Understanding H20 Degassing in Natural Phonolite Melts: An Experimental Study

岩浆脱气始于气泡的成核和生长，并与喷发式有关。在所有喷发的岩浆成分都知道脱气的基本原理之前，到底是什么导致了火山爆发，我们才能完全了解。目前，关于非流纹岩熔体中H2O气泡成核和长大的实验研究只有两种。需要更多的实验来了解气泡的成核和生长过程是如何随着熔体组成的变化而变化的。本项目将利用对公元79年维苏威声石的天然样品的实验来测量：1)均匀和非均匀气泡成核所需的临界水过饱和度。2)作为减压速率和路径的函数，保留在熔体中的过量(不平衡)H2O的量。3)气泡生长速率是熔体温度、成分和晶体含量的函数。这些结果将被用作特别关注公元79年喷发的动力学模型的输入，以及一般碱性岩浆的气泡形成和喷发动力学的输入。一个目标是将声岩喷发过程与钙碱性流纹岩和英安岩在模拟的上升速率范围内进行比较。这项工作将有助于更好地了解K声石熔体中的脱气过程，这些熔体普遍存在于非常危险和人口稠密的火山，如意大利的维苏威火山。它还将提供洞察，了解岩浆上升过程中极端熔体过饱和度的积累是否合理，以解释碱性岩浆的喷发动力学，就像流纹岩所建议的那样。这项研究的数据将提供给对维苏威火山和其他碱性系统的声石岩浆感兴趣的其他研究人员，并将提供用于解释浮石中气泡结构的实验约束条件。结果将在出版物和会议介绍中广泛传播。这些出版物将不仅关注实验，还将关注喷发动力学模型，以及与公元79年浮石纹理的比较。这一奖项将为PI和意大利研究人员以及理论建模社区之间的新合作提供一条途径。

Magmatic degassing begins with bubble nucleation and growth, and is linked to eruptive style. What exactly causes explosive volcanism will not be fully understood until the fundamentals of degassing are known in all magma compositions that erupt explosively. At this point, only two experimental studies of H2O bubble nucleation and growth exist in non-rhyolite melts. More experiments are needed to understand how the bubble nucleation and growth processes change as a function of melt composition. This project will use experiments on natural samples of the 79 AD Vesuvius phonolite to measure: 1) Critical H2O super-saturation needed for homogeneous and heterogeneous bubble nucleation. 2) The amount of excess (disequilibrium) H2O retained in the melt as a function of decompression rate and path. 3) Bubble growth rates as a function of melt temperature, composition, and crystal contents. The results will be used as input for dynamical models focusing specifically on the 79 AD eruption, and on vesiculation and eruption dynamics of alkalic magmas in general. One goal is to compare phonolite eruption processes with calc-alkaline rhyolites and dacites at a range of modeled ascent rates. This work will help provide a better understanding of the degassing process in K phonolite melts that are prevalent at very dangerous and heavily populated volcanoes, such as Vesuvius in Italy. It will also provide insight into whether the build-up of extreme melt super-saturation during magmatic ascent is reasonable to explain the eruption dynamics of alkalic magmas, as has been suggested for rhyolites. Data from this research will be made available to other researchers interested in phonolite magmas at Vesuvius and other alkalic systems, and will provide experimental constraints to be used in interpreting vesicle textures in pumices. The results will be broadly disseminated in publications and meeting presentations. The publications will focus not only on the experiments, but also on eruption dynamical models, and comparisons with the 79 AD pumice textures. This award will provide an avenue for new collaborations between the PI and Italian researchers and the theoretical modeling community.