2024-04-222024-04-2220232023-10-01Barrett et al. (2023). Deciphering the origin(s) of H and Cl in Apollo 15 quartz monzodiorites: Evidence for multiple processes and reservoirs, Geochimica et Cosmochimica Acta, 358, pp192-206. (https://doi.org/10.1016/j.gca.2023.08.004)1872-9533https://hdl.handle.net/10125/108046Supp_Mat_for Barrett_et_al_2023_GCA-1 - Data file in pdf Supp_Mat_for Barrett_et_al_2023_GCA-2 - Data file in EXCEL TJ_Barrett_Quartz_Monzodiorite_paper_Scholarspace - preprint article in pdfAbstract Apollo 15 quartz monzodiorites (QMDs) are reported to contain some of the most deuterium-depleted apatite found in lunar samples. In this study, apatite from six Apollo 15 QMDs, including three samples from 15405 not previously investigated, were analyzed for their H and Cl isotopes. Apatite in 15405 are extremely 2H (or D)-poor, with δD values ranging from −658 ± 53 to −378 ± 113‰, comparable to apatite data from related samples 15403 and 15404. In addition to new H isotope data, the first Cl-isotope data for lunar QMDs are presented. Apatite in 15405 and related samples are enriched in 37Cl with respect to Earth, with measured δ37Cl values ranging from +13 to +37‰. These values are within the reported δ37Cl range for KREEP-rich samples. The fact that the Cl isotopic composition of apatite in QMDs are similar to those in other lunar lithologies, but the H isotopic data are distinct and unique, provides possible further evidence for the existence of a D-poor reservoir in the lunar interior. Raman spectroscopy of the silica polymorph in sample 15405 reveals it to be a mixture of quartz and cristobalite. Based on available experimental data on the stability of various silica phases over a range of pressure and temperature regime, a deep-seated origin in the crust for QMDs may be possible which would support an endogenous origin of the H-Cl isotope systematics of the QMDs. The role of impact-induced transformation of silica phases and its contributing towards low D/H ratio in apatite, however, cannot be ruled out.Article15 pageshttp://rightsstatements.org/vocab/InC/1.0/Moon rocksApollo 15 quartz monzodiorites