Collaborative Research: Volatile Loss During Magma Ascent and Cooling

控制火山喷发方式和活力的一个关键参数是岩浆从储存区上升和退化到地表的速度。岩浆上升速度反过来又控制着岩浆、熔体和晶体中挥发性物质流失的时间。该项目旨在直接评估火山晶体和玻璃在几分钟到几个月的时间尺度上岩浆的挥发性损失，并由此提供对定量了解喷发过程至关重要的岩浆上升速率的估计。这里的重点是爆炸性的玄武岩到玄武岩安山岩喷发，人们对导致喷发的岩浆上升和脱气过程知之甚少。这种方法是由分析技术的新发展推动的，这些技术使得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)。三种不同类型的测量将在不同的时间尺度上询问火山系统：1)晶体内熔体中的挥发性浓度分布(通过NanSIMS离子探针)，这可能反映出与外部的扩散重新平衡，脱气岩浆在几分钟(水)到几个小时(硫)的时间尺度上。2)名义上无水斑晶中的水分含量，可在数小时(橄榄石)至数月(单斜辉石)的时间尺度上保持扩散交换。3)橄榄石熔体包裹体中的挥发分含量，这可能反映了影响熔体海湾和晶体的时间尺度和过程。经过充分研究的中美洲火山(塞罗内格罗、伊拉苏、阿雷纳尔)将能够比较不同喷发风格的挥发性损失和上升率。该项目对了解与火山爆发有关的火山危害有影响，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.