Water diffusion in basaltic to dacitic glasses
Water diffusion in basaltic to dacitic glasses
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DOI：
10.1016/j.chemgeo.2005.09.009
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发表时间：
2006-03
期刊：
影响因子：
3.9
通讯作者：
S. Okumura;S. Nakashima
中科院分区：
文献类型：
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作者：
S. Okumura;S. Nakashima
1.1、0.7和1.0 wt.%的玄武质、安山质和英安质玻璃的脱水实验在400-675 °C和0. IMPa下分别进行总水的测量。通过原位红外（IR）光谱法测量脱水速率，并通过假设一种组分水（总水）的扩散来建模。玄武岩和英安岩中的总水扩散系数与总水含量呈线性关系，而安山岩中的扩散系数在本研究的含水量和温度范围内与总水含量呈弱相关或不相关。玄武岩和英安岩中的总水扩散系数是通过假设扩散系数与总水含量线性相关来确定的，而安山岩中的总水扩散系数是通过假设扩散系数恒定来确定的。所获得的总水的扩散系数D（μm2/s）可以由以下等式表示：其中C是以重量百分比计的总水含量; C 0是1.1和1.0重量%的参考总水含量分别为玄武岩和英安岩; T为开尔文温度。这些方程涵盖400-575、500-675和500-675 °C的温度范围，以及<1.1、0.7和1.0重量%的水含量范围。分别为玄武岩、安山岩和英安岩。所获得的玄武岩、安山岩和英安岩中总水的扩散系数以及流纹岩中水扩散系数的先前数据表明，在0.7wt.在400-675 °C范围内，从流纹岩到安山岩，水的总扩散系数逐渐减小，但玄武岩的总扩散系数大于英安岩，小于流纹岩。另一方面，本研究的结果预测，在玄武岩流纹岩的总水的扩散系数增加与解聚的硅酸盐结构在较高的温度下，这是从扩散温度趋势的交叉的结果。
Dehydration experiments on basaltic, andesitic and dacitic glasses with 1.1, 0.7 and 1.0 wt.% total water, respectively, were performed at 400–675 °C and 0.1 MPa. The dehydration rates were measured by in situ infrared (IR) spectroscopy and modeled by assuming the diffusion of one component water (total water). The diffusivities of total water in basalt and dacite were found to be linearly dependent on total water contents, but that in andesite was weakly dependent on or independent of total water contents at water content and temperature ranges of this study. The total water diffusivities in basalt and dacite were determined by assuming the linear-dependent diffusivity on total water contents and that in andesite was obtained by assuming the constant diffusivity. The obtained diffusivities of total water D (μm2/s) can be expressed by the following equations:where C is the total water contents in weight percent; C0, reference total water contents of 1.1 and 1.0 wt.% for basalt and dacite, respectively; and T, temperature in Kelvin. These equations cover the temperature ranges of 400–575, 500–675 and 500–675 °C, and the water content ranges of <1.1, 0.7 and 1.0 wt.% for basalt, andesite and dacite, respectively. The obtained diffusivities of total water in basalt, andesite and dacite and previous data for water diffusivity in rhyolite show that at 0.7 wt.% and 400–675 °C, the total water diffusivity decreases from rhyolite to andesite, but the total diffusivity in basalt is higher than that in dacite and lower than that in rhyolite. On the other hand, the results of this study predict that the diffusivities of total water in basalt to rhyolite increase with depolymerization of silicate structures at higher temperatures, which results from the crossovers of diffusivity–temperature trends.