NEW SPECULATION OF THE AGE OF THE METAMORPHIC ROCK SERIES OF THE DUNHANG MASSIF

During 1:50000 regional surveys.the Dunhuang Group of the intermediate-and high- grademetamorphic rock series in the Dunhuang massif was determined to have Sm-Nd isochron age val-ues of 2935Ma , 2946Ma and 3487Ma,belonging to the Archean, Samples from the intermediate-and high-grade metamorpnic rock series in the south zone of the Beishan Mounains gave Sm-Ndisochron age values of 2949Ma,2956Ma,3237Ma ,2203Ma and 2059Ma,which are respectively as-signed to the Dunhuang Group and determined to be of Proterozoic age. Stromatolites such asBaicaliia were collected from the low-grade rock series and ages of 1622 Ma were obtained,so theseries is assigned to the middle Upper Proterozic.