Strong Plate, Weak Slab Dichotomy

Abstract:

Models of mantle convection on Earth produce styles of convection that are not observed on Earth.
Moreover non-Earth-like modes, such as two-sided downwellings, are the de facto mode of convection in such models.
To recreate Earth style subduction, i.e. one-sided asymmetric recycling of the lithosphere, proper treatment of the plates and plate interface are required.

Previous work has identified several model features that promote subduction.
A free surface or pseudo-free surface and a layer of material with a relatively low strength material (weak crust) allow downgoing plates to bend and slide past overriding without creating undue stress at the plate interface. (Crameri, et al. 2012, GRL)
A low viscosity mantle wedge, possibly a result of slab dehydration, decouples the plates in the system. (Gerya et al. 2007, Geo)
Plates must be composed of material which, in the case of the overriding plate, are is strong enough to resist bending stresses imposed by the subducting plate and yet, as in the case of the subducting plate, be weak enough to bend and subduct when pulled by the already subducted slab. (Petersen et al. 2015, PEPI)

Though strong surface plates are required for subduction such plates may present a problem when they encounter the lower mantle.
As the subducting slab approaches the higher viscosity, lower mantle stresses are imposed on the tip.
Strong slabs transmit this stress to the surface.
There the stress field at the plate interface is modified and potentially modifies the style of convection.

In addition to modifying the stress at the plate interface, the strength of the slab affects the morphology of the slab at the base of the upper mantle. (Stegman, et al 2010, Tectonophysics)
Slabs that maintain a sufficient portion of their strength after being bent require high stresses to unbend or otherwise change their shape.
On the other hand slabs that are weakened though the bending process are more amenable to changes in morphology.

We present the results of computational models of convective systems across a range of Rayleigh numbers with strong plates and slabs with strength decreased due to bending to examine and compare the convective style of the system, the stress field, and slab morphology.