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桂北地区丹洲群是南华裂谷盆地南段的一套连续裂谷充填沉积,厘定各组沉积时限及区域地层关系,对理解华南新元古代裂谷作用期次具有重要意义。本文利用LA-ICP-MS锆石U-Pb同位素测年,获得丹洲群合桐组二段和拱洞组底部凝灰岩夹层形成年龄分别为801±4 Ma和781±5 Ma。研究表明,丹洲群白竹组和合桐组一段与下江群甲路组和乌叶组、板溪群沧水铺组和马底驿组、西乡群孙家河组及陆良组一段相当,沉积时限为820~800 Ma;合桐组二段与下江群番召组相当,沉积时限为800~780 Ma;拱洞组可与下江群清水江组、平略组和隆里组,板溪群五强溪组中上部和牛牯坪组,西乡群大石沟组中上部和三郎铺组,陆良组二段及澄江组、开建桥组、莲沱组、虹赤村组和上墅组的中上部直接对比,沉积时限为780~725 Ma。华南新元古代裂谷盆地系统的典型地层锆石年龄存在5组高峰,峰值年龄分别为818±2 Ma、802±1 Ma、780±4 Ma、756±4 Ma及728±5 Ma。综合华南新元古代岩浆活动特征及盆地沉积演化过程,确定华南新元古代裂谷作用可分为两期:820~800 Ma和800~725 Ma。此外,华南新元古代岩浆活动与裂谷作用之间存在明显的耦合关系,但各期岩浆活动对各裂谷盆地的影响程度存在差异。
The Danzhou Group in the northern part of Guangxi is a series of continuous rift-filling sediments in the southern segment of the South China Rift Basin. It is of great significance to understand the depositional stages of Neoproterozoic rifting in southern China. In this paper, LA-ICP-MS zircon U-Pb zircon dating was used to obtain the formation age of tuff interlayer 801 and 4 Ma and 781 ± 5 Ma respectively in the second section of Tongdu Formation and the bottom of arch cave group. The results show that the first section of Bajian and He Tong formations in Danzhou Group is similar to the first section of Xiajia Group Jialu Formation and Wuye Formation, Banxi Group Cangshuipu Formation and Madianyi Formation, Xixiang Group Sunjiahe Formation and Luliang Formation, With a time interval of 820-800 Ma; the second section of He Tong Formation is equivalent to the Lower Fanqu group and the sedimentary period is 800-780 Ma; and the arch tunnel group can be connected with the Lower Jiangqu Qingshuijiang Formation, Pingliao Formation and Longli Formation, The upper middle part of the Wuqiangxi Formation of Xiqun and the Niudingping Formation, the middle and upper part of the Dashigou Formation of Xixiang Group and the Sanlangpu Formation, the second member of the Luliang Formation and the Chengjiang Formation, the Kaijianqiao Formation, the Liantuo Formation, the Hongchicun Formation and the Shangshu Formation The direct contrast between the upper part of the deposition time is 780 ~ 725 Ma. There are 5 groups of typical zircon age of Neoproterozoic rift basin system in South China, with peak ages of 818 ± 2 Ma, 802 ± 1 Ma, 780 ± 4 Ma, 756 ± 4 Ma and 728 ± 5 Ma respectively. Based on the characteristics of Neoproterozoic magmatic activity and sedimentary evolution in South China, the Neoproterozoic rifting in South China can be divided into two phases: 820 ~ 800 Ma and 800 ~ 725 Ma. In addition, there is a clear coupling between the Neoproterozoic magmatism and rifting in South China, but there are differences in the extent of magmatic activity in each rift basin.