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

铁是唯一具有多种价态的元素（铁金属或Fe0，亚铁或Fe2+，三铁或Fe3+），是造岩矿物的主要成分。长期以来，分析地球化学家的目标一直是开发出一种方法来单独分析每种矿物质的含量，因为它们的相对丰度记录了矿物质形成系统中氧气的演化过程。氢也是了解岩浆演化的一个重要元素。这个项目将发展一种方法，利用两种光谱学对一种重要矿物组：角闪石进行这种测量。x射线吸收光谱将测量铁价态，拉曼光谱将测量铁价态和氢的存在量。这项工作很重要，因为它将使地球化学家能够追踪岩浆中氢和铁的不同价态在角闪石结晶过程中的行为。它还将通过提供动手实验室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的准备做出贡献。该项目将承担四项相互关联的任务，旨在利用拉曼光谱和x射线吸收光谱创建和应用角闪洞矿物中氢、铁和亚铁的校准。该团队将使用x射线吸收光谱（XAS）创建一个角闪孔校准，用于铁的微量分析。开发Fe3+/Fe2+微量分析技术仍然是标准薄片地质样品原位分析的重中之重。对角闪石的需求尤其迫切，因为它是火成岩和变质岩中含铁铁的主要硅酸盐寄主。该技术的校准需要访问数十个已知Fe3+和H含量的角闪孔样品，并对定向单晶进行耗时的分析。2. 该团队将创建一个具有相同特征的样品的拉曼光谱库，用于解释和潜在地推导Fe3+和H含量。汉堡大学的一个小组最近的工作表明，Fe3+和H都可以从角闪石的拉曼光谱中测定出来。测试这项工作并建立稳健的拉曼校准将使拉曼散射成为探测角闪石中铁和氢含量的一种方法，并可应用于实验室和现场收集的极其多样化的角闪石数据集。并将现有RRUFF数据库中稀疏的角闪孔单晶数据用粉末数据填充，增加数据库的可行性。该团队将在受控的实验条件下表征闪洞和熔体之间Fe3+和H的分配。测量角闪石中铁和氢的含量，只有能够解释控制熔体和晶体的地球化学分配和角闪石脱氢的密集和广泛的变量，才能提供巨大的地质价值。在可控的P、T、XH2O和fO2条件下进行角闪孔合成实验。合成角闪石、玻璃和伴生矿物将分析氢和铁的分配行为。通过对一系列初始成分和氧逸度进行实验，他们将建立一个可应用于天然角闪石的数据库。该团队将以Shiveluch火山超含水岩浆为例，探索Fe3+对角闪洞分区和地压的影响。利用以上三个任务的校准，他们将能够更好地约束全新世世界上最爆炸性的火山Shiveluch火山的P-T- fO2演变。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。

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.