巢湖北部青苔山推覆构造的特征及其成因

Characteristics and formation of Qingtaishan thrust structure in northern Chaohu area

青苔山推覆构造是滁河断裂带的重要组成部分。推覆体主要为震旦系、寒武系的灰岩,由NW→SE推覆掩盖在志留系页岩之上,主滑脱面倾角较小(10°～20°)。推覆体中有多期断层存在:高角度逆冲断层倾角60°至直立,并伴随有较大的碎裂岩带,东强西弱;有2组走滑断层发育:一组是NE向的左行走滑断层,与郯庐断裂带有密切的成因联系;另一组为NW向走滑断层,形成时代较晚,破坏早期逆冲断层和NE向走滑断层。推覆体中最晚一期的低角度逆掩断层以主滑脱面为代表,倾角较小,数量较少。青苔山推覆构造形成于早、中侏罗世,是山前盆地冲断变形的产物。晚侏罗世—早白垩世在中国东部大地构造背景下,表现为左行平移;晚白垩世—早第三纪伸展为主,其西侧发育有K2—E红色沉积物;晚第三纪以来再一次逆冲挤压,沿早期逆冲断层再次活动,最终形成现在的推覆构造。

Qingtaishan thrust structure is an important part of Chuhe fault zone. Thrust nappes consist of the limestone of Sinian and Cambrian which thrusted over the shale of Silurian with NW→SE thrust direction and had a drape cline thrust surface. There are fault thrust,strike slip fault and over thrust in this thrust nappe.Thrust fault is a cataclasite zone. The dip angle of thrust faults surface is from 60° to 90°. Strike slip faults have two directions of NE and NW. The formation time of NE strike slip faults is earlier than that of NW strike slip faults.The dip angle of over thrusts is from 10° to 20° in Qingtaishan thrust nappe. The chief slip plane under Qingtaishan mountain thrust faults were formed by foreland basin deformation in early Jurassic age.Fromlate Jurassic to early Cretaceous they were sinistral fault, and showed extensibility from late Cretaceous to Eogence. Over thrust faults have moved since Neogene age.The thrust distance of Qingtaishan thrust is about 2 km.