Reconciling Mars InSight Results, Geoid, and Melt Evolution With 3D Spherical Models of Convection

We investigate the geodynamic and melting history of Mars using 3D spherical shell models of mantle convection, constrained by the recent InSight mission results. The Martian mantle must have produced sufficient melt to emplace the Tharsis rise by the end of the Noachian–requiring on the order of 1–3 × 10⁹ km³ of melt after accounting for limited (∼10%) melt extraction. Thereafter, melting declined; however, abundant evidence for limited geologically recent volcanism necessitates some present-day melt even in the cool mantle inferred from InSight data. We test models with two mantle activation energies and a range of crustal Heat Producing Element (HPE) enrichment factors and initial core-mantle boundary temperatures. We also test the effect of including a hemispheric (spherical harmonic degree-1) step in lithospheric thickness to model the Martian dichotomy. We find that a higher activation energy (350 kJ mol⁻¹) rheology produces present-day geotherms consistent with InSight results, and crustal HPE enrichment factors of 5–10-times produce localized melting near or up to present-day. The 10-times crustal HPE enrichment is consistent with both InSight and geochemical results and also produces present-day geoid power spectra consistent with Mars. However, calculations that match the present-day geoid power spectra require more than 60% melt extraction to produce the Tharsis swell. The addition of a degree-1 hemispheric dichotomy, as an equatorial step in lithospheric thickness, does not significantly improve upon melt production or the geoid.