Stress distribution within subducting slabs and their deformation in the transition zone

The mechanical behavior of slabs in the mantle transition zone is a poorly understood phenomenon. To obtain a better understanding of the stress and deformation pattern inside subducting slabs, we performed 2D numerical simulations of the subduction process in a purely viscous, non-linear rheological model including diffusion creep, dislocation creep and a stress limiting mechanism. The model calculations are used to investigate the effects of yield stress, plate age and surface boundary condition (free-slip versus given plate velocity) on the stress development in and around a subducting slab and on the deformation of the subducting plate in the transition zone. The deformation and morphology of subducted slabs may differ between free-slip and kinematic boundary condition models in some cases, especially for young and relatively weak slabs. Even though kinematically driven subduction morphology may look realistic in most cases, our results show that stress distributions can differ significantly if the discrepancy between free-slip and kinematic subduction velocity is large, and in some model cases even influence the ability of the plate to penetrate into the lower mantle. Stress distributions such as the ones presented in this study can be a valuable tool in understanding the complex and enigmatic interaction between subducting slabs and the transition zone.