Collaborative Research: Timescales of Crystal Residence and Magma Mixing at Mount Hood, Oregon

合作研究：俄勒冈州胡德山水晶住宅和岩浆混合的时间尺度

• 批准号: 0838421
• 负责人: Adam Kent
• 金额: $ 17.8万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-02-01 至 2012-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0838421&HistoricalAwards=false
• 关键词: Collaborative; Research; Timescales; Crystal; Residence

Intellectual Merit. An essential component of studies of magmatic systems is the ability to place the thermal, physical, and compositional evolution of magmas within a temporal context. In recent years there has been increased interest in constraining the rates of igneous processes and also an emerging awareness that crystals in magmatic systems often record complex histories of magmatic processes that are obscured in the liquid fractions of magmas. Three effective techniques used to constrain the timescales of crystallization and crystal residence in intermediate and silicic magma systems include textural studies, studies of diffusional relaxation of chemical gradients in crystals, and uranium-series crystal dating. However, efforts to apply these techniques have also revealed large variations (up to four orders of magnitude) in the apparent timescales of crystal storage and magma residence. Although this likely reflects natural variations in crystal residence times between different types of magmatic systems, there also appear to be systematic differences in the results recorded by each technique, which implies that each technique may respond to and record somewhat different signals. Accordingly, this project has two goals: (1) to quantify the characteristic timescales of crystal residence prior to eruption and to investigate whether these timescales vary over time at a single volcano, and (2) to apply and compare three different techniques for estimating magmatic timescales on the same suite of rock samples. To this end, this project addresses timescales of crystal residence and magma mixing at Mount Hood, Oregon. Existing data indicate that mixing between felsic and mafic magmas there has been remarkably consistent throughout the ~500 ka life of the modern edifice, Crystal populations derived from the respective endmembers are readily recognized, and importantly, initial results suggest that the pre-eruptive residence times of crystals from each of these populations have remained broadly constant throughout the volcano?s history. This hypothesis will be tested by measuring pre-mixing crystal residence times, and estimating the time elapsed between mixing and eruption. It is proposed to quantify the timescales of crystal and magma storage and magma mixing at Mount Hood by applying textural quantification (CSD), diffusional relaxation and 238U-230Th-226Ra dating. There have been few studies that directly compare any two of these techniques on the same sample suites, and none that have applied all three. Direct comparison will provide an increased level of confidence in estimates of magmatic timescales and provide a methodology that can be used for other studies. Moreover, the three techniques interact to provide more information than would be provided by using any one technique in isolation.Broader Impacts. This study will provide valuable insight into the behavior of intermediate composition silicic volcanoes and likely will have valuable implications for understanding the hazard potential of such volcanoes to nearby transportation corridors (Columbia River) and metropolitan regions (Portland). The project will promote collaboration between scientists from Oregon State and UC-Davis, as well as from Durham Univ. (Dougal Jerram - an expert in quantification of magmatic textures) and the USGS. It will advance the careers of a female PI and a promising female graduate student. Jerram will teach an informal workshop while in Corvallis, and his visit will be scheduled so as to allow for participation by the graduate students supported by this proposal in addition to others in the Northern California and Pacific Northwest region. The proposal will also support continued outreach efforts to demonstrate basic volcanologic principles to undergraduate and K-12 students in the Corvallis area.

智力优点。岩浆系统研究的重要组成部分是能够将岩浆的热，物理和组成演化放置在时间环境中。近年来，人们对限制火成点过程的速度的兴趣增加了，也是一种新兴的意识：岩浆系统中的晶体经常记录岩浆过程中岩浆过程中的复杂历史。用于限制中间和硅质岩浆系统中结晶和晶体居住时间的三种有效技术包括纹理研究，晶体中化学梯度扩散弛豫的研究以及铀系列晶体的测定。但是，应用这些技术的努力也揭示了在晶体存储和岩浆住宅的明显时间尺度上发生了很大的变化（最多四个数量级）。尽管这可能反映了不同类型的岩浆系统之间水晶停留时间的自然变化，但每种技术记录的结果似乎也存在系统的差异，这意味着每种技术都可以响应并记录一些不同的信号。因此，该项目有两个目标：（1）在喷发前量化晶体居住的特征时间尺度，并研究这些时间表在单火山上随着时间的流逝而变化，以及（2）应用和比较三种不同的技术来估算同一岩石样品套件上的岩浆时间标准。为此，该项目解决了俄勒冈州胡德山的水晶住宅和岩浆混合的时间尺度。现有数据表明，在米菲岩浆和镁铁质岩浆之间的混合在整个现代建筑物的500 ka寿命中都非常一致，从各自的末日衍生而来的水晶种群很容易被认识到，而且最重要的是，最初的结果表明，这些人群的晶体前爆发前的停留时间在整个Volcano的历史上保持了较宽的恒定。该假设将通过测量预混合晶体停留时间，并估算混合和喷发之间经过的时间来检验。提议通过应用纹理定量（CSD），扩散弛豫和238U-230th-226RA约会来量化晶体和岩浆存储和岩浆混合的时间尺度。很少有研究直接将这些技术中的任何两种在同一样品套件上进行比较，而没有应用所有这三种技术。直接比较将对岩浆时间尺度的估计值提高信心，并提供可用于其他研究的方法。此外，这三种技术相互作用以提供比使用任何一种孤立技术所提供的信息更多的信息。 这项研究将为中间组成硅火山的行为提供宝贵的见解，并可能对了解此类火山对附近的运输走廊（哥伦比亚河）和大都市（波特兰）的危害潜力具有宝贵的影响。该项目将促进来自俄勒冈州和加州大学戴维斯分校的科学家以及达勒姆大学的合作。 （Dougal Jerram-岩浆纹理量化的专家）和USGS。它将推进女性PI和有前途的女研究生的职业。杰拉姆（Jerram）将在科瓦利斯（Corvallis）教授非正式的讲习班，他的访问将安排在北加州和西北太平洋地区的其他人之外，还允许该提案支持的研究生参与。该提案还将支持继续宣传工作，以向科瓦利斯地区的本科生和K-12学生展示基本的火山学原则。