Critical external and internal factors for plate tectonics

Convective mantle flow in terrestrial planets is governed by a temperature- and pressure-dependent rheology. This results in a stagnant-lid regime observed on most terrestrial planets. Plastic deformation can lead to breaking of the strong upper lithosphere, which resembles plate tectonics on Earth. Most efforts to model mantle convection with self-consistent plate tectonics combine Newtonian diffusion creep with a stress-dependent pseudo-plastic rheology in the form of a yield criterion. However, in the uppermost mantle, where stresses are high, deformation is thought to be driven in large parts by deformation via dislocation creep. As numerical models get more robust and capable of more complexity, viscoplastic models should therefore include non-Newtonian dislocation creep.

In our models we employ a composite viscosity, combining both Newtonian and Non-Newtonian power laws in a viscoplastic approach. We study the influence of varying rheologies on plate tectonics simulations, by testing several internal and external parameters, such as grain size and surface temperature. In a 2D-spherical annulus geometry we employ an interior structure model for an Earth-like planet to obtain local information on thermodynamics properties of the main minerals present in Earth’s mantle. We evaluate the models by computing common diagnostic values used to recognize plate-like surface deformation. The goal of this study is to identify key planetary factors for the occurrence or absence of plate tectonics.