^1,2Sen Hu et al. (>10)
Geochimica et Cosmochimica Acta (in Press)
Open Access Link to Article [DOI: 10.1016/j.gca.2026.10.007]
¹Key Laboratory of Planetary Science and Frontier Technology, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
²University of Chinese Academy of Sciences, Beijing 100190, China

Copyright Elsevier

Chlorine (Cl) serves as a crucial volatile element, providing insight into the magmatic processes and volatile inventory of the Moon. The lunar rocks have notably elevated Cl isotopic compositions; however, no information is available about the Cl and its isotopes on the farside. Here, we report a petrographic, chemical, and Cl isotopic study of apatite in the Chang’e-6 (CE6) mare basalt collected from the South Pole–Aitken (SPA) basin. CE6 mare apatite was measured to have a Cl abundance of 0.04–3.36 wt%. We estimated a Cl abundance of ∼0.6 μg g⁻¹ for the CE6 mantle source, slightly higher than that (0.26–0.32 μg g⁻¹) estimated from Apollo low-titanium mare basalts and lower than that (∼1.3 μg g⁻¹) of Chang’e-5 low-titanium mare basalt. Cl abundances in the mantle source of low-titanium mare basalts exhibit a positive correlation towards the crystallization ages, highlighting a heterogeneous distribution of chlorine in the lunar mantle. The measured chlorine isotopic compositions (δ³⁷Cl, 14.5 ± 2.0‰ to 27.2 ± 2.2‰) are mostly higher than that of nearside mare basalts (0–20‰). CE6 mare apatite shows a positive correlation between Cl abundances and Cl isotopic compositions, comparable with the trend defined by the low-titanium mare apatite collected from the nearside hemisphere. We infer that the high δ³⁷Cl values of CE6 mare apatite were associated with magmatic fractionation of Cl coupled with an elevated chlorine isotopes in the mantle source, favoring the model that the massive formation impact event of SPA would have imprinted the chlorine isotopic compositions in the underlying mantle rocks.

¹Daniel R. Crocker, ²Conel M. O’D. Alexander, ³Mark H. Thiemens, ¹David T. Johnston
Proceedings of the National Academy of Sciences, 123, e2605307123
Link to Article [DOI: 10.1073/pnas.2605307123]
¹Department of Earth and Planetary Science, Harvard University, Cambridge, MA 02138
²Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC 20015
³Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093

Unraveling the complex formation and alteration history for extraterrestrial organic matter is key to understanding the chemical evolution of the solar system (SS) and potentially even life’s emergence on Earth. In this study, we performed high-precision triple oxygen isotope measurements on insoluble organic matter (IOM) sourced from a diverse suite of carbonaceous chondrites (CCs). Remarkably, the IOM from primitive Type 1 and 2 CCs—including CI, CM, CR, Bells, and Tarda—have oxygen isotope compositions that cluster on or near the CCAM line, which is itself related to the mixing of primitive oxygen isotope reservoirs residing within the early SS. This finding suggests that primitive meteoritic OM acquired oxygen of primitive origin and that those isotopic signatures have been minimally altered by parent body processes, offering critical constraints to assess the synthetic origin of meteoritic OM and evolution of SS oxygen reservoirs.