Plate Tectonics on Earth and on Alien Worlds - Novel Insights into Mantle Dynamics

Abstract:

We derive the framework of how common assumptions behind parameterized 1D and full convection 2D/3D models, as well as planet mass, interior structure and composition impact the evolution of plate tectonics on Earths and super-Earths. This approach additionally allows us to resolve previous disagreements between groups that studied plate tectonics on super-Earths and to unveil major problems when modeling the thermal evolution of plate tectonics with both 1D and 2D/3D models.

How planet properties impact the evolution of plate tectonics is highly sensitive to a planet’s initial thermal conditions, the rheology of mantle rock, the scaling of interior heat and yield stress with planet mass, and especially to whether shear or normal stresses drive plate tectonics.

Based on the currently most likely model configuration and for planets starting molten, we find that plate tectonics is less likely to occur on super-Earths, for increasing iron and radiogenic heat contents within the mantle, and also with decreasing core to mantle mass fractions. Interestingly, we also find that water within a planet’s mantle has a negative impact on plate tectonics and that only surface water can beneficially impact subduction (but not the initiation of plate tectonics). This emphasizes how the distribution and exchange of water between surface and mantle reservoirs are crucial for plate tectonics, and how difficult it is to find positive water-plate tectonics correlations.