Lying in Wait? Evolution of Dacite Beneath Santa Maria Volcano, Guatemala

躺着等待？

• 批准号: 0738007
• 负责人: Bradley Singer
• 金额: $ 30.64万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-01-01 至 2011-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0738007&HistoricalAwards=false
• 关键词: Lying; Wait; Evolution; Dacite; Beneath

The origin of silica- and volatile-rich andesitic and dacitic magma is a question fundamental to the understanding of how continental crust evolves, how many of the world's active volcanoes grow, and for fully appreciating the hazards posed by these potentially dangerous volcanoes. The main aim of this project is to improve our understanding of the physical and chemical processes by which this kind of magma originates and evolves. This project will focus on Santa Maria Volcano, Guatemala, a relatively simple volcano whose history mirrors that of Mount St. Helens, including explosive eruption of more than 8 cubic kilometers of dacitic ash and pumice in 1902, followed by decades of lava dome extrusion. By linking the record of historic eruptions to a well-dated record of chemical changes in the basaltic lava flows that erupted to form the 12,400 foot high volcano between 72,000 and 36,000 years before the present, our study will provide an unprecedented long-term evaluation of basaltic-andesitic-dacitic magma evolution over the lifetime of a typical subduction zone volcano. This is a unique opportunity to quantify not only the processes responsible for the cataclysmic 1902 eruption, but the time scales and kinetics of these processes as well.The research project is motivated by recent theoretical and numerical modeling of how magma cools within its surrounding rocks when lodged tens of kilometers deep within the crust. These models predict that, rather than the conventional idea of magma stored briefly at shallow depths below the volcano, basaltic magma formed by melting in the Earth's mantle may become trapped within the lower crust for thousands of years, lose heat slowly and crystallize to form volatile-rich dacite before ascending to the surface. In laboratories at the University of Wisconsin-Madison, the team has made advances on several analytical fronts including: age dating of very young lava flows using the 40Ar/39Ar variant of the potassium-argon decay clock, application of short-lived radioactive isotopes of thorium and uranium to determine how long before eruption a magma begins to crystallize, and secondary ion mass spectrometry to measure the concentration of water and carbon dioxide in tiny inclusions of melt trapped within the crystallizing minerals. Analyses using these approaches to study lava flows and ash deposits from Santa Maria Volcano will enable us to track the rates at which the volcano and underlying magma bodies grew, the depth at which the dacite magma began to lose heat and crystallize, and whether, or not, the arrival of a brand new batch of mantle-derived basaltic magma into the crust triggered the massive eruption that killed several thousand inhabitants in October, 1902. Moreover, in Guatemala and other Central American countries, dozens of similarly large volcanoes have erupted in the last few thousand years, or are active today, putting tens of thousands of nearby people at risk. Understanding better the processes that control long-term growth of these volcanoes, and in particular how volatile-rich dacitic magma forms - perhaps deeply hidden for tens of millenia - and erupts violently with little warning, is an overarching goal. As part of this project, the researchers will catalyze collaboration with Guatemalan volcanologists and civilian authorities and involve a graduate student who will pursue the PhD while acquiring expertise in field methods, laboratory analysis, and scientific communication.

二氧化硅和挥发性富裕的安第斯山脉和山地岩岩浆的起源是对理解大陆壳的发展，世界上有多少活火山的发展以及充分欣赏这些潜在危险的火山构成的危害的问题。 该项目的主要目的是提高我们对这种岩浆产生和发展的物理和化学过程的理解。 该项目将重点关注危地马拉的圣玛丽亚火山，这是一座相对简单的火山，其历史反映了圣海伦斯山（Mount St. Helens），包括1902年超过8立方公里的Dacitic Ash和Pumice的爆炸性喷发，随后是数十年的Lava Dome挤出。 通过将历史爆发的记录与玄武岩熔岩流的化学变化记录联系起来，在现在，爆发的化学变化是在现在的72,000至36，000年之间爆发的，我们的研究将提供前所未有的长期长期评估，对典型的典型过渡区的生命，对典型的质体层次进行了底层 - - 奇异的岩浆进化。 这是一个独特的机会，不仅可以量化导致1902年灾难的过程的过程，而且还量化了这些过程的时间尺度和动力学。研究项目是由于最新的理论和数值模型的动机是岩浆在周围的岩石中如何冷却周围的岩石中的岩石中，而岩浆在甲壳中的数量深度深。 这些模型预测，岩浆在火山下方的浅水深处短暂存储的常规思想，而是通过在地球地幔中熔化而形成的玄武岩岩浆可能会被困在下层地壳中数千年，而是在升至表面之前降温并形成富含挥发性的dacite。 在威斯康星大学 - 麦迪逊分校的实验室中，该团队在几个分析方面取得了进步二氧化碳在熔融矿物质中的微小融合物中。 使用这些方法进行研究来研究熔岩流和灰烬沉积物的分析将使我们能够跟踪火山和基础岩浆生长的生长的速度，dacite岩浆开始失去热量和结晶的深度，以及是否逐渐消失了千市场，该杂物逐渐散发出了巨大的岩浆杂物，该杂物又散发出了巨大的迹象。此外，1902年10月。在危地马拉和其他中美洲国家，过去几千年来爆发了数十个类似的大型火山，或者今天活跃，使附近成千上万的人处于危险之中。 更好地了解控制这些火山的长期增长的过程，尤其是富有挥发性的富含大岩岩的形成 - 也许是对数十千年的隐藏 - 并且很少警告猛烈爆发，这是一个总体目标。 作为该项目的一部分，研究人员将催化与危地马拉火山学家和民政当局的合作，并参与一名研究生，他们将在获得现场方法，实验室分析和科学沟通方面获得专业知识的同时攻读博士学位。