大别山碰撞造山带的地球动力学  

GEODYNAMICS OF THE DABIESHAN COLLISIONAL OROGENIC BELT

作　　者：王清晨[1] 林伟[1] 

机构地区：[1]中国科学院地质与地球物理研究所,北京100029

出　　处：《地学前缘》2002年第4期257-265,共9页Earth Science Frontiers

基　　金：国家自然科学基金资助项目 (4 97940 42 )

摘　　要：大别山碰撞造山带的形成和其中超高压变质岩的形成折返具有统一的动力学过程。对大别山超高压变质岩形成 -折返的研究表明 ,大别山的超高压变质作用是冷大陆地壳被前导洋壳下拽而持续俯冲的结果。超高压变质岩的折返是多阶段的。第一阶段 (2 30～ 2 10Ma)在低地温梯度 (约10℃ /km)下发生同俯冲折返 ;第二阶段 (2 10～ 170Ma)的折返由深俯冲板片的断离引发 ,浮力开始起作用 ;第三阶段 (170～ 12 0Ma) ,以区域性岩浆活动、穹隆伸展构造活动和深剥蚀沉积为特征。从分析超高压变质岩的形成折返过程入手 ,以侏罗纪末作为时间参照点 ,以合肥盆地的侏罗系顶界作为当时的地理参照点 ,根据不同岩石单元中岩石的形成深度和碰撞造山中的位移状态 ,可把大别山碰撞造山带划分为原位系统、准原位系统、异位系统和热穹隆改造系统等结构单位。陆陆碰撞造山带形成的物理学前提是俯冲陆壳物质的低密度 ,而最终形成造山带的直接动力学过程则是深俯冲板片的断离及其引发的一系列近垂向运动的地质过程。The formation of the Dabieshan Orogenic Belt (DOB) and the formation-exhumation of the ultrahigh-pressure (UHP) metamorphic rocks in the DOB followed one and the same geodynamics. The UHP metamorphism happened in the DOB during deep subduction of the cold continental crust that was dragged down by oceanic crust subducting. The UHP rocks were exhumed in more than one stage. Syn-subduction exhumation proceeded in the first stage (230～210 Ma). Breakoff of the subduction slab resulted in squeezing up the buoyant UHP metamorphosed crust material in the second stage (210～170 Ma), when the geothermal gradient was enhanced. The third stage (170～120 Ma) is characterized by regional magmatism and dome-extension structures. From the viewpoint of exhumation, four units can be recognized in the DOB if taking into account of their forming depth, deformation and displacement. These units are the autochthonous, para-autochthonous, allochthonous, and dome-reworked units. The presupposition for a collision orogenic belt to form is the low density of the subducted crust, while the direct impetus for building up the orogen is the breaking-off of the deep subducting slab and the subsequently upward going processes in the mantle depth.

关 键 词：超高压变质岩 碰撞造山带 大别山 地球动力学 

分 类 号：P541[天文地球—构造地质学]