Bubble Nucleation in Magmas: Experimental Constraints on the Influences of Gas and Melt Composition

智力优势。了解岩浆如何脱气和喷发是火山学家的一个关键目标。脱气和喷发的关键步骤是气泡成核，因此解决气体预算如何控制成核的开始将进一步朝着实现这一目标取得进展。对于由逃逸挥发物驱动的喷发（例如，CO2、H2O）作为推进剂，流体逃逸或囊泡形成的机制提供了关键控制。该过程取决于熔体的表面张力和其他性质，而这些性质又取决于熔体的组成，甚至取决于CO2和H2O的相对比例。由于现有的数据太有限，完全预测这些关系，PI提出了一个系统的研究，最终将导致一个正式的表达式，这些各种参数来预测挥发性的溶解度和脱气，使用各种熔体饱和混合挥发性的内容将使结果适用于不同的火山系统，从大洋中脊俯冲带。需要解决的关键问题包括：[1] CO2如何影响不同硅酸盐熔体中的气泡成核？和[2]表面张力的变化可以从气体溶解度预测吗？这些问题将通过减压实验来解决，减压实验旨在限制各种熔体中气泡成核的速率和大小。该项目旨在教育一个MS。研究生（Kathy Goepfert）和博士。在实验岩石学和定量分析技术（包括电子显微探针和傅里叶变换红外（FTIR）光谱）的数据的规划，收集，分析和演示方面，研究生（TBA）。该项目还将支持一名本科荣誉学生，他将从PI和研究生的指导中获得进行科学调查的宝贵见解。

Intellectual Merit. Understanding how magmas degas and erupt is a key goal for volcanologists. The critical step for degassing and eruption is bubble nucleation, and so addressing how the gas budget controls the onset of nucleation will further progress towards reaching that goal. For eruptions driven by escaping volatiles (e.g., CO2, H2O) as propellants, the mechanisms of fluid escape, or vesiculation, provide critical control. This process depends on surface tension and other properties of the melts, which in turn depend on melt composition and even the relative proportions of CO2 and H2O. Because existing data are too limited to fully predict these relations, the PI proposes a systematic study that will ultimately lead to a formal expression relating these various parameters to predict volatile solubilities and degassing, Using various melts saturated with mixed volatile contents will make results applicable to diverse volcanic systems ranging from mid-ocean ridges to subduction zones. Critical questions to be addressed include: [1] How does CO2 influence bubble nucleation in different silicate melts?, and [2] Can variations in surface tension be predicted from gas solubilities? These questions will be addressed via decompression experiments designed to constrain rates and magnitudes of bubble nucleation in various melts.Broader Impacts. This project is designed to educate a M.S. graduate student (Kathy Goepfert) and a Ph.D. graduate student (TBA) in the planning, collection, analysis, and presentation of data from experimental petrology and quantitative analytical techniques, including electron microprobe and Fourier Transform Infrared (FTIR) spectroscopy. This project will also support an undergraduate honors student who will gain valuable insight into carrying out scientific investigations from mentorship by the PI and the graduate students.