扬子西缘新元古代澄江组火山—沉积序列及其对盆地性质的约束

It has been controversial that the nature and dynamic mechanism of Neoproterozoic sedimentary basin in the western margin of Yangtze Block for decades. The Chengjiang Formation is one of the most significant Neoproterozoic stratigraphic units developed in the western margin of Yangtze Block, of which volcanic-sedimentary successions have recorded the crucial information during its development, e.g. sedimentary overlap, basin filling, magmatic activities and tectonic process. Based on field investigation, section measure and petrological study, this project aims to reconstruct the basin depositional filling process by studying depositional facies and microfacies, paleocurrent directions, sedimentary environment and sequence evolution of the Chengjiang Formation, which represent early sedimentary filling of Neoproterozoic sedimentary basin; Meanwhile, situ zircon U-Pb dating, major and trace elements and Sr-Nd-Hf isotopes studies will be also carried on volcanic rocks of the Chengjiang Formation with the purpose of revealing their formation time, petrogenesis and tectonic background. Combined with regional relevant data, we will try to improve understanding of the nature and dynamic mechanism of Neoproterozoic sedimentary basin in the western margin of Yangtze Block, and thus this project may shed light on the sedimentary-tectonic history of Neoproterozoic sedimentary basins in South China and its relationships to the synchronous global geological events.

扬子西缘新元古代沉积盆地性质及其动力学机制一直存在很大争议。澄江组是扬子西缘新元古代地层的重要单元，其发育的火山—沉积序列记录了其形成时沉积超覆、盆地充填、岩浆活动及构造作用等关键信息。本申请项目拟在野外调查、剖面测制和岩石学研究的基础上，对澄江组所代表的新元古代早期充填沉积开展沉积相和微相、古流向、沉积环境及序列演化研究，以恢复盆地沉积充填过程；对其中的火山岩开展锆石U-Pb定年、主微量元素及Sr-Nd-Hf同位素研究，以揭示其形成时限、岩石成因及构造背景。结合区域相关研究成果，分析扬子西缘新元古代沉积盆地性质，综合限定盆地演化的动力学机制，进而为探讨华南新元古代盆地的沉积—构造演化史及其与全球地质事件的关系提供依据。

本项目按照研究计划完成。于2013-2016年期间，对扬子西缘新元古代澄江组及其华南相关地层开展了系统的野外调研。通过详细的沉积学、地球化学和同位素年代学研究，恢复了盆地沉积充填过程、厘定了澄江组底部火山岩的喷发时限及成因、限定了新元古代沉积盆地的构造属性。. 澄江组火山岩岩相主要沿盆地边缘断裂发育，向东逐渐演变为冲积扇相、河流相和三角洲相，与典型半地堑盆地的充填模式相吻合。澄江组底部玄武岩及其上覆凝灰岩的锆石SHRIMP U-Pb年龄分别为806.4 ± 6.7 Ma和788.4 ± 5.9 Ma，指示玄武岩形成时限为800 Ma左右。地球化学方面，澄江组底部玄武岩属拉斑玄武岩系列，未见明显Nb-Ta亏损；它们显示几乎恒定且与OIB接近的Nb/Ta和Zr/Hf比，指示其未经历明显地壳混染；形成于板内裂谷环境的软流圈-岩石圈相互作用。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，华南成冰纪江口冰期和南沱冰期的启动时限分别为ca. 715 Ma和ca. 650 Ma，与Rodinia超大陆其他陆块的Sturtian和Marinoan冰期完全同步。. 项目执行过程中，培养博士生1名、硕士生2名。迄今发表期刊论文14篇，其中3篇为SCI论文。