V013-0009
Mapping Hydrogen Variations in Silicate Glasses: Record of Lunar Eruptive Degassing

Wednesday, 9 December 2020
Poster
Erin Recchuiti, University of Tennessee, Knoxville, TN, United States, Molly C McCanta, University of Tennessee, Earth and Planetary Sciences, Knoxville, TN, United States, Melinda Darby Dyar, Mount Holyoke College, South Hadley, MA, United States, Elizabeth Sklute, Mount Holyoke College, Astronomy, South Hadley, MA, United States and Antonio Lanzirotti, Center for Advanced Radiation Sources, University of Chicago, Chicago, IL, United States
Abstract:
Explosive volcanism has been recognized on the Moon in the presence of picritic glass beads returned from all landing sites during the Apollo program [1]. Identification of measurable H2O concentrations in these lunar glass beads suggest the melts were degassed during ascent and eruption on the lunar surface [i.e., 2]. The precise amount of diffusive H2O loss is significant as degassed glasses are the only samples of endogenous lunar H2O that are available. The oxidation state (fO2) of a melt may provide additional insight into H2O concentration, as H and fO2 are often correlated [e.g., 3]. For example, as water is diffusively lost (primarily as H2 or OH) during magmatic degassing, the remaining system becomes more oxidizing. Therefore, analyzing the H2O and fO2 of volcanic glasses in situ in the same sample may provide important information regarding volatile degassing processes.

A MORB pillow basalt glass sourced from the East Pacific Rise was previously analyzed for variations in its redox chemistry using in situ core to rim traverses collected via X-ray absorption spectroscopy (XAS) at the GSECARS X-ray Microprobe (13-ID-E) at the Advanced Photon Source at Argonne National Lab [4]. Oxidation increasing rimward was observed in this glass. For this study, core to rim glass H concentrations in the same MORB sample were mapped in situ using reflectance FTIR at UMass on a Bruker Vertex 70 with a Hyperion 3000 microscope and an MCT focal plane array detector to determine whether H2O loss may have driven the observed oxidation.

Terrestrial analogues, such as the MORB glass studied, provide insight into the correlation between H2O and fO2 that can be applied to constrain lunar glass H2O content. The main goal of ANGSA-funded SCARAB (Spectroscopy Consortium Addressing Redox Acquired by Beads) is to apply these same techniques to lunar glasses to constrain the diffusive loss of H2O during eruption and therefore, the initial H2O content of the lunar interior. The combination of redox and volatile mapping provides insight into the degassing processes undergone during eruptive transport.

[1] Heiken et al. (1991) Lunar Sourcebook, Cambridge Univ. Press. [2] Saal et al. (2008) Nature 454, 192-196. [3] Hauri et al. (2011) Science 333, 213-215. [4] Lanzirotti et al (2018) Am Min 103.

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