Bjorn

Mysen

Elucidating the role of sulfur on the structure of silicate glasses and melts at elevated pressures and temperatures is important for understanding transport properties, such as electrical conductivity and viscosity, of magma oceans and mantle-derived melts. These properties are fundamental for modeling the evolution of terrestrial planets and moons. Despite several investigations of sulfur speciation in glasses, questions remain regarding the effect of S on complex glasses at highly reducing conditions relevant to Mercury. Glasses were synthetized with compositions representative of the Northern Volcanic Plains of Mercury and containing quantities of S up to 5 wt %. Multiple spectroscopic methods and microprobe analyses were employed to probe the glasses, including in situ impedance spectroscopy at 2- and 4-GPa pressures and temperatures up to 1740 K using a multi-anvil press, Si-29 NMR spectroscopy, and Raman spectroscopy. Electrical activation energies (Ea) in the glassy state range from 0.56 to 1.10 eV, in agreement with sodium as the main charge carrier. The electrical measurements indicate that sulfide improves Na+ transport and may overcome a known impeding effect of the divalent cation Ca2+. The glass transition temperature lies between 700 and 750 K, and for temperatures up to 970 K Ea decreases (0.35-0.68 eV) and the conductivities of the samples converge (similar to 5-8 x 10(-3) S/m). At T-quench, the melt fraction is 50-70% and melt conductivity varies from 0.7 to 2.2 S/m, with the sample containing 5 wt% S the most conductive among the set. Si-29 NMR spectra reveal that a high fraction of S bonds with Si in these complex glasses, a characteristic that has not been recognized previously. Raman spectra and maps reveal regions rich in Ca-S or Mg-S bonds. The evidence of sulfide interactions with both Si and Ca/Mg suggest that alkaline earth sulfides can be considered weak network modifiers in these glasses, under highly reduced conditions.

In order to characterize rhenium transport via infiltration of fluids in the Earth's interior, the solubility and solution mechanisms of ReO2 in aqueous fluids were determined to 900 & DEG;C and about 1710 MPa by using an externally-heated hydrothermal diamond anvil cell. In order to shed light on how Re solubility and solution mechanisms in aqueous fluids can be affected by interaction of Re with other solutes, compositions ranged from the comparatively simple ReO2-H2O system to compositionally more complex Na2O-ReO2-SiO2-H2O fluids. Fluids in the ReO2-SiO2-H2O, SiO2-H2O, Na2O-SiO2-H2O, and Na2O-ReO2-H2O systems also were examined. The presence of Na2O enhances the ReO2 solubility so that in Na2O-ReO2-H2O fluids, for example, Re solubility is increased by a factor of 10-15 compared with the Re solubility in Na2O-free ReO2-H2O fluids. The SiO2 component in ReO2-SiO2-H2O causes reduction of ReO2 solubility compared with ReO2-H2O fluids. The ReO2 solubility in the Na-bearing Na2O-ReO2-SiO2-H2O fluids is greater than that in fluids in both the ReO2-H2O and ReO2-SiO2-H2O systems. Rhenium is dissolved in aqueous fluid as ReO4-complexes with Re in fourfold coordination with oxygen. Some, or all, of the oxygen in these complexes is replaced by OH-groups depending on whether Na2O also is present. It is proposed that during dehydration of hydrated subduction zone mineral assemblages in the upper mantle, the alkali/alkaline earth ratio of the source of the released aqueous fluid affects the extent to which Re (and other HFSE) can be transported into an overlying peridotite mantle wedge. The infiltration of such fluids will, in turn, affect the Re content (and Re/Os ratio) of magma formed by partial melting of this peridotite wedge.

