The confirmation of the age of Caledonian Chencai Group in Zhuji area of Zhejiang Province and its geological significance

Chencai Group is one of the most important lithostratigraphic units in southeastern Zhejiang Province, which has been considered as the major component of the metamorphic basement of Cathaysia block. In the last century, many geologists carried out their research work on this group. This paper selected Chencai Group in Xiaosi District of Zhuji City in Zhejiang Province as the study object and carried out in detail the LA-ICP-MS dating work. Zircon CL images and trace element characteristics indicate that the zircons are of metamorphic type, and the weighted average value of 206Pb/238U age obtained from 17 analytical points is 435±4Ma, suggesting Caledonian. This paper holds that this age represents the main regional metamorphic age of Chencai Group in Zhuji area. In combination with high-precision age record of Caledonian period already reported by previous researchers, the authors investigated the time limit and nature of the Caledonian Movement in South China. The result shows that the Caledonian Movement in South China occurred mainly in the period between 420～445Ma, with 435Ma as the peak.