Geochemical Insights Into the Post-Caldera Architecture of the Yellowstone Magma Reservoir

对黄石岩浆库火山口后建筑的地球化学见解

• 批准号: 2204816
• 负责人: Kari Cooper
• 金额: $ 56.24万
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-08-01 至 2025-07-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2204816&HistoricalAwards=false
• 关键词: Geochemical; Insights; Into; Post; Caldera

Volcanic systems such as Yellowstone in Wyoming produce very large, highly explosive eruptions that form immense craters called calderas. The volcanic system at Yellowstone has had three of these caldera-forming eruptions over the past two million years. In between these very large eruptions the system has also produced many smaller eruptions that were less explosive, which fed large lava flows that partially filled the caldera. As a result, the potential hazards and destructiveness of an eruption at volcanoes such as Yellowstone can vary widely, ranging from nation-wide or even global effects to more local hazards. An open question in volcano science is what factors control whether a volcano produces a very large explosive eruption or a smaller lava flow in a particular eruption. This probably depends partly on how the “plumbing system” beneath volcanoes changes over time, and whether large bodies of mostly-liquid magma are present continuously, whether they build up slowly over long periods of time, or whether they are only present just before an eruption. For example, does generating a very large eruption require a longer time to build a big pool of magma? Does it require more magma bodies to be present than a smaller eruption, or are there the same number of magma bodies present at all times but more of them get triggered to produce a very large eruption? In this project researchers will use chemical “fingerprints” of different magma bodies to identify how many different magma bodies have been tapped in the most recent series of smaller eruptions at Yellowstone, and will compare this to the number of magma bodies that have been identified as part of the most recent caldera-forming eruption to help answer these questions. Understanding how different kinds of eruptions are produced will contribute to volcanic hazard forecasting and risk management. The project will also train graduate and undergraduate students, contributing to the scientific workforce, and public outreach about the results will help contribute to scientific understanding for the general public.Large silicic systems produce a wide range of eruption styles and eruptive hazards, but the connections between the architecture of the magma storage region and the type of eruption produced are not well understood. For example, does a caldera-forming eruption require a different distribution of melts within the shallow reservoir, and/or a different triggering mechanism, than a smaller eruption? As a contribution to answering these broad questions, this team proposes to compare the architecture of the magma system during intra-caldera eruptions to existing data for caldera-forming eruptions at Yellowstone Caldera, Wyoming. New high-precision 40Ar/39Ar dating of the most recent intracaldera eruptions at Yellowstone (the Central Plateau Member, CPM) shows that they were erupted in five episodes, each of which spanned at most 1-2 kyr. This provides an opportunity to examine the number and distribution of magma bodies during each of five snapshots of the magma system, and to compare this with published work on the Yellowstone caldera-forming eruptions. They will investigate compositional diversity recorded in sanidine and zircon crystals both within and between individual eruptions and eruptive episodes using 238U-230Th age data coupled with geochemical data for both sanidine and zircon. Based on previous work, the sanidine and zircon surface compositional data will provide insights into the number of distinct magma bodies present during the period immediately prior to CPM eruptive episodes, as well as constraining the time scale of assembly and storage of different magma bodies prior to eruption. In contrast, zircon interiors are typically older with ages spanning 10s of kyr prior to eruption, which will provide a measure of compositional diversity present on a longer time scale, between eruptive episodes. The team will test the hypothesis that the basic architecture of the magma reservoir consists of multiple compositionally distinct magma bodies within a more heterogeneous crystal mush, and that the state of the system is similar before CFE and recent intracaldera eruptions. The data collected will also allow them to assess whether there are systematic changes in the average composition of erupted crystals over time, which may reflect secular variations in the proportions of mantle-derived and crustal-derived melts contributing to the system. Synthesizing their new data with data for Yellowstone CFE and data for other silicic systems will provide additional insights into the development and evolution of large silicic magma reservoirs. Broader impacts will include outreach by the PI to increase scientific literacy and public engagement, training and mentoring of diverse graduate and undergraduate students, strengthening partnerships between academia and the USGS, and contributing information that will be used to inform public policy and volcanic hazard mitigation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

