Effects of surface processes on multilayer detachment folding: a numerical approach

Over the past decades, the interaction between surface processes and development of mountain belts has been extensively studied. While syntectonic sedimentation appears to control the external development of the fold-and-thrust belts, erosion strongly influences the evolution of internal regions within mountain belts. The effects of surface processes on brittle deformation have been thoroughly studied using analogue and numerical models of accretionary wedges, however, most of the numerical studies used a 2D model of deformation and/or a simple formulation for the surface processes, where both sedimentation and erosion are rarely present together. Coupled analogue models of deformation and surface processes are challenging, due to material and scaling issues, and often only reproduce two end-member cases (no erosion vs very strong erosion, where all the material is removed), but fail to investigate the transitional cases. In contrast, interactions between surface processes and ductile deformation (e.g. multilayer detachment folding) have been poorly investigated. Thin-skinned fold and thrust belts are seen as the result of compressional deformation of a sediment pile over a weak layer acting as a décollement level. The resulting surface expression has often been interpreted, based on geometrical criteria in terms of fault bend folds, propagation folds and/or detachment folds. A few analogue studies have demonstrated that fold morphology can be influenced by erosion rates or preferential localization of sedimentation, and additionally, that the fold growth can be stopped by increasing the supply of sediments. Here we aim to numerically investigate the effects of surface processes and multilayer folding in three dimensions. For this purpose, we have developed a finite-element based landscape evolution model (both erosion and sedimentation) using PETSc, and coupled it to the 3D mechanical code LaMEM. The landscape evolution model uses a non-linear diffusion formulation (Simpson and Schlunegger, 2003), taking into account both hillslope and channel processes. We present here preliminary results of the coupling between sediment loading and folding.