扬子克拉通中元古代年代地层序列厘定

Revision of Mesoproterozoic chronostratigraphic sequence of the Yangtze Craton,China

扬子克拉通中元古代地层主要分布于克拉通北缘和西缘,随着火山岩夹层(主要指过去不易识别的斑脱岩化凝灰岩)的识别和年代学测试技术的发展,陆续报道了大批新的可靠的地层年龄数据,扬子克拉通的中元古代地层层序划分和对比方案得以不断修正和厘定。已有大量资料表明,江南造山带一线原定中元古代的梵净山群、四堡群等实际属于新元古代;扬子北缘原中元古代火地垭群、三花石群等也应划归新元古代;扬子西缘大红山群、苴林群分别划归中元古代早期和晚期,西缘大红山群、河口群和东川群下部可对比,昆阳群、会理群、苴林群和北缘神农架群上亚群、马槽园群可大致对比。扬子西缘登相营群和峨边群沉积时代仍存中元古代和新元古代之争议。

The Mesoproterozoic strata of the Yangtze Craton are mainly distributed in the northern and western margins.With the identification of volcanic intercalations(especially bentonite tuffs that were difficult to identify in the past)in sedimentary strata and the development of dating techniques,a lot of age data have been reported and the subdivision and time framework of the Mesoproterozoic sequence in the Yangtze Craton has been revised.Plenty of new lines of evidence demonstrates that the Fanjingshan Group,Sibao Group,etc.,distributing along the Jiangnan Orogenic belt,that were originally attributed to the Mesoproterozoic are actually Neoproterozoic strata.The Huodiya Group,Sanhuashi Group in the northern margin of the Yangtze Craton are changed into Neoproterozoic from Mesoproterozoic.Dahongshan Group and Julin Group in the western margin of the Yangtze Craton are classified into the early and late Mesoproterozoic respactively.The Dahongshan Group,Hekou Group and the lower part of Dongchuan Group in the western margin are comparable with each other.Kunyang Group,Huili Group and the Julin Group can be correlated with the upper subgroup of the Shennongjia Group and the Macaoyuan Group in the northern margin.There are still disputes about the the depositional age(Mesoproterozoic or Neoproterozoic)of the Dengxiangying Group and the Ebian Group in the western margin of the Yangtze block.