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 $$^{\circ }\hbox {C}$$ ∘ C . 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 ( $$D_0$$ D 0 ) for Fe–Mg diffusion in the ilmenite polycrystal were found to be Q = $$188 \pm 15\hbox { kJ mol}^{-1}$$ 188 ± 15 kJ mol - 1 and $${\text {log}} D_0$$ log D 0 = $$-6.0 \pm 0.6\hbox { m}^2\hbox { s}^{-1}$$ - 6.0 ± 0.6 m 2 s - 1 . For the geikielite single crystal, Fe–Mg interdiffusion has $$Q = 220 \pm 16\hbox { kJ mol}^{-1}$$ Q = 220 ± 16 kJ mol - 1 and $${\text {log}} D_0 = -4.6 \pm 0.7\hbox { m}^2\hbox { s}^{-1}$$ log D 0 = - 4.6 ± 0.7 m 2 s - 1 . 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 = $$264 \pm 30\hbox { kJ mol}^{-1}$$ 264 ± 30 kJ mol - 1 and $${\text {log}} D_0$$ log D 0 = $$-2.9 \pm 1.3\hbox { m}^2\hbox { s}^{-1}$$ - 2.9 ± 1.3 m 2 s - 1 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 $$^{\circ }\hbox {C}$$ ∘ C . 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.

中文翻译：

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钛铁矿中的 Fe-Mg 和 Fe-Mn 相互扩散对使用氧化物的地球速度测量法的影响

钛铁矿的 Fe-Mg 和 Fe-Mn 相互扩散系数已被确定为温度和晶体取向的函数。扩散退火实验在 800 和 1100 $$^{\circ }\hbox {C}$$ ∘ C 之间以 1.5 GPa 进行。对于 Fe-Mg 相互扩散，每个扩散对由钛铁矿多晶和菱镁矿定向单晶组成。钛铁矿多晶中 Fe-Mg 扩散的活化能 ( Q ) 和指前因子 ( $$D_0$$ D 0 ) 被发现为 Q = $$188 \pm 15\hbox { kJ mol}^{-1 }$$ 188 ± 15 kJ mol - 1 和 $${\text {log}} D_0$$ log D 0 = $$-6.0 \pm 0.6\hbox { m}^2\hbox { s}^{-1 }$$ - 6.0 ± 0.6 m 2 s - 1 。对于geikielite单晶，Fe-Mg相互扩散有$$Q = 220 \pm 16\hbox { kJ mol}^{-1}$$ Q = 220 ± 16 kJ mol - 1 和$${\text {log} } D_0 = -4.6 \pm 0。7\hbox { m}^2\hbox { s}^{-1}$$ log D 0 = - 4.6 ± 0.7 m 2 s - 1 。我们的结果表明晶体取向没有显着影响扩散速率。对于 Fe-Mn 相互扩散，每个扩散对由一个钛铁矿多晶和一个含锰的钛铁矿多晶组成。对于 Fe-Mn 相互扩散，Q = $$264 \pm 30\hbox { kJ mol}^{-1}$$ 264 ± 30 kJ mol - 1 和 $${\text {log}} D_0$$ log D 0 = $$-2.9 \pm 1.3\hbox { m}^2\hbox { s}^{-1}$$ - 2.9 ± 1.3 m 2 s - 1 在钛铁矿中。我们没有发现 Fe-Mg 和 Fe-Mn 相互扩散系数的显着浓度依赖性。将我们在钛铁矿中的阳离子扩散实验结果与之前报道的赤铁矿实验结果进行比较，我们已经确定，在 <1100 $$^{\circ }\hbox {C}$$ ∘ C 的温度下，钛铁矿中的阳离子扩散速度比赤铁矿中的快. 在方铁矿-磁铁矿缓冲区附近的氧逸度处，钛铁矿和钛磁铁矿的 Fe 和 Mn 扩散速率相似。我们将这些实验确定的阳离子扩散速率应用于从天然火山样品中观察到的钛铁矿中观察到的不平衡，以估计 Bishop Tuff、Fish Canyon Tuff、Mt. 的扰动和喷发之间的时间。云仙山 圣海伦斯和金伯利岩。当与化学分区钛铁矿的自然观察以及对喷发前温度和晶粒尺寸的限制相结合时，我们通过实验确定的钛铁矿扩散率可用于估计岩浆扰动和喷发之间的最短时间，时间尺度为数小时到数月。我们将这些实验确定的阳离子扩散速率应用于从天然火山样品中观察到的钛铁矿中观察到的不平衡，以估计 Bishop Tuff、Fish Canyon Tuff、Mt. 的扰动和喷发之间的时间。云仙山 圣海伦斯和金伯利岩。当与化学分区钛铁矿的自然观察以及对喷发前温度和晶粒尺寸的限制相结合时，我们通过实验确定的钛铁矿扩散率可用于估计岩浆扰动和喷发之间的最短时间，时间尺度为数小时到数月。我们将这些实验确定的阳离子扩散速率应用于从天然火山样品中观察到的钛铁矿中观察到的不平衡，以估计 Bishop Tuff、Fish Canyon Tuff、Mt. 的扰动和喷发之间的时间。云仙山 圣海伦斯和金伯利岩。当与化学分区钛铁矿的自然观察以及对喷发前温度和粒度的限制相结合时，我们通过实验确定的钛铁矿扩散率可用于估计岩浆扰动和喷发之间的最短时间，时间尺度为数小时到数月。