Some remarks on the models of plate tectonics on terrestrial planets: From the view-point of mineral physics

• Physical properties controlling mantle convection changes with pressure.
• Rayleigh number may decrease with the planetary size if pressure effect is large.
• The depth of partial melt changes with planetary size.
• There may be an optimum planetary size at which the plate thickness is minimum.

Some mineral physics-related issues are reviewed that are closely related to the operation of plate tectonics on terrestrial planets with different mass. Plate tectonic style of convection would occur when the surface layer has only modest strength relative to the stress generated by mantle convection so that it can deform and subduct into the mantle. Both the stress on the lithosphere generated by mantle convection and the resistance of the lithosphere for subduction depend on the relevant materials properties. A review is presented on the scaling relationships between relevant physical properties and planet mass and on the strength of the lithosphere. It is shown that if physically plausible scaling is made both for the relevant materials properties and the macroscopic energy balance, a large Earth-like planet may not necessarily have plate tectonics. In addition to the internal processes, the surface conditions such as the surface temperature may also play an important role via its effects on the thickness of thermal or chemical lithosphere, making it difficult for plate tectonics to operate on small planets. Therefore, in this model, plate tectonics would operate on planets with modest size like Earth, but the validity of this conclusion hinges on the characterization of (i) the influence of pressure-dependent properties on the vigor of convection and of (ii) the resistance for subduction. In particular, the processes determining the resistance for subduction have an important influence on the operation of plate tectonics. Key issues are highlighted that require further studies including the influence of depth-dependent properties on convection and the formulation of the resistance of the lithosphere for subduction.