Non-Newtonian Stagnant Lid Convection and Magmatic Resur facing on Venus

Abstract

Mantle convection on Venus is likely to occur in the regime known as stagnant lid convection. We investigate this regime for internally heated convection with temperature- and pressure-dependent power-law viscosity (dislocation creep). Scaling relationships obtained for large aspect ratio convection are different from steady-state square box calculations but agree well with scaling theory and boundary layer stability analysis. Results for Arrhenius viscosity and pressure dependent viscosity show that the efficiency of heat transport is sensitive to the viscosity function at the bottom of the lid. New scaling relationships are applied to parameterized convection calculations of the thermal history of Venus assuming that plate tectonics could not occur during evolution. The onset of convection beneath the lid is delayed even for initial potential temperatures near the solidus. During the conductive regime, melting is suppressed due to the development of a thick cold lid at the surface. After convection begins, the lid becomes thinner and the planet undergoes a period of widespread melting and volcanism. The timing of the beginning and ending of melting depends on various factors such as the initial conditions and mantle rheology. The episode of melting predicted by the models can be reconciled with the cessation of global resurfacing on Venus 300–800 Myr ago. The models yield present-day lithospheric thicknesses around 200 km which is similar to previously suggested estimates.