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 and CO2 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.