The Fe–Mg and Fe–Mn interdiffusion coefficients for ilmenite have been determined as a function of temperature and crystallographic orientation. Diffusion annealing experiments were conducted at 1.5 GPa between 800 and 1100 ∘C\documentclass[12pt]{minimal}
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\begin{document}$$^{\circ }\hbox {C}$$\end{document}. For Fe–Mg interdiffusion, each diffusion couple consisted of an ilmenite polycrystal and an oriented single crystal of geikielite. The activation energy (Q) and pre-exponential factor (D0\documentclass[12pt]{minimal}
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\begin{document}$$D_0$$\end{document}) for Fe–Mg diffusion in the ilmenite polycrystal were found to be Q = 188±15kJmol-1\documentclass[12pt]{minimal}
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\begin{document}$$188 \pm 15\hbox { kJ mol}^{-1}$$\end{document} and logD0\documentclass[12pt]{minimal}
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\begin{document}$${\text {log}} D_0$$\end{document} = -6.0±0.6m2s-1\documentclass[12pt]{minimal}
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\begin{document}$$-6.0 \pm 0.6\hbox { m}^2\hbox { s}^{-1}$$\end{document}. For the geikielite single crystal, Fe–Mg interdiffusion has Q=220±16kJmol-1\documentclass[12pt]{minimal}
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\begin{document}$$Q = 220 \pm 16\hbox { kJ mol}^{-1}$$\end{document} and logD0=-4.6±0.7m2s-1\documentclass[12pt]{minimal}
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\begin{document}$${\text {log}} D_0 = -4.6 \pm 0.7\hbox { m}^2\hbox { s}^{-1}$$\end{document}. Our results indicate that crystallographic orientation did not significantly affect diffusion rates. For Fe–Mn interdiffusion, each diffusion couple consisted of one ilmenite polycrystal and one Mn-bearing ilmenite polycrystal. For Fe–Mn interdiffusion, Q = 264±30kJmol-1\documentclass[12pt]{minimal}
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\begin{document}$$264 \pm 30\hbox { kJ mol}^{-1}$$\end{document} and logD0\documentclass[12pt]{minimal}
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\begin{document}$${\text {log}} D_0$$\end{document} = -2.9±1.3m2s-1\documentclass[12pt]{minimal}
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\begin{document}$$-2.9 \pm 1.3\hbox { m}^2\hbox { s}^{-1}$$\end{document} in the ilmenite. We did not find a significant concentration dependence for the Fe–Mg and Fe–Mn interdiffusion coefficients. In comparing our experimental results for cation diffusion in ilmenite with those previously reported for hematite, we have determined that cation diffusion is faster in ilmenite than in hematite at temperatures <1100 ∘C\documentclass[12pt]{minimal}
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\begin{document}$$^{\circ }\hbox {C}$$\end{document}. At oxygen fugacities near the wüstite–magnetite buffer, Fe and Mn diffusion rates are similar for ilmenite and titanomagnetite. We apply these experimentally determined cation diffusion rates to disequilibrium observed in ilmenites from natural volcanic samples to estimate the time between perturbation and eruption for the Bishop Tuff, Fish Canyon Tuff, Mt. Unzen, Mt. St. Helens, and kimberlites. When integrated with natural observations of chemically zoned ilmenite and constraints on pre-eruptive temperature and grain size, our experimentally determined diffusivities for ilmenite can be used to estimate a minimum time between magmatic perturbation and eruption on the timescale of hours to months.
