CAREER: The Longevity and Evolution of Giant Magma Bodies: A Textural Study of Selected Supereruption Deposits Formed in Different Tectonic Environments Worldwide

在几天到几周的时间里，超级喷发将大量（1000立方千米）的物质喷射到地球表面，这表明，在地表以下几公里处偶尔存在着密度低、结晶性差的巨大岩浆体——比目前已知的任何岩浆体都要大得多。我们对这些事件的了解有限，很大程度上是因为地球上最后一次已知的超级火山爆发发生在大约26000年前。1815年的坦博拉火山喷发是已知历史上最大的一次喷发，导致1816年北美和欧洲出现了“没有夏天的一年”。然而，超级火山喷发喷出的岩浆至少要多出一个数量级，这表明这些巨大的火山喷发不仅会在局部范围内造成广泛的破坏，还会对全球产生重大影响，尤其是对气候的影响。在他的CAREER研究计划中，研究者将努力回答一些关于巨型岩浆体的基本问题：它们结晶的时间尺度是什么？是什么导致了从平静（爆发前）状态到最终导致超级爆发的剧烈爆发状态的转变？从晶体和囊泡群的研究中可以学到什么？研究超级喷发形成岩浆体结晶的时间尺度，收集矿物和玻璃的信息，探讨这些时间尺度的意义，并评估巨型岩浆体的演化。该项目的目的是更清楚地了解巨型岩浆体在时间和空间上的演化，形成它们演化的过程，以及导致喷发的条件。工作将包括：(a)使用x射线断层成像进行纹理表征；(b) x射线相衬层析成像法表征玻璃夹杂物；(c)利用阴极发光成像和通过电子、x射线和激光烧蚀微探针进行微量元素分析确定矿物分带；(d)利用电子背散射衍射（EBSD）成像技术研究晶体团簇的晶体学；(e)发展晶体尺度问题的分析和数值解决办法。该研究将重点关注分布在4大洲的3个矿床：哈克贝利岭凝灰岩（美国）、Oruanui凝灰岩（新西兰）和Paraná-Etendeka流纹岩（南美和西非）。它们都是已知的最大的火成岩矿床，但它们形成于不同的构造环境，在喷发历史、矿物学和岩石学方面都具有不同的特征。同时使用相同的概念框架和工具对这些矿床进行研究，将使我们对产生超级喷发的巨大岩浆体的时间尺度和演化的认识有质的飞跃。研究和教学将通过在巴西南部、纳米比亚和新西兰的夏季课程的开发和提供紧密联系在一起，这些课程由范德比尔特大学正式提供，旨在提供(a)来自美国、巴西和新西兰大学的教师和学生参与的合作研究和学习的全球和国际经验；(b)为学生提供广泛而有意义的实地经验，从研究生到非专业学生；(c)为本科生提供独特的学习体验，他们将参与到知识构建的过程中，这一目标在常规课程中往往难以实现。

Supereruptions eject huge amounts (1,000 km3) of material onto the Earth's surface in a matter of days to weeks, showing that giant bodies of low-density, crystal-poor magma - much larger than any currently known magma body - occasionally exist just a few kilometers below the surface. Our knowledge of these events is limited, largely because the last known supereruption on Earth occurred ca. 26,000 years ago. The 1815 eruption of Tambora - the largest known historic eruption - led to the 'Year without a summer' in North America and Europe in 1816. Yet, supereruptions eject at least an order of magnitude more magma, demonstrating that these giant eruptions can not only cause widespread devastation at the local scale, but can also have a significant worldwide impact, particularly on climate. In his CAREER research plan, the investigator will endeavor to answer some fundamental questions about giant magma bodies: What are the timescales over which they crystallize? What causes the transition from a quiet (pre-eruptive) state to the vigorous eruptive state that ultimately leads to a supereruption? What can be learned from studying crystal and vesicle populations? It is planned to investigate the timescales of crystallization of supereruption-forming magma bodies to gather information on minerals and glasses, explore the significance of these timescales, and assess the evolution of giant magma bodies. The project will be designed to obtain a clearer picture of the evolution of giant magma bodies in time and space, the processes that shape their evolution, and the conditions that lead to eruption. The work will include: (a) Texture characterization using x-ray tomography; (b) Glass inclusion characteri-zation using phase-contrast x-ray tomography; (c) Mineral zoning characterization using cathodolumines-cence (CL) imaging and trace-element analysis via electron, x-ray and laser ablation microprobes; (d) Study of the crystallography of crystal clusters using electron back-scattered diffraction (EBSD) imaging; and (e) Development of analytical and numerical solutions for problems at the crystal-scale. The study will focus on 3 deposits spread over 4 continents: Huckleberry Ridge Tuff (USA), Oruanui Tuff (New Zea-land), and Paraná-Etendeka rhyolites (South America and West Africa). All are among the largest known ignimbrite deposits, but they formed in different tectonic environments and are characteristically different from each other in eruptive history, mineralogy and petrography. Simultaneous study of these deposits employing the same conceptual framework and tools should allow for a qualitative jump in our knowledge of the timescales and evolution of the giant magma bodies that give rise to supereruptions. Research and teaching will be intimately connected through the development and offering of summer session courses in southern Brazil, Namibia, and New Zealand, formally offered by Vanderbilt University, which are aimed to provide (a) global and international experiences of collaborative research and learning with the participa-tion of faculty and students from universities from the US, Brazil and New Zealand; (b) extensive and meaningful field experience for students, from graduate students to non-majors; and (c) a unique learning experience for undergraduates who will participate in the process of construction of knowledge, a goal that is often difficult to accomplish in regular courses.