Isotopic evidence for chondritic Lu/Hf and Sm/Nd of the Moon

Rb-Sr, Sm-Nd and Lu-Hf isotope systematics of the lunar Mg-suite: the age of the lunar crust and its relation to the time of Moon formation

“…The slope of the best fit line through all the data shown in figure 7 is 0.00198 ± 0.00037, which corresponds to an age of 4416 (68 Ma half-life) to 4352 Ma (103 Ma half-life). The initial 142 Nd/ 144 Nd indicated by this 'planetary isochron' is 9 ppm lower than the accessible Earth would have at this time, within uncertainty of the 7 ppm deficit suggested by Sprung et al [35]. The statistical uncertainty on the line corresponds to an error in the age on the order of 20-30 Ma.…”

“…The slope of this line corresponds to an age of 4347 ± 29 Ma with initial εHf = −0.5 ± 0.5. This age has chronological significance only if the three rocks that define the line formed at the same time, from the same source, but we note the close correspondence of this age with the Sm-Nd and Lu-Hf model ages for KREEP [34,35,64]. Nd from the average chondrite reference [45]) and μ 142 Nd (ppm difference between the initial 142 Nd/ 144 Nd and the value the terrestrial standard would have at the formation age of the sample when age corrected on the assumption of a chondritic Sm/Nd ratio).…”

“…For 78238 and 76355, concentration calculations were done iteratively first using terrestrial standard Hf, then a Hf isotopic composition adjusted for the 180 Hf/ 177 Hf calculated from the spike corrected value found in the first iterative step. In this second step, the deviation of the sample's ε 178 Hf from the standard was assumed to equal 0.607 times that of the ε 180 Hf based on fitting the lunar basalt data from Sprung et al [35]. Using the same dataset, the neutron correction to ε 176 Hf = 1.64 * ε 180 Hf and is therefore −0.82 for 76335 and −2.0 for 78238.…”

“…Many Mg-suite samples show evidence of shock metamorphism including formation of maskelynite and the presence of impact melt glass. Finally, exposure of the lunar surface to cosmic ray irradiation produces secondary neutrons that can substantially influence the isotopic composition of samples that have long exposure histories, with important consequences for 146 Sm- 142 Nd and Lu-Hf results [31][32][33][34][35]. (8) 67075 (7) 60025 (6) 67215 (4) Y86032 (5) 60025 (3) 62236 (1) 60016, 3A (2) (a) (9) 73255 (10) 15445,247 (11) 76535 (12) 76355 (13) 76535 (14) 77215 (15) 77215 (16) 78238 (17) 78236 (10) 78236 (18) 15445, 17 (11) FAN range [12]; 2-Marks et al [13]; 3-Borg et al [14]; 4-Norman et al [15]; 5-Nyquist et al [16]; 6-Carlson & Lugmair [17]; 7-Nyquist et al [18]; 8-Alibert et al [19]; 9-Carlson & Lugmair [20]; 10-Carlson & Lugmair [21]; 11-Shih et al [22]; 12-Lugmair et al [23]; 13-Edmunson et al [24]; 14-Borg et al [25]; 15-this study; 16-Nakamura et al [26]; 17-Edmunson et al [27] and 18-Nyquist et al [28].…”

Major element composition of an Early Enriched Reservoir: constraints from 142Nd/144Nd isotope systematics in the early Earth and high-pressure melting experiments of a primitive peridotite

“…However, the isotope ratios of lunar and Martian rocks observed on the surface of these bodies need to be corrected for the effect of exposure to cosmic rays, which is not straightforward. As such, it has even been argued that the lunar and Martian rocks have chondritic Sm/Nd ratios (Sprung et al 2013). At present, the bulk compositions of the Moon and Mars remain imprecisely determined.…”