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

The new age of sample return missions affords opportunities to intercalibrate observational and laboratory results. This session invites studies using observational tools, return mission data and materials, and meteorites to advance our knowledge of asteroids.

Monday, 20 October 2025
8:00 AM - 12:00 PM
HBGCC, 214A

The Hydrogen Isotopic Composition of the Ureilite Parent Body

Paper number: 83-11
Program: Technical Sessions
Time: 10:50 AM – 11:10 AM

Authors

Abstract

Introduction: Evidence for silica-rich melts on the ureilite parent body (UPB) has been preserved and recorded in rare fragments of the Almahata Sitta meteorite suite, which originated from the asteroid 2008 TC3 (Bischoff et al., 2014). These unique trachyandesite fragments demonstrated that ancient crust-forming volcanism on small planetary bodies was not simply restricted to mafic lithologies. The evaluation of the water content of these fragments by Peterson et al. (2023) allowed for early reconstructions of the bulk water content of the UPB. Here, we report on two recent Northwest Africa (NWA) finds, NWA 15820 and NWA 16789, that expand the known quantity of silica-rich material from the UPB by a factor of two, allowing for a more representative investigation into the chemical and isotopic variations among these unique lithologies.

Methods: In this study, we undertook established techniques to evaluate their mineralogy and chemistry through SEM and EPMA, their Pb-Pb ages through SIMS, cosmic ray exposure histories by mass spectrometry and the water content and isotopic composition of nominally anhydrous silicates, phosphates and glass using NanoSIMS.

Results and Discussion: The bulk UPB water content, estimated based on the water content of the silicates, results in a revised estimate of 13 – 46 μg/g H2O, marginally higher than previous estimates. Furthermore, we report the hydrogen isotopic composition of water in the UPB. While the D/H ratio of late-stage phosphates and glass is highly fractionated as a result of magmatic degassing, the nominally anhydrous silicate, pyroxene, better records the original hydrogen isotopic composition (δD) of the UPB. In particular, the pyroxene within NWA 16789 records a value of 83 ± 79 ‰. We infer this isotopic value as the best estimate for the original isotopic composition of the UPB and may be attributed to the restricted protoplanetary disk reservoir in which it accreted.

References:

Bischoff, A., Horstmann, M., Barrat, J-A., Chaussidon, M., Pack, A., Herwartz, D., Ward, D., Vollmer, C., Decker, S. 2014. Trachyandesitic volcanism in the early Solar System. Proceedings of the National Academy of Sciences 111, 12689-12692. https://doi.org/10.1073/pnas.1404799111

Peterson, L. D., Newcombe, M. E., Alexander, C. M., Wang, J., Sarafian, A. R., Bischoff, A., Nielsen, S. G. 2023. The H2O content of the ureilite parent body. Geochimica et Cosmochimica Acta. 340, 141-157. https://doi.org/10.1016/j.gca.2022.10.036

 

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

doi: 10.1130/abs/2025AM-412560

© Copyright 2025 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.