Dynamics of plate bending at the trench and slab‐plate coupling

Abstract

[1] The bending strength of subducting lithosphere plays a critical role in the Earth's plate tectonics and mantle convection, modulating the amount of slab pull transmitted to the surface and setting the boundary conditions under which plates move and deform. However, it is the subject of a lively debate how much of the potential energy of the downgoing plate is consumed in bending the plate and how the lithospheric strength is defined during this process. We model the subduction of a viscoelastic lithosphere, driven solely by the downgoing plate's buoyancy, freely sinking in a passive mantle, represented by drag forces. To investigate the dynamics of bending, (1) we vary the density and the viscosity profile within the plate from isoviscous, where strength is distributed, to strongly layered, where strength is concentrated in a thin core, and (2) we map the stress, strain, and dissipation along the downgoing plate. The effective plate strength during bending is not a simple function of average plate viscosity but is affected by rheological layering and plate thinning. Earth-like layered plates allow for the transmission of large fractions of slab pull ($75-80%) through the bend and yield a net slab pull of F SP net = 1 to 6 Â 10 12 N m À1 , which varies with the buoyancy of plates. In all models, only a minor portion of the energy is dissipated in the bending. Surprisingly, bending dissipation hardly varies with lithospheric viscosity because in our dynamic system, the plates minimize overall dissipation rate by adjusting their bending curvature. As a result, bending dissipation, F B , is mainly controlled by the bending moment work rate exerted by slab pull. We propose a new analytical formulation that includes a viscosity-dependent bending radius, which allows for assessment of the relative bending dissipation in the Earth's subduction zones using parameters from a recent global compilation. This yields estimates of F B /F TOT < 20%. These results suggest that plates on Earth weakly resist bending, yet are able to propagate a large amount of slab pull.

Evolution of Subduction Zone Curvature and its Dependence on the Trench Velocity and the Slab to Upper Mantle Viscosity Ratio

“…This would indicate that in nature less than 1% of the slab's potential energy is dissipated in the slab during plan view curvature. As shown in recent laboratory and numerical experiments of Earth‐like subduction settings, most of the potential energy of the slab is dissipated in the ambient mantle, while a relatively small percentage (<20%) is dissipated in the hinge of the subducting plate [ Stegman et al , 2006; Capitanio et al , 2007, 2009; Krien and Fleitout , 2008; Schellart , 2009]. Note, however, that other recent work argues that ∼45% is dissipated in the plate during subduction [ Di Giuseppe et al , 2008].…”

Dynamical geochemistry of the mantle

“…7.3. However Korenaga's model depends on assuming a small and unchanging radius of curvature of bending plates, and this is not supported by current observations (Wu et al, 2008) nor by recent modelling that indicates the radius of curvature will be larger for thicker plates (Capitanio et al, 2009). If even modestly more plausible radii of curvature are assumed the recent thermal history reverts to being close to previous conventional histories (Davies, 2009a) and the reconciliation with cosmochemical estimates is lost.…”

A regime diagram of mobile lid convection with plate-like behavior

“…The weak crust has a lower yield strength than the underlying material and accommodates the plastic deformation of the bending plate (Capitanio et al, 2009). Using a different model setup, found that the combination of sticky air and weak crust promotes 1-sided subduction.…”