Collaborative Research: Volatile Loss During Magma Ascent and Cooling

控制火山喷发的风格和活力的一个关键参数是岩浆从储存区上升和脱气到地表的速度。岩浆上升速率反过来控制着岩浆中挥发性物质、熔体和结晶流失的时间。该项目旨在直接评估岩浆在几分钟到几个月的时间尺度上的挥发性损失，如火山晶体和玻璃的测量，并从中提供岩浆上升速率的估计，这对定量理解喷发过程至关重要。这里的重点是爆炸性的，玄武岩到玄武岩安山岩喷发，对于导致喷发的岩浆上升和脱气过程知之甚少。该方法的动力来自于分析技术的新发展，该技术能够以精细的空间分辨率测量挥发性物质（包括水和二氧化碳）。三种不同的测量方法将在不同的时间尺度上考察火山系统：1)晶体内熔体的挥发性浓度分布（通过纳米sims离子探针），这可能反映与外部的扩散再平衡，在分钟（水）到小时（硫）的时间尺度上脱气岩浆。2)名义上无水现象晶体内的含水量，这可能在数小时（橄榄石）到数月（斜辉石）的时间尺度上保持扩散交换。3)含橄榄石的熔体包裹体的挥发性含量，这可能反映了影响熔体包裹体和晶体的时间尺度和过程。对中美洲火山（Cerro Negro、Irazu、Arenal）进行充分研究，可以比较不同喷发方式的挥发性损失和上升速度。该项目对了解与爆炸性火山活动有关的火山危害具有重要意义，将支持两名研究生的培训和发展，并为哥伦比亚大学（科学前沿）每年招收500名新生的课程提供讲座和研讨会材料。

A critical parameter governing the style and vigor of volcanic eruptions is the rate at which magma ascends and degases from the storage region to the surface. The magma ascent rate, in turn, controls the time available for loss of volatile species from the magma, melts and crystals. This project aims to assess directly the volatile loss from magmas over timescales of minutes to months, as measured in volcanic crystals and glass, and from this provide estimates of magma ascent rates critical to a quantitative understanding eruptive processes. The focus here is on explosive, basaltic to basaltic andesite eruptions, for which very little is yet known about the magma ascent and degassing processes leading to eruption. The approach is motivated by new developments in analytical techniques that enable measurement of volatile species (including water and carbon dioxide) at fine spatial resolution. Three different kinds of measurements will interrogate volcanic systems at different timescales: 1) volatile concentration profiles in melt embayments within crystals (by nanoSIMS ionmicroprobe), which may reflect diffusive re-equilibration with the exterior, degassing magma over the timescale of minutes (water) to hours (sulfur). 2) water contents within nominally anhydrous phenocrysts, which may preserve diffusive exchange over the timescale of hours (olivine) to months (clinopyroxene). 3) volatile contents in olivine-hosted melt inclusions, which may reflect timescales and processes intermediate between those that affect melt embayments and crystals, above. Well-studied Central American volcanoes (Cerro Negro, Irazu, Arenal) will enable comparisons of volatile loss and ascent rates for different eruptive styles. The project has implications for the understanding of volcanic hazards associated with explosive volcanism, will support the training and development of two graduate students, and provide lecture and seminar material for a course at Columbia University (Frontiers of Science) that engages 500 freshmen each year.