Résumé
As shown by laboratory experiments, olivine, which is the dominant mineral in the upper mantle and hence the major component of both the lithospheric plates and of the asthenosphere, can flow over geological scales by a combination of dislocation motions and diffusional processes, with different behaviour depending on temperature and strain rates. Dislocation creep is expect to dominate over diffusion creep in regions submitted to strong deformation. The rheology of a material deforming by dislocation creep is usually described by a power law, but the later description breaks out at high stresses and low temperatures. Geodynamic models therefore often use 2 different laws: a power law at high-temperature and a (pseudo-Peierls) law at low-temperature, that mimics the exponential dependence of strain rate on stress observed at high stresses. Based on the results of recent dislocation dynamic calculations, we have derived one single "modeler-friendly" parameterization describing the rheology for dislocation creep of olivine over a large temperature and stress range. In this parameterization, stress is expressed as a function of strain rate which makes the calculation of an effective viscosity straightforward. The parameterisations use sigmoid functions mimicking the asymptotic behaviour towards null stress at low strain rates. We implemented this new rheology in subduction models to study the feedback between strain rate and viscosity, which plays a major role for subduction dynamics.