Influence of Mantle Rheology on the Formation of Plate Tectonic Style of Mantle Convection

We examine the influence of material- and pressure-dependent rheological properties on the generation of plate tectonic style of mantle convection through two-dimensional numerical modeling. The influence of two key parameters is investigated: the activation enthalpy (energy and volume) of mantle viscosity and the friction coefficient in the lithosphere with the constraints of viscosity at 150 km and 1000 km from geodynamic studies. We consider a two-layer model of rheological properties and explore the influence of different rheological parameters. We find that, among other, the activation volume for high-temperature creep in the upper mantle has strong influence on the style of mantle convection. The style of mantle convection is characterized by (surface velocity)/(average convection velocity), the spatial distribution of viscosity (temperature) and stress and the temporal variation in surface velocities. We also calculate convective stress and compare it with the lithosphere strength. The mobile-lid (plate tectonics) regime of convection occurs when convection stress is large enough to deform the lithosphere. We find that the mobile-lid (plate tectonics) style of convection is favored for large activation volumes of the upper mantle (Vum=9–12 × 10−6 m3/mol or a little larger) with a low friction coefficient (μ<0.05). These values are consistent with the mineral and rock physics observations on the strength of rocks, and we conclude that the operation of plate tectonics on Earth (but not on Venus) can be explained by the well-established mineral-rock physics together with the known difference in the atmospheric temperature without invoking other factors (or processes) such as “damage” development and/or the influence of water.