09:00 〜 09:15
[SIT20-13] The effect of hydrogen on the metal-silicate partitioning of sulfur
★Invited Papers
Cosmochemical/geochemical estimates suggest that sulfur concentration in the Earth’s core is ~2 wt%, which is ~100 times higher than that in the mantle (McDonough, 2014). Due to its siderophile behavior, core-mantle partitioning of sulfur is coupled with that of highly siderophile elements and chalcogen elements, taking models of the Hadean Matte or a late veneer into account (Rubie et al., 2009; Wang & Becker, 2013). Despite its importance, previous studies reported pressure- and temperature-dependences of the metal-silicate partition coefficient of sulfur (DS) inconsistent with each other. While studies using a large volume press showed that metal/silicate DS increases with increasing pressure (e.g., Boujibar et al., 2014), experiments using a diamond-anvil cell (DAC) yielded smaller DS at higher pressures and suggested a large temperature dependence (Suer et al., 2017). In addition to pressure and temperature, metal composition (in other words, coexisting other impurity elements) may also be a dominant factor controlling the DS. It is known that sulfur and carbon mutually decrease the metal/silicate partition coefficients (Boujibar et al., 2014; Tsuno et al., 2018). However, the effect of hydrogen on DS has not been examined while they have strong interactions leading to a wide immiscibility field between S-rich and H-rich liquid iron (Yokoo et al., 2022).
Here, we present the results of the metal-silicate partitioning experiments on sulfur with and without hydrogen (water) using a DAC. Textural characterizations and SIMS (secondary ion mass spectrometry) measurements revealed that the distribution of small metallic particles enhances the apparent sulfur content in a silicate melt and decreases DS in a DAC sample. Our SIMS measurements of a silicate melt portion free of metallic particles show DS = ~1000 at ~50 GPa and 4500 K, which is consistent with previous low-pressure studies using a large volume press. Experiments performed in the presence of hydrogen demonstrated that hydrogen in metal decreases DS. Core formation models using the partition coefficients of sulfur and hydrogen suggest that the estimated sulfur abundance in the present mantle can be reproduced by considering H-rich (> 0.5 wt% H) core compositions or the addition of sulfur to the mantle by the late veneer after the core formation.
Here, we present the results of the metal-silicate partitioning experiments on sulfur with and without hydrogen (water) using a DAC. Textural characterizations and SIMS (secondary ion mass spectrometry) measurements revealed that the distribution of small metallic particles enhances the apparent sulfur content in a silicate melt and decreases DS in a DAC sample. Our SIMS measurements of a silicate melt portion free of metallic particles show DS = ~1000 at ~50 GPa and 4500 K, which is consistent with previous low-pressure studies using a large volume press. Experiments performed in the presence of hydrogen demonstrated that hydrogen in metal decreases DS. Core formation models using the partition coefficients of sulfur and hydrogen suggest that the estimated sulfur abundance in the present mantle can be reproduced by considering H-rich (> 0.5 wt% H) core compositions or the addition of sulfur to the mantle by the late veneer after the core formation.