Work

The hydrogen isotopic composition and content of the ureilite parent body: constraints from new ungrouped achondrites

Year: 2026

Type: article

Abstract: Evidence for SiO 2 -rich melts on the ureilite parent body (UPB) stems from feldspathic clasts within polymict ureilites and has been additionally preserved and recorded in rare fragments of the Almahata Sitta meteorite suite, which originated from the asteroid 2008 TC 3 . These unique fragments demonstrated that ancient crust-forming volcanism on small planetary bodies was not simply restricted to basaltic lithologies. Two recent Northwest Africa finds (NWA) 15,820 and NWA 16789 expand the known quantity of SiO 2 -rich material from the UPB, allowing for a more representative investigation into the chemical and isotopic variations among these unique lithologies. Here, we measured the H abundance and isotopic composition (δD) of NWA 15820 and NWA 16789 to evaluate the bulk UPB water content, resulting in a revised minimum bulk water content of 13 µg/g H 2 O. Furthermore, we report the δD 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, nominally anhydrous silicate pyroxene better records the original δD of the UPB. In particular, the pyroxene within NWA 16789 records a δD value of 83 ± 79‰, which we infer is the best estimate for the original δD of water in the UPB.

Source: Geochimica et Cosmochimica Acta

DOI: 10.1016/j.gca.2026.07.047