83-9 The Volatile History of Evolved Achondrite DOM 10100 from NanoSIMS Analyses and Petrographic Studies

Session: Asteroid Observations, Return Missions, and Meteoritics: Interweaving Perspectives and Data

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The abundance of volatiles in extraterrestrial samples of ancient planetary crusts has important implications for planetary formation and evolution in the early Solar System. Important insights have been made by examining hydrous minerals, but they are not always present and likely represent a late-stage record. Subsequently, several studies have estimated volatile abundances by analyzing H in nominally anhydrous minerals (NAMS) via SIMS in ancient crustal materials. In this study, we expand on previous work that focused on the volatile content of achondrite DOM 10100; a howardite (basaltic, Vestan derived lithology) containing a clast with an evolved, dacitic composition. We collected analyses of H in tridymite, clinopyroxene, and plagioclase phases that comprise the majority of the dacitic clast, as well as H measurements for anhydrous silicate phases within the host howardite, to 1) determine whether there is a genetic link between the host and clast and 2) whether there was partial equilibration of volatiles in the clast due to additional impact/melt heating the dacitic clast post-crystallization. We also conducted detailed petrographic observations to better understand the temporal relationships between the crystallization of NAMS phases and apatite, and subsequently reconstruct the volatile loss history of the dacite.

Initial results suggest that the dacitic clast and howardite share a common origin, as evidenced from the similarities in major element geochemistry for the NAMS phases. Furthermore, NanoSIMS measurements contain similarly low H₂O abundances for NAMS phases outside of the clast. Apatites are OH poor and F rich, indicating they formed from a melt relatively rich in halogens or one that had already experienced degassing (McCubbin et al., (2021). While it is difficult to differentiate between these two scenarios, magmatic textures in apatite and the presence of merrillite imply late-stage crystallization from a dacitic melt. Previous NAMS measurements and model estimates imply that the magnitude of H₂O loss ranges from < 100 ppm to > 4500 ppm (Gorce et al., 2024), and established H2O/F values suggest that a dacitic melt could have had a maximum of 230 ppm F before cooling and crystallization occurred. In contrast, initial measurements of F in plagioclase via NanoSIMS indicate low concentrations of F in the melt. Future trace element work will be used to explore how to differentiate between petrogenetic hypotheses. 

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7343

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