A nonlinear and time-dependent visco-elasto-plastic rheology model for studying shock-physics phenomena

We present a simple and efficient implementation of a viscous creep rheology based on diffusion creep, dislocation creep, and the Peierls mechanism in conjunction with an elasto-plastic rheology model into a shock-physics code, the iSALE impact code. Our approach is based on the calculation of an "effective viscosity" which is then used as a reference viscosity for any underlying viscoelastic (or even visco-elasto-plastic) model. Here we use a Maxwell-model which best describes stress relaxation and is therefore likely most important for the formation of large meteorite impact basins. While common viscoelastic behavior during mantle convection or other slow geodynamic or geological processes is mostly controlled by diffusion and dislocation creep, we show that the Peierls mechanism dominates at the large strain rates that typically occur during meteorite impacts. Thus, the resulting visco-elasto-plastic rheology allows implementation of a more realistic mantle behavior in computer simulations, especially for those dealing with large meteorite impacts. The approach shown here opens the way to more faithful simulations of large impact basin formation, especially in elucidating the physics behind the formation of the external fault rings characteristic of large lunar basins.