Water strongly modulates the physical and chemical properties of planetary materials, influencing mantle convection, magmatism, and plate tectonics, and thus Earth’s habitability (1). Despite its importance, the timing and mechanism of Earth’s water acquisition remain unresolved. Competing models invoke late delivery by volatile-rich bodies (2), inheritance from water-bearing enstatite chondrites (3), or incorporation of hydrogen from a nebular H₂-rich environment during early accretion (4). Hydrogen isotopes provide a powerful tracer for distinguishing among these scenarios, yet their interpretation is complicated by large-scale hydrogen partitioning during core formation.

Geochemical and geophysical evidence indicates that more than 75% of Earth’s hydrogen was sequestered into the metallic core during differentiation (5, 6), making the core the planet’s largest hydrogen reservoir. Consequently, the bulk Earth’s hydrogen isotope composition depends critically on hydrogen isotope fractionation between silicate and metallic melts at core-forming pressures and temperatures. However, this key fractionation factor remains poorly constrained.

Here, we address this long-standing problem by combining first-principles calculations with machine-learning–accelerated path-integral molecular dynamics to quantify equilibrium hydrogen isotope fractionation between silicate and metallic melts under core-forming conditions. Our simulations explicitly capture nuclear quantum effects and extend to pressures and temperatures relevant to Earth’s early magma ocean and core formation. We incorporate these fractionation factors into models of hydrogen isotope evolution during planetary differentiation and accretion, allowing us to reconstruct the bulk Earth’s D/H ratio. These results provide new constraints on the sources of Earth’s water and clarify the role of metal–silicate equilibration in shaping the planet’s volatile inventory during its earliest history.

References

1. K. Regenauer-Lieb, Water and geodynamics. Rev. Mineral. Geochem. 62, 451-473 (2006)

2. Z. Wang, H. Becker, Ratios of S, Se, and Te in the silicate Earth require a volatile-rich late veneer. Nature 499, 328-331 (2013).

3. L. Piani, Y. Marrocchi, T. Rigaudier, L. G. Vacher, D. Thomassin, B. Marty, Earth's water may have been inherited from material similar to enstatite chondrite meteorites. Science 369, 1110-1113 (2020).

4. E. D. Young, A. Shahar, H. E. Schlichting, Earth shaped by primordial H₂ atmospheres. Nature 616, 306-311 (2023).

5. S. Tagawa, N. Sakamoto, K. Hirose, S. Yokoo, J. Hernlund, Y. Ohishi, H. Yurimoto, Experimental evidence for hydrogen incorporation into Earth's core. Nat Commun 12, 2588 (2021).

6. Y. Li, L. Vocadlo, T. Sun, J. P. Brodholt, The Earth's core as a reservoir of water. Nat. Geosci. 13, 453-458 (2020).

How to cite: Wang, W., Zhang, Y., Deng, Z., Wu, Z., and Chen, B.: Hydrogen isotope fractionation during core formation of terrestrial planets, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6129, https://doi.org/10.5194/egusphere-egu26-6129, 2026.

The fate of sulfur in magmatic systems influences a wide range of processes including chalcophile element behavior, magma redox evolution, and volcanic degassing. However, understanding sulfur behavior can be complicated by the presence of multiple sulfur valence states (S^2- and S⁶⁺) in silicate melts. The transition from S^2- to S⁶⁺ occurs over a narrow range of oxygen fugacities (f_O2) such that small changes in melt f_O2 may significantly impact sulfur transport and its partitioning between minerals, silicate melt, and vapor. In recent years, we have learned much more about the dependence of this transition on temperature and melt composition, but the effect of pressure remains poorly constrained.

Here, we present a new suite of experiments allowing us to quantify the effect of pressure on mafic silicate melts. We integrate these experimental results with existing calibrations to explore how sulfur-iron redox equilibria influences the generation of basaltic magmas. Using a simplified mantle melting and melt extraction model, we show that sulfur valence state remains relatively stable during mantle melting and extraction. However, we also show that sulfur and iron continuously exchange electrons during melt ascent, leading to a small but non-negligible change to f_O2 relative to the QFM buffer. This example showcases the importance of integrating sulfur-iron redox equilibria into petrologic models, and how we can leverage recent advances in analytical and experimental methodologies to do so accurately.

How to cite: Muth, M.: The importance of sulfur in the generation of basaltic magmas, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15162, https://doi.org/10.5194/egusphere-egu26-15162, 2026.