A Regime Diagram of Mobile-lid Convection with Plate-like Behaviour

Abstract:

Terrestrial planetary bodies that undergo solid-state convection can exhibit a variety of tectonic styles, from stagnant-lid one-plate planets to those with mobilized lithosphere.
In computational models the de facto mode of recycling of this strong lithosphere into the planetary interior is typically achieved through two-sided and symmetric downwelling flows.
However, lithosphere recycling on Earth occurs in a distinctly one-sided and asymmetric mode known as subduction.
Using numerical models of mantle convection in which the viscosity of planetary mantle material is strongly temperature dependent, yet maintains a finite material strength as dictated by its yield stress, we investigate the continuum of mobile-lid convection with plate-like behavior.
Three distinct modes are found to occur: the stagnant-lid mode, two-sided subduction mode, and a mode that alternates between one- and two-sided subduction.
We classify the style of convective downwelling for a range of models and show that mode selection strongly depends on the strength of the downgoing plate.
Surface mobility provides a good metric for indicating the convective mode.
We develop a measure of plate strength which incorporates the effective viscosity profile of the plate and plate geometry.
Mantle convection models frequently employ mechanisms for dynamic weakening to affect subduction.
Yield strength, damage rheologies and viscosity reducing hydration all work to generate an effective viscosity.
An abstract measure of strength provides a criterion for comparing subduction style across models with differing mechanisms for dynamic weakening.
Using these measurements, we have developed a regime diagram that can predict whether a particular system will be in one of those three modes.