Collaborative Research: Building and Applying a Universal Plagioclase Oxybarometer using X-ray Absorption Spectroscopy

合作研究：使用 X 射线吸收光谱法构建和应用通用斜长石氧压计

• 批准号: 2243746
• 负责人: Molly McCanta
• 金额: $ 18.99万
• 依托单位: University of Tennessee Knoxville
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-07-01 至 2026-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2243746&HistoricalAwards=false
• 关键词: Collaborative; Research; Building; Applying; Universal

The project focuses on how volcanic magmas change as they travel toward the surface and erupt. The team is interested in the oxygen content of magma as it ascends, and they will use the most common rock-forming mineral in the Earth’s crust, feldspar, to study that . This oxidation state of a magma is important because it plays a large role in regulating the style of the eruption and how explosive it is. The project will apply a new analytical technique to volcanic products from Mounts Shasta and St. Helens to gain a more thorough understanding of how their magmas have changed as they ascend to the surface before eruption. This work could lead to better indices of hazard assessment in active volcanic systems. This project supports a postdoctoral researcher who will build their expertise in spectroscopic measurements and gain experience in project leadership. It will also provide undergraduates valuable experience with laboratory research in the geosciences. Both PIs have dedicated much of their careers to encouraging and working with students from underrepresented groups in the STEM fields to grow diversity of scientific thoughts and backgrounds and opportunities for all.The project will enable in situ measurements of feldspar chemistry and fO2, using a large diverse calibration suite of 180 samples. It will then use the resultant XAS calibrations to examine partitioning of Fe3+ and variations in fO2 in three natural systems: the Bushveld complex, Mount Shasta, and Mount St. Helens. It will result in new geochemical calibrations available to the geologic community and new insights into the role played by feldspar in partitioning cations with coexisting melts. Specifically, this project includes tasks that will enable Fe valence state and fO2 to be evaluated directly from feldspar single crystals using XAS, and will be complemented by other types of spectroscopic measurements: 1) Grow liquidus feldspars over a range of bulk compositions, fO2, and temperature to be used as standards for an XAS fO2 calibration; 2) Create a feldspar calibration for microanalysis of Fe3+ in feldspar using polarized, high-resolution XAS measurements of independently constrained standards using the pre-edge and main-edge regions of oriented single crystals; 3) Use the equilibrated feldspars with known fO2 to create a feldspar calibration for fO2 using polarized, high-resolution XAS; 4) Test and apply our feldspar calibration for fO2 on Bushveld, Shasta, and Mount St. Helens samples; 5) With undergraduate researchers leading the work, characterize the same suite of samples assembled for the oxybarometers using Raman, Mössbauer, ultraviolet (UV), visible (VIS), attenuated total reflectance (ATR) and reflectance FTIR spectroscopies, looking for linkages between composition and spectral response.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

该项目的重点是火山岩浆在向地表移动和喷发时如何变化。该团队对岩浆上升时的含氧量感兴趣，他们将使用地壳中最常见的造岩矿物长石来进行研究。研究表明，岩浆的这种氧化态很重要，因为它在调节喷发方式及其爆炸性方面发挥着重要作用。该项目将采用一种新的分析技术来分析来自蒙特斯的火山产物。沙斯塔和圣海伦斯火山将更全面地了解岩浆在喷发前上升到地表时的变化，这项工作可能会为活跃火山系统的危险评估提供更好的指标。两位 PI 都致力于鼓励和与 STEM 领域代表性不足的群体的学生合作，以提高他们在光谱测量方面的专业知识并获得项目领导经验。增加科学思想和背景的多样性，并为所有人提供机会。该项目将使用由 180 个样本组成的大型多样化校准套件，对长石化学和 fO2 进行原位测量，然后使用由此产生的 XAS 校准来检查 Fe3+ 的分配和变化。三个自然系统中的 fO2：布什维尔德综合体、沙斯塔山和圣海伦斯山 这将为地质界带来新的地球化学校准，并对长石的作用产生新的见解。在分配共存熔体的阳离子中，该项目包括的任务将能够直接从长石单晶中评估 Fe 价态和 fO2，特别是使用 XAS，并将通过其他类型的光谱测量进行补充：1）在用作 XAS fO2 校准标准的散装成分、fO2 和温度范围 2) 创建用于 Fe3+ 微量分析的长石校准；使用定向单晶的前边缘和主边缘区域，使用独立约束标准的偏振、高分辨率 XAS 测量长石；3) 使用具有已知 fO2 的平衡长石，使用偏振、高分辨率对 fO2 进行长石校准XAS；4) 在布什维尔德、沙斯塔和圣海伦斯山样品上测试并应用我们的长石校准；5) 由本科生研究人员领导工作，表征了为氧压计组装的同一组样品，反射拉曼、穆斯堡尔、紫外 (UV)、可见光 (VIS)、衰减全反射 (ATR) 和反射 FTIR 光谱，寻找成分和光谱响应之间的联系。该奖项 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。