Collaborative Research: Redox Ratios in Amphiboles as Proxies for Volatile Budgets in Igneous Systems

铁是唯一具有多价态的元素（铁金属或Fe 0，亚铁或Fe 2+，三价铁或Fe 3+），是岩石形成矿物的主要成分。长期以来，分析地球化学家的一个目标是开发出单独分析每种矿物含量的方法，因为它们的相对丰度记录了氧在形成矿物的系统中的演变。氢也是了解岩浆演化的重要元素。该项目将制定方法，利用两种光谱学对一个重要的矿物类别：角闪石进行这种测量。X射线吸收光谱法将测量铁的价态，而拉曼光谱法将测量铁的价态和存在的氢的量。这项工作很重要，因为它将使地球化学家能够追踪氢和铁的不同价态在角闪石结晶时在岩浆中的行为。它还将通过提供实验室实践培训来支持本科生和研究生研究人员，为劳动力发展和研究生院准备做出贡献。该项目将开展四项相互关联的任务，旨在使用拉曼和X射线吸收光谱仪创建和应用角闪石矿物中氢、三价铁和亚铁的校准。1.该团队将使用X射线吸收光谱法（XAS）创建用于三价铁微量分析的闪石校准。发展Fe 3 +/Fe 2+的微量分析技术仍然是标准薄切片地质样品原位分析的高度优先事项。角闪石的需求特别迫切，因为它是火成岩和变质岩中三价铁的主要硅酸盐宿主。这种技术的校准需要获得数十个已知Fe 3+和H含量的角闪石样品，并对定向单晶进行耗时的分析。2.该团队将创建一个拉曼光谱库，用于解释和潜在的推导Fe 3+和H含量相同的良好表征的样品。汉堡大学的一个小组最近的工作表明，Fe 3+和H都可以从角闪石的拉曼光谱中确定。测试这项工作和建立强大的拉曼校准将使使用拉曼散射作为一种方式来探测角闪石的三价铁和氢含量，并可以应用于一个非常多样化的一组角闪石数据收集在实验室和现场。它还将填补现有RRUFF数据库中稀疏的角闪石单晶数据，增加数据库的可行性。该小组将在受控的实验条件下表征角闪石和熔体之间的Fe 3+和H的分配。角闪石中三价铁和氢含量的测定，只有在能解释控制熔体和晶体之间的地球化学分配以及角闪石脱氢作用的大量和大量变量的情况下，才能提供巨大的地质价值。将在控制P、T、XH 2 O和fO 2的条件下进行角闪石合成实验。将分析合成角闪石、玻璃和伴生矿物的氢和铁分配行为。通过对一系列起始成分和氧逸度进行实验，他们将建立一个可应用于天然闪石的数据库。该小组将探索Fe 3+对涉及角闪石的分区和地质压力计的影响，使用Shiveluch火山超含水岩浆作为案例研究。利用上述三项任务的校准，他们将能够更好地限制Shiveluch火山角闪石的P-T-fO 2演化，Shiveluch火山是全新世期间世界上最具爆炸性的火山。该奖项反映了NSF的法定使命，并被认为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来支持。

Iron is the only element with multiple valence states (iron metal or Fe0, ferrous iron or Fe2+, and ferric iron or Fe3+) that is a major constituent in rock-forming minerals. It has long been a goal of analytical geochemists to develop methods to analyze the amounts of each of these individually, because their relative abundances record how oxygen evolved in the systems from which the minerals formed. Hydrogen is also an important element in understanding magma evolution. This project will develop methodology to make such measurements on one important mineral group: amphiboles using two types of spectroscopy. X-ray absorption spectroscopy will measure iron valence state, and Raman spectroscopy will measure both iron valence state and the amount of hydrogen present. This work is important because it will enable geochemists to trace how hydrogen and the different valence states of iron behave in magmas as amphiboles crystallize. It will also support undergraduate and graduate student researchers by providing hands-on laboratory training, contributing to workforce development and graduate school preparation.This project will undertake four interrelated tasks aimed at creating and applying a calibration for hydrogen, ferric, and ferrous iron in amphibole minerals using Raman and x-ray absorption spectroscopies.1. The team will create an amphibole calibration for microanalysis of ferric iron using x-ray absorption spectroscopy (XAS). Development of techniques for microanalysis of Fe3+/Fe2+ remains a high priority for in situ analyses of geological samples in standard thin sections. The need is particularly acute for amphiboles, as it is a dominant silicate host for ferric iron in igneous and metamorphic rocks. Calibration of this technique requires access to dozens of amphibole samples with known Fe3+ and H contents and time-consuming analyses of oriented single crystals. 2. The team will create a Raman spectral library of the same well-characterized samples for use in interpreting and potentially deriving Fe3+ and H contents. Recent work by a group at the University of Hamburg suggests that both Fe3+ and H may be determined from Raman spectra of amphiboles. Testing this work and establishing robust Raman calibrations will enable the use of Raman scattering as a way to probe both the ferric iron and hydrogen content of amphiboles, and could be applied to an extremely diverse set of amphibole data collected both in the lab and in the field. It will also fill in the sparse amphibole single-crystal data in the existing RRUFF database with powder data increasing the viability of the database.3. The team will characterize the partitioning of Fe3+ and H between amphibole and melt in controlled experimental conditions. Measuring the ferric iron and H contents in amphiboles will provide immense geologic value only if they can account for the intensive and extensive variables that control the geochemical partitioning between melt and crystal, and the dehydrogenation of amphibole. Amphibole synthesis experiments at controlled P, T, XH2O and fO2 will be conducted. The synthetic amphiboles, glasses, and associated minerals will be analyzed for hydrogen and iron partitioning behavior. By conducting experiments with a range of starting compositions and oxygen fugacities, they will build a database that can be applied to natural amphiboles.4. The team will explore the effect of Fe3+ on partitioning and geobarometers involving amphibole using the Shiveluch volcano super-hydrous magmas as a case study. Using the calibrations from the above three tasks, they will be able to better constrain the P-T- fO2 evolution of amphiboles from Shiveluch volcano, the most explosive volcano in the world during the Holocene.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.