Volatile Clues to the Initial Controls on Large Explosive Volcanic Eruptions

该项目的目标是更好地了解大规模爆炸性火山喷发是如何开始的，以及可能作为即将喷发的警告信号的前兆活动的时间尺度(几天或几周或更长时间)。在最近的地质历史中发生了巨大的爆炸性喷发(称为超级喷发)，其规模比历史上发生的任何一次喷发都大许多倍。一些最好的和最年轻的例子，在黄石公园，在加利福尼亚州东部，在新西兰将在这个项目中进行研究。一个主要目标是确定外部因素，如地震和沿断层的运动，是否会导致这种喷发开始，或者相反，它们是从地球上的岩浆体开始爆发的？S地壳变得超压并破裂，就像破裂的气球一样。该项目将涉及对火山喷发初期形成的火山灰和浮石沉积物进行化学分析，因为这些沉积物保存了有关火山喷发是如何以及为什么开始的信息，以及岩浆移动到地球表面需要多长时间。这个项目将测试一些基本的想法，关于大规模的爆炸性流纹岩喷发是如何开始的，以及火山口坍塌是什么时候发生的。尽管在这些过程的模拟方面取得了许多重要进展，但令人惊讶的是，缺乏关于大型爆炸性喷发最早沉积的地球化学数据，这些数据可能会为关于喷发触发的辩论提供信息。通过测量熔体包裹体中挥发物(H2O、CO2、Cl、S、F)和石英中重入物(未封闭包裹体)中挥发物的浓度和梯度，以及斜长石中的OH含量，可以获得这些喷发开始阶段之前和期间岩浆减压和上升速率的定量记录。由于岩浆上升速率反映了下伏岩浆体中超压的程度，因此使用挥发分的扩散损失来限制喷发最早物质的上升速率可以提供关于内部(岩浆超压)或外部(很少或没有超压)触发因素的洞察。根据Huckleberry Ridge Fall矿床(黄石公园)的初步结果，这些数据似乎提供了就在喷发开始阶段之前和期间喷口发育过程和时间尺度的独特记录，并暗示了火山口坍塌发生的时间和原因以及上地壳岩浆体的配置方式。这项调查的结果将提供有关超级喷发开始速度的定量信息，并将为可能在超级喷发之前的地球物理信号模型提供数据。该项目涉及与美国和新西兰的其他科学家合作，进行一些专门的化学分析，并使用结果进行计算机建模。

The goal of this project is to better understand how large explosive volcanic eruptions start and the timescales (days or weeks or more) of precursory activity that might serve as a warning sign of an impending eruption. Enormous explosive eruptions (known as supereruptions) have occurred in the recent geologic past that are many times larger than any eruptions that have taken place in historic times. Some of the best and youngest examples, at Yellowstone, in eastern California, and in New Zealand will be studied in this project. A primary goal is to determine if external factors, like an earthquake and movement along a fault, can cause such eruptions to start, or whether instead, they start when a magma body in the earth?s crust becomes overpressured and bursts, like a ruptured balloon. The project will involve chemical analysis of ash and pumice deposits that were created during the opening stages of the eruptions because these preserve a record of information about how and why the eruptions started and how long it took for magma to move to the Earth's surface. This project will test some fundamental ideas about how large explosive rhyolitic eruptions start and when caldera collapse occurs. Despite many important advances in modeling of these processes, there is a surprising lack of geochemical data on the very earliest deposits from large explosive eruptions that could inform the debate about eruption triggering. A quantitative record of magma decompression and ascent rates shortly before and during the opening stages of these eruptions will be obtained by measuring concentrations and gradients of volatiles (H2O, CO2, Cl, S, F) in melt inclusions and reentrants (unsealed inclusions) in quartz and the OH contents of plagioclase. Because magma ascent rates reflect the extent of overpressure in the underlying magma body, constraining ascent rates for the earliest materials from an eruption using diffusive loss of volatiles can provide insight into whether internal (magma overpressure) or external (little or no overpressure) triggers were involved. Based on preliminary results for the Huckleberry Ridge fall deposit (Yellowstone), such data appear to provide a unique record of the processes and timescales of vent development just prior to and during the opening phases of an eruption, with implications for when and why caldera collapse develops and how magma bodies were configured in the upper crust. The results of this investigation will provide quantitative information about how rapidly supereruptions begin and will contribute data to models of geophysical signals that could precede them. This project involves collaborations with other scientists in the U.S. and New Zealand for some of the specialized chemical analyses that will be done and for computer modeling using the results.