TY - JOUR
T1 - Multiple reservoirs of volatiles in the Moon revealed by the isotopic composition of chlorine in lunar basalts
AU - Barnes, Jessica J.
AU - Franchi, Ian A.
AU - McCubbin, Francis M.
AU - Anand, Mahesh
N1 - Funding Information: We would like to thank NASA’s Curation and Analysis Planning Team for Extraterrestrial Materials (CAPTEM) for allocation of Apollo samples and the lunar meteorite MIL 05035 for this study. The US Antarctic meteorite samples are recovered by the Antarctic Search for Meteorites (ANSMET) program which has been funded by NSF and NASA and characterized and curated by the Department of Mineral Sciences of the Smithsonian Institution and Astromaterials Acquisition and Curation Office at NASA Johnson Space Center. Addi Bischoff is thanked for allocation of Kalahari 009 to this work. We thank Marc Norman and James Day for the editorial handling of this manuscript and for very helpful reviews. We also thank Adam Sarafian, Steve Elardo, and an anonymous reviewer for their constructive criticisms and insightful reviews that helped to improve this manuscript. This work was supported by UK Science and Technology Facilities Council (grant # ST/L000776/1 to M.A. and I.A.F.). F.M.M. acknowledges support from NASA’s Planetary Science Research Program. J.J.B. would like to thank the NASA Post-Doctoral Program for the fellowship under which the majority of the manuscript writing was completed. Romain Tartèse, Jeremy Boyce, and Rosalind Armytage are thanked for fruitful discussions. Funding Information: We would like to thank NASA's Curation and Analysis Planning Team for Extraterrestrial Materials (CAPTEM) for allocation of Apollo samples and the lunar meteorite MIL 05035 for this study. The US Antarctic meteorite samples are recovered by the Antarctic Search for Meteorites (ANSMET) program which has been funded by NSF and NASA and characterized and curated by the Department of Mineral Sciences of the Smithsonian Institution and Astromaterials Acquisition and Curation Office at NASA Johnson Space Center. Addi Bischoff is thanked for allocation of Kalahari 009 to this work. We thank Marc Norman and James Day for the editorial handling of this manuscript and for very helpful reviews. We also thank Adam Sarafian, Steve Elardo, and an anonymous reviewer for their constructive criticisms and insightful reviews that helped to improve this manuscript. This work was supported by UK Science and Technology Facilities Council (grant # ST/L000776/1 to M.A. and I.A.F.). F.M.M. acknowledges support from NASA's Planetary Science Research Program. J.J.B. would like to thank the NASA Post-Doctoral Program for the fellowship under which the majority of the manuscript writing was completed. Romain Tart?se, Jeremy Boyce, and Rosalind Armytage are thanked for fruitful discussions. Publisher Copyright: © 2019 The Authors
PY - 2019/12/1
Y1 - 2019/12/1
N2 - The isotopes of chlorine (37Cl and 35Cl) are highly fractionated in lunar samples compared to most other Solar System materials. Recently, the chlorine isotope signatures of lunar rocks have been attributed to large-scale degassing processes that occurred during the existence of a magma ocean. In this study we investigated how well a suite of lunar basalts, most of which have not previously been analyzed, conform to previous models. The Cl isotope compositions (δ37Cl (‰) = [(37Cl/35Clsample/37Cl/35ClSMOC) − 1] × 1000, where SMOC refers to standard mean ocean chloride) recorded range from ∼+7 to +14‰ (Apollo 15), +10 to +19‰ (Apollo 12), +9 to +15‰ (70017), +4 to +8‰ (MIL 05035), and +15 to +22‰ (Kalahari 009). The Cl isotopic data from the present study support the mixing trends previously reported by Boyce et al. (2015) and Barnes et al. (2016), as the Cl isotopic composition of apatites are positively correlated with bulk-rock incompatible trace element abundances in the low-Ti basalts, inclusive of low-Ti and KREEP basalts. This trend has been interpreted as evidence that incompatible trace elements, including Cl, were concentrated in the urKREEP residual liquid of the lunar magma ocean, rather than the mantle cumulates, and that urKREEP Cl had a highly fractionated isotopic composition. The source regions for the basalts were thus created by variable mixing between the mantle (Cl-poor and relatively unfractionated) and urKREEP. The high-Ti basalts show much more variability in measured Cl isotope ratios and scatter around the trend formed by the low-Ti basalts. Most of the data for lunar meteorites also fits the mixing of volatiles in their sources, but Kalahari 009, which is highly depleted in incompatible trace elements, contains apatites with heavily fractionated Cl isotopic compositions. Given that Kalahari 009 is one of the oldest lunar basalts and ought to have been derived from very early-formed mantle cumulates, a heavy Cl isotopic signature is likely not related to its mantle source, but more likely to magmatic or secondary alteration processes, perhaps via impact-driven vapor metasomatism of the lunar crust.
AB - The isotopes of chlorine (37Cl and 35Cl) are highly fractionated in lunar samples compared to most other Solar System materials. Recently, the chlorine isotope signatures of lunar rocks have been attributed to large-scale degassing processes that occurred during the existence of a magma ocean. In this study we investigated how well a suite of lunar basalts, most of which have not previously been analyzed, conform to previous models. The Cl isotope compositions (δ37Cl (‰) = [(37Cl/35Clsample/37Cl/35ClSMOC) − 1] × 1000, where SMOC refers to standard mean ocean chloride) recorded range from ∼+7 to +14‰ (Apollo 15), +10 to +19‰ (Apollo 12), +9 to +15‰ (70017), +4 to +8‰ (MIL 05035), and +15 to +22‰ (Kalahari 009). The Cl isotopic data from the present study support the mixing trends previously reported by Boyce et al. (2015) and Barnes et al. (2016), as the Cl isotopic composition of apatites are positively correlated with bulk-rock incompatible trace element abundances in the low-Ti basalts, inclusive of low-Ti and KREEP basalts. This trend has been interpreted as evidence that incompatible trace elements, including Cl, were concentrated in the urKREEP residual liquid of the lunar magma ocean, rather than the mantle cumulates, and that urKREEP Cl had a highly fractionated isotopic composition. The source regions for the basalts were thus created by variable mixing between the mantle (Cl-poor and relatively unfractionated) and urKREEP. The high-Ti basalts show much more variability in measured Cl isotope ratios and scatter around the trend formed by the low-Ti basalts. Most of the data for lunar meteorites also fits the mixing of volatiles in their sources, but Kalahari 009, which is highly depleted in incompatible trace elements, contains apatites with heavily fractionated Cl isotopic compositions. Given