Zoom Link for Colloquium 04/05/2022 3:00pm PST.
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Presented By: Ardith Bravenec
Abstract:
The original budget and speciation of major volatiles, such as hydrogen (H) and carbon (C), in the silicate material and atmospheres of rocky bodies was determined during their formation and early evolution. Nearly all the large rocky bodies in the Solar System are thought to have experienced at least one magma ocean phase as an outcome of formation processes. Highly reducing conditions well below the iron-wüstite buffer (IW) characterized by low oxygen fugacity (fO2) are expected to be prevalent during the differentiation stages of rocky bodies. In such highly reducing conditions, the effect of volatile speciation on the mineral/melt partitioning and on H solubility in olivine and pyroxene is largely unknown. After three decades of interest, the influence of pressure, temperature, and composition is fairly well constrained for the storage capacity and solubility of H in olivine. However, considerably less work has been conducted on the effect of fO2 on H solubility in olivine and pyroxene, especially at very low fO2, and the few available reports on this topic show substantial inconsistency.
My results include SIMS and Raman data to determine the H content and speciation of C-O-H volatiles in olivine, pyroxene, and silicate glasses from experiments at high pressure and temperature under various redox conditions. Results demonstrate the systematic variance of C-O-H speciation, solubility, and partitioning as a function of fO2. Using the results, a new solubility model is applied to Martian meteorites, such as the nakhlites, which may contain low water contents. Finally, semi-empirical models derived from thermodynamics and melt structure are discussed. The diminished H contents of these minerals under reducing conditions indicates that future work concerning magma ocean crystallization or the reducing deep mantle of the Earth must consider the effects of low fO2, high fH2, and the existence of appreciable amounts of C.