Collaborative Research: Crustal Modulation of Flood Basalts--Integrating Field, Geochemical and Computational Data for the Steens Basalts

合作研究：溢流玄武岩的地壳调制——整合斯廷斯玄武岩的现场、地球化学和计算数据

• 批准号: 1427737
• 负责人: Wendy Bohrson
• 金额: $ 18.2万
• 依托单位: Central Washington University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1427737&HistoricalAwards=false
• 关键词: Collaborative; Research; Crustal; Modulation; Flood

Flood basalt eruptions are geologically short-lived, catastrophic volcanic events that pour enormous volumes of lava - tens to hundreds of thousands of times greater than the 1980 Mount St Helens eruption? onto Earth's surface. They are important geologic events that completely change the landscape and also have the potential to impact climate and ecosystems. The only flood basalt in the United States is the Columbia River Flood Basalt (CRB), which dominates the landscape in parts of Washington and Oregon. Most of the CRB lavas erupted mainly 16 -15 million years ago and are noted for being among the world's largest individual lava flows. Among the oldest part of the CRB is the Steens Basalt (16.8-16 million years old), which overran 53,000 km2 of land surface in what is now Oregon. The Steens Basalts are compositionally more magnesian than the bulk of the CRB and so provide a unique record of the interaction between mantle-derived basalt and the crust (the outer rocky shell of Earth that extends ~40 km below the surface). At Steens Mountain, in southeastern Oregon, as many as 200 lava flows are spectacularly exposed in a nearly kilometer-thick stack that records how magma (molten rock) changed composition during the earliest stages of the CRB event. Fieldwork at Steens Mountain will yield a temporal (older to younger) sequence of lava samples that will be chemically analyzed using an array of tools. These data will be assessed with a range of computer models, including the latest generation of model called the Magma Chamber Simulator. Modeling results will provide estimates of the amount of new magma added to the crust from the mantle, the ultimate source of the basalt, and also how much crust is incorporated into magma. The sequential sampling allows documentation of how these parameters change with time as the magmatic pulse waxes and wanes. The methodology of combining field and chemical data with computer analysis can be broadly applied to other volcanic terrains, and the results of this study provide a quantitative basis for understanding other large volume magmatic events on Earth. We hypothesize that the lower Steens Basalt represents magmatism dominated by high rates of magma input during an earlier, energetically waxing stage of magmatism. In contrast, Upper Steens Basalt experienced more interaction with the crust in a thermally waning system, as the locus of CRB activity migrated north and the crustal magmatic system moved to shallower depths in the crust. These hypotheses will be tested by fieldwork, where a representative suite of lava samples will be collected; collection of whole-rock major and trace elements, O-, Sr-, Nd-, Pb-, Hf-, Os- and He-isotopes, petrography and mineral chemistry data; and thermobarometric calculations and other computational petrologic models. Results of this study will allow the petrologic evolution of Steens magmas to be placed in context with mass and thermal exchange that occurred between crust and mantle during the onset of the Columbia River flood basalt event. The broader impacts include (1) involvement of a diverse group of scientists including 2 PIs, 1 PhD student, 2 MS students and several undergraduates. At least 5 are female scientists (including one Latina); (2) development/refinement and presentation of modeling tutorials; (3) scientific outreach in the form of public lectures and field trips; (4) dissemination of results via publications, and conferences; (5) integration of results and rock samples into classes.

洪水玄武岩喷发是地质上短暂的、灾难性的火山事件，它会倾泻出大量的熔岩——比1980年圣海伦火山喷发大数万到数十万倍。到地球表面它们是重要的地质事件，完全改变了景观，也有可能影响气候和生态系统。美国唯一的洪水玄武岩是哥伦比亚河洪水玄武岩（CRB），它主导了华盛顿和俄勒冈州部分地区的景观。大多数CRB熔岩主要在1600万至1500万年前喷发，并以世界上最大的熔岩流而闻名。CRB最古老的部分是Steens玄武岩（1680 - 1600万年），它覆盖了现在俄勒冈州53,000平方公里的陆地表面。斯滕斯玄武岩在成分上比CRB的大部分含镁元素更多，因此提供了地幔衍生玄武岩与地壳（延伸至地表以下约40公里的地球外部岩壳）之间相互作用的独特记录。在俄勒冈州东南部的斯滕斯山，多达200个熔岩流壮观地暴露在近一公里厚的熔岩堆中，记录了岩浆（熔融岩石）在CRB事件的早期阶段是如何改变成分的。在斯滕斯山的野外工作将产生一个熔岩样本的时间序列（从老到新），这些样本将使用一系列工具进行化学分析。这些数据将通过一系列计算机模型进行评估，包括最新一代的岩浆室模拟器模型。建模结果将提供从地幔（玄武岩的最终来源）添加到地壳中的新岩浆的数量，以及地壳被岩浆吸收的数量。顺序采样允许记录这些参数如何随时间变化，因为岩浆脉冲的蜡和减弱。野外化学资料与计算机分析相结合的方法可以广泛应用于其他火山地形，研究结果为认识地球上其他大体积岩浆事件提供了定量依据。我们假设，下斯滕斯玄武岩代表岩浆活动，在岩浆活动的早期，能量上蜡阶段，岩浆输入率高。相比之下，上斯滕斯玄武岩在一个热衰减系统中经历了更多的与地壳的相互作用，因为CRB活动的轨迹向北迁移，地壳岩浆系统向地壳的较浅深度移动。这些假设将通过实地工作来验证，在实地工作中，将收集一组具有代表性的熔岩样本；全岩主微量元素、O-、Sr-、Nd-、Pb-、Hf-、Os-和he -同位素、岩石学和矿物化学资料的收集；以及热气压计算和其他计算岩石学模型。这项研究的结果将使Steens岩浆的岩石学演化与哥伦比亚河洪水玄武岩事件发生时地壳和地幔之间发生的质量和热交换联系起来。更广泛的影响包括：(1)参与了不同的科学家群体，包括2名pi， 1名博士生，2名硕士学生和几名本科生。至少5名女性科学家（包括一名拉丁裔）；(2)建模教程的开发/改进和呈现；(3)开展公开讲座和实地考察等形式的科学推广活动；(4)通过出版物和会议传播成果；(5)将结果与岩样进行分类。