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

长英质岩浆是大陆地壳的基石成分，也是地球上通常发生的最具爆炸性的火山爆发的来源。 长英质岩浆演化和喷发行为的主要因素是其水含量和氧化程度。 在这项研究中，同步加速器光谱将被用来探索斜长石晶体保存有关氧化态和晶体生长的岩浆的水浓度的信息的可能性。 这两个Fe 3+/G Fe和H2的浓度在名义上无水斜长石将被测量和它们的使用作为代理，分别为，氧逸度和水浓度的岩浆，产生的晶体，将被探索。 斜长石晶体中Fe的氧化态的同步加速器microXANES（X射线吸收近边结构）光谱是基于测量与氧结合的亚铁离子和三价铁离子之间的阳离子/氧键的小能量差。 与传统的傅里叶变换红外光谱一样，同步辐射显微傅里叶变换红外光谱提供了吸收光的波长与矿物中化学键的性质之间的相关性。斜长石中H2的同步辐射显微傅里叶变换红外光谱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分析晶体。 这些技术将在安第斯高原普纳火山杂岩中的下普里科熔结凝灰岩（约1 Ma）上进行测试，对此，已通过西姆斯和傅里叶变换红外光谱对最大岩浆水浓度进行了独立测量，deSilva（1989年，1991年）和施密特等人（1998年）根据结晶温度和矿物平衡确定了氧逸度。 沿着这些新技术的测试，本研究的目标包括深入了解氧逸度，水浓度，矿物组合的相互作用，以及硅质岩浆在大范围的地质时代的喷发风格。

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.