Chlorine diffusion in rhyolite under low-H2O conditions.
Chlorine diffusion in rhyolite under low-H2O conditions.
复制标题
低水条件下氯在流纹岩中的扩散。
DOI：
10.1016/j.chemgeo.2018.03.032
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发表时间：
2018
期刊：
影响因子：
3.9
通讯作者：
S.
中科院分区：
文献类型：
--
作者：
Yoshimura;S.
在650 °C - 950 °C和1.5-11.8 MPa条件下，测定了含<1.2 wt% H2O的流纹岩熔体中的氯扩散率。采用纯Cl2流体、Cl2+ H2O混合流体、熔融NaCl和NaCl水溶液四种氯源对流纹岩黑曜石进行扩散实验。在纯cl2实验中，氯的扩散系数范围为7.7 × 10−18m2/s（650 °C）至8.2 × 10−16m2/s(950 °C)；它比以前报道的流纹岩熔体值低得多。Cl2+ H2O混合流体实验表明，氯的扩散系数与水的含量密切相关：当熔体水的含量增加到~1 wt%时，氯的扩散系数增加了1 - 2个数量级。在熔融NaCl实验中，钠渗透到熔体中，钾扩散出去。氯的扩散系数比纯氯实验高4-10倍。使用NaCl溶液作为氯源的单一实验结果显示Cl扩散率最高，可能是由于高H2O和高钠含量。氯扩散活化能为135 ~ 202 kJ/mol，与碱性熔体的活化能相当。由于氯的扩散系数远小于H2O和CO2的扩散系数，在岩浆泡化和脱气过程中，预计会发生强烈的扩散分馏作用。在无水条件下，钙扩散是氯扩散的副产物。在纯Cl2experiments、钙扩散系数介于6.2 × 10−17平方米/ s(650 °C) 3.9 × 10−14平方米/ s(950 °C),和活化能是177 ± 15 焦每摩尔。在熔融NaCl实验中，钙的扩散系数提高了一个数量级，活化能与纯氯化钠实验相似。
The chlorine diffusivity in rhyolitic melts containing <1.2 wt% H2O was determined at 650 °C–950 °C and 1.5–11.8 MPa. Diffusion experiments were carried out by reacting rhyolitic obsidian with four types of chlorine sources including a pure Cl2fluid, Cl2+ H2O fluid mixture, molten NaCl, and NaCl aqueous solution. In the pure Cl2experiments, the chlorine diffusivity ranged from 7.7 × 10−18m2/s (650 °C) to 8.2 × 10−16m2/s (950 °C); it is much lower than previously reported values for rhyolitic melt. The Cl2+ H2O fluid mixture experiments revealed that the chlorine diffusivity strongly depends on the water content: it increased by 1–2 orders as the water content of the melt increased to ~1 wt%. In the molten NaCl experiments, sodium infiltrated into the melt while potassium diffused out. The chlorine diffusivity was higher than that in the pure Cl2experiments by a factor of 4–10. A single experiment using NaCl solution as a chlorine source resulted in the highest Cl diffusivity, probably due to the high H2O and sodium contents. The activation energy of chlorine diffusion was 135–202 kJ/mol, and it is comparable to the activation energy in more mafic melts. Because the diffusivity of chlorine is much smaller than that of H2O and CO2, a strong diffusive fractionation is expected to occur during magma vesiculation and degassing. Calcium diffusion was observed as a by-product of chlorine diffusion under anhydrous conditions. In the pure Cl2experiments, calcium diffusivity ranged from 6.2 × 10−17m2/s (650 °C) to 3.9 × 10−14m2/s (950 °C), and the activation energy was 177 ± 15 kJ/mol. In molten NaCl experiments, the calcium diffusivity was higher by one order of magnitude, and the activation energy was similar to that for the pure Cl2experiments.