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.
