Effect of sulphur on the structure of silicate melts under oxidizing conditions

Abstract

International audienceIn magmatic systems, sulphur is an important volatile element after C, H and O. Under oxidizing conditions, S dissolves in aluminosilicate melt as sulphate groups (SO42 −). The way SO42 − groups dissolve in the melt is currently poorly understood. We present experimental results of the effect of SO42 − dissolution on the aluminosilicate melt structure. Glasses of haplogranitic (HPG) and anorthite-diopside eutectic (An-Di) compositions were synthesized at 300 MPa and 1250 °C and under oxidizing conditions (ΔFMQ + 1.7 to + 3.0). Starting compositions were equilibrated under fluid-saturated conditions with a mixture of S (0 to 5 wt.%) and H2O (5 wt.%). The S and H2O contents of the recovered glasses were determined with EPMA and FTIR, respectively. Solid state NMR was used to investigate the glass structure. Micro-Raman analyses were performed to identify S species present in glass and coexisting fluid phases. The S content determined in glasses changes from 0 to 979 ppm and 0 to 7519 ppm for HPG and An-Di, respectively. S is present in the glasses as Mn +SO42 − groups (Mn + is possibly Ca2 + in An-Di and Na+ in HPG). 29Si NMR analyses show important changes in the An-Di glass structure upon S dissolution. High S content in An-Di glasses induces a strong polymerization of the glass which we explain by the presence of non-bridging oxygen (NBO) promoting the dissolution of S as SO42 − groups. On the contrary, the dissolution of S within HPG melt does not produce visible changes in the silicate melt structure due to the low concentration in NBO in this melt composition. The observed structural changes suggest that An-Di melt physical properties might be affected by S dissolution. S might produce large changes in melt viscosity, but opposite, as compared to H2O for slightly depolymerized aluminosilicate melts

A NMR and molecular dynamics study of CO2-bearing basaltic melts and glasses

“…The acquired 29 Si Direct MAS spectrum exhibits a slight peak asymmetry witnessing that the 29 Si spectrum is a complex convolution of individual peaks; each of these being attributed to a given Q n species (e.g. Lippmaa et al, 1980;Grimmer et al, 1984;Schramm et al, 1984;Maekawa et al, 1991;Stebbins, 1995;Zhang et al, 1997;Schmidt et al, 2000;Schneider et al, 2003;Mysen and Cody, 2005;Malfait et al, 2007b;Angeli et al, 2011;Davis et al, 2011;Morizet et al, 2013b). The evidence for several Q n species is further asserted by the various NMR experiments we have conducted.…”

“…The 29 Si NMR spectrum deconvolution procedure has been reported in previous work (Morizet et al, 2013b(Morizet et al, , 2014b; and references therein). The 29 Si NMR spectrum deconvolution was conducted simultaneously on the entire set of spectra and using three Gaussian peaks.…”

Spectroscopic studies of oxygen speciation in potassium silicate glasses and melts

“…Many papers have quantified the uptake of water, CO 2 , and sulfur in silicate glasses and magmas and have noted their importance to magmatic and volcanic processes. 30,31,[35][36][37][38][39][40][41][42][43][44] Because the uptake of CO 2 is reasonably well documented, we consider qualitatively the reaction of CO 2 with oxygen species in melts. The early studies of Eggler and Rosenhauer 86 demonstrated that gaseous CO 2 dissolved in melts exists as CO 2 and CO 3 2-, and it is generally agreed 30,31,[35][36][37][38][39][99][100][101][102] that the overall stoichiometric reaction for CO 2 uptake is…”

Thermal properties of sodium borosilicate glasses as a function of sulfur content

“…Raman analysis, Figure , was used to understand the bond and structure changes caused by SO 3 additions. It has been shown that, under oxidizing conditions, silicate and borosilicate glasses with sulfur additions will exhibit a large S 6+ –O symmetric stretching mode from 990 to 1000/cm . This peak was clearly seen, and the intensity of the peak grew with increasing sulfur loading.…”

“…In particular, the coordination of the oxygen and ratio of bridging (O 0 ), non‐bridging (O − ), and free oxygen (O 2− ) in the melt system will affect incorporation. Sulfur reduction‐oxidation state (redox) thus plays an important role in determining solubility and structure in the glass . The sulfur species incorporated into the glass is usually described as isolated sulfate units, typically surrounded by network‐modifying cations such as sodium .…”