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

合作研究：角闪石的氧化还原比作为火成岩系统中不稳定预算的代表

• 批准号: 2042421
• 负责人: Molly McCanta
• 金额: $ 5.54万
• 依托单位: University of Tennessee Knoxville
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-06-15 至 2024-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2042421&HistoricalAwards=false
• 关键词: Collaborative; Research; Redox; Ratios; Amphiboles

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.

铁是唯一具有多价态的元素（金属铁或 Fe0、二价铁或 Fe2+、以及三价铁或 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是开发方法来单独分析每种元素的含量，因为它们的相对丰度记录了氧气在矿物形成系统中的演化过程。氢也是了解岩浆演化的重要元素。该项目将开发方法，使用两种光谱法对一个重要的矿物组进行此类测量：角闪石。 X射线吸收光谱将测量铁的价态，拉曼光谱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角闪石结晶时氢和铁的不同价态在岩浆中的行为。它还将通过提供实践实验室培训、促进劳动力发展和研究生院准备来支持本科生和研究生研究人员。该项目将承担四项相互关联的任务，旨在创建和应用角闪石中氢、三价铁和二价铁的校准使用拉曼和X射线吸收光谱的矿物。1．该团队将使用 X 射线吸收光谱 (XAS) 创建用于三价铁微量分析的角闪石校准。 Fe3+/Fe2+ 微量分析技术的开发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三价铁的主要硅酸盐宿主。该技术的校准需要获取数十个已知 Fe3+ 和 H 含量的角闪石样品，并对取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 都可以通过角闪石的拉曼光谱来确定。测试这项工作并建立可靠的拉曼校准将使拉曼散射能够用作探测角闪石的三价铁和氢含量的一种方法，并且可以应用于在实验室和实验室收集的极其多样化的角闪石数据集。场地。还将用粉末数据填充现有RRUFF数据库中稀疏的角闪石单晶数据，增加数据库的可行性。 3．该团队将在受控实验条件下表征角闪石和熔体之间 Fe3+ 和 H 的分配。测量角闪石中的三价铁和氢含量只有在能够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的密集和广泛变量时才能提供巨大的地质价值。将在受控的 P、T、XH2O 和 fO2 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角闪石的数据库。4。该团队将以 Shiveluch 火山超含水岩浆作为案例研究，探讨 Fe3+ 对涉及角闪石的分区和地质气压计的影响。利用上述三项任务的校准，他们将能够更好地约束 Shiveluch 火山（全新世期间世界上最具爆炸性的火山）角闪石的 P-T- fO2 演化。该奖项反映了 NSF 的法定使命，并被认为是值得的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来提供支持。