Understanding the Volatile Evolution of Arc Magmas: Alkalies and Mixed (H2O + CO2) Volatile Solubility in Basalts and Basaltic Andesites

智力上的优点。这一建议旨在提高对混合(H2O+CO2)岩浆挥发分在广泛成分范围内的镁铁质、弧型熔岩中的溶解度关系的理解。最近的工作表明，在镁铁质弧熔岩中发现的成分变化可以导致溶解行为的重大变化，这在目前的模型中解释得很少。缺乏对这种基本化学行为的约束，严重阻碍了对电弧环境中涉及挥发物的观测工作的解释，特别是对熔体夹杂物测量的解释。这直接影响到我们理解基本过程的能力，如岩浆挥发分含量对岩浆化学和喷发/脱气动力学的影响，或弧形火山过程在全球H2O和CO2预算中的作用。拟议的工作将通过在与喷发前岩浆条件相关的压力和温度下，用各种H_2O_2流体实验饱和具有战略选择的成分的镁铁质熔体来满足这一重要需求。实验将在活塞筒装置中进行，使用新技术准确地实现次火山压力(200-500兆帕)，同时保持该装置的快速淬火优势。100兆帕的支持实验也将在快速淬火内热压力容器中进行。在每个实验中，将通过真空压力计精确测量流体相的H2O/CO2比，并使用高温压力计、FTIR光谱以及SIMS测量熔体中溶解的H2O和CO2。由此收集的数据将被用来开发一个经验模型，以准确计算一系列玄武岩成分的混合挥发分饱和度。了解镁铁质弧岩浆中挥发分的行为和演化是解释俯冲带岩浆作用的岩石学和火山学观察的关键部分。只有结合测量喷发前岩浆的挥发分含量和精确估计给定岩浆成分的挥发分溶解行为，才能实现这一理解。这项拟议的工作代表着朝着产生关键实验数据迈出的重要一步，这些数据需要用来解释目前由其他工作人员在广泛的镁铁质、弧形岩浆成分范围内测量的混合挥发分含量。这项工作所在的实验岩石学实验室在培训毕业生和本科生以及许多国际合作者和独立研究人员方面取得了非常成功的高压-高温技术。这项具体的建议包括支持两名女本科生，并将有助于实验室继续开发新的实验方法和应用于实验岩石学。我们还预计，将有大量测压分析玻璃用于二次挥发分测量技术的比较，如SIMS和FTIR。

Intellectual merit. This proposal aims to improve understanding of the solubility relationships of mixed (H2O + CO2) magmatic volatiles in mafic, arc-related lavas over a broad composition range. Recent work has shown that the compositional variability found in mafic arc lavas can lead to significant changes in solubility behavior that are poorly accounted for in current models. The lack of constraints on such fundamental chemical behavior severely hampers the interpretations of observational work involving volatiles in arc settings, particularly that of melt inclusion measurements. This directly affects our ability to understand critically fundamental processes such as the influence of magmatic volatile contents on magma chemistry and eruption/degassing dynamics, or the role of arc volcanic processes in global H2O and CO2 budgets.The proposed work will address this important need via experimentally saturating mafic melts of strategically chosen compositions with various H2OCO2 fluids at pressures and temperatures relevant to pre-eruptive magmatic conditions. The experiments will be conducted in a piston cylinder apparatus using new techniques that accurately achieve sub-volcanic pressures (200-500 MPa), while maintaining the rapid-quench advantage of the device. Supporting experiments at 100 MPa will also be conducted in a rapid-quench internally heated pressure vessel. In each experiment, the H2O/CO2 ratio of the fluid phase will be precisely measured by vacuum manometry, and the dissolved H2O andCO2 in the melt measured using high temperature manometry, FTIR spectroscopy, as well as SIMS. The data thereby gathered will be used to develop an empirical model to accurately calculate mixed volatile saturation over a range of basaltic compositions.Understanding the behavior and evolution of volatiles in mafic arc magmas is a key part of interpreting petrologic and volcanologic observations of subduction-zone magmatism. This understanding can only achieved by combined measurements of pre-eruptive magmatic volatile content and precise estimates of the volatile solubility behavior of a given magma composition. The proposed work represents a significant step towards generating critical experimental data needed to interpret the mixed volatile contents currently being measured by other workers over a broad compositional range of mafic, arc-related magmas.Broader impacts. The experimental petrology laboratory where this work will be conducted has been very successful in training graduates and undergraduates, as well as many international collaborators and independent researchers, in high pressure-temperature techniques. This specific proposal includes support for two female undergraduates, and will help the lab to continue to develop novel experimental approaches and applications to experimental petrology. We also anticipate the large number of manometrically analyzed glasses that will result to be useful for comparison of secondary volatile measurement techniques such as SIMS and FTIR.