Olivine and Pyroxene Diversity in the Crust of Mars

Data from the Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) on the Mars Express spacecraft identify the distinct mafic, rock-forming minerals olivine, low-calcium pyroxene (LCP), and high-calcium pyroxene (HCP) on the surface of Mars. Olivine- and HCP-rich regions are found in deposits that span the age range of geologic units. However, LCP-rich regions are found only in the ancient Noachian-aged units, which suggests that melts for these deposits were derived from a mantle depleted in aluminum and calcium. Extended dark regions in the northern plains exhibit no evidence of strong mafic absorptions or absorptions due to hydrated materials.

Mars Surface Diversity as Revealed by the OMEGA/Mars Express Observations

The Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) investigation, on board the European Space Agency Mars Express mission, is mapping the surface composition of Mars at a 0.3- to 5-kilometer resolution by means of visible-near-infrared hyperspectral reflectance imagery. The data acquired during the first 9 months of the mission already reveal a diverse and complex surface mineralogy, offering key insights into the evolution of Mars. OMEGA has identified and mapped mafic iron-bearing silicates of both the northern and southern crust, localized concentrations of hydrated phyllosilicates and sulfates but no carbonates, and ices and frosts with a water-ice composition of the north polar perennial cap, as for the south cap, covered by a thin carbon dioxide-ice veneer.

Spectral evidence for weathered basalt as an alternative to andesite in the northern lowlands of Mars

Mineral abundances derived from the analysis of remotely sensed thermal emission data from Mars have been interpreted to indicate that the surface is composed of basalt (Surface Type 1) and andesite (Surface Type 2). The global distribution of these rock types is divided roughly along the planetary dichotomy which separates ancient, heavily cratered crust in the southern hemisphere (basalt) from younger lowland plains in the north (andesite). But the existence of such a large volume of andesite is difficult to reconcile with our present understanding of the geological evolution of Mars. Here we reinterpret martian surface rock lithologies using mineral abundances from previous work and new mineralogies derived from a spectral end-member set representing minerals common in unaltered and low-temperature aqueously altered basalts. Our results continue to indicate the dominance of unaltered basalt in the southern highlands, but reveal that the northern lowlands can be interpreted as weathered basalt as an alternative to andesite. The coincidence between locations of such altered basalt and a suggested northern ocean basin implies that lowland plains material may be composed of basalts weathered under submarine conditions or weathered basaltic sediments transported into this depocentre.

Geochemical evidence for magmatic water within Mars from pyroxenes in the Shergotty meteorite

Observations of martian surface morphology have been used to argue that an ancient ocean once existed on Mars. It has been thought that significant quantities of such water could have been supplied to the martian surface through volcanic outgassing, but this suggestion is contradicted by the low magmatic water content that is generally inferred from chemical analyses of igneous martian meteorites. Here, however, we report the distributions of trace elements within pyroxenes of the Shergotty meteorite--a basalt body ejected 175 million years ago from Mars--as well as hydrous and anhydrous crystallization experiments that, together, imply that water contents of pre-eruptive magma on Mars could have been up to 1.8%. We found that in the Shergotty meteorite, the inner cores of pyroxene minerals (which formed at depth in the martian crust) are enriched in soluble trace elements when compared to the outer rims (which crystallized on or near to the martian surface). This implies that water was present in pyroxenes at depth but was largely lost as pyroxenes were carried to the surface during magma ascent. We conclude that ascending magmas possibly delivered significant quantities of water to the martian surface in recent times, reconciling geologic and petrologic constraints on the outgassing history of Mars.