A Raman calibration for the quantification of SO42− groups dissolved in silicate glasses: Application to natural melt inclusions

Abstract : Sulfur is an important volatile element involved in magmatic systems. Its quantification in silicate glasses relies on state-of-the-art techniques such as electronprobe microanalyses (EPMA) or X-ray absorption spectroscopy but is often complicated by the fact that S dissolved in silicate glasses can adopt several oxidation states (S6+ for sulfates or S2− for sulfides). In the present work, we use micro-Raman spectroscopy on a series of silicate glasses to quantify the S content. The database is constituted by 47 silicate glasses of various compositions (natural and synthetic) with S content ranging from 1179 to 13 180 ppm. Most of the investigated glasses have been synthesized at high pressure and high temperature and under fully oxidizing conditions. The obtained Raman spectra are consistent with these fO2 conditions and only S6+ is present and shows a characteristic peak located at ~1000 cm−1 corresponding to the symmetric stretch of the sulfate molecular group (ν1 SO42−). The intensity of the ν1 SO42− peak is linearly correlated to the parts per million of S6+ determined by EPMA.