皖南歙县岑山盆缘断裂年代学特征及构造意义

Chronology analysis and tectonic significance of Censhan basin marginal fault in Shexian,Anhui Province

为探讨皖南休宁-屯溪中生代红层盆地白垩纪以来的伸展作用及其与周围地层、岩浆岩的时序关系,研究了歙县岑山盆缘断裂带内两条硅化脉.硅化脉具破裂结构的锯齿状,镜下石英呈贝壳状,半自形结构,表面具小孔洞及撞击碎裂特征的结晶带杂乱分布,指示快速拉张的形成环境.CL图像和稀土元素配分模式具岩浆锆石特征,锆石U-Pb年代学研究结果揭示了区内至少发生过3次构造-岩浆活动,分别发生在晋宁晚期、加里东晚期、燕山期.岑山盆缘断裂为歙县-祁门断裂带产生的次级断裂,形成时间可界定为451.0±1.9?441.7±1.0 Ma;早白垩世晚期NW-SE向伸展开始时间为132.8±2.1Ma,构造活动强烈,到112.3±1.2 Ma岩浆活动基本停止,构造活动微弱,标志白垩纪红层盆地的形成,因此早白垩世伸展的时间为132.8?112.3 Ma.厘定了区域构造活动、岩浆作用的时序关系,为皖南地区白垩纪弧后伸展环境提供了辅助证据,对认识皖南乃至整个华南地区的构造背景及地质演化具有重要意义.

In order to explore the extensional action of the Xiuning-Tunxi Mesozoic red basin and its temporal relationship with the surrounding strata and magmatic rocks since the Cretaceous,two silicified veins in the Censhan basin margin fault zone were studied.The silicide veins were serrated with a fractural structure,and the quartz under the microscope was shell-shaped and semi-automorphic,with a disorganized crystal zone characterized by small holes on the surface and impact fragmentation,indicating a rapidly tensioned formation environment.The cathodoluminescence diagram and chondrite-normalized rare earth element diagram showed characteristics of magmatic zircon.The zircon U-Pb chronology revealed that there were at least three tectono-magmatic activities in the area.The censhan basin margin fault was a secondary fault generated in Shexian-Qimen fault zone,and the time of formation could be defined as 451.0±1.9 Ma to 441.7±1.0 Ma.In the early Cretaceous,NW-SE extension began at 132.8±2.1 Ma,with a strong tectonic activity and ended at 112.3±1.2 Ma,indicating the formation of the Cretaceous red basin.The extension time of the early Cretaceous was 132.8 to 112.3 Ma.The temporal relationship of regional tectonic activity and magmatism was determined,providing auxiliary evidence for the environment of cretaceous retro-arc extension in southern Anhui Province.The results can present an important basis for the understanding of tectonic background and geological evolution in southeast China.