碰撞带倾角和摩擦系数对陆-陆碰撞变形的影响

借助一个简单的大陆与大陆碰撞模型,即把两个大陆的碰撞简化为两个粘弹性块体的碰撞,两个块体之间的不连续变形面对应两个大陆之间的碰撞断裂带,运用三维粘弹性拉格朗日非连续变形有限元(LDDA)方法,通过分析模型中不连续变形面的存在对两个粘弹性块体碰撞变形的影响,探讨了大陆碰撞断裂带的倾角和摩擦系数对两个大陆碰撞变形影响的一般规律,给出了大陆碰撞变形的一些显著的特点。尽管运算模型的几何尺寸、边界条件等参考了印度和欧亚大陆碰撞的实际特征,但所得结果适用于更一般的情况。研究结果表明,碰撞断裂带倾角和摩擦系数对陆-陆碰撞变形有着重要的影响。当断裂带倾角在15~30°时,两个大陆板块碰撞导致的仰冲板块一侧隆升高度相对更大,利于形成高大的山脉,其中以15°倾角对应的仰冲板块一侧隆升最高;当断裂带倾角在30~45°时,两个大陆板块碰撞导致的俯冲板块的俯冲深度相对更深,利于形成深陷的盆地,其中以45°倾角对应的俯冲陆块一侧俯冲最深;当断裂带倾角≥75°时,两个大陆板块之间的相对俯冲和仰冲作用变得不明显。碰撞断裂带摩擦系数越小,碰撞过程中两个大陆板块之间相对俯冲和仰冲作用越强,形成高大的山脉和深陷的盆地要求碰撞断裂带摩擦系数≤0.2。从大陆与大陆碰撞变形构造特征看,除发育前陆盆地-山脉系统外,在仰冲陆块一侧靠近造山带后缘还发育呈不对称结构的挤压性凹陷,当两个大陆板块碰撞断裂带倾角在15~30°时,该类型凹陷更容易形成,其中以30°倾角对应的凹陷最深,反映其形成可能是大陆碰撞过程中陆块之间相对俯冲和仰冲运动的综合结果。

The effects of the dip angle and friction factor of a collision-related fracture zone on the deformation caused by the collision between two continental plates

We study a simple model of the deformation caused by the collision between two continental plates,in which the continental collision is simplified as the collision between two viscoelastic plates.A discontinuous deformation interface is chosen to approximate the fracture zone between the two continental plates.A finite element approach—three dimensional viscoelastic Lagrangian discontinuous deformation analysis(LDDA) is used to study the role of the discontinuous deformation interface on the collisional deformation between two viscoelastic plates.Based on this,we investigate the influence of the dip angle and friction factor of a collision-related fracture zone on the deformation caused by the collision between two continents.The results show some remarkable characteristics.Although the model's geometric size and boundary conditions are patterned after the India-Asia collision,the outcome may be applicable to more general situations.The results show that whether the dip angle or friction factor of the fracture zone does have an important effect on the continental collision deformation.With a dip angle between 15° and 30°,the uplift of an obducted plate during continental collision is much higher,and able to form a high mountain.The uplift is greatest with a dip angle of 15°;whereas with a dip angle between 30° and 45°,the subduction depth of a plate is much deeper,and able to form a deep basin.The subduction depth is greatest with a dip angle of 45°.When the dip angle is equal to or greater than 75°,subduction and obduction movements between two continents become undistinguishable.On the other hand,the less the friction factor of a collision-related fracture zone,the stronger the subduction and obduction movements between two continents,and the friction factor should not be larger than 0.2 so as to be able to form a high mountain and a deep basin by the collision between two continents.The general feature of deformation caused by the collision between two continents also reveals that,during the collision process,apart from a foreland basin and high mountains being formed,there is another compressive depression with an asymmetric structure developed on the side of the obducted plate,which is much easier to be formed when the dip angle of the collisional fracture zone is between 15° and 30° and is the deepest with a dip angle of 30°.This implies that the compressive depression is controlled by both subduction and obduction between two continents.