Elucidating the role of sulfur on the structure of silicate glasses and melts at elevated pressures and temperatures is important for understanding transport properties, such as electrical conductivity and viscosity, of magma oceans and mantle-derived melts. These properties are fundamental to modeling the evolution of terrestrial planets and moons. Despite several investigations of sulfur speciation in glasses, questions remain regarding the effect of S on complex glasses at highly reducing conditions relevant to Mercury. Glasses were synthetized with compositions representative of the Northern Volcanic Plains of Mercury and containing quantities of S as high as 5 wt.%. Multiple spectroscopic methods and microprobe analyses were employed to probe the glasses, including in situ impedance spectroscopy at 2- and 4-GPa pressures and temperatures up to 1740 K using a multi-anvil press, 29Si NMR spectroscopy, and Raman spectroscopy. Electrical activation energies (Ea) in the glassy state range from 0.56 to 1.10 eV, in agreement with sodium as the main charge carrier. The electrical measurements suggest that sulfide improves Na+ transport and may overcome a known impeding effect of the divalent cation Ca2+. The glass transition temperature lies between 700-750 K, and for temperatures up to 970 K Ea decreases (0.35-0.68 eV) and the conductivities of the samples converge (~5-8 *10-3 S/m). At Tquench, the melt fraction is 50-70% and melt conductivity varies from 0.7 to 2.2 S/m, with the sample containing 5 wt.% S the most conductive among the set. 29Si NMR spectra reveal that a high fraction of S bonds with Si in these complex glasses, an important insight that has not been recognized previously. Raman spectra and maps reveal regions rich in Ca-S or Mg-S bonds. The evidence of sulfide interactions with both Si and Ca/Mg suggest that alkaline earth sulfides can be considered weak network modifiers in these glasses, under highly reduced conditions. Experimental data from impedance spectroscopy, NMR spectroscopy, Raman spectroscopy and electron microprobe analyses. The description of the experiments and analyses is explained the manuscript. # Title of Dataset Data used in manuscript GCA-D-23-00571 entitled Experimental Investigation of the Bonding of Sulfur in Highly Reduced Silicate Glasses and Melts by A. Pommier, M. J. Tauber, H. Pirotte, G.D. Cody, A. Steele, E.S. Bullock, B. Charlier, and B.O. Mysen (Geochimica et Cosmochimica Acta). The spreadsheet lists all the measurements shown in the figures of the manuscript. Each tab correspond to a figure: -Figures 2 and 3: electron microprobe analyses. -Figures 4 and 5: impedance spectroscopy -Figure 6: NMR spectroscopy -Figures 8 and 9: Raman spectroscopy -Figure 10: NBO/T estimates The reader is referred to the manuscript for details about the experimental procedures and results. ## Description of the data and file structure * Figure 2 tab: Each sample name starts with BBC. For each sample, electron microprobe analyses are shown for traverses across the sample and the content of each oxide is in wt.%. * Figure 3 tab: Microprobe traverse in sample BBC16. The content of each oxide is in wt.%. * Figure 4: Impedance spectra of samples BBC13 and BBC17 at selected temperatures. For each temperature, the different columns correspond to the frequency, time, real component (Z') and imaginary component (Z"). * Figure 5 tab: electrical resistance (R) and conductivity (EC) of different samples as a function of temperature (T). Each sample name starts with BBC. For each sample, the different columns correspond to temperature (in degC and K), inverse T, resistance, conductivity and Ln (conductivity). * Figure 6: NMR spectra for four starting glasses (VT48, 52, 53, 54). The first column is the chemical shift, and the other columns correspond to the intensity of each sample. * Figure 7: Raman spectrum of starting glass VT55. The first column is the Raman shift, and the second column corresponds to the intensity of the sample. * Figure 8: Raman spectra of sulfide components in starting glass VT52 and samples from experiments BBC17 and BBC18. For each sample, the first column is the Raman shift, and the second column corresponds to the intensity of the sample. Copyright: CC0 1.0 Universal (CC0 1.0) Public Domain Dedication

The Earth's fluid budget is dominated by species in the system C-O-H-N-S together with halogens such as F and Cl. H2O is by far the most abundant. Such fluids are one of the two main mass transport agents (fluid and magma) in the Earth. Among those, in particular aqueous fluids are efficient solvents of geochemically important components at high temperature and pressure. The solution capacity of aqueous fluids can be enhanced further by dissolved halogens and sulfur. CO2 or nitrogen species has the opposite effect.

Tracing the deep geological water cycle requires knowledge of the hydrogen isotope systematics between and within hydrous materials. For quenched hydrous alkali-silicate melts, hydrogen NMR reveals a distinct heterogeneity in the distribution of stable hydrogen isotopes (D, H) within the silicate tetrahedral network, where deuterons concentrate strongly in network regions that are associated with alkali cations. Previous hydrogen NMR studies performed in the sodium tetrasilicate system (Na2O x 4SiO2, NS4) with a 1:1 D2O/H2O ratio showed on average 1300 %o deuterium enrichment in the alkali-associated network, but the effect on varying bulk D2O/ H2O ratios on this intramolecular isotope effect remained unconstrained. Experiments in the hydrous sodium tetrasilicate system with 8 wt% bulk water and varying bulk D2O/H2O ratios were performed at 1400 degrees C and 1.5 GPa. It is found that both hydrogen isotopes preferably partition into the silicate network that is associated with alkali ions. The partitioning is always stronger for the deuterated than for the protonated hydrous species. The relative enrichment of deuterium over protium in the alkali-associated network, i.e., the intramolecular isotope effect, correlates positively with the D2O/H2O bulk ratio of the hydrous NS4 system. Modeled for natural deuterium abundance (D/H near 1.56 x 10-4), a 1.4-fold (c. 340 %o) deuterium enrichment in the alkaliassociated silicate network is predicted. The partitioning model further predicts a positive correlation between the bulk water content of the silicate melt and the intramolecular deuterium partitioning into the alkaliassociated silicate network. Such heterogeneities may explain the magnitude and direction of hydrogen isotope fractionation in hydrous silicate melts coexisting with silicate-saturated fluids. As such, this intramolecular isotope effect appears to be an effective mechanism for deuterium separation, particularly in hydrous magmatic settings, such as subduction zones.