郯庐断裂带泗县徐井段晚第四纪新活动的宏微观现象初步研究

摘要

New activities since Late Quaternary are discovered by the trenches of the Tancheng-Lujiang fault zone,Xujing of Sixian county,Anhui province,showing reverse fault type colluvial wedge,tensile fracture wedge,fragmentation flow and seismic fault.Based on comprehensive analysis of the phenomena on site,we make preliminary inferences that after the Middle Pleistocene deposits,the trench was pressed first,the Late Cretaceous brick red sandstone thrust collapsed on the Middle Pleistocene deposits from the west to the east,forming a reverse fault type colluvial wedge.Then the tensile fracture activity occurred,splitting the wedge open.High speed extrusion thrust faults occur,along the east edge of the wedge,cross section extrusion,the fragmentation flow was generated and formed a reverse fault type colluvial wedge.The latest activities of the fracture occurred after black soil overlying sediments,showing the small amplitude thrust activity,caused faults on both sides of the black soil thickness difference.It is indicated that after the Middle Pleistocene deposits,the fault underwent successively four activities in the form of "extrusion-tension-extrusion-extrusion".The latest activity occurred into the Late Quaternary.Although known to be confirmed by the age of the samples tested and results of the analysis of the microscopic observation,these attempts to understand the new activity in the Early Holocene.According to the formation of reverse fault type colluvial wedge,tensile fracture wedge,seismic fault,these activities should be high speed stick slip activity and corresponding to several strong events of prehistoric earthquakes.The above understanding is partly confirmed by the results of the original microscopic observation.%探槽揭示,郯庐断裂带安徽泗县徐井一带第四纪以来的新活动表现为逆断型崩积楔、张裂楔、碎裂流和地震断层.根据现场分析初步认为,中更新统沉积后,探槽所在部位先遭受挤压,晚白垩世砖红色砂岩自西向东上冲垮塌到中更新世沉积之上,形成逆断型崩积楔-1;接着发生张性断裂活动,形成开口向上的张裂楔;随后,所在部位又遭受挤压,沿张裂楔的东边界断面挤压逆冲活动产生碎屑物质上抛流动,形成逆断型崩积楔-2;其上逐步形成更新沉积,当黑土层堆积以后,再次遭受挤压,使得断面上下黑土层堆积厚度显现差异.这表明中更新统沉积以后,断裂曾先后发生挤压-引张-挤压-挤压共4次活动,最新活动在全新世早期.根据逆断型崩积楔、张裂楔和地震断层等的成因,这几次活动应属高速粘滑活动,对应几次强烈的史前地震活动事件.上述认识部分得到原态微观观测分析结果的证实.