Geochemical and climatic controls on the sulfur cycle in volcanic settings: Implications for the origin of sulfur-rich deposits investigated by the Spirit and Opportunity rovers on Mars

• Main Author: Moore, Rhianna D
• Format: Text
• Language: unknown
• Published: TRACE: Tennessee Research and Creative Exchange 2022
• Subjects: sulfur; hydrothermal; mars; Iceland; Hawaii; hydrological; Earth Sciences; Geochemistry; Geology; Hydrology; Gusev; The Landing
• Online Access: https://trace.tennessee.edu/utk_graddiss/7661; https://trace.tennessee.edu/cgi/viewcontent.cgi?article=9006&context=utk_graddiss

On Earth, volcanic activity with elevated sulfur (S) degassing in the presence of water leads to the formation of hydrothermal deposits enriched in S-bearing minerals. Similar processes may have been an important source of S on Mars. The landing sites of Gusev crater and Meridiani Planum investigated by the Spirit and Opportunity rovers, respectively, showed elevated SO42- [sulfate] concentrations, suggesting high- and low-temperature aqueous processes. However, the SO42- contribution from subsequent aqueous weathering of hydrothermal S deposits has been poorly constrained, thus its importance to regional S cycling in the landing sites is unclear. In this study, geochemical and hydrological approaches were used to determine sediment and aqueous S sources in terrestrial volcanic terrains at local and regional scales. The results of local scale studies in Iceland and the U.S. showed that hydrothermal sediments are typically enriched in elemental S (~0.3-22 wt.% S) with minor sulfide (~0.1-3.9 wt.% S) and sulfate (~0.1-2.7 wt.% S), and their concentrations decrease in wet climates. Sulfur isotopes suggested that subsequent oxidation of elemental S and sulfide to SO42- is controlled by water-rock interactions under varied temperatures and oxidant availability (O2 [oxygen]/Fe3+ [ferric iron]). Despite the prevalence of sulfate minerals rather than elemental S/sulfides in the hydrothermal deposits of Gusev crater, the total S concentration is comparable to those formed in coastal Iceland. It is inferred that complete oxidation of Gusev hydrothermal deposits to SO42- took place later under low water-to-rock conditions with little S emission. The results of regional scale studies in Hawaii and Iceland showed that significantly higher SO42- loads (~20-260 tons/yr/km2) occur in aqueous systems on younger, wetter volcanic terrains with active hydrothermal S degassing and mineralization. Conversely, smaller SO42- loads (~2.1-10 tons/yr/km2) occur in older, drier and non-active terrains. Comparison of terrestrial SO42- loads ...