Semester of Graduation

Spring 2026

Degree

Master of Science (MS)

Department

Geology and Geophysics

Document Type

Thesis

Abstract

The temperature at Earth’s inner core boundary (ICB) is set by the melting temperature of the iron-rich outer core at core pressures, yet this remains uncertain because melting depends strongly on composition and pressure. Light elements are required to explain the core’s density deficit, but the identity, abundance, and combined influence of these elements on melting under ICB conditions are still debated. This thesis quantifies how candidate light elements modify the melting behavior of iron alloys at ICB-relevant pressures and uses these composition-dependent melting relations to constrain ICB temperature.

Melting relations were determined using molecular dynamics simulations in VASP accelerated by machine-learning force fields, enabling large supercells and long coexistence runs at extreme conditions. Melting temperatures were constrained with the solid–liquid coexistence method by bracketing the temperature range where solid growth switches to liquid growth. Binary Fe–X systems (X = H, C, O, S, Si, Ni) were evaluated over a range of compositions at pressures spanning ~250–360 GPa, and a ternary Fe–S–H system was investigated at 330 GPa to assess multicomponent coupling.

At 330 GPa, pure Fe melts at 6230 K in this dataset. At 15 at% light element, melting temperatures decrease to ~5430 K (Fe–H), ~5230 K (Fe–C), ~5330 K (Fe–O), and ~5780 K (Fe–S), corresponding to melting depressions of ~800 K, ~1000 K, ~900 K, and ~450 K relative to pure Fe, respectively. Silicon shows a smaller and non-monotonic effect: ~6080 K at 2 at% Si (≈150 K below pure Fe) but rising to ~6280 K at 15 at% Si (~50 K above pure Fe). Nickel increases the melting point, from ~6250 K at 0.9 at% Ni to ~6430 K at 4 at% Ni. Using literature-based abundances, the 330 GPa curves map to ICB temperatures of ~5400 K (3.7 wt% O), ~5530 K (2 wt% C), ~5950 K (3.5 wt% S), ~6125 K (1.9 wt% Si), and ~5240 K (0.36 wt% H). The Fe-S-H ternary results show near-additive behavior at low sulfur but an additional melting depression (~100 K to 200 K beyond additivity) at moderate-to-high sulfur, indicating non-ideal multicomponent coupling at ICB pressure.

Together, these results provide internally consistent melting constraints that translate proposed core compositions into quantitative ICB temperature bounds and motivate expanded ternary and multicomponent studies to better reflect realistic core conditions.

Date

3-26-2026

Committee Chair

Wang, Jianwei

LSU Acknowledgement

1

LSU Accessibility Acknowledgment

1

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