滇东北待补地区碎屑锆石U-Pb年龄及其对新元古代康滇裂谷盆地沉积古地理演化的启示

U-Pb ages of detrital zircons from Daibu area,northeastern Yunnan Province:the implication Neoproterozoic paleogeographic evolution of the Kangdian rift basin

扬子西缘新元古代康滇裂谷盆地是华南新元古代裂谷盆地系统的重要组成单元,其充填序列和演化模式研究对华南扬子古大陆的形成演化具有重要意义。报道了位于扬子西缘待补地区新元古代康滇裂谷盆地中“板溪-南华楔状地层”成熟期相当的澄江组顶部碎屑锆石(PM109-51)LA-ICP-MS U-Pb年龄,获得10组峰值年龄,认为最年轻的一组年龄加权平均值(723±9 Ma)代表了区域内华南长安冰期(Sturtian)的启动时间;通过与区内早寒武世沧浪铺组底部碎屑锆石(PM005-14)LA-ICP-MS U-Pb年龄值比较,发现两者在801 Ma峰值与816 Ma峰值区间的物源贡献率上存在较大的差别,结合前人资料数据的分析,认为在新元古代康滇裂谷盆地的发展期甚至物源无明显变化的震旦纪—早寒武世地层中,这些表现为裂谷盆地幼年期的物源贡献率突变现象,代表了康滇裂谷半地堑盆地系统对物源的约束控制作用:早期由裂谷肩老地层或岩浆岩提供物源,由于小型半地堑盆地群的存在,物源对远离主边界断裂的区域贡献率较低,随着小型半地堑盆地的连通性加强,后期物源辐射则更广泛。

The Neoproterozoic Kangdian rift basin of the western margin of the Yangtze is an important component of the Neoproterozoic rift basin system in South China.The study of its filling sequence and evolution model is of great significance to the formation and evolution of the ancient Yangtze Continent in South China.This paper reports the LA-ICP-MS U-Pb age of detrital zircon at the top of the Chengjiang Formation(PM109-51)in the mature period of the"Banxi-Nanhua Wedge Formation"in the Neoproterozoic Kangdian Rift Basin in the western margin of Yangtze,acquired 10 groups peak age,and the earliest weighted average age(723±9 Ma)is limited to represent the start time of the Chang’an ice age(Sturtian)in southern China.Comparing with the LA-ICP-MS U-Pb age value of detrital zircon at the bottom of the Early Cambrian Canglangpu Formation in the region,It is found that there is a big difference in the source contribution rate between the 801 Ma peak and the 816 Ma peak,Combined with the analysis of previous data,it is believed that during the development period of the Neoproterozoic Kangdian rift basin and even the Sinian-Early Cambrian strata without obvious changes in provenance,these performances are the source contribution of the rift basin in the early stage The rate mutation phenomenon represents the constraining control effect of the Kangdian rift half-grain basin system on the provenance.In the early stage,the old rift shoulder stratigraphy or magmatic rock provided the source.Due to the existence of the half graben basin group,the provenance contribution rate to the area away from the main boundary fault is low.As the connectivity of the half graben basin increases,the later sources are more widely radiated.