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

• Numerical models of mantle convection show continuous spectrum of styles.
• Viscous coupling results in de facto style of 2-sided downwellings.
• Mechanical strength of plates is a strong control on system mobility and style.

Terrestrial planetary bodies that undergo solid-state convection can exhibit a variety of tectonic styles, from stagnant lid one-plate planets to those with a mobilized lithosphere. For modeled planetary convection the de facto mode of recycling of lithosphere into the planetary interior is typically achieved through 2-sided and symmetric downwelling flows. However, lithosphere recycling on Earth occurs in a distinctly 1-sided 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. The models span a parameter space of Rayleigh number and plate strength, and explore convective systems with low yield stresses resulting in weak subduction hinges that bend easily and highly deformable subducted slabs. Three distinct modes are found to occur in convective systems with weak plates: the stagnant lid mode, 2-sided downwelling mode, and a mode that alternates between 1-sided subduction and 2-sided downwellings. We classify the style of convective downwelling for a range of models and show that mode selection strongly depends on the combination of surface mobility and strength of the downgoing plate. Using these measurements, we have developed a regime diagram that can predict whether a particular system will be in one of those three modes.