From a report submitted by Stephanie Halwa, University of Manchester.
We used the Meteoritical Society research grant funds to support 3 days of secondary ion mass spectrometry (SIMS – shown in Fig. 1) analyses of Apollo 16 highland-derived impact glass beads and agglutinates at CRPG CNRS–Université de Lorraine, Nancy, France. These samples were hand-picked out of regolith sub-samples from the Apollo 16 double drive tube 60014/60013 and were also within a thin section of the regolith (60013,6049 – shown in Fig. 2), in order to represent a depth profile through the lunar regolith column (up to 60 cm depth).
There is currently no published dataset on nitrogen abundances in lunar impact glass beads, so the work provides the first in situ constraints on nitrogen concentrations and isotopic compositions in these volatile-hosting grains. We analysed 2–3 impact glass beads from five different core depths and eight beads and agglutinates within the thin section, where most samples had generally low (<50 ppm) nitrogen abundances, but a few exceeded 50 ppm, which allowed for robust nitrogen isotope measurements (nitrogen abundance of at least ~50 ppm is required for reliable N isotope analyses; see Deligny et al., 2021, 2023). The corresponding d15N values range from about −6 to +180 ‰ and are progressively heavier with increasing nitrogen abundance, suggesting addition of an isotopically heavy, non-solar volatile component to the regolith, delivered by X such as micrometeorites, interplanetary dust particles, or blown-off Earth atmosphere (Earth-wind).
During the same analyses we were able to derive corresponding water abundances, where, in general, the grain’s water contents increase with its nitrogen abundance. This indicates potentially related implantation processes and/or volatile sources, and we will compare these results to NanoSIMS-derived water contents and hydrogen isotopic compositions measured before and after the SIMS analysis. Overall, our findings highlight that the Apollo 16 impact glass beads and agglutinates form a significant volatile component in the regolith, and a potential in situ lunar volatile resource. This work has formed the basis of a thesis chapter and a planned journal manuscript following PhD completion.
The Meteoritical Society research grant directly subsidised laboratory costs for SIMS beam time and analyses at CRPG, which were essential to acquiring this unique nitrogen and water abundance dataset.