像怀俄明州的黄石公园这样的火山系统会产生非常大的、高度爆炸性的喷发，形成巨大的火山口，称为火山口。黄石公园的火山系统在过去的200万年里已经有过三次这样的破火山口喷发。在这些非常大的喷发之间，该系统还产生了许多较小的喷发，这些喷发的爆炸性较小，它们提供了部分填充破火山口的大型熔岩流。因此，像黄石这样的火山爆发的潜在危害和破坏性可能差异很大，从全国性甚至全球性影响到更多的地方性危害。火山科学中的一个悬而未决的问题是什么因素控制着火山在特定的喷发中是产生非常大的爆炸性喷发还是较小的熔岩流。这可能部分取决于火山下面的“管道系统”如何随时间变化，以及大部分液体岩浆是否持续存在，它们是否在很长一段时间内缓慢积聚，或者它们是否只在爆发前存在。例如，产生一个非常大的喷发需要更长的时间来建立一个大的岩浆池吗？它需要更多的岩浆体比一个较小的喷发，或有相同数量的岩浆体存在，但更多的人被触发，以产生一个非常大的喷发？在这个项目中，研究人员将使用不同岩浆体的化学“指纹”来确定在黄石公园最近一系列较小的喷发中有多少不同的岩浆体被挖掘，并将其与已被确定为最近火山口形成喷发的一部分的岩浆体数量进行比较，以帮助回答这些问题。了解不同类型的火山爆发是如何产生的将有助于火山灾害预测和风险管理。该项目还将培训研究生和本科生，为科学工作者做出贡献，并将结果的公众宣传有助于公众对科学的理解。大型岩浆系统产生广泛的喷发风格和喷发危险，但岩浆储存区的结构和所产生的喷发类型之间的联系还没有得到很好的理解。例如，与较小的喷发相比，形成破火山口的喷发是否需要在浅储层内不同的熔体分布和/或不同的触发机制？作为回答这些广泛的问题的贡献，这个团队建议比较火山口内喷发的岩浆系统的架构，现有的数据在黄石火山口，怀俄明州火山口形成喷发。新的高精度40 Ar/39 Ar测年法对黄石公园（中央高原段，CPM）最近的火山喷发进行了测年，结果显示它们分五次喷发，每次喷发的时间最多为1- 2kyr。这提供了一个机会，检查在岩浆系统的五个快照的每一个岩浆体的数量和分布，并将其与黄石火山口形成喷发的出版工作进行比较。他们将调查成分的多样性记录在透长石和锆石晶体内和之间的个别喷发和喷发事件使用238 U-230 Th年龄数据，再加上地球化学数据的透长石和锆石。基于以前的工作，透长石和锆石表面成分数据将提供洞察力的数量不同的岩浆体存在于CPM喷发事件之前的一段时间内，以及约束的时间尺度的组装和存储不同的岩浆体喷发之前。相比之下，锆石内部通常年龄较大，在喷发前年龄跨越10 s的Kyr，这将提供一个衡量成分多样性存在于较长的时间尺度上，喷发事件之间。该团队将测试一个假设，即岩浆库的基本结构由多个成分不同的岩浆体组成，这些岩浆体位于一个更加异质的晶体糊状物中，并且该系统的状态在CFE和最近的火山喷发之前是相似的。收集到的数据还将使他们能够评估喷发晶体的平均成分是否随时间发生系统性变化，这可能反映出构成该系统的幔源和壳源熔体比例的长期变化。将他们的新数据与黄石CFE的数据和其他岩浆系统的数据相结合，将为大型岩浆库的发展和演变提供更多的见解。更广泛的影响将包括PI的推广，以提高科学素养和公众参与，培训和指导不同的研究生和本科生，加强学术界和美国地质勘探局之间的伙伴关系，该奖项反映了NSF的法定使命，并通过使用基金会的知识产权进行评估，被认为值得支持。优点和更广泛的影响审查标准。