Slab-mantle flow interaction: Influence on subduction dynamics and duration

We investigate the influence of mantle flow relative to the lithosphere on subduction dynamics. We use 2D thermo-mechanical models assuming incompressible non-Newtonian fluid rheology. Different mantle flow velocities consistent with absolute plate motion models are tested, as well as both directions of flow, either sustaining or opposing slab dip. The effects of different inflow/outflow velocity profiles, slab strengths and upper-lower mantle viscosity contrasts are also evaluated. Slab dip deviations between models with opposite mantle flow directions range from 37° for relatively strong slabs (?max = 1025 Pa s) to 50° for weaker slabs (?max = 1024 Pa s), accounting for a significant amount of natural slab dip variability. For imposed mantle flow supporting the slab, the initial stage of slab steepening is followed by a stage of continuous slab dip decrease. This slab shallowing eventually leads to mantle wedge closure, subduction cessation and slab break-off, possibly driving subduction flips.

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