Oxygen and Hydrogen Fugacity of the Purico Ignimbrite Magmas, Northern Chile

智利北部普里科熔凝岩岩浆的氧和氢逸度

• 批准号: 0001081
• 负责人: Sheila Seaman
• 金额: $ 4.31万
• 依托单位: University of Massachusetts Amherst
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-07-01 至 2003-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0001081&HistoricalAwards=false
• 关键词: Oxygen; Hydrogen; Fugacity; Purico; Ignimbrite

EAR-0001081SeamanFelsic magmas are the sources of the keystone components of continental crust, and of the most explosive volcanic eruptions that commonly occur on Earth. The major factors in the evolution and eruptive behavior of felsic magmas are their water concentrations and their degree of oxidation. In this study, synchrotron spectroscopy will be used to explore the possibility that plagioclase crystals preserve information about the oxidation state and the water concentration of the magmas from which the crystals grew. Both Fe 3+/G Fe and H2 concentrations in the nominally anhydrous plagioclase will be measured and their use as proxies, for, respectively, oxygen fugacity and water concentration of the magmas that produced the crystals, will be explored. Synchrotron microXANES (X-ray absorption near-edge structure) spectroscopy of oxidation state of Fe in plagioclase crystals is based on measuring small energy differences in cation/oxygen bonds between ferrous and ferric ions that bond to oxygen. Synchrotron microFTIR (Fourier transform infrared) spectroscopy, like conventional FTIR spectroscopy, provides a correlation between the wavelength of light absorbed and the nature of chemical bonds in the mineral. Synchrotron microFTIR analysis of H2 in plagioclase will utilize a very bright source, eliminating the need to remove and polish oriented single crystals, and allowing for the analysis of crystals in their spatial context. These techniques will be tested on the Lower Purico ignimbrite (~1 Ma) in the Andean Altiplano Puna Volcanic Complex, for which independent measurements of maximum magmatic water concentrations have already been determined by SIMS and FTIR, and oxygen fugacity determinations have been made on the basis of crystallization temperatures and mineral equilibria by deSilva (1989, 1991) and Schmitt et al. (1998). Along with testing these new techniques, goals of this study include acquiring insight into the interplay of oxygen fugacity, water concentration, mineral assemblage, and the eruption style of siliceous magmas across a large range of geologic time.

EAR-0001081Seaman长英质岩浆是大陆地壳主要成分的来源，也是地球上常见的最具爆炸性的火山喷发的来源。 长英质岩浆演化和喷发行为的主要因素是它们的水浓度和氧化程度。 在这项研究中，同步加速器光谱将用于探索斜长石晶体保留有关晶体生长的岩浆的氧化态和水浓度信息的可能性。 将测量标称无水斜长石中的 Fe 3+/G Fe 和 H2 浓度，并将探索它们分别作为产生晶体的岩浆的氧逸度和水浓度的代表。 斜长石晶体中 Fe 氧化态的同步加速器 microXANES（X 射线吸收近边缘结构）光谱基于测量与氧键合的亚铁离子和三价铁离子之间的阳离子/氧键的微小能量差异。 同步加速器微型 FTIR（傅里叶变换红外）光谱与传统 FTIR 光谱一样，提供了吸收的光波长与矿物中化学键性质之间的相关性。 对斜长石中的 H2 进行同步加速器 microFTIR 分析将利用非常明亮的光源，无需去除和抛光定向单晶，并允许在其空间背景下对晶体进行分析。 这些技术将在安第斯高原普纳火山群的下普里科火凝灰岩（约 1 Ma）上进行测试，其中最大岩浆水浓度的独立测量已经通过 SIMS 和 FTIR 确定，并且 deSilva（1989、1991）和 Schmitt 等人已根据结晶温度和矿物平衡确定了氧逸度。 （1998）。 除了测试这些新技术之外，这项研究的目标还包括深入了解大范围地质时期内氧逸度、水浓度、矿物组合和硅质岩浆喷发方式之间的相互作用。