扬子地块新元古代裂谷盆地莲沱组沉积分异及其物源分析  

Depositional Differentiation and Porvenance Analysis of Liantuo Formation in Neoproterozoic Rift Basin,Yangtze Block

作　　者：杜秋定 王剑[1,2] 汪正江 邓奇[3] 杨菲[3] Du Qiuding;Wang Jian;Wang Zhengjiang;Deng Qi;Yang Fei(School of Geoscience and Technology,Southwest Petroleum University,Chengdu 610500,China;Qiangtang Institute of Sedimentary Basin,Southwest Petroleum University,Chengdu 610500,China;Chengdu Center,China Geological Survey,Chengdu 610081,China;College of Earth Sciences,Chengdu University of Technology,Chengdu 610059,China)

机构地区：[1]西南石油大学地球科学与技术学院,四川成都610500 [2]西南石油大学羌塘盆地研究院,四川成都610500 [3]中国地质调查局成都地质调查中心,四川成都610081 [4]成都理工大学地球科学学院,四川成都610059

出　　处：《地球科学》2021年第7期2529-2543,共15页Earth Science

基　　金：国家自然科学基金项目“新元古代中期湘黔桂盆地重要变革期的沉积学响应研究”(No.41672108);“扬子东南缘中新元古代沉积超覆界面性质及盆地转换过程研究”(No.41672112);“鄂西裂陷槽在扬子古大陆裂解中的沉积响应及其油气地质意义”(No.41972121);“扬子地块莲沱组沉积环境及其时代归属研究”(No.41302091);中国石油-西南石油大学创新联合体科技合作项目(No.2020CX010000)。

摘　　要：扬子地块莲沱组及相当地层单元的划分和对比,一直是我国南华系(即Cryogenian)研究关键难题之一.新元古代裂谷盆地开启早期,构造-沉积分异作用,同裂谷相变很大,使得盆地边缘区地层序列不完整.过分依赖岩石地层单元对比,历存分歧,典型的就是关于莲沱组与板溪群地层对比、时代归属以及莲沱组的沉积环境问题.本文通过对扬子地块东南缘莲沱组沉积古环境分析和锆石U-Pb精确定年,认为莲沱组沉积时限为790~720 Ma,相当于板溪群中上部,是华南新元古代裂谷盆地沉积充填序列的第Ⅱ旋回.莲沱组顶部U-Pb最小年龄约720 Ma,制约了扬子地块Sturtian冰期的启动年龄≤720 Ma.通过对中扬子地块从北向南展布的莲沱组陆相-海陆过渡相-海相不同的沉积单元岩相组合的沉积特征观察研究,分析沉积环境并建立了沉积模式;莲沱组及休宁组碎屑锆石记录了莲沱组沉积时该盆地在780~760 Ma经历了持续热隆升与地层剥蚀,揭示了中国南方扬子和华夏地块聚合与裂解事件的重要信息.The division and correlation of the Liantuo Formation and its equivalent stratigraphic units in the Mid-Yangtze block has been one of the key problems in study of the Nanhuan System(Cryogenian)in China.In the early stage of the Neoproterozoic rift basin,tectonic-sedimentary differentiation,which made the stratigraphic sequence of the basin margin incomplete.Due to the excessive reliance on the lithostratigraphic unit comparison,which are typically related to the stratigraphic correlation between the Liantuo Formation and the Banxi Group.The geochronology and paleoenvironment of the Liantuo Formation are still highly controversial.An integrated approach of facies analysis,paleogeography,and geochronology provides new insights into the sedimentology and paleogeography in the Precambrian.The Liantuo Formation was deposited ca.790-720 Ma,which was equivalent to the Wuqiangxi Formation in the middle-upper part of the Banxi Group.Due to the uplift and subsidence of the earth’s crust,the sea water gradually overflows from south to north.Different sedimentary units of the Liantuo Formation,continental,transitional and Marine facies,have been developed from north to south in the Mid-Yangtze block.Detrital zircons from the Liantuo and Xiuning formations record that the basin experienced continuous heat uplift and stratigraphic denudation in 780-760 Ma during the deposition of the Liantuo Formation,which reveals the important information about the convergence and rift events of the Yangtze and Cathaysia blocks in south China.

关 键 词：年代学和古环境 莲沱组 构造-沉积分异 物源 沉积学 

分 类 号：P597[天文地球—地球化学]