Thickness of the Martian crust: improved constraints from geoid-to-topography ratios

[1] The average crustal thickness of the southern highlands of Mars was investigated by calculating geoid-to-topography ratios (GTRs) and interpreting these in terms of an Airy compensation model appropriate for a spherical planet. We show that (1) if GTRs were interpreted in terms of a Cartesian model, the recovered crustal thickness would be underestimated by a few tens of kilometers, and (2) the global geoid and topography signals associated with the loading and flexure of the Tharsis province must be removed before undertaking such a spatial analysis. Assuming a conservative range of crustal densities (2700–3100 kg m3), we constrain the average thickness of the Martian crust to lie between 33 and 81 km (or 57 ± 24 km). When combined with complementary estimates based on crustal thickness modeling, gravity/topography admittance modeling, viscous relaxation considerations, and geochemical mass balance modeling, we find that a crustal thickness between 38 and 62 km (or 50 ± 12 km) is consistent with all studies. Isotopic investigations based on Hf-W and Sm-Nd systematics suggest that Mars underwent a major silicate differentiation event early in its evolution (within the first 30 Ma) that gave rise to an ‘‘enriched’ ’ crust that has since remained isotopically isolate