Understanding H20 Degassing in Natural Phonolite Melts: An Experimental Study

了解天然声乐石熔体中的 H2O 脱气：一项实验研究

• 批准号: 0511070
• 负责人: Jessica Larsen
• 金额: $ 19.55万
• 依托单位: University of Alaska Fairbanks Campus
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-07-15 至 2008-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0511070&HistoricalAwards=false
• 关键词: Understanding; H20; Degassing; Natural; Phonolite

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.

岩浆脱气始于气泡成核和生长，与喷发风格有关。究竟是什么引起爆炸性的火山，直到所有爆发爆发的岩浆成分中都知道脱气的基本原理。在这一点上，非胆料熔体中仅存在两个H2O气泡成核和生长的实验研究。需要更多的实验来了解气泡成核和生长过程如何随熔体组成的函数而变化。该项目将对79 AD Vesuvius语音石的天然样品进行实验来测量：1）均质和异质气泡成核所需的临界H2O H2O超饱和度。 2）在熔体中保留的过量（不平衡）H2O的量是减压率和路径的函数。 3）气泡生长速率与熔体温度，成分和晶体含量的关系。该结果将用作专门针对79次爆发的动力学模型的输入，以及一般而言碱岩浆的囊泡和喷发动力学。一个目标是将语音爆发过程与钙碱性流纹岩和Dacites进行比较，并以一系列建模的上升速率进行比较。这项工作将有助于更好地理解K语音融化的脱气过程，这些过程在非常危险且人口稠密的火山（例如意大利的Vesuvius）中很普遍。它还将提供有关在岩浆上升期间的极端熔体超饱和度的积累是否合理地解释碱性岩浆的喷发动态的，这是流纹岩的建议。这项研究的数据将提供给对Vesuvius和其他碱性系统语音岩浆感兴趣的其他研究人员，并将提供实验性约束，用于解释Pumices中的囊泡纹理。结果将在出版物和会议演讲中广泛传播。这些出版物不仅将重点放在实验上，而且还将重点放在喷发动力学模型上，并将其与79个Ad Pumice纹理进行比较。该奖项将为PI与意大利研究人员与理论建模社区之间的新合作提供途径。