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

职业：巨型岩浆体的寿命和演化：对全球不同构造环境中形成的选定超级喷发沉积物的结构研究

• 批准号: 1151337
• 负责人: Guilherme Gualda
• 金额: $ 50.04万
• 依托单位: Vanderbilt University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-05-15 至 2018-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1151337&HistoricalAwards=false
• 关键词: CAREER; Longevity; Evolution; Giant; Magma

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.

超级喷发在几天到几周内向地球表面喷射出大量物质(1000千米)，表明低密度、晶体贫乏的巨型岩浆--比目前已知的任何岩浆体都要大得多--偶尔存在于地表以下几公里处。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喷发发生在大约26,000年前。1815年坦博拉火山喷发--已知的最大规模的历史性喷发--导致了1816年北美和欧洲的“无夏之年”。然而，超级喷发喷出的岩浆至少多出一个数量级，这表明这些巨大的喷发不仅可以在当地造成广泛的破坏，而且还可以对全球产生重大影响，特别是对气候的影响。在他的职业研究计划中，这位研究人员将努力回答一些关于巨大岩浆体的基本问题：它们结晶的时间尺度是什么？是什么导致了从平静(喷发前)状态到猛烈喷发状态的转变，最终导致了超级喷发？从研究晶体和囊泡种群中可以学到什么？计划调查形成超级喷发的岩浆体的结晶时间尺度，以收集关于矿物和玻璃的信息，探索这些时间尺度的意义，并评估巨大岩浆体的演化。该项目旨在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。这项工作将包括：(A)使用X射线层析成像对结构进行表征；(B)使用相衬X射线层析成像对玻璃包裹体进行表征；(C)使用阴极射线成像并通过电子、X射线和激光烧蚀微探头进行微量元素分析，对矿物分带进行表征；(D)使用电子背散射衍射成像研究晶体簇的结晶学；(E)为晶体级别的问题制定解析和数值解决方案。这项研究将集中于分布在四大洲的三个矿床：哈克贝里岭凝灰岩(美国)、奥鲁努伊凝灰岩(新泽兰)和巴拉纳-埃滕代卡流纹岩(南美洲和西非)。它们都是已知的最大的褐沸石矿床，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各有不同的特点。利用相同的概念框架和工具同时研究这些矿床，应该能够使我们对引起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。通过在巴西南部、纳米比亚和新西兰开发和提供由范德比尔特大学正式提供的暑期课程，研究和教学将密切联系在一起，旨在提供(A)全球和国际合作研究和学习的经验，来自美国、巴西和新西兰的大学的教职员工和学生参与；(B)为从研究生到非专业学生的广泛和有意义的实地经验；以及(C)将参与知识构建过程的本科生的独特学习体验，这是常规课程往往难以实现的目标。