Volatile diffusion in silicate melts and its effects on melt inclusions
Volatile diffusion in silicate melts and its effects on melt inclusions
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硅酸盐熔体中挥发分的扩散及其对熔体包裹体的影响
DOI：
10.4401/ag-3227
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发表时间：
2005
影响因子：
1
通讯作者：
P. Scarlato
中科院分区：
文献类型：
--
作者：
D. Baker;C. Freda;R. Brooker;P. Scarlato
介绍了成分与天然火成岩相似的硅酸盐熔体中水、二氧化碳、硫、氟和氯的扩散测量及其阿累尼乌斯方程的概要。水在无水熔体中的扩散已得到很好的研究和理解，然而，对于中间到基本组成的熔体，几乎没有数据。数据表明，水的浓度和无水熔体组合物影响水的扩散系数。二氧化碳扩散似乎仅弱地依赖于，至多，不含挥发物的熔体组成，并且没有观察到二氧化碳浓度的影响，尽管进行了很少的实验。根据一项研究，水的流纹岩熔体增加了二氧化碳扩散的数量级的值类似于6wt%的水。硫在中间到中间熔体中的扩散取决于无水熔体的组成和水的浓度。在含水的碳酸盐熔体中，硫的扩散速度比水慢2到3个数量级。氯扩散受水浓度和无水熔体组成的影响;其值通常介于水和硫的值之间。有关氟扩散的信息很少，但无挥发物的熔体组成对其扩散有很强的控制作用。目前，水、二氧化碳、硫和氯的扩散可以在岩浆温度下的岩浆熔体中进行估计。水和二氧化碳在碱性至中间熔体中的扩散仅在有限的温度和组成下是已知的。流纹质熔体在800°C下的扩散数据与生长晶体前不相容元素富集的标准模型结合在一起，表明快速晶体生长，大于10 −10 ms −1，可以显著增加晶体-熔体界面处的挥发物浓度，并且通过熔体夹杂物的形成而捕获的任何熔体都不能被再现。代表本体熔体。然而，在1300°C下捕获的玄武岩熔体包裹体更可能含有大量的水和二氧化碳。
A compendium of diffusion measurements and their Arrhenius equations for water, carbon dioxide, sulfur, flu- orine, and chlorine in silicate melts similar in composition to natural igneous rocks is presented. Water diffusion in silicic melts is well studied and understood, however little data exists for melts of intermediate to basic com- positions. The data demonstrate that both the water concentration and the anhydrous melt composition affect the diffusion coefficient of water. Carbon dioxide diffusion appears only weakly dependent, at most, on the volatile- free melt composition and no effect of carbon dioxide concentration has been observed, although few experi- ments have been performed. Based upon one study, the addition of water to rhyolitic melts increases carbon dioxide diffusion by orders of magnitude to values similar to that of 6 wt% water. Sulfur diffusion in intermedi- ate to silicic melts depends upon the anhydrous melt composition and the water concentration. In water-bearing silicic melts sulfur diffuses 2 to 3 orders of magnitude slower than water. Chlorine diffusion is affected by both water concentration and anhydrous melt composition; its values are typically between those of water and sulfur. Information on fluorine diffusion is rare, but the volatile-free melt composition exerts a strong control on its dif- fusion. At the present time the diffusion of water, carbon dioxide, sulfur and chlorine can be estimated in silicic melts at magmatic temperatures. The diffusion of water and carbon dioxide in basic to intermediate melts is on- ly known at a limited set of temperatures and compositions. The diffusion data for rhyolitic melts at 800°C to- gether with a standard model for the enrichment of incompatible elements in front of growing crystals demon- strate that rapid crystal growth, greater than 10 −10 ms −1 , can significantly increase the volatile concentrations at the crystal-melt interface and that any of that melt trapped by the formation of melt inclusions may not be rep- resentative of the bulk melt. However, basaltic melt inclusions trapped at 1300°C are more likely to contain bulk melt concentrations of water and carbon dioxide.