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Creators/Authors contains: "Elardo, Stephen"

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  1. We investigate the implications of prolonging the equilibrium crystallization (EQX) stage of lunar magma ocean (LMO) solidification beyond the oft-modeled 50% volume solids, to 60%. Most models of two-stage LMO crystallization halt the EQX phase once 50% of a molten Moon (post-core formation) solidifies, after which the remaining 50% of the LMO solidifies via fractional crystallization (FRX). We quantitatively show through a simple scaling analysis that compares crystal settling velocity to vertical convective velocity that the early EQX regime can operate up to (and possible even slightly beyond) 60% volume solids. Phases that stabilize during the EQX and FRX regimes are then computed using Perple_X (thermodynamic calculator) along with the hp633ver database and associated activity-composition relations for solid solutions, and consider an adiabat that remains between the liquidus and solidus. Early results show two key findings: 1) only low volumes (~2%) of ilmenite form over ~50-km thick upper mantle layers for both 50% and 60% EQX regimes, suggesting that a mantle overturn may have been sluggish and/or limited in depth (dense ilmenite is thought to have been a critical driver of late-stage mantle mixing); and 2) contrary to most published two-stage LMO models, a refractory-enriched (i.e. high Al2O3) bulk silicate Moon is not required to produce garnet in the lunar mantle, assuming an Earth-like bulk silicate Moon composition with an alumina content of ~4 wt.%. To complement and test these numerical phase equilibria model results, a series of piston-cylinder experiments is underway that simulate the pressures and temperatures experienced by an FeO+TiO2-rich residual LMO in order to assess the volume and distribution of ilmenite produced during LMO solidification. These results are compared to those of the numerical phase equilibria models. Despite the model-dependent nature of these results, they provide a unique insight into potential LMO crystallization that has not been previously considered in the literature. 
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    Free, publicly-accessible full text available December 2, 2025