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

该项目的重点是火山岩浆在向地表移动并喷发时如何变化。该团队对岩浆上升时的氧含量感兴趣，他们将使用地壳中最常见的造岩矿物长石来研究。岩浆的这种氧化状态很重要，因为它在调节喷发的方式和爆炸性方面起着重要作用。该项目将对沙斯塔山和圣海伦斯山的火山产物采用一种新的分析技术，以更透彻地了解火山喷发前岩浆上升到地表时的变化。这项工作可能会导致更好的指数，在活火山系统的危险评估。该项目支持博士后研究人员，他们将建立光谱测量方面的专业知识，并获得项目领导经验。它还将为本科生提供地球科学实验室研究的宝贵经验。这两个PI都致力于他们的职业生涯中的大部分时间来鼓励和与STEM领域代表性不足的群体的学生合作，为所有人增加科学思想和背景的多样性和机会。该项目将使用180个样本的大型多样化校准套件，实现长石化学和fO 2的原位测量。然后，它将使用由此产生的XAS校准检查分区的Fe 3+和fO 2的变化在三个自然系统：布什维尔德复杂，沙斯塔山和圣海伦火山。这将导致新的地球化学校准提供给地质界和新的见解所发挥的作用长石在分区阳离子与共存的熔体。具体而言，该项目包括的任务将使Fe价态和fO 2能够使用XAS直接从长石单晶中进行评估，并将通过其他类型的光谱测量进行补充：1）在一系列本体成分、fO 2和温度范围内生长液相线长石，用作XAS fO 2校准的标准; 2）使用取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，创建用于长石中Fe 3+的微量分析的长石校准; 3）使用具有已知fO 2的平衡的长石，使用偏振的高分辨率XAS创建fO 2的长石校准; 4）在Bushveld、Shasta和Mount St. Helens样品上测试并应用我们的fO 2长石校准; 5）在本科研究人员的领导下，使用拉曼、穆斯堡尔、紫外（UV）、可见（维斯）、衰减全反射（ATR）和反射FTIR光谱表征为氧气压计组装的同一套样品，该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估的支持。

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.