Abstract Most natural examples of transpression zones developed at oblique convergence regime are inherently 3D and have inclined boundaries. A 3D finite element model with an elasto-plastic rheology is used to investigate the structural and mechanical evolution of inclined transpression zones in a rock sequence above a frictional basal detachment. Inelastic constitutive relationships allow permanent strains to develop in response to the applied loads. FE-modelling results show that oblique convergence is accommodated by discrete deformation at the main pre-existing inclined faults (=70°) and by distributed brittle and ductile deformation at active blocks. Oblique contraction at the active blocks resulted mainly in layer-parallel shortening, orthogonal to the model outer boundaries, whereas thickening in the horizontal and vertical directions was accommodated via layer-parallel, fault strike-parallel extension and up-dip extrusion (i.e., inclined extrusion). Lateral extrusion should have compensated the rest and/or volume loss took place. Folding and thickening of the mobile backstop produced a non-cylindrical, asymmetric, bi-vergent anticline where permanent strains developed principally in the steep forelimb. Secondary, conjugate fault zones also accommodate oblique slip and contribute to uplift. Displacement vectors within the transpression zone are rotated counter-clockwise (ca. 20°–30°) with respect to vectors in the fixed backstop. Areas with higher rotation values seem to correlate with those showing higher ellipticity values. The presence of pre-existing faults favored strain partitioning from the onset of deformation. FE-modelling results compared with analytical, natural example, and analogue modelling results show that our mechanical modelling can overall match inclined transpression zones geometry that present different modes of strain partitioning and localisation.

中文翻译：

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倾斜、脆性-延展性受压区的变形力学：来自 3D 有限元建模的见解

摘要 在倾斜收敛状态下形成的压压带的大多数自然例子本质上是 3D 的，并且具有倾斜的边界。具有弹塑性流变学的 3D 有限元模型用于研究摩擦基底分离上方岩石序列中倾斜压压区的结构和机械演化。非弹性本构关系允许响应施加的载荷产生永久应变。有限元建模结果表明倾斜收敛是由主要预先存在的倾斜断层（= 70°）的离散变形和活动块的分布的脆性和韧性变形所适应的。活动块的斜收缩主要导致平行于层的缩短，与模型外边界正交，而水平和垂直方向的增厚是通过层平行、断层走向平行延伸和上倾挤压（即倾斜挤压）来适应的。横向挤压应该已经补偿了剩余的和/或发生的体积损失。移动式逆止器的折叠和加厚产生了一个非圆柱形、不对称、双收敛的背斜，永久应变主要发生在陡峭的前肢。次生共轭断层带也适应倾斜滑动并有助于抬升。压缩区域内的位移矢量相对于固定逆止器中的矢量逆时针旋转（约 20°–30°）。旋转值较高的区域似乎与椭圆率值较高的区域相关。预先存在的断层的存在有利于变形开始时的应变分配。有限元建模结果与分析、自然示例和模拟建模结果的比较表明，我们的机械建模可以整体匹配倾斜的受压区几何形状，这些几何形状呈现不同的应变分配和定位模式。