Consolidated chemical provinces on Mars: implications for geologic interpretations

Abstract

Chemical provinces were defined on Mars a decade ago using orbital nuclear spectroscopy of K, Th, Fe, Si, Ca, Cl, and H2O. However, past multivariate analyses yielded three sets of provinces, suggesting methodologic variability. Province-stability to the inclusion of Al and S is also unknown, presenting additional uncertainties for geologic insight. Here we consolidate key multivariate methods to define the first cross-validated provinces. In southern highlands, the highly incompatible K and Th show non-uniform distribution with higher values in mid Noachian and Hesperian than late Noachian-early Hesperian volcanic terrains. Silica- and Al-depletion trends from Noachian to Amazonian indicate highly differentiated mantle with variable degree of melting. Late Hesperian lowlands are highly depleted in Al and enriched in K and Th, consistent with volcanic resurfacing from a lo-degree partially melted, garnet-rich mantle. Furthermore, older volatile-rich regions such as Medusae Fossae Formation exhibit igneous geochemistry, consistent with water-limited isochemical weathering throughout Mars's history.