Martian crustal dichotomy and Tharsis formation by partial melting coupled to early plume migration

Abstract

A recently proposed model links the formation and early evolution of the Tharsis volcanic province on Mars to the preexisting hemispheric dichotomy (Zhong, 2009). A key aspect of this model is the assumption of a deep lithospheric root below the thicker crust of the southern highlands. We implemented a parameterization of partial melting into the 3‐D spherical shell mantle convection code CitcomS in order to investigate whether the required lithospheric thickness variation can be generated self‐consistently by partial melting when stiffening of the melt residue due to devolatilization is considered. The rate of melt production strongly depends on the mantle temperature, and additional strong coupling between the flow and partial melting is introduced through the stiffening effect on the melt residue. We find that it is possible to generate a lithospheric keel by partial melting above a single upwelling that excites a relative rotation between the one‐plate lithosphere and the mantle below while producing the amount of melt distributed in a broad region constrained to one hemisphere that is necessary to form the crustal dichotomy. This scenario thus offers an internal mechanism for the Martian dichotomy formation and validates the hypothesis of Zhong (2009).