Hydrogen isotope fractionation between coexisting vapor and silicate glasses and melts at low pressure
Hydrogen isotope fractionation between coexisting vapor and silicate glasses and melts at low pressure
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DOI：
10.1016/0016-7037(89)90143-9
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发表时间：
1989-10
影响因子：
5
通讯作者：
P. Dobson;S. Epstein;E. Stolper
中科院分区：
文献类型：
--
作者：
P. Dobson;S. Epstein;E. Stolper
进行了一系列实验以确定水蒸气和溶解在流纹岩和长石玻璃及熔体中的羟基的“水”之间的氢同位素分馏因子。实验在装有大量过量水的石英管中进行，温度为 530–850° C，PH 2 O= 1.4–2.8 巴。水浓度分布的红外测量和同位素反转实验表明，在 210-5400 小时的运行过程中达到了平衡。当温度从 530°C 升高到 750°C 时，玻璃中的蒸汽和溶解水之间的分馏因子（[D H 蒸汽]/[D H 玻璃）从流纹石玻璃的约 1.051 降低到 1.040，钠长石-正长石玻璃的分馏因子从 1.049 降低到 1.035。这些分馏大于在这些温度下大多数含水矿泉水系统观察到的分馏，可能反映了玻璃中羟基的强氢键作用。研究了眼镜。测量的流纹岩熔体分馏因子解释了观察到的 δD 随着年轻流纹岩火山喷发的黑曜石含水量的降低而降低，并支持这些岩浆的两阶段脱气历史。爆发性喷发黑曜石的 δD 值随含水量的变化可以通过封闭系统蒸气-熔体分配来解释，而静止喷发的圆顶和流的低含水量和 δD 值则被解释为开放系统脱气的结果。
A series of experiments was performed to determine the hydrogen isotope fractionation factors between water vapor and “water” dissolved as hydroxyl groups in rhyolitic and feldspathic glasses and melts. Experiments were carried out in quartz tubes with a large excess of water at 530–850° C and P H 2 O= 1.4–2.8 bars. Infrared measurements of water concentration profiles and isotopic reversal experiments indicate that equilibrium was attained during the 210–5400 hr runs. The fractionation factors ([D H vapor]/[D H glass) between the vapor and dissolved water in the glasses decrease from about 1.051 to 1.040 for rhyolite glass and 1.049 to 1.035 for albite-orthoclase glass as temperature increases from 530 to 750° C. These fractionations are greater than those observed for most hydrous mineral-water systems at these temperatures, perhaps reflecting the strong hydrogen bonding of hydroxyl groups in the studied glasses. The measured fractionation factor for rhyolitic melt accounts for the observed decreases in δD with decreasing water contents of obsidians erupted from young rhyolitic volcanoes and supports a two-stage degassing history of these magmas. The variation of δD values with water contents of explosively erupted obsidians can be explained by a closed-system vapor-melt partitioning, whereas the low water contents and δD values of the quiesciently erupted domes and flows are interpreted to be a result of open-system degassing.