SUPER-ERUPTIONS IN NORTHWESTERN ARABIA TERRA INDICATE DISTINCT MANTLE EVOLUTION ON EARLY MARS

Arabia Terra is one of the oldest martian landscapes, and as such is home to a diverse and complex geologic history. This region contains a high density of morphological evidence indicating abundant fluvial activity, which suggests it functioned as an ancient floodplain. However, this narrative contrasts with the regional chemistry of Arabia Terra as reported by Gamma Ray Spectroscopy (GRS) data from the Mars Odyssey orbiter. This chemistry is more indicative of igneous activity, likely the result of locally derived volcanism. Evidence for such volcanism was also presented in prior work, which geomorphologically identified several features within Arabia Terra, and interpreted their morphology as consistent with caldera collapse. This work suggested that these calderas could have borne eruptions akin to terrestrial Plinian eruptions, which would have great potential for altering the early martian climate. However, this research presented only morphological evidence, leaving the door open for many other interpretations regarding the history of the features. Through examination and comparisons of GRS data within Arabia Terra to other contemporaneous volcanic and sedimentary regions, it is clear that the chemistry within Arabia is unique among many other geologic features on Mars. Our geochemical results indicate that the chemistry of this region in Arabia is consistent with explosive style volcanism, due to the enriched nature of key volatile species (S, Cl) and large iron lithophiles (K, Th). We also find that the elastic thickness within NW Arabia is T_e < 20km, with an inferred heat flux exceeding the range of some known volcanoes. These data suggest super-eruptions capable of exhaling climate-altering ~10⁸ kg of S-phases. The chemistry of these eruptions also provides insight on the composition of the martian mantle at the time of eruption. This chemistry notably differs from what is predicted by prior mantle evolution models that are based on meteoritic petrology and regional volcanic geochemistry. These models predict temporally decreasing partial melting, elevating large ion lithophile concentrations (e.g., K, Th) in younger volcanism, with inversely varying Si. But they overlook Noachian volcanism, obscuring early mantle conditions, suggesting that these models may oversimplify magmatic processes.