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首页> 外文期刊>Contributions to Mineralogy and Petrology >Hydrogen diffusion in spinel grain boundaries and consequences for chemical homogenization in hydrous peridotite
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Hydrogen diffusion in spinel grain boundaries and consequences for chemical homogenization in hydrous peridotite

机译：氢在尖晶石晶界中的扩散以及水合橄榄岩中化学均质化的后果

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Hydrogen can be stored in the structure of nominally anhydrous minerals as point defects, and these impurities substantially modify many physical properties of Earth’s mantle minerals. However, mantle rocks are composed of mineral grains separated by grain boundaries and interphase grains boundaries. Therefore, as a potential hydrogen reservoir, grain boundaries should be given proper attention. Here, I report an experimental investigation into hydrogen diffusion through grain boundaries in polycrystalline aggregates. Sintering and diffusion experiments were performed using a gas-medium high-pressurevessel at under pressure of 300 MPa and over a temperature range of 900–1,250℃. The diffusion assembly consisted of a polycrystalline cylinder of aluminous spinel+olivine crystals with a talc cylinder as the main hydrogen source. A Ni capsule was used to buffer the oxygen fugacity at Ni–NiO. Experimental durations varied from 5 min to 5 h. The presence of hydrogen in the crystals was measured by Fourier-transform infrared spectroscopy. The calculation of the diffusion coefficients was based on the estimation of the characteristic distance. The absence or presence of hydrogen recorded by the ‘hydrogen sensor’ olivines embedded in the aggregate allows the estimation of bounds on this characteristic distance. Results presented here suggest that hydrogen effective diffusion coefficients are only one order of magnitude faster (～10~(-9)m~2s~(-1) at 1,000℃) than in an olivine single crystal along the [100] axis. Resulting diffusion coefficients for hydrogen in grain boundary are four orders of magnitude faster than in a single crystal, but this diffusivity is not fast enough to affect hydrogen mobility in mantle rocks with grain sizes greater than ～1 mm. Thus, very limited chemicalhomogenization would occur using grain boundaries diffusion in mantle hydrous peridotite for incompatible and volatile element, such as hydrogen.
机译：氢可以存储为名义上无水矿物的结构中的点缺陷，这些杂质会大大改变地球地幔矿物的许多物理性质。但是，地幔岩石由被晶界和相间晶界分隔的矿物晶粒组成。因此，作为潜在的氢储库，应适当注意晶界。在这里，我报告了对氢在多晶聚集体中通过晶界扩散的实验研究。烧结和扩散实验是在300 MPa的压力和900-1,250℃的温度范围内使用气态高压容器进行的。扩散组件由铝尖晶石+橄榄石晶体的多晶圆柱体组成，其中滑石圆柱体为主要氢源。镍胶囊用于缓冲Ni–NiO的氧逸度。实验时间从5分钟到5小时不等。通过傅立叶变换红外光谱法测量晶体中氢的存在。扩散系数的计算基于特征距离的估计。嵌入聚集体中的“氢传感器”橄榄石记录的氢的存在与否，可以估算出该特征距离的界限。此处的结果表明，氢的有效扩散系数仅比沿[100]轴的橄榄石单晶快一个数量级（在1000℃时约为10〜（-9）m〜2s〜（-1））。氢在晶界的扩散系数比单晶快4个数量级，但这种扩散速度还不足以影响粒径大于〜1 mm的地幔岩石中的氢迁移率。因此，对于不相容且易挥发的元素（例如氢），在地幔含水橄榄岩中使用晶界扩散会发生非常有限的化学均质化。

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