Connecting exoplanet mantle mineralogy to surface dynamic regime

Based on stellar compositions, we know that rocky exoplanets show a diversity in interior compositions, and therefore mantle mineralogies. The mantle mineralogy controls physical parameters of the mantle, such as viscosity, and therefore strongly affects thermal and dynamical evolution of the interior. However, it is unknown whether mantle mineralogy plays a role in establishing a planets surface dynamic regime (e.g., mobile lid, stagnant lid, episodic lid), which plays a pivotal role in determining a planets’ habitability. Here, we investigate the long-term dynamical evolution of Earth-sized planets with a range of mantle mineralogies based on stellar compositions.We explore the long-term evolution of an Earth-sized rocky planet, varying mantle mineralogy, by employing a 2D global-scale model of thermochemical mantle convection. We include the effects of composition on planet structure, mantle physical properties, and mantle melting. We investigate how composition affects thermal evolution, and whether it has an effect on the propensity of a planet towards plate tectonics-like behaviour.We find that density contrast between crustal material and the underlying mantle, governed by mantle Fe content, plays a vital role in determining dynamical behaviour. A very light crust is unable to subduct, locking a planet into a stagnant lid regime. Meanwhile, a very dense crust may settle at the core-mantle boundary, unable to be re-entrained into the overlying mantle. This leaves a depleted, infertile mantle and could potentially lock most of the planets water and heat producing element budget into the lowermost mantle. Mantle viscosity,  governed by Mg/Si ratio, plays a primary role in discerning between an episodically mobile and a fully stagnant lid, but has little effect on the propensity towards a fully mobile lid regime. Therefore, while composition plays a major role in determining planet material properties and dynamics, its effects on habitability are not straightforward.