The sulfur content of volcanic gases on Mars

By F. Gaillard, Bruno Scaillet. 2009

177 citations recorded by the source corpus.

Both high sulfur contents of the martian regolith and lack of detection of extensive carbonate deposits suggest that the latest geological events that shaped the landscapes of Mars were dominated by acidic waters possibly related to appreciable SO2 concentrations in the atmosphere. On the basis of fundamental thermochemical principles, we model here the likely sulfur contents of (1) the martian and terrestrial mantles and (2) the volcanic gases delivered by the corresponding basaltic magmas. We find that the martian mantle contains at least 3–4 times as much sulfur as its terrestrial counterpart, yielding basaltic melts richer in sulfur than those on Earth. Such an S-enrichment is explained by contrasted redox conditions prevailing during magma ocean equilibration, which lead to distinct iron contents of the martian and terrestrial mantles and of their basaltic derivatives. Calculated volcanic gas compositions in equilibrium with a magma ocean sustaining a denser atmosphere are shown to be dominated by CO ± CO2 and H2 ± H2O species, depending on fO2, sulfur species amounting to only ~ 1%. In contrast, volcanic gases supplied at later stages of Mars evolution, such as during the building of the Tharsis province, are shown to be significantly richer in sulfur, with S contents on average 10–100 times that of gases emitted by magmas on Earth. If degassing during such a period occurred in a tenuous atmosphere (1 bar or less), volcanic gases were dominated by SO2 rather than by H2S, which should have favored the acidification of any persistent water layer. The calculated amounts of S emitted by the Tharsis volcanic region turn out to be equivalent to a 20–60 m thick layer of sulfate minerals if uniformly covering the martian surface, in qualitative agreement with remote sensing of the martian regolith.

Subfields: Astronomy and Astrophysics, Geophysics

View Paper: https://www.semanticscholar.org/paper/30e9604a992eea31a6a7d7d14e47bf26d01478b1

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In Astronomy and Astrophysics

1. F. Gaillard
2. Bruno Scaillet
3. P. King
4. S. McLennan
5. Y. Sano
6. I. Franchi

In Geophysics

1. F. Gaillard
2. Bruno Scaillet
3. I. Franchi

Citations in the corpus

• A theoretical framework for volcanic degassing chemistry in a comparative planetology perspective and implications for planetary atmospheres (2014, methodology): “Mars, though having a presentday CO2-rich atmosphere, is covered by widespread sulfate deposits (King and McLennan, 2010; Gaillard et al., 2013), hinting at a volcanic source in the recent past (Halevy et al., 2007; Gaillard and Scaillet, 2009; Gaillard et al., 2013).”
• The abundance, distribution, and isotopic composition of Hydrogen in the Moon as revealed by basaltic lunar samples: Implications for the volatile inventory of the Moon (2013, background): “However, S is much more stable in the melt than in the gas phase for oxygen fugacity below IW+1 (O’Neill and Mavrogenes, 2002; Gaillard and Scaillet, 2009), and degassing of S-bearing species might have thus been very limited.”
• Sulfur on Mars (2010, background): “There is little direct evidence for the S content of Mars’s mantle, although enrichments compared to Earth’s mantle are expected (Gaillard and Scaillet 2009; Righter et al. 2009).”