the bottom of Xixiang Group belongs to the Paleoproterozoic group, while the Sunjiahe Formation in the middle and upper part is the Mesoproterozoic-Archean. The ubiquitous K-Ar and Rb-Sr ages from 700 to 800 Ma reflect a large-scale tectono-thermal event in the Jinning period