Collaborative Research: The Provenance of the Excess Sulfur Released in Arc Volcanoes During Plinian Eruptions

合作研究：普林尼亚火山喷发期间弧形火山释放的过量硫的来源具有智力价值。尽管人们普遍认为，岩浆中挥发性元素的行为控制着喷发动力学，但浅层岩浆系统中蒸气的释放深度和数量以及气泡的分布和运输仍然受到很少的约束。该项目旨在开发一种新的多学科方法，以量化蒸气脱气发生的地点和数量，不同岩浆环境中蒸气气泡的输送速度，它们是否预计会在系统的较浅部分积累，以及这种积累将对喷发动力学产生多大影响。需要解释的一个基本观察结果是，在爆炸性喷发期间释放的挥发物与喷发前可在熔体中溶解的挥发物(过量脱气)之间存在差异。过量脱气的最明显的例子与S的质量平衡有关，因为S在喷发期间和喷发后的释放量可以通过光谱方法准确地测量出来。将讨论几个悬而未决的问题：(1)喷发前岩浆中可以存在多少水蒸气，与较深的未喷发岩浆(非原地)相比，有多大比例的水蒸气在原地喷发出来？(2)如果非原地脱气很重要，是什么控制了岩浆体最浅部分的气泡积累，以及它如何影响岩浆的喷发行为？拟议的工作具有变革性，因为它将利用PIS开发的新的数值模型来探索人们对岩浆系统中出溶的挥发分的运输和储存缺乏了解，并将把地球化学数据(磷灰石和磁黄铁矿中的痕量元素)与热力学模型(预期的蒸汽含量作为结晶度的函数)和流体动力学模型结合在一起，形成一种新的方法来量化岩浆中的挥发分收支。现有的热力学模型包括H2O(例如熔体)和H2O-CO2(例如VolatileCalc)的溶解度，以确定在一系列合理的初始条件下，给定的具有S过剩记录的普林尼安喷发(圣海伦斯火山1980年、El Chichon 1982年、Pinatubo 1991、克拉卡托1883年、Katmai 1912年、公元181年)以及较大、较老的S单元(Kos高原凝灰岩160 Ky和鱼峡谷凝灰岩28 Ma)中逸出蒸汽的百分比，对于这些单元，S的大气负荷约束很差。在同一单位，将利用已公布的数据和(或)电子探针对磷灰石和磁黄铁矿的分析来确定(A)岩浆在喷发前是否在其浅层储集层中处于气相饱和状态(使用我们开发的一种地球化学测试)和(B)利用磷灰石中的分带剖面，确定喷发前挥发性元素含量的变化情况。最后，将使用不同的数值技术开发多相流模型，以估计气泡在岩浆系统中的移动程度，以及它们在喷发前在水库中积累的速度。这样的模型将为火山喷发的动力学提供宝贵的新见解。更广泛的影响。该项目将支持一名研究生，并将在高度多学科和内在量化的环境中对她/她进行培训，使他/她能够掌握现代科学的基本技能。它将提供一名新的研究人员(Huber，没有事先资助)资金，以发展一个活跃的物理火山学小组，并将允许两名年轻教员继续开展积极的多学科合作，这种合作在过去几年中取得了成功。最后，PIS建议为高级本科生和研究生开发一门短期课程，内容是将建模技术和应用于岩浆过程的地球化学分析相结合。过去两年，Pi Huber一直在加州大学伯克利分校、瑞士日内瓦大学和莱斯大学教授这门课程的一个版本，作为为期一周的一系列讲座和实践练习。根据学生对这门课的热烈反应，我们预计在佐治亚理工学院和华盛顿大学举办这样的课程可能会吸引许多当地学生，并将有力地帮助我们的社区提高对地球科学定量方法的认识和熟练程度。

Collaborative Research: The provenance of the excess sulfur released in arc volcanoes during Plinian eruptionsIntellectual merit. Although it is commonly accepted that the behavior of volatile elements in magmas controls eruption dynamics, the depth and amount of vapor exsolved, as well as the distribution and transport of vapor bubbles in shallow magmatic systems remain poorly constrained. This project aims to develop a novel multidisciplinary methodology to quantify where and how much vapor degassing occurs, how fast vapor bubbles are transported in different magmatic environments, if they are expected to accumulate in the shallower portion of the system and how much effect this accumulation will have on eruption dynamics. A fundamental observation to be explained is the discrepancy between emitted volatiles released during explosive eruptions and the amount of volatiles that can be dissolved in the melt prior to eruption (excess degassing). The clearest example of excess degassing is associated with S mass balance, because S release during and after eruptions can be measured accurately by spectroscopic methods. Several open questions will be addressed: (1) How much vapor can be present in a magma prior to an eruption and what fraction was exsolved in-situ versus transported from deeper unerupted magma (ex-situ)? (2) If ex-situ degassing is important, what controls the accumulation of bubbles in the shallowest part of the magma body and how does it affect the eruptive behavior of the magma? The proposed work is transformative in that it will explore the poorly understood transport and storage of exsolved volatiles in magmatic systems with new numerical models developed by the PIs, and it will integrate geochemical data (trace elements in apatites and pyrrhotite) with thermodynamic modeling (expected vapor content as function of crystallinity) and fluid dynamics modeling into a novel approach to quantify the volatile budget in magmas. Existing thermodynamic models will be used that include H2O (e.g., MELTS) and H2O-CO2 (e.g., VolatileCalc) solubilities to determine, for a range of reasonable initial conditions, the percentage of exsolved vapor in given examples of Plinian eruptions with documented S excess (Mount St. Helens 1980, El Chichon 1982, Pinatubo 1991, Krakatau 1883, Katmai 1912, Taupo 181 AD) as well as for larger, older S-rich units (Kos Plateau Tuff 160 ky, and Fish Canyon Tuff 28 Ma) for which the S atmospheric load is poorly-constrained. In the same units, published data and/or analyses of apatites and pyrrhotites by electron microprobe will be used to determine (a) whether the magmas were vapor-saturated in their shallow reservoirs prior to eruption (using a geochemical test we have developed) and (b) using zoning profiles in apatites, how volatile element contents vary prior to eruption. Finally, multi-phase flow models will be developed using different numerical techniques to estimate how mobile vapor bubbles are across the magmatic system and how quickly they accumulate in reservoirs before an eruption. Such models will provide invaluable new insights in the dynamics of volcanic eruptions. Broader impacts. This project will support a graduate student, and will train her/him in a highly multi- disciplinary and inherently quantitative environment, enabling him/her with those fundamental skills of modern science. It will provide a new investigator (Huber, no prior funding) funds to develop an active group in physical volcanology and will also allow two young faculty members to continue an active multi-disciplinary collaboration that has been successful over the last few years. Finally, the PIs propose to develop a short course for advanced undergraduate and graduate students on merging modeling techniques and geochemical analyses applied to magmatic processes. PI Huber has been teaching a version on this course, over the last two years, as a week-long series of lectures and practical exercises at the University of California, Berkeley, the University of Geneva (Switzerland), and at Rice University. On the basis of the enthusiastic response of the students to this class, we expect that organizing such a course at Georgia Tech and University of Washington is likely to attract many local students, and would strongly help our community to become more aware and proficient in quantitative methods in Earth Sciences.