Volatile inventory of lunar meteorites from the dominion range

Introduction: Lunar samples returned by various missions have significantly expanded our knowledge of the lunar geological history. These samples, however, are from an area that represents ~ 5 % of the lunar surface [1]. Upcoming sample return missions aim to collect material from previously unsampled regions of the Moon (e.g., Artemis and Chang’e 6). Until these samples are available, lunar meteorites potentially provide a more diverse and less biased sampling of the Moon. Lunar meteorites also provide insights into the distribution and abundance of volatile species (e.g., H, Cl), and a snapshot of the Moon’s evolution by sampling some of the oldest material (e.g., cryptomare basalts) [2]. The Ca-phosphate mineral apatite is the primary volatile bearing phase in lunar samples and is ubiquitous in all lithologies except the ferroan anorthosites (FAN) [3]. The endurance of apatite through impact processing and thermal weathering during formation of lunar breccias [4] (apatite grains being present within lithic clasts or as isolated grains in the matrix) has broadened the sample set for analysis of lunar volatiles. Lunar basaltic breccias Dominion Range (DOM) 18262 and 18666 were found in 2018 by the ANSMET program [5–6]. It has been suggested that the DOM pairing group (of which 18262 and 18666 are a part) has textural similarities to Meteorite Hills (MET) 01210 [7], one of the YAMM group of lunar meteorites — also including Yamato (Y)-793169, Asuka (A)-881757, and Miller Range (MIL) 05035 [8]. The YAMM group are thought to sample an ancient basalt flow [8–9], and to date volatile data has only been collected on one sample (MIL 05035) [10–13]. Assuming DOM 18262 and 18666 are paired with the YAMM group [14], analysis of their volatiles will provide greater context on processes taking place within and on the Moon at the time of their eruption (3.8–3.9 Ga) [8]. This can be compared to other ancient basalts (e.g., Kalahari 009) [2] to better constrain volatile evolution in the Moon’s early history. Here we report on stable isotope analysis of Cl and H in DOM 18262 and DOM 18666 and assess their pairing relationship with the YAMM group. Methods: Cl and H isotopic compositions and abundances were measured using the CAMECA NanoSIMS 50L at The Open University (OU), following modified protocols [9, 15–16]. Negative secondary ions of C, O, Cl, Cl, and CaF were acquired simultaneously on electron multipliers in imaging mode. Negative secondary ions of C, H, H, and O were collected in spot mode over Cl pits. Results: The δCl values for apatite in DOM 18262 (− 1.0 to + 26.0 ‰) and 18666 (+ 5.5 to + 19.6 ‰; Fig. 1) [17] are similar to Apollo 11 high-Ti, Apollo 12 lowTi [10–11, 18–19], and Apollo 14 high-Al basalts [20]. The lightest δCl (~ − 1 to + 1 ‰) is comparable to MIL 05035 (δCl down to − 4 ‰) [11]. Apatite in DOM 18262 and DOM 18666 display a range in Cl abundance from < 20 ppm to ~ 3.65 wt. % [17]. The δD values for apatite in DOM 18262 (~ − 830 to − 660 ‰) and 18666 (~ − 30 to + 340 ‰; Fig. 2) [17] are comparable to Apollo 15 QMDs (− 750 to – 600 ‰) [20] and low-Ti basalt apatite and melt inclusions (− 600 to + 1440 ‰) [10–12, 21–26]. Apatite in DOM 18666 have higher H2O abundances (~ 1210–3790 ppm) than in DOM 18262 (~ 250–300 ppm) [17].