Collaborative Research: Effects of Composition and Cooling Rate on Fe XANES Glass Calibrations

岩浆是探测地球物理状况和化学性质的探测器。室内。探索这些喷发的熔体的矿物学可以让我们深入了解地球持续的地质演化。除了基本的地球化学之外，温度和压力等参数对于量化地球内部的条件也很重要。与上述物理参数同样重要的是氧逸度（fO2），这是对岩浆结晶的氧化环境的测量。在岩浆中的所有元素中，铁是唯一一种通常以多种价态存在的主要造岩元素。因此，对价态（Fe3+/Fe2+）的准确了解为矿物结晶时存在的氧量提供了最佳代理，并允许估计岩浆氧逸度。岩浆的氧逸度与温度、压力和含水量一样，是决定岩浆质量的主要参数之一。S的结晶路径，以及由此产生的矿物的组成。为了破译任何火成岩的起源，必须首先了解在给定fO2的封闭系统中岩浆作用可能引起的成分差异、相变化和结晶序列变化。氧气压计已被开发用于量化岩浆系统的fO2，利用化学或多价元素的分配行为，如矿物（例如，铁钛氧化物，辉石）或玻璃中的铁。评估Fe3+/Fe2+的最佳校准方法是湿化学和Mössbauer光谱学，这两种方法都利用大量样品来混淆小规模变化。Fe XANES允许在玻璃中原位测量Fe3+，但存在主要与成分和冷却历史引起的熔体结构变化有关的重大分析问题。因此，特定成分的校准和复杂的多变量分析技术对于玻璃中Fe3+/Fe2+的稳健微量分析是必要的。因此，本提案的目标是提供广泛的独立分析Fe3+/&amp；#931；玻璃的铁标准跨越了广泛的地质可行条件。研究人员建议在精心控制的fO2条件下进行一系列广泛的实验，并将所得产品置于多种分析技术中以量化Fe3+。这些实验的结果将为Fe XANES技术提供强大的校准，用于广泛的地质相关成分和冷却历史。

Magmas are probes of the physical conditions and chemistry of the Earth?s interior. Exploring the mineralogy of these erupted melts provides insight into the continuing geologic evolution of the planet. In addition to basic geochemistry, parameters such as temperature and pressure are important to quantify to constrain the conditions present within the Earth. Of equal importance to the above physical parameters is oxygen fugacity (fO2), a measure of the oxidative environment a magma crystallized under. Of all the elements in magmas, iron is the only major rock-forming element that commonly exists in multiple valence states. Thus, accurate knowledge of the valence state (Fe3+/Fe2+) provides the best proxy for the amount of oxygen that was present when the minerals crystallized, and allows for estimation of magmatic oxygen fugacity. The oxygen fugacity of a magma is one of the principal parameters, along with temperature, pressure, and water content, that determines a magma?s crystallization path, as well as the composition of the resulting minerals. In order to decipher the origin of any igneous rock, it is essential to first understand the compositional differences, phase changes, and crystallization sequence variations that can be caused by magmatic processes in a closed system at a given fO2. Oxybarometers have been developed to quantify the fO2 of a magmatic system using the chemistry or partitioning behavior of multivalent elements such as iron within a mineral (e.g., FeTi oxides, pyroxene) or glass. The best-calibrated methods for evaluating Fe3+/Fe2+ are wet chemistry and Mössbauer spectroscopy, both of which use utilize bulk samples that obfuscate small-scale variations. Fe XANES allows for in situ Fe3+ measurements in glass, but there are significant analytical issues primarily related to changes in melt structure arising from composition and cooling history. Therefore composition-specific calibrations and sophisticated multivariate analysis techniques are necessary for robust microanalyses of Fe3+/Fe2+ in glasses. The goal of this proposal is thus to provide a broad range of independently-analyzed Fe3+/ΣFe standards for glasses spanning a broad range of geologically-feasible conditions. The investigators propose a wide ranging series of experiments under carefully controlled fO2 conditions with the resulting products subjected to multiple analytical techniques to quantify Fe3+. The results of these experiments will provide a robust calibration of the Fe XANES technique for a wide range of geologically-relevant compositions and cooling histories.