Volatile Clues to the Initial Controls on Large Explosive Volcanic Eruptions

该项目的目标是更好地了解大型火山爆发是如何开始的，以及前兆活动的时间尺度（几天或几周或更长时间），这些活动可能作为即将爆发的警告信号。巨大的爆炸性喷发（被称为超级喷发）发生在最近的地质历史中，比历史上发生的任何喷发都要大很多倍。在这个项目中，我们将研究位于加州东部黄石公园和新西兰的一些最好和最年轻的例子。一个主要的目标是确定外部因素，比如地震和断层运动，是否会导致这样的喷发，或者它们是否会在地球上的岩浆体中开始？地壳变得超压并破裂，就像破裂的气球。该项目将包括对火山爆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火山爆发的方式和原因以及岩浆移动到地球表面所需时间的信息记录。这个项目将测试一些关于大型流纹岩爆发是如何开始的以及何时发生火山口坍塌的基本观点。尽管在这些过程的建模方面取得了许多重要的进展，但令人惊讶的是，关于大型爆炸喷发最早沉积物的地球化学数据缺乏，这些数据可以为关于喷发触发的争论提供信息。通过测量熔融包裹体中挥发物（H2O、CO2、Cl、S、F）和石英中再入物（未密封包裹体）的浓度和梯度以及斜长石中OH的含量，可以定量记录火山爆发前和爆发初期的岩浆减压和上升速率。由于岩浆上升速率反映了下伏岩浆体的超压程度，通过挥发物的弥漫性损失来限制喷发中最早物质的上升速率，可以深入了解是内部（岩浆超压）触发还是外部（超压很少或没有）触发。根据哈克贝利岭瀑布沉积物（黄石）的初步结果，这些数据似乎提供了一个独特的记录，记录了火山爆发之前和爆发期间喷口发育的过程和时间尺度，并暗示了火山口崩塌的时间和原因，以及岩浆体如何在上地壳中形成。这项调查的结果将提供有关超级火山爆发速度的定量信息，并将为可能发生超级火山爆发之前的地球物理信号模型提供数据。这个项目包括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，并利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.