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和喷发时是如何变化的。研究小组对岩浆上升过程中的氧含量很感兴趣，他们将利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程度方面起着重要作用。该项目将对沙斯塔山和圣海伦火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。该研究可为活火山系统的灾害评价提供更好的指标。该项目支持一名博士后研究员，他将在光谱测量方面建立自己的专业知识，并获得项目领导经验。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pi的大部分职业生涯都致力于鼓励和与STEM领域中代表性不足的群体的学生合作，为所有人提供科学思想和背景的多样性和机会。该项目将使用180个样品的大型不同校准套件，实现长石化学和fO2的原位测量。然后，它将使用得到的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。它将为地质界提供新的地球化学校准，并对长石在分配阳离子与共存熔体中的作用有新的认识。具体来说，该项目包括使用XAS直接从长石单晶中评估铁价态和fO2的任务，并将通过其他类型的光谱测量进行补充：1)在一定范围内生长液态长石，并将其用作XAS fO2校准的标准；2)利用定向单晶的前边缘和主边缘区域，利用独立约束标准的极化、高分辨率XAS测量，创建长石校准，用于长石中Fe3+的微量分析；3)利用已知fO2的平衡长石，利用偏振、高分辨率XAS创建fO2的长石校准；4)在Bushveld、Shasta和Mount St. Helens样品上测试并应用我们的fO2长石校准；5)在本科研究人员的领导下，利用拉曼光谱、Mössbauer光谱、紫外光谱、可见光光谱、衰减全反射光谱和反射FTIR光谱对氧气压计组装的同一组样品进行表征，寻找成分与光谱响应之间的联系。该奖项反映了美国国家科学基金会的法定使命，并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，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.