Calcium isotopic composition of the lunar crust, mantle, and bulk silicate Moon: A preliminary study. (1st February 2020)

• Record Type: Journal Article
• Authors: Wu, Wei; Xu, Yi-Gang; Zhang, Zhao-Feng; Li, Xin
• Is Part Of: Geochimica et cosmochimica acta. Volume 270(2020)
• Page Start: 313
• Page End: 324
• Publication Date: 2020-02-01
• Subjects: Ca isotopes -- Bulk silicate Moon -- Lunar crust and mantle -- KREEP-rich material -- Lunar meteorites; Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2019.12.001
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: Calcium isotopes have the potential to explore genetic links between the Moon and Earth. Here, we constrain calcium isotopic composition of the bulk silicate Moon (BSM), using petrological, geochemical and calcium isotopic data obtained from five lunar meteorites (two basalts and three feldspathic breccia rocks), and on four anorthite crystals from two feldspathic breccia meteorites. The δ 44/40 Ca of lunar feldspathic breccias are 0.76 ± 0.06‰ (2SD, n = 3), 0.78 ± 0.10‰ (2SD, n = 6) and 0.82 ± 0.02‰ (2SD, n = 3), respectively, consistent with previously determined calcium isotopic composition of feldspathic breccias. Four anorthite crystals yield a mean δ 44/40 Ca value of 0.75 ± 0.13‰ (2SD, n = 4), inferred to represent the δ 44/40 Ca value of the lunar crust. The δ 44/40 Ca values of the two lunar basalts are 0.90 ± 0.07‰ (2SD, n = 3) and 0.96 ± 0.11‰ (2SD, n = 4), respectively, slightly heavier than the feldspathic breccias and anorthites. The δ 44/40 Ca of the studied lunar basalts and literature data show negative correlations with CaO, Al2 O3, and anorthite mode, pointing to the effect of contamination by lunar crust rocks. Using the heaviest δ 44/40 Ca found in the least contaminated lunar basalts and a 0.10–0.20‰ fractionation of calcium isotopes during partial melting, we estimate the δ 44/40 Ca value of the lunar mantle to be 0.96–1.11‰. The δ 44/40 Ca values of the BSM is estimated to be 0.89–0.95‰, using a two-end member mixing model. The Ca isotopic composition of the BSM is within error to that of the bulk silicate Earth (0.94 ± 0.05‰), providing insights into the information of the comparison of the Earth-Moon system and the planets of inner Solar System.