Hemispheric dichotomy in lithosphere thickness on Mars caused by differences in crustal structure and composition

Abstract

Estimates of the Martian elastic lithosphere thickness suggest small values of ∼25 km during the Noachian for the southern hemisphere and a large present-day difference below the two polar caps (≥300 km in the north and >110 km in the south). In addition, young lava flows suggest that Mars has been volcanically active up to the recent past. We run Monte Carlo simulations using a 1-D parameterized thermal evolution model to investigate whether a north/south hemispheric dichotomy in crustal properties and composition can explain these constraints. Our results suggest that 55–65% of the bulk radioelement content are in the crust, and most of it (43–51%) in the southern one. The southern crust can be up to 480 kg/m3 less dense than the northern one and might contain a nonnegligible proportion of felsic rocks. Our models predict a dry mantle and a wet or dry crustal rheology today. This is consistent with a mantle depleted in radioelements and volatiles. We retrieve north/south surface heat flux of 17.1–19.5 mW/m2 and 24.8–26.5 mW/m2, respectively, and a large difference in lithospheric temperatures between the two hemispheres (170–304 K in the shallow mantle). This difference could leave a signature in the seismic signals measured by the future InSight mission.