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。研究小组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--长石来研究这一点。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发挥了很大作用。该项目将对沙斯塔山和圣海伦斯山的火山产物应用一种新的分析技术，以更彻底地了解它们的岩浆在喷发前上升到地表时是如何变化的。这项工作可能会带来更好的活火山系统危险评估指数。该项目支持博士后研究人员，他们将在光谱测量方面积累专业知识，并在项目领导方面获得经验。它还将为本科生提供宝贵的地球科学实验室研究经验。两位专业人士在职业生涯的大部分时间都致力于鼓励STEM领域中代表性不足的群体的学生，并与他们合作，为所有人培养多样化的科学思想、背景和机会。该项目将使用一个由180个样品组成的大型多样化校准套件，实现对长石化学和fO2的现场测量。然后，它将使用产生的XAS校准来检查三个自然系统中Fe3+的分配和fO2的变化：布什维尔德复合体、沙斯塔山和圣海伦斯山。这将为地质界带来新的地球化学定标，并对长石在分配阳离子与共存熔体方面所起的作用有新的见解。具体地说，这个项目包括的任务将使铁价状态和fO2能够直接从长石单晶使用XAS进行评估，并将得到其他类型的光谱测量的补充：1)在一系列块状成分、fO2和温度范围内生长液相长石，用作XAS fO2校准的标准；2)使用偏振的、高分辨率的XAS测量，使用独立约束标准的极化、高分辨率XAS测量，创建用于微量分析长石中Fe3+的长石校准；3)使用已知的fO2的平衡长石，使用极化的、高分辨率的XAS来创建fO2的长石校准；4)在布什维尔德、沙斯塔和圣海伦斯山的样品上测试和应用我们的长石fO2校准；5)在本科生研究人员的领导下，使用拉曼、穆斯堡尔、紫外线(UV)、可见光(VIS)、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，寻找成分和光谱响应之间的联系。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.