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RESEARCH PRODUCT

The effect of rheological approximations in 3-D numerical simulations of subduction and collision

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Abstract Subduction and collision zones evolve differently from one another due to different rheological properties, different amounts of regional isostatic compensation, and the different mechanisms by which forces are applied to the convergent plates. The rheology of mantle and lithosphere is known to have the largest influence on the dynamics of subduction and continental collision. However, previous 3-D geodynamic models of subduction/collision processes have used various rheological approximations, making their results difficult to compare, since there is no clear understanding on the extent of these approximations on the dynamics. Here, we test the effect of rheological approximations in a geometrically simplified 3-D model in which the dynamics of subduction and collision is entirely driven by slab-pull (i.e., “free subduction”). The results exhibit a wide range of behaviors depending on the rheological law employed: from linear viscous (LV) to temperature-dependent visco-elasto-plastic (VEP) rheology that takes into account both diffusion and dislocation creep. Rheological approximations exert a strong effect on slab morphology, trench migration rates and topography in the upper plate. For example, we find that slab dynamics varies drastically between end member models. In LV approximations, slabs do not break-off, but instead buckle at the transition zone. The dynamics is dominated by low strain rates and diffuse stresses, and topography is controlled by lateral extrusion of material which homogenizes amplitudes in the upper plate. In simulations with non-linear VEP rheology, slab break-off occurs at the corners of the indenting continent, opening of a back-arc basin is fast and topography has a laterally heterogenous distribution of amplitudes. Opening of a back-arc basin is observed only in simulations with non-linear VEP rheology. When the rheology is approximated with multiple discrete layers, the dynamics also resembles more the non-linear VEP case.