75-37 Effect of Light Elements on the Melting Behavior of Liquid Iron Alloys under Earth’s Inner Core Boundary Conditions.

Session: Mineralogy, Geochemistry, Petrology, and Volcanology Student Session (Posters)

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Constraining the temperature at Earth’s inner core boundary (ICB) is critical for modeling the planet’s thermal evolution, inner core formation, and geodynamo. While geophysical constraints have narrowed down the depth of the ICB, considerable uncertainty remains regarding the temperature at which iron alloys solidify under core pressures. This temperature directly affects estimation of core composition and interpretations of heat flow and Earth’s deep interior dynamics. Although the melting behavior of pure iron has been extensively studied at high pressures by both experiments and computations, limited work has systematically explored how incorporation of light elements (LE) modifies this behavior under ICB conditions (~330 GPa). The influence of specific LE concentrations on the phase stability of iron alloys remains poorly quantified. Addressing this data gap allows for targeted insight into how each element alters the melting temperature, helping to refine core thermal models and evolution of Earth’s core. This study employed molecular dynamics simulations empowered by a machine-learning-based interatomic potential trained on first-principles data. Simulations were conducted across a range of atomic compositions (at%) for binary Fe-X systems (X: H, C, S, O, Si, Ni) under core-relevant pressures. Melting points were determined using the solid–liquid coexistence method, within temperature intervals where solid and liquid phases exchange dominance at phase equilibrium. The simulation results show that H, C, O, S, and Si cause systematic depressions in iron’s melting point. Starting from just 0.5 at%, these elements significantly reduce melting temperatures, reaching 5430 K (H), 5230 K (C), 5330 K (O), and 5780 K (S) at 8 at%, while Si at 1 at% yields 6080 K. These represent melting point depressions of ~800 K, 1000 K, 900 K, 450 K, and 150 K compared to pure iron (6230 K) at ICB. At high Si concentrations (Si > 1 at%), Si increases melting points, reaching 6280 K at 8 at%. For Fe-Ni alloy, Ni consistently raises melting point steadily from 0.5 at%, reaching 6430 K at 2 at%. Such contrasting behaviors emphasize the strong element-specific impact of light elements on thermal and structural stability of iron alloys. The substantial melting point depressions induced by H, C, O, and S suggest inner core solidification likely begins at lower temperatures than predicted by pure Fe. These findings refine estimates of ICB temperature and provide basic data for modeling Earth’s core composition, structure, and the Earth's  geodynamo.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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