Ages of Some Precambrian Metamorphic Rocks in North China

Rb－Sr age determination is undertaken on minerals and whole rock samples of crystalline rocks collected from several localities in the Precambrian Platform of North China. Results are 1874 m.y. for the biotite augen gneiss, 1405 m.y. for the biotite muscovite gneiss, 1401 m.y. for the muscovite biotite microcline gneiss, 1430 m.y. for the biotite hornblende schist and 183 m.y. for the biotite hornblende andesite. Three distinct epochs of metamorphism with acid igneous activities of every 500 m.y. may be distinguished in the Precambrian history of the North Chinese Platform by compilation of previous age data together with the results of this paper.