Implications of reactions between SO2 and basaltic glasses for the mineralogy of planetary crusts

1,3C.J. Renggli,1A.B. Palm,1P.L. King,2P. Guagliardo
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2019JE006045]
1Research School of Earth Sciences, The Australian National University, Canberra ACT 2601, Australia
2Centre for Microscopy, Characterization and Analysis, University of Western Australia, PerthWA 6009, Australia
3Institute for Mineralogy, University of Münster, Münster,48149, Germany
Published by arrangement with John Wiley & Sons

Basalts 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 h and 24 h. 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. In 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.

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