大别造山带南界襄樊—广济断裂带的演化规律与构造意义

自中三叠世扬子与华北板块发生碰撞—深俯冲作用以来,大别造山带南界上的襄樊—广济断裂带主要经历过两次变形事件: 1)早期变形事件发生在中三叠世末—晚三叠世初的造山带折返阶段,表现为造山带南边界上的韧性剪切带。这期北西—南东走向的剪切带向南西陡倾,发育北西—南东向的矿物拉伸线理,主要为右行走滑的运动性质,属于造山带斜向折返的侧边界走滑剪切带。造山带折返过程中将前陆褶断带北缘原先东西向褶皱改造为北西—南东走向。2)晚期变形事件发生在晚侏罗世,表现为脆性逆冲断层,使得前陆褶断带向北东逆冲在造山带南缘之上,同时在前陆上形成了一系列的逆冲断层。该断裂带的晚期逆冲活动与郯庐断裂带左行平移同时发生,代表了滨太平洋构造活动的开始。

Evolution and tectonic implications of the Xiangfan-Guangji fault zone along the southern border of the Dabie orogenic belt

The Xiangfan-Guangji fault zone experienced two phases of deformation events since collision and deep subduction of the Yangtze and north China plates in Middle Triassic.The earlier deformation event took place during the orogenic exhumation of the latest Middle Triassic to earliest Late Triassic,and resulted in formation of ductile shear zone along the southern border of the orogenic belt.The NW-SE shear zone dips SW steeply,shows NW-SE mineral lineation and thrusting dextral shear sense.It represents a boundary strike-slip shear zone developed during oblique exhumation of the orogenic belt.The exhumation caused previous E-W folds in the northern foreland fold and thrust belt being changed into NW-SE trends.The later deformation event in the fault zone happened in Late Jurassic,and resulted in brittle thrusts and NE-ward thrusting of the foreland fold and thrust belt over the orogenic belt.A series of thrusts in the foreland fold and thrust belt were also associated with this deformation event.The later thrusting in the Xiangfan-Guangji fault zone is coeval with sinistral faulting of the Tan-Lu fault zone,and represents initiation of the circum-Pacific tectonic regime.