X-ray microspectroscopy of sulfur in basaltic glass inclusions. Inference on the volcanic sulfur emissions

Abstract

It is commonly accepted that sulfur is carried out as sulfide (S $\rm ^{II-}$) or/and sulfate (S $\rm ^{VI}$) by Earth mantlederived melts, before being released as SO 2 and/or H 2S in volcanic emissions. By analyzing reference compounds and a selection of minute glass inclusions in olivine crystals using $\mu$XANES (X-ray Near Edge Structure) spectroscopy at the sulfur K-edge, we demonstrated the ubiquitous presence of sulfite (S $\rm ^{IV}$) in addition to sulfate (S $\rm ^{VI}$) in these rare inclusions representative of oxidized and water rich-basaltic magmas, prior to loss of sulfur and water. The sulfide (S $\rm ^{II-}$) when exists is minor. We proposed that sulfite (S $\rm ^{IV}$) acts as an intermediate, metastable species which results in partitioning of sulfur into the volcanic gas emissions.