Mars mantle convection: Influence of phase transitions with core cooling

The influence of phase transitions in the Martian mantle, the two exothermic phases, olivine to β ‐ spinel and β ‐ to γ ‐ spinel transitions, and the endothermic spinel to perovskite phase transition, has been studied with an axisymmetric spherical shell model. An extended Boussinesq model with a temperature and depth dependent viscosity, including the decay of radioactive elements and the cooling of the core has been used with two different sizes of the Martian core as we do not know its composition. In the case of a small core, the endothermic phase transition tends to inhibit the convective flow. Decreasing in depth with the core cooling, that phase transition can disappear after about 1 billion years, inducing a sudden increase of the heat flux out of the core who could explain a core dynamo reactivation. In the present work, we conclude that it is difficult to rejuvenate a dynamo, even in the presence of a thin perovskite layer at the bottom of the mantle. Core–mantle heat flux evolution is very sensitive to the onset of the whole mantle convection, which depends on initial conditions, but the endothermic phase prevents the core from cooling and allows melt generation in hot plumes. In large core case, uncertainties on the iron content of the mantle allow to compare models with two exothermic phase transitions or only a single thicker one. Our results demonstrate that these both configurations have same influence on the mantle convection and no degree one convection can be obtained as the core is cooling.