浙江雁荡山地区晚中生代火山—沉积岩系地层归属讨论

Discussion on the Stratgraphic Position of Late Mesozoic Volcanic-Sedimentary Rooks in Yandangshan Ares, Zhejiang Province

浙江雁荡山地区晚中生代火山 -沉积岩系的地层归属 ,存在磨石山群和永康群两种截然不同的认识。本文在详细分析对比了该区与浙东南磨石山群和永康群的地层层序、岩相组合、接触关系 ,古生物组合 ,同位素地质年龄 ,Nd同位素体系特征以及火山构造类型等方面的资料 ,认为除原划为永康群盆地外 ,仅桥下地区有面积不大的永康群 ,其余均为早白垩世早期的磨石山群 ,而不是早白恶世晚期至晚白垩世早期的永康群。特别是在永嘉枫林村北 ,首次发现并证实了不整合覆于震旦系浅变质岩之上的大爽组地层 ,为浙东南沿海晚中生界火山

There are two various ideas on the stratigraphies position of Late Mesozoic volcanic-sedimentary rocks in Yandangshan area, Zhejiang Province: some geologists think that these stratigraphies belong to Moshishan Group, the others think that they belong to Yongkang Group. Based on the analysis and comparison of stratigraphic sequence, petrological facies assemblege, contact relation, paleontological ssemblege, isotopic age Nd isotopic composition and volcanic structure etc. between Moshishan group and Yongkang Group of this area and these of Southeast Zhejiang. We think that most volcanic-sedimentary rocks in Yandangshan area belong to Moshishan Group of early stge of Early Cretaceous, except that Yongkang basin and Qiaoxia area to Yongkang Group of late stage of Early Cretaceous. Especially, we found first the Dashuang Formation at the north of Fengling , which is above the metamorphic rocks of sinian period. These data are the base of the stratigraphic-position study for the late Mesozoic vocanic-sedimentary rocks in Southeast Zhejiang.