~(40)Ar-~(39)Ar CHRONOLOGY AND METAMORPHIC AGE OF CHENCAI GROUP,ZHEJIANG PROVINCE, CHINA
浙江省陈蔡群的^40Ar—^39Ar年龄与变质年代

Metamorphic rocks of Chencai group were dated by 40Ar-39Ar method in this paper.The plateau age of 415.1 Ma obtained in Chencai,Zhuji represents the cooling time of the main metamorphic event. The sample from Shangyang Yiwu is affected by Yanshanian volcanismand has apparent argon loss. The age related to the main metamorphism is also lowered,which is only 315. 3 Ma. A plateau age of 276. 9 Ma is obtained from Dongshu, Longquan,which can be regarded as the cooling age of the widely developed migmatization in this area. Based on a discussion on the up-to-date chronological data, the authours pointed out that the evolution of the main metamorphism of Chencai group was recorded by different decay series,i.e., Rb-Sr isotope was homogenized in 552. 4 to 660. 6 Ma, correspondent to the early and middle stage of the metamorphism. The U-Ph system in zircon and apatite redistrutednear the summit of the event and is recorded by the lead loss ages of 508. 4 to 578 Ma. Allthe above data confirm that the main metamorphism of Chencai group took place in Caledonian period.