Our work focuses on understanding the evolution and structural style of sedimentary basins and passive margins in 3D using state of the art computational modelling techniques. To date very few 3D models exist that follow the evolution of tectonic processes into large deformation modes
with sufficient resolution to resolve individual faults and shear zones. The code we use, DOUAR, is one of them: it is an ALE thermo-mechanically coupled fully parallel Finite Element code developed in the past three years which solves for visco-plastic flows in 3D. It relies on an adaptive grid based on octrees and has the ability to track interfaces and, in particular, the free surface, by using a dual representation based on a set of particles placed on the interface and the computation of a level set function. Controls on the geometry and spacing of three-dimensional frictional-plastic shear zones in simple two-layer models are investigated. We specifically focus on the mechanisms underlying along axis variation of rift polarity and rift segmentation for varying rheological stratification.