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

洪水玄武岩喷发是地质学上短暂的灾难性火山事件，倾倒了大量的熔岩-比1980年的圣海伦火山喷发大几十到几十万倍？到地球表面。它们是完全改变景观的重要地质事件，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），它在华盛顿和俄勒冈州的部分地区占据主导地位。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。在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。Steens玄武岩的成分比CRB的大部分更含镁，因此提供了幔源玄武岩与地壳（延伸到地表以下约40公里的地球外部岩石壳）之间相互作用的独特记录。在俄勒冈州东南部的Steens山，多达200个熔岩流在一个几乎更厚的堆栈中暴露出来，记录了岩浆（熔融岩石）在CRB事件的最早阶段如何改变成分。在Steens山的实地考察将产生一个时间序列（从老到新）的熔岩样本，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，包括称为岩浆室模拟器的最新一代模型。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量的估计，以及有多少地壳被纳入岩浆中。顺序采样允许记录这些参数如何随着岩浆脉冲的增减而随时间变化。野外和化学数据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，本研究的结果为了解地球上其他大体积岩浆事件提供了定量依据。我们推测，较低的Steens玄武岩代表岩浆活动为主的高利率的岩浆输入在早期，积极打蜡阶段的岩浆活动。相比之下，上Steens玄武岩经历了更多的相互作用与地壳中的热衰减系统，作为轨迹的CRB活动北移和地壳岩浆系统移动到较浅的深度在地壳中。这些假设将通过实地考察进行检验，实地考察将收集一套有代表性的熔岩样品;收集全岩主要和微量元素、O-、Sr-、Nd-、Pb-、Hf-、Os-和He-同位素、岩相学和矿物化学数据;以及温压计算和其他计算岩石学模型。这项研究的结果将允许Steens岩浆的岩石学演化的背景下，发生在哥伦比亚河洪水玄武岩事件的发病过程中的地壳和地幔之间的质量和热交换。 更广泛的影响包括：（1）不同科学家群体的参与，包括2名PI，1名博士生，2名MS学生和几名本科生。至少有5名女科学家（包括一名拉丁裔）;（2）开发/完善和介绍建模教程;（3）以公开讲座和实地考察的形式进行科学宣传;（4）通过出版物和会议传播成果;（5）将成果和岩石样本纳入课堂。

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.