Temporal Stress Patterns in Episodic Plate Tectonics Models with Implications for the Initiation of Plate Tectonics on Terrestrial Planets

English Abstract:

Spherical shell mantle convection models are used to explore an episodic mode of plate tectonics. The time evolution of shear and normal stresses are tracked to determine how the stress levels vary coming into a global lithospheric failure event. The results indicate that an increase in convective mantle shear stress initiates lithosphere failure and an associated period were the lithosphere actively participates in convective mantle overturn (as is the case for the Earth's plate tectonics regime at present). The implication is that once the lithosphere is active, then normal stresses can exceed shear stress but it is not the normal stress itself that initiates the active lid mode of behavior. Based on our numerical results, we used 1D thermal evolution models to study the consequences of this shear-stress dominance for the initiation of plate tectonics. We find a reduced likelihood of initiating plate tectonics with increasing planet mass and interior heat. Moreover, our results indicate that for Earth an early (<500 Myr) or considerably later (0.5-3 Gyr after formation) start for plate tectonics are both possible. Once started, plate tectonics associated cooling of the interior can aid in its maintenance. In that situation, our thermal evolution models suggest the continuation for plate tectonics on Earth for the lifetime of the sun as a main sequence star.