Analytical and Numerical Investigation of 3D Multilayer Detachment Folding

Folding is a common mode of deformation in geology when mechanically layered rocks are subjected to compression. They occur on a wide range of scales from mm-scale to 10’s of kilometers in places where upper crustal rocks are compressed as a result of tectonic plate convergence (such as in the Zagros mountains, Iran). The physical instability that results in the formation of folds has been studied for different rheologies: e.g. elastic, viscous andvisco-elastic [1], power law [2] andmore recently, also for visco-elasto-plastic [3]. However, most of the studies focus on the problem of a competent layer embedded in a matrix [1] or the case of a multilayer system embedded in a matrix [4], and therefore they consider only two different material properties. This is appropriate for small-scale folds, but on a crustal scale it was recently demonstrated that the viscosity contrast between various sedimentary layers also plays an important role [3]. Here, we therefore focus on the case of a multilayer system overlying a matrix or lower detachment layer [4, 5] affected by gravity with three different material viscosities: lower detachment or salt layer (ηs), overlying weak layers (ηw) and competent layers (ηc).