The influences of surface temperature on upwellings in planetary convection with phase transitions

Abstract

The importance of surface temperature for mantle convection appears with the presence of adiabatic heating and cooling and the release and consumption of latent heat in the presence of phase transitions. For some planetary bodies these effects cannot be neglected. The dimensionless surface temperature T 0 , which is the ratio between the temperature at the top of the convective region and the temperature drop across the mantle, is close to one for Mars and Venus. For the Earth, T 0 lies between 0.2 and 0.5. The dynamical influence of T 0 is especially poignant for internally heated convection with temperature-dependent viscosity. There is a tight coupling between the magnitude of the temperature field and the viscosity itself. We have studied temperature-dependent viscosity convection for both low-T 0 (0.2) and high-T 0 (1.2) situations and with internal heating in mantle convection with two upper-mantle phase transitions. Our results show that within this range of T 0 there exist two regimes for the evolution of upwellings in the mantle. In transient situations plume-plume collisions lead to the formation of megaplumes for high-T 0 regimes but are less likely to do so for low T 0 . In the long-term regime, plumes with low T 0 are prone to develop from the transition zone with a supply of hot material coming from the shallow lower mantle. In systems with high T 0 , however, long-lived plumes tend to have deeper mantle origins. In quasi-layered situations high T 0 may act as a positive feed-back mechanism in inducing powerful hot upwellings into the upper mantle.

Chemical stratification in a two‐dimensional convecting mantle with magmatism and moving plates

“…These hot plumes occur as a return flow of subducting slabs and are hotter than the surrounding upper mantle because the temperature in the return flow is raised by the latent heat release at the endothermic 660 km phase boundary; the return flow takes the form of narrow jets rather than a diffuse back ground flow when the flow crosses the 660 km phase boundary. Similar plumes are observed in earlier numerical models of thermal convection with the 660 km phase boundary [see, e.g., Steinbach and Yuen , 1998, Figure 1a], too.…”