Date of Award
Doctor of Philosophy (PhD)
The chapters of this dissertation detail experimental studies that have been conducted in order to determine the diffusivity of iron in the mineral ilmenite (FeTiO3) and the high-temperature behavior of iron isotopes during magma crystallization. The experimental study in Chapter 2 is the first to quantify the rates of cation diffusion in ilmenite. Integrating experimentally determined Fe-Mg and Fe-Mn interdiffusivities with disequilibrium preserved in ilmenite grains from natural volcanic samples, this work has established a new geospeedometry tool with which to estimate the time between magmatic perturbation and eruption on the timescale of hours to months. Chapter 3 investigates the effects of olivine crystallization on high-temperature iron isotopic fractionation over a range of oxygen fugacities and melt titanium compositions. The results demonstrate that there is no resolvable equilibrium fractionation of iron isotopes between olivine and melt at the experimental oxygen fugacities (where iron is mainly Fe2+), nor is there a measurable effect of melt titanium composition on iron isotopic fractionation in the investigated compositional range. These experiments also led to the discovery that iron loss in reducing one-atmosphere gas-mixing experiments occurs not only as loss to the metal wire sample container, but also as evaporative loss, and each mechanism of experimental iron loss has an associated iron isotopic fractionation. In Chapter 4, the equilibrium partitioning of iron and titanium isotopes between ilmenite and melt was experimentally determined in order to evaluate the role of ilmenite in generating the compositional variability among the lunar mare basalts. The results of the experiments in Chapters 3 and 4 were then incorporated into models of lunar magma ocean crystallization and used to estimate the iron and titanium isotopic compositions of components in mare basalt parent magmas. The iron, titanium, and magnesium isotopic compositions of the lunar mare basalts indicate Fe-Mg interdiffusion has occurred in the Ti-rich component of the mare basalt source regions via subsolidus reaction between ilmenite cumulates and the olivine- and pyroxene-rich lunar mantle. Though additional experimental constraints will be required to fully assess the effects of diffusive isotopic fractionation in ilmenite-bearing rocks, combining the experimental results for Fe-Mg interdiffusion in ilmenite from Chapter 2 with the ilmenite-melt iron isotopic fractionations in Chapter 4 establishes the foundation upon which to build future studies.
Chair and Committee
Michael J. Krawczynski
Nicolas Dauphas, Robert F. Dymek, Bradley L. Jolliff, Jill D. Pasteris,
Prissel, Kelsey Brianne, "Experimental Constraints on Igneous Iron Isotopic Fractionation and Diffusion" (2020). Arts & Sciences Electronic Theses and Dissertations. 2337.