Reconciling Mars InSight Results, Geoid, and Melt Evolution with 3D
Spherical Models of Convection
Abstract
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, but abundant evidence for
limited geologically recent volcanism necessitates some melt even in the
cool present-day 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 of those the cases with HPE enrichment factors of 5–10x
produce localized melting near or up to present-day. 10x crustal
enrichment is consistent with both InSight and geochemical results, and
those models also produce present-day geoid power spectra consistent
with Mars. However, it is very difficult to produce sufficient melt to
form Tharsis in a mantle that also matches the present-day geotherm,
without assuming extremely efficient extraction of melt to the surface.
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.