Chronological study and tectonic significance of Precambrian metamorphic rocks in Zhalantun area of Da Hinggan Mountains

A lot of Precambrian metamorphic rocks are exposed in the Zhalantun area of Da Hinggan Mountains, which include Paleoproterzoic Xinghuadukou Group, Neoproterozoic Jiageda Formation and Neoproterozoic-Early Cambrian Wolegen Group, how-ever, accurate chronological evidence has been lacking. Based on the LA-ICP-MS zircon U-Pb dating, the authors determined the original rock age of these three metamorphic groups. The results show that zircons from the chlorite muscovite schist in the Hinghua Dukou Group has a weighted average ²⁰⁶Pb/²³⁸U age of 520.1±4.3Ma, the weighted average ²⁰⁶Pb/²³⁸U ages of zircons from the Changliang mylonites in the Jiapigang Formation are 512.0±2.9Ma, the weighted mean ²⁰⁶Pb/²³⁸U age of the youngest zircons of the green-stone sericite schist in the Injalagenian rock mass is 491.7 ±11.9Ma, and the weighted average ²⁰⁶Pb/²³⁸U age of most intensive areas is 516.7±4.5Ma. The features of zircon images and Th/U values exhibit magmatic zircon characteristics. The above data indicate that the Xinghuadukou Group, Jiageda Formation and Wolegen Group were formed in Early Paleozoic rather than previously thought "Precambrian". At the same time, the above age pedigree indicates that there are two strong magmatic events in 480~500Ma and 500~530Ma in this area, which were related to the late Pan African metamorphic magmatic events in Northeast China.