Implications of Reactions Between SO2 and Basaltic Glasses for the Mineralogy of Planetary Crusts

Christian J Renggli,Penelope L King,Paul Guagliardo,Andrew B Palm

doi:10.1029/2019je006045

Abstract

AbstractBasalts are ubiquitous in volcanic systems on several planetary bodies, including the Earth, Mars, Venus, and Jupiter's moon Io, and are commonly associated with sulfur dioxide (SO2) degassing. We present the results of an experimental study of reactions between SO2 and basaltic glasses. We examined Fe‐free basalt, and Fe‐bearing tholeiitic and alkali basalts with a range of Fe3+/Fetotal (0.05 to 0.79) that encompass the oxygen fugacities proposed for most terrestrial planetary bodies. Tholeiitic and alkali basalts were exposed to SO2 at 600, 700, and 800 °C for 1 hr and 24 hr. Surface coatings formed on the reacted basalts; these contain CaSO4, MgSO4, Na2SO4, Na2Ca(SO4)2, Fe2O3, Fe3O4, Fe‐Ti‐(Al)‐oxides, and TiO2. Additionally, the SO2‐basalt reaction drives nucleation of crystalline phases in the substrate to form pyroxenes and possible Fe‐oxides. A silica‐rich layer forms between the substrate and sulfate coatings. More oxidized basalts may readily react with SO2 to form coatings dominated by large Ca‐sulfate and oxide grains. On less oxidized basalts (NNO−1.5 to NNO−5), reactions with SO2 will form thin, fine‐grained aggregates of sulfates; such materials are less readily detected by spectroscopy and spectrometry techniques. In contrast, in very reduced basalts (lower than NNO−5), typical of the Moon and Mercury, SO2 is typically a negligible component in the magmatic gas, and sulfides are more likely.

Highlights

Basalt is the most common volcanic rock on the terrestrial planets and is typically associated with gaseous sulfur dioxide (SO2; Basaltic Volcanism Study Project, 1981; Taylor & McLennan, 2009)
On Mars, basaltic volcanism provided the primary source of S to the surface through both SO2 emissions, sulfides, and sulfates; these materials were redistributed as abundant sulfate minerals on the surface (Franz et al, 2018; Gaillard & Scaillet, 2009; King & McLennan, 2010; McSween et al, 2006)
Despite placing the reacted glass samples in a desiccator immediately after taking them out of the gas‐mixing furnace, Raman analysis was performed under air and so we suspect that hydration of MgSO4 occurred after the experiments

Summary

Introduction

Basalt is the most common volcanic rock on the terrestrial planets and is typically associated with gaseous sulfur dioxide (SO2; Basaltic Volcanism Study Project, 1981; Taylor & McLennan, 2009). On Venus, basalts are the dominant volcanic rock type (McSween et al, 2006; Nimmo & McKenzie, 1998). Thermodynamic and experimental data suggest that SO2 interacted with the surface of basalt deposits on Venus in the past (Berger et al, 2019; Fegley & Prinn, 1989; Zolotov, 2018). On the Moon, basalt is a dominant rock type (Haskin & Warren, 1991); SO2 is likely negligible because oxygen fugacity (fO2) of the volcanic gas and the magmatic source were too low (Renggli et al, 2017). Mercury has vast flood basalts (Denevi et al, 2013) and basaltic pyroclastic deposits (Kerber et al, 2011), and surface sulfur concentrations of up to 4 wt. Mercury has vast flood basalts (Denevi et al, 2013) and basaltic pyroclastic deposits (Kerber et al, 2011), and surface sulfur concentrations of up to 4 wt. % (Nittler et al, 2011; Starr et al, 2012; Weider et al, 2012)

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Conclusion