武当群地层划分与时代归属
STRATIGRAPHIC CLASSIFICATION OF THE WUDANG GROUP AND ITS AGE ASSIGNMENT
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摘要: 武当群出露广泛,厚度达万余米,为一套酸性火山喷发—碎屑沉积岩系,多期变形特征明显,变质程度达绿片岩相。本文根据火山喷发旋回和沉积韵律性特征,建立地层层序,划分为三大岩组,自下而上为姚坪组、杨坪组和双台组,并进一步划分十二个亚组。通过上覆地层时代及不整合关系,武当群所含疑源类组合与同位素年代学资料解析,其形成年代在1400~1044Ma之间,相当于中元古代,可归属于蓟县系。Abstract: The Wudang Group is widespread and up to more than ten thousand metres in thickness, and is represented by an acid volcanic-clastie sedimentary rock series. It exhibits the obvious character of polyphase deformation, and its metamorphic grade reaches greenschist facies. According to the volcanic cycles and sedimentary rhythms, a stratigraphie sequence has been established. The group may be divided in ascending order into the Yaoping Formation, Yangping Formation and Shuangtai Formation and may be further divided into 12 subformations. In the light of the age of the overlying strata andunconformable relationship as well as the acritareh assemblage contained in the Wudang Group and isotopic geochronological data, the age of its formation has been determined to range between 1400 and 1044 Ma, being equivalent to middle Proterozoic, so the group may be assigned to the Jixian System.