Constraining the Martian Crustal Structure From Gravity and Topography

Abstract

To better constrain the evolutional as well as the structural models of Mars, one of the most important tasks is to obtain a reliable value of the Martian mean crustal thickness and bulk density. Here we present some constraints on these quantities using the means of the gravity/topography modeling. Further we introduce methods to consider density gradient zones in the crust. We have examined both one- and two-layer crust structures from the viewpoint of two independent and complementary methods: (1) the GTR analysis using Airy isostasy concept [ Wieczorek and Zuber, 2004] and (2) the Bouguer inversion which provides a minimum crustal thickness. We have focused on the southern highlands region (with Hellas basin as the most distinctive feature) which seems to be a generally homogeneous unit with respect to lateral density variations and compensation state. The combined means of these two methods gives some constraints on the crustal properties, e.g. the maximum crustal density for a one-layer crust. We have also tested the assumption that the compensation of the surface features occurs at a potential gabbro-eclogite transition zone in the crust (this transition zone has been suggested for Mars by Babeyko and Zharkov [2000]) rather than at the crust/mantle interface. If present, this transition would imply an unrealistically large value of the mean crustal thickness for a complete global compensation. However such a transition may locally be possible underneath major volcanoes, in which case all the published estimates on the local crustal thicknesses may be lower bounds only. Reference: Babeyko, A.Yu., and V. N. Zharkov (2000), Martian crust: a modeling approach, PEPI, 117(1-4), 421-435. Wieczorek, M. A. and M. T. Zuber (2004), Thickness of the Martian crust: Improved constraints from geoid-to-topography ratios