Mantle plumes and long-lived volcanism on Mars as a result of a layered mantle

Previous studies of the Martian interior have highlighted the difficulty in forming and maintaining plumes throughout the history of the planet. A deep, gravitationally stable layer at the base of the mantle, possibly produced by magma ocean crystallization followed by an overturn event, could provide a heat source for plumes and therefore a source of long-lasting, localized volcanism. To address the influence of a layered mantle on the thermal evolution of the Martian interior, we have run a series of numerical convection simulations with temperature-dependent viscosity in spherical geometry. 3D simulations were run to a steady state to investigate the effect that a deep layer and a crustal dichotomy would have on the generation of plumes and their spatial locations. 3D and 2D experiments were also used to access the accuracy of 1D thermal evolution models. The 1D models were modified to include melt generation, from both small-scale convection and plumes, to examine the effect that a layered mantle has on the magmatic history of Mars. Using our 1D models, we also determine the compositional density anomaly required for the layer to remain at the base of the mantle for the entire history of the planet; our scaling is consistent with the results of published numerical simulations. We find that a layer enriched in radiogenic elements is necessary to have layer generate plumes throughout the history of the planet. 1D models accurately predict the large-scale thermal evolution in the 2D and 3D models. 1D modeling indicates that the existence of the layer increases both the amount of melting and duration of melting. A layered mantle permits volcanism over the entire history of Mars.