皖南地区北东向断裂左行走滑时代及构造背景讨论

Discussion on the sinistral strike-slip age and tectonic background of northeast fault in southern Anhui Province

皖南地区地处扬子板块的东部,晚中生代发育多期与古太平洋板块俯冲有关的岩浆活动及构造变形。其中北东向断裂作为控制构造格架的重要断裂,自印支期以来经历了多期演化。前人多集中于探讨断裂的活动期次,对于各期活动时限的研究存在争论,这恰恰是制约深入研究皖南地区乃至中国东部中生代以来构造演化的关键。本文通过野外调查发现北东向断裂的左行走滑表现为高角度平移断层,古构造应力场反演指示其形成于NNE-SSW向挤压环境,锆石U-Pb年代学及地层切割关系指示皖南地区左行走滑时代为早白垩世末期。结合前人古生物、地层等方面研究,认为皖南地区左行走滑活动时限应在121~110 Ma。该期活动或与早白垩世末期伊泽奈崎板块运动方向的改变有关。

Lying in the east of the Yangtze plate,southern Anhui experienced multiple periods of magmatic activity and tectonic deformation related to the subduction of the Paleo-Pacific Plate during the late Mesozoic.As an important structure controlling the tectonic framework,the NE-trending fault has undergone multiple stages of evolution since the Indosinian period.Previous studies mainly focused on the active stages of faults,and there were disputes on the active periods of each stage,which restricted the indepth study of tectonic evolution in southern Anhui and even eastern China since Mesozoic.The field investigation reveals that sinistral strike-slip deformation of the NE-trending fault in southern Anhui is actually a high-angle translational fault.The inversion of the paleo-tectonic stress field indicates that it was formed in the NNE-SSW compression environment.Zircon U-Pb geochronology and stratigraphic cutting relationship indicate that its sinistral strike-slip age is at the end of Early Cretaceous.Combined with previous studies on paleontology and stratigraphy,it is believed that its sinistral strike slipping was formed in 121-110Ma,and may be related to the movement direction change of the Izenizaki Plate at the end of the Early Cretaceous.