Discriminating secondary from magmatic water in rhyolitic matrix-glass of volcanic pyroclasts using thermogravimetric analysis
Discriminating secondary from magmatic water in rhyolitic matrix-glass of volcanic pyroclasts using thermogravimetric analysis
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DOI：
10.1016/j.gca.2014.10.017
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发表时间：
2015-01-01
影响因子：
5
通讯作者：
Gouldstone, Andrew
中科院分区：
文献类型：
--
作者：
Giachetti, Thomas;Gonnermann, Helge M.;Gouldstone, Andrew
来自爆炸性喷发的火山碎屑，如公元1060年加州梅迪辛湖火山的玻璃山爆炸性喷发，含有大量的水。这可能是火山玻璃在喷发后被流星（二次）水扩散再水化的结果。区分火山碎屑基质玻璃中的岩浆水和次生水是很重要的，因为岩浆水的脱气影响火山喷发的强度。这种区分仍然是一个具有挑战性的问题，特别是因为在低温和大气压下硅酸盐玻璃中水扩散的某些方面仍然受到很差的限制。我们使用热重分析法来分析天然火山玻璃和在实验室中在岩浆温度和压力下水合的玻璃的水分损失。热重分析过程中扩散失水的数值模拟解释了分子水（H（2）Om）和羟基（OH）的相互转化，表明玻璃山浮石在过去950年中含有0.2 - 0.5wt%的原生水，但通过扩散再水化获得了1 - 2wt%的大气降水。这些结果证实了大部分岩浆水在爆炸性喷发过程中从岩浆中流失。此外，热重分析和数值模拟的集成有助于区分火山玻璃的岩浆和次生水含量。(C)2014爱思唯尔有限公司版权所有。
Pyroclasts from explosive eruptions, such as the 1060 CE explosive Glass Mountain eruption of Medicine Lake volcano, California, contain large amounts of water. This may be the consequence of diffusive rehydration of the volcanic glass by meteoric (secondary) water after the eruption. Discriminating between magmatic and secondary water in the matrix glass of pyroclasts is important, because the degassing of magmatic water affects the intensity of volcanic eruptions. Such discrimination has remained a challenging problem, especially because some aspects of water diffusion in silicate glasses at low temperatures and atmospheric pressure remain poorly constrained. We used thermogravimetry to analyze the loss of water from natural volcanic glasses and glasses that were hydrated in the laboratory at magmatic temperatures and pressures. Numerical modeling of diffusive water loss during thermogravimetric analyses accounted for the interconversion of molecular water (H(2)Om) and hydroxyls groups (OH), and indicates that Glass Mountain pumices contain 0.2-0.5 wt% primary water, but gained 1-2 wt% of meteoric water by diffusive rehydration during the past 950 years. These results confirm that the majority of magmatic water is lost from the magma during explosive eruptions. Furthermore, the integration of thermogravimetric analysis and numerical modeling facilitates discrimination between the magmatic and secondary water content of volcanic glasses. (C) 2014 Elsevier Ltd. All rights reserved.