Collaborative Research: Refining Geothermobarometry in Pyroxenes using In Situ Measurements of Fe3+

该项目通过为国家设施--阿贡国家实验室的先进光子源--提供校准，从而促进科学进步；这些结果也将对世界各地其他同步加速器设施的用户有用。这些校准解决了一个科学问题，即当一种矿物通过分析一种代用品结晶时，存在多少氧气。代用品是多价元素铁的氧化态。这种理解对于理解氧气如何控制冷却岩浆的结晶路径和成分至关重要，也提供了对岩浆移动到地表时可能在岩浆上和岩浆中进行操作的过程的洞察。该项目将资助曼荷莲学院、田纳西大学诺克斯维尔分校和爱达荷大学的研究生和本科生，其中至少包括三名女性。由于大多数造岩矿物固有的各向异性，导致它们的晶体结构与光子的相互作用根据晶体取向的不同而不同，因此在亚纳米和PM尺度上测量氧化还原态的能力是一个巨大的分析挑战。该项目研究定向单晶，以探索晶体取向对X射线吸收光谱测量的影响，重点是辉石矿物组，这是火成岩中最常见的相之一。该团队将利用这些数据建立一个通用的校准，以量化含辉石样品中的氧分压(氧逸度)。这项工作有可能推进多个地质学科的知识。它还将使世界各地使用雅典娜软件包的同步加速器能够以已知的精密度和准确度快速、轻松地测定辉石矿物中的Fe3含量。最后，该项目将机器学习技术应用于光谱数据的研究。这种方法的发展可以输出到其他领域，例如光谱学的医学、生物学和法医用途，在这些领域它具有潜在的社会影响。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。

This project promotes the progress of science by providing calibrations for use at a national facility, the Advanced Photon Source at Argonne National Laboratory; these results will also be useful for users of other synchrotron facilities worldwide. The calibrations address the scientific question of how much oxygen was present when a mineral crystallized by analyzing a proxy, which is the oxidation state of the multivalent element iron. This understanding has vital importance for understanding how oxygen controls the crystallization path and composition of cooling magmas, also providing insight into processes that may have operated on and in the magma as it moved to the surface. Graduate and undergraduate students at Mount Holyoke College, the University of Tennessee at Knoxville, and the University of Idaho will be supported by this project, including at least three women. The ability to measure redox states at sub-nm and pm scales is a formidable analytical challenges due to the inherent anisotropy of most rock-forming minerals, which causes their crystal structures to interact with photons differently according to crystal orientation. This project studies oriented single crystals to explore the effects of crystallographic orientation on x-ray absorption spectroscopy measurements, focusing on the pyroxene mineral group, one of the most common phases in igneous rocks. The team will use these data to build a universal calibration appropriate for quantifying the partial pressure of oxygen (oxygen fugacity) in pyroxene-bearing samples. This work has the potential to advance knowledge in multiple geological disciplines. It will also enable synchrotrons around the world that use the Athena software package to quickly and easily determine Fe3+ contents of pyroxene minerals with known precision and accuracy. Finally, this project applies machine learning techniques to the study of spectroscopic data. Development of this methodology is exportable to other fields, such as medical, biological, and forensic uses of spectroscopy, where it has the potential for societal impact.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.