Non-Newtonian stagnant lid convection and magmatic resurfacing on Venus

Mantle convection on Venus is likely to occur in the regime known as stagna nt lid convection. We investigate this regime for internally heated convect ion with temperature- and pressure-dependent power-law viscosity (dislocati on creep). Scaling relationships obtained for large aspect ratio convection are different from steady-state square box calculations but agree well wit h scaling theory and boundary layer stability analysis. Results for Arrheni us viscosity and pressure dependent viscosity show that the efficiency of h eat transport is sensitive to the viscosity function at the bottom of the l id. New scaling relationships are applied to parameterized convection calcu lations of the thermal history of Venus assuming that plate tectonics could not occur during evolution. The onset of convection beneath the lid is del ayed even for initial potential temperatures near the solidus. During the c onductive regime, melting is suppressed due to the development of a thick c old Iid at the surface. After convection begins, the lid becomes thinner an d the planet undergoes a period of widespread melting and volcanism. The ti ming of the beginning and ending of melting depends on various factors such as the initial conditions and mantle rheology. The episode of melting pred icted by the models can be reconciled with the cessation of global resurfac ing on Venus 300-800 Myr ago. The models yield present-day lithospheric thi cknesses around 200 km which is similar to previously suggested estimates. (C) 1999 academic Press.