The Impact of a Long‐Lived Basal Magma Ocean on the Thermochemical Evolution of Mars

A basal magma ocean (BMO) has been suggested to form as a consequence of cumulate overturn following crystallization of an initial global magma ocean. As a consequence of enrichment in iron and heat‐producing elements (HPE), the BMO stabilizes gravitationally at the base of the planetary mantle, affecting the efficiency of mantle convection and crustal production. Seismic data collected during the recent Mars InSight mission provide compelling evidence for the presence of a molten silicate layer at the bottom of the Martian mantle. Here, we study the role of a BMO on the long‐term evolution of Mars's interior using two‐dimensional geodynamic models in spherical annulus geometry. We compare our model predictions with available observational constraints, including crustal HPE enrichment, seismically constrained present‐day crustal and lithospheric thicknesses, and mantle temperatures. Among the parameters explored, we find that the interstitial porosity, which controls the initial HPE distribution between the BMO and the mantle, plays an important role on mantle thermal structure throughout Mars's evolution. Models with an intermediate interstitial porosity (20%–60%), and with a reference mantle viscosity of Pas (at ) provide the best match to the most observational constraints. This suggests that HPE partitioning between mantle and BMO has not been controlled by end‐member fractional crystallization of the initial magma ocean, and that chemical re‐equilibration must have occurred to some extent during cumulate overturn. Crustal growth constraints nevertheless remain difficult to reconcile independent of HPE enrichment of the BMO. Better understanding of the earliest stages of Martian differentiation is required.