Diffusion rates of hydrogen defect species associated with site-specific infrared spectral bands in natural olivine
Diffusion rates of hydrogen defect species associated with site-specific infrared spectral bands in natural olivine
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DOI：
10.1016/j.epsl.2022.117406
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发表时间：
2022-03
影响因子：
5.3
通讯作者：
Y. Li;S. Mackwell;D. Kohlstedt
中科院分区：
文献类型：
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作者：
Y. Li;S. Mackwell;D. Kohlstedt
我们研究了天然存在的，含铁样品的San卡洛斯橄榄石，氢化在200或300 MPa和1173至1303 K或脱氢在室温压力和1191至1358 K。化学扩散系数由来自每个样品的正交方向上的一系列红外光谱的各个O-H伸缩带的扩散曲线确定。在实验的不确定性，扩散系数与所有的个别频带是在良好的协议与彼此在加氢和脱氢实验。如前所述，氢化通过两种扩散机制进行。更快的过程涉及质子的间隙扩散，加上极化子的反向通量，质子扩散速率限制氢化。对于该机制，沿沿着橄榄石[100]方向的扩散比沿沿着[010]和[001]方向的扩散快，这与橄榄石中质子扩散和导电性的各向异性一致。较慢的过程涉及间隙质子扩散与金属空位的平行通量，空位扩散速率限制氢化。对于这种机制，沿着[001]的扩散比沿沿着[100]和[010]的扩散快，这与先前报道的橄榄石中金属阳离子扩散的各向异性一致。从我们的新的脱氢实验的扩散系数是相同的幅度和各向异性，在我们以前的氢化实验中确定的。该协议表明，使用我们的氢化实验的结果来分析橄榄石捕虏晶和地幔捕虏体中的橄榄石的脱氢配置文件，以确定从地球内部的源区岩浆上升率的研究的有效性。
We investigated hydrogen transport in naturally occurring, iron-bearing samples of San Carlos olivine that were hydrogenated at confining pressures of 200 or 300 MPa and 1173 to 1303 K or dehydrogenated at room pressure and 1191 to 1358 K. Chemical diffusion coefficients were determined from diffusion profiles for individual O-H-stretching bands from series of infrared spectra in orthogonal directions across each sample. Within experimental uncertainty, the diffusivities associated with all the individual bands are in good agreement with one another in both the hydrogenation and the dehydrogenation experiments. Hydrogenation proceeds by two diffusion mechanisms, as reported previously. The faster process involves interstitial diffusion of protons coupled with a counter-flux of polarons, with proton diffusion rate-limiting hydrogenation. For this mechanism, diffusion is faster along the olivine [100] direction than along [010] and [001], consistent with the anisotropy reported for proton diffusion and conductivity in olivine. The slower process involves interstitial proton diffusion coupled with a parallel flux of metal vacancies, with vacancy diffusion rate-limiting hydrogenation. For this mechanism, diffusion is faster along [001] than along [100] and [010], consistent with the anisotropy previously reported for the diffusion of metal cations in olivine. Diffusivities from our new dehydrogenation experiments are identical in both magnitude and anisotropy to those determined in our earlier hydrogenation experiments. This agreement demonstrates the validity of studies that used the results of our hydrogenation experiments to analyze dehydrogenation profiles in olivine xenocrysts and olivine in mantle xenoliths to determine rates of magma ascent from the source regions in Earth's interior.