Collaborative Research: Hydrogen and Ferric Iron in Felsic Melts

硅酸盐熔体中氢和氧的逸性限制了熔体的水浓度，因此是粘度、爆炸性、结晶温度和矿物结晶顺序的主要控制因素。氢和氧是含水矿物结晶的关键，它们的丰度可能驱动岩浆沿钙碱性或拉斑岩分异路径演化。本项目的目标是评估长硅熔体及其结晶产物的Fe3+/Fe2+和H含量，并将这些含量与起始熔体的fo2和fH2O联系起来。我们计划1)使用同步加速器和常规（全球）FTIR光谱测量岩浆系统中矿物和玻璃中的H浓度，这些系统对fH2O有独立的约束；2)利用微xanes光谱测量天然熔体、长石以及共存的氧化物和铁镁相（如角闪洞）中Fe3+的含量，这些相对fO2有独立的约束。从这些数据中，我们可以独立地从测量的Fe3+/SFe中得出氧和氢逸度值，并将这些结果与先前确定的值进行比较。来自Bishop凝灰岩（加利福尼亚）、Timber Mountain凝灰岩（内华达州）、Mt. Erebus（南极洲）、Purico杂岩（智利）和Katmai杂岩（阿拉斯加）的样品将用于本研究。为了将氧和氢逸度值与测量的Fe3+/SFe相联系起来，我们将使用共存的水相，角闪石或黑云母，实验数据可以提供Fe3+/SFe和H2O缺水量之间的校准，作为fH2， T和p的函数。因为我们将从熔体内含物的独立工作中知道H2O浓度，我们将测量Fe3+/SFe，我们将能够计算fH2。由熔体包裹体中水的浓度计算出的fH2和fH2O，我们将能够计算出fO2。我们还计划将我们的结果与Sugawara（2001）基于热力学模型开发的氧气气压计的结果进行比较，以计算结晶系统中的氧逸度。

Seaman EAR-0229607 The fugacities of hydrogen and oxygen in silicate melts limit the water concentration of melts, and hence are a major control of viscosity, explosivity, crystallization temperature, and order of crystallization of minerals. Both H and O are key to the crystallization of hydrous minerals, and their abundance may drive magmas along calc-alkaline or tholeiitic differentiation paths. The goal of this project is to assess the Fe3+/Fe2+ and H contents of felsic melts and their crystallization products, and to relate those contents to the fo2 and fH2O of the starting melt. We plan to 1) measure the H concentrations in minerals and glasses from magmatic systems for which independent constraints on fH2O are available, using both synchrotron and conventional (globar) FTIR spectroscopy; and 2) measure the Fe3+ contents of naturally-produced melts, feldspars, and coexisting oxide and ferromagnesian phases (such as amphibole) for which independent constraints on fO2 are available, using micro-XANES spectroscopy. From these data, we can independently derive oxygen and hydrogen fugacity values from the measured Fe3+/SFe and compare these results to previously determined values. Samples from the Bishop Tuff (California), the Timber Mountain Tuff (Nevada), Mt. Erebus (Antarctica), the Purico complex (Chile), and the Katmai complex (Alaska) will be used in this study. To associate oxygen and hydrogen fugacity values with measured Fe3+/SFe, we will use coexisting hydrous phases, either hornblende or biotite, for which experimental data are available that provide a calibration between Fe3+/SFe and H2O deficiency as a function of fH2, T, and P. Because we will know H2O concentration from independent work on melt inclusions, and we will measure Fe3+/SFe, we will be able to calculate fH2. From the calculated fH2 and fH2O derived from water concentrations in melt inclusions, we will be able to calculate fO2. We also plan to compare our results to results with the oxygen barometers developed by Sugawara (2001) based on thermodynamic models to calculate oxygen fugacity in the crystallizing system.