Strain localization in a visco-elasto-plastic medium using strain-dependent weakening and healing rheology

The formation and maintenance of narrow, lithospheric shear zones and their importance in plate-tectonics remain one of the major problems in geodynamics. While the cause and consequence of strain localization and weakening within the lithosphere remain debated, it is clear that these processes play an essential role in lithospheric deformation across a wide range of spatio-temporal scales. Here, we analyze the efficiency of strain localization in a 2-D visco-elasto-plastic medium for a strain-dependent weakening and healing (SDWH) rheology using 2-D numerical, thermo-mechanical experiments with kinematic boundary conditions. Such a parameterized rheology successfully mimics more complex transient weakening and healing processes, akin to a grain-size sensitive composite (diffusion and dislocation creep) rheology. In addition, the SDWH rheology allows for memory of deformation. This enables self-consistent formation and reactivation of inherited weak zones within the lithosphere and sustains those weak zones over an extended period of time. We further analyze the resulting shear zone patterns and seek to answer the questions: What is the typical, effective intensity of strain localization? What are the dimensions of the resulting shear zones? Are such shear zones mesh-dependent in numerical models and, if so, can we exploit existing regularization approaches for the SDWH rheology?