Mesoproterozoic age for Xiamaling Formation in North China Plate indicated by zircon SHRIMP dating

Zircon grains of magmatic origin from tuffite layers in the Xiamaling Formation at Zhaojiashan Village, Xuanhua area, Hebei Province, were used for zircon dating with a Sensitive High-Resolution Ion Microprobe （SHRIMP Ⅱ）, which gives a weighted mean ^207Pb/^206Pb age of 1366±9 Ma. It shows a very similar age （1368±12 Ma） as the zircon dating from the Xiamaling Formation in Western Hill, Beijing. This age proposes that the Xiamaling Formation in the North China plate should be of Mesoproterozoic, instead of Neoproterozoic based on K-Ar, Ar-Ar dating. The new zircon age also indicates the development of macrofossils algae from the Mesoproterozoic age.