Figures
Fig. 1 Photomicrographs of two basalts. Photomicrographs of two basalts analyzed in this study, with yellow crosses marking the locations of analyses. (A) Subhedral apatite grains (outlined in yellow for clarity) forming a cluster in Apollo 12039,42. (B) Euhedral to subhedral apatite grains in Apollo 12040,211 that show skeletal growth with hollow centers.
Fig. 2 Plots of Cl and H2O versus δ37Cl. (A and B) Plots of Cl (A) and H2O (B) concentrations versus δ37Cl values in apatite from the Moon. Each data point represents a single apatite grain in a rock, including data from the literature plotted as smaller symbols (11, 12, 33); magenta symbols are high-Ti basalts; blue symbols are low-Ti basalts; gray symbols are KREEP basalts. There are no statistically significant correlations observed for any of the sample types studied here. Elevated δ37Cl values are associated with both high H2O and high Cl concentrations: The former is inconsistent with the idea that elevated δ37Cl values are only associated with anhydrous conditions, and the latter is inconsistent with a simple, single-stage fractionation model.
Fig. 3 δD versus H2O. δD versus H2O for new data (large symbols) and data from the literature (small symbols). Hollow symbols are multiple hydrogen abundance measurements plotted with bulk δD values. Data have been previously interpreted as representing mixing between a high-δD, high-H2O end member (possibly comets), and a low-δD, low-H2O end member (possibly solar wind), or evolution from or contamination with a material of chondritic composition (16, 24, 25, 33), though neither explanation explains all the data. Note the large number of analyses with δD values in the range for bulk chondrites (+750 to −200‰) (58).
Fig. 4 Plot of δD versus δ37Cl. Plot of δD versus δ37Cl for data generated in this study and those from previous studies (plotted as smaller symbols). Hollow symbols indicate in situ δ37Cl measurements plotted versus bulk or mean apatite δD from the literature. The presence of high δ37Cl apatite with low δD values is inconsistent with the prediction that elevated δ37Cl would accompany elevated δD, because both isotopes should shift toward higher δ values during degassing. The lack of correlation between δD and δ37Cl suggests that the two isotope systems are at least partially decoupled and that multiple processes may be at work.
Fig. 5 Bulk Th and La/Lu versus δ37Cl. (A and B) Measures of KREEP contribution, bulk rock Th abundance (A), and bulk rock La/Lu (B), as a function of δ37Cl, with trace element data from (43, 54, 59). Symbols are the same as those in previous figures. For all basalts, δ37Cl is strongly correlated with Th and La/Lu, suggesting that pure urKREEP would have δ37Cl ≥+30‰.
Tables
- Table 1 New data generated for this study.
Sample Section Grain H2O (ppm) H2O 2σ Cl (ppm) Cl 2σ δ37Cl δ37Cl 2σ δD δD 2σ Category 10044 12 10 1105 29 365 104 +9 3 +933 31 High Ti basalt 10044 12 1a 728 27 292 11 +6 3 +954 27 High Ti basalt 10044 12 1b — — — — +6 4 — — High Ti basalt 10044 12 1c 1220 30 300 11 +2 4 +781 23 High Ti basalt 10044 644 2 877 26 250 10 +11 3 +536 57 High Ti basalt 10044 644 8 421 22 3976 122 +15 3 — — High Ti basalt 10044 644 4a 826 25 219 10 +12 3 +606 33 High Ti basalt 10044 644 4b 1155 29 479 16 +12 3 +702 28 High Ti basalt 75055 55 1 604 23 398 14 +8 3 +621 35 High Ti basalt 75055 55 2 1225 35 485 16 +6 3 +794 26 High Ti basalt 75055 55 3 1241 30 334 12 +14 3 +968 27 High Ti basalt 75055 55 4 1430 34 410 14 +6 3 +794 26 High Ti basalt 75055 55 101 — — — — +5 3 — — High Ti basalt 12039 42 4 1996 43 928 29 +18 3 +720 30 Low Ti basalt 12039 42 6 2379 47 477 16 +17 3 +830 31 Low Ti basalt 12039 42 10 — — — — +16 3 — — Low Ti basalt 12039 42 11 — — — — +17 3 — — Low Ti basalt 12039 42 17a 2784 95 1157 36 +17 3 +729 28 Low Ti basalt 12039 42 17b 2916 57 665 21 +16 3 +698 28 Low Ti basalt 12040 211 1 105 21 15884 489 +17 3 +9 163 Low Ti basalt 12040 211 4 3 20 2689 83 +13 3 +14 84 Low Ti basalt 12040 211 5 16 20 3388 104 +14 4 −150 26 Low Ti basalt MIL 05035 — 1 — — — — −4 2 — — Low Ti basalt
