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在浙江诸暨丁家坞剖面采集陈蔡群变质岩系黑云斜长片麻岩样,分离出单矿物锆石。由5 个不同粒级的锆石组分,得出不和谐 U-Pb 年龄值为1438_(-122)~(+150)和578_(-72)~(+55)Ma。前者代表陈蔡群原岩沉积时代的极限,后者代表陈蔡群原岩沉积后引起锆石中大量 Pb 丢失的一次较强烈地质事件的年代。综合分析已有同位素年龄数据和区域地质资料,可推断陈蔡群原岩形成于900—1400Ma 前,属中元古时期。变质作用发生约在800—900Ma 前,相当于晋宁变质期。
The Chencai Group Metamorphic Rock Biotite plagioclase gneiss was collected from the Dingjiwu section of Zhuji, Zhejiang, and single mineral zircon was isolated. The results show that the discordant U-Pb ages are 1438 ~ (-122) ~ (+150) and 578 ~ (-72) ~ (+55) Ma for five zircons with different grain sizes. The former represents the limit of Chen Caiqun’s protolith depositional age, the latter represents the age of a more intense geological event that caused a large amount of Pb loss in zircon after the deposition of Chencaiqun protolith. Based on the comprehensive analysis of the isotopic data and regional geological data, it can be deduced that the original Chencai Group protolith formed before 900-1400 Ma, belonging to the Mesoproterozoic. Metamorphism occurred before about 800-900Ma, equivalent to Jinning deterioration period.