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黔东南地区下江群是分布在江南造山带西段的一套前寒武纪浅变质陆源碎屑岩夹火山碎屑岩组合,其地层时代归属与划分特别是区域地层对比一直未能得到很好解决.在对该区前寒武纪地层广泛而详细的剖面测制和地质调查基础上,运用LA-ICP-MS技术,对地层中沉凝灰岩、含凝灰质碎屑岩和碎屑岩进行锆石U-Pb年代学测试,获得一批高精度的年龄.四堡群河村组顶部的碎屑岩和下江群乌叶组第1段顶部的含凝灰质碎屑岩、清水江组底部与中部的沉凝灰岩、平略组中上部的含凝灰质碎屑岩、隆里组中下部的碎屑岩等样品中锆石U-Pb最小年龄组的加权平均年龄分别为819.8±6.4 Ma和779.5±4.7Ma、764.0±6.3Ma与(756.8±7.6Ma、756.0±13.0Ma)、733.9±8.8Ma及725.0±10.0Ma.这些数据将四堡群和下江群的时代限制为新元古代.结合研究区隆里组与长安组整合接触关系和全球低纬度南华系冰期起始年龄(717.4Ma)的地质事实,将下江群沉积时限约束在815~717Ma之间.根据区域岩浆事件进一步约束了下江群各组段的地层时限,并开展江南造山带下江群及其相当层位的地层划分与对比,认为新元古代岩浆作用制约着黔东南下江群盆地的演化.
The Lower Yangtze Group in Southeast Guizhou is a set of Precambrian epithermal terrigenous clastic rock volcanic clastic assemblages distributed in the western segment of the Jiangnan orogenic belt. The stratigraphic age belonged to the strata, especially the regional stratigraphic contrast has not been very Based on extensive and detailed profiling and geological survey of the Precambrian stratigraphy in this area, LA-ICP-MS technique was used to study the sedimentary tuff, tuffaceous clastic rocks and clastic rocks in the strata Zircon U-Pb geochronology test to obtain a group of high-precision ages.Clastic clastic rocks at the top of the first section of the Lower Cambrian Wuye Formation and the bottom of the Qingshuijiang Formation The weighted average age of the zircon U-Pb zircons in the middle part of the tuff, the tuffaceous clastic rocks in the upper part of the Pingliao Formation and the clastic rocks in the middle and lower parts of the Longli Formation are 819.8 ± 6.4 Ma and 819.8 ± 6.4 Ma, respectively 779.5 ± 4.7Ma, 764.0 ± 6.3Ma and (756.8 ± 7.6Ma, 756.0 ± 13.0Ma), 733.9 ± 8.8Ma and 725.0 ± 10.0Ma, respectively. These data limited the age of the Si Bao Group and Xiajiang Group to the Neoproterozoic. Based on the integrated contact relationship between Longli Formation and Chang’an Formation in the study area and the start of the global low latitude South China System glacial period (717.4Ma), the sedimentary time of Xiajiang Group is constrained to be between 815 and 717Ma.According to the regional magmatic events, the stratigraphic time-limits of each group of Xiajiang Group are further restrained and the Jiangjiang Group and its The stratigraphic division and contrast of the corresponding strata suggest that the Neoproterozoic magmatism restricts the evolution of the Lower Jiang Qun Basin in Southeast Guizhou.