Consolidated Chemical Provinces on Mars: Implications for Geologic Interpretations.

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 low‐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. Plain Language Summary: Topographically Mars can be divided into two large regions: southern highlands and northern lowlands. However, the compositional evolution of these two landforms and their source characteristics remains unclear. Therefore, using enhanced satellite nuclear spectroscopic data, we develop a set of consolidated geochemical provinces of Mars using three multivariate analysis techniques. We identified the correlation of distinct geochemical provinces with mapped geologic units, which demonstrates the effect of bedrock composition over bulk soil composition. Our study depicts discrete igneous provinces within the southern highlands, which follow a secular chemical pattern, indicating a highly differentiated mantle source with an evolving formation pressure and degree of melting. The northern lowlands, on the other hand, are uncorrelated with the chemical trend of southern highland provinces, suggesting a distinct evolution. Our findings further reveal that regardless of volatile enrichment, igneous crustal composition dominates over chemical alteration signatures indicating a limited role of liquid water on the martian landscape. Key Points: We have consolidated three key multivariate methods, yielding the first unified set of chemical provinces of MarsIgneous geochemistry pervades volatile‐rich regions, consistent with water‐limited isochemical weathering throughout Mars's geologic historySecular chemical trends suggest complex processes of mantle melting for highlands, which differs from a possibly garnet‐rich lowland source [ABSTRACT FROM AUTHOR]