Global volcanism and tectonism on Mercury: comparison with the Moon

Both morphologic and tectonic studies indicate that Mercury and the Moon have quite different internal histories, despite their apparently similar morphologies. The evaluation of the volcanic surfaces indicates a decreasing volcanism on Mercury at the largest impacting time, despite short and local reactivations. On the Moon, the basaltic volcanism was increasing at the same time and continued for 1 billion years. That indicates a strongly different thermal evolution for these two planetary bodies.A widespread graben pattern is present on the Moon, with a statistical dominance of radial or tangential orientation with respect to the Imbrium basin, thus suggesting a relation between this major basin and the expansion of the Moon.Azimuthal studies show that the compressive structures, observed on the stereographic covered surface of Mercury are not randomly oriented, but seem radial towards the Caloris basin, thus indicating a possible influence of this largest basin on Mercurian contraction.The qualitative and quantitative formulations of these tectonic perturbations induced by large basins will be developed in a companion paper 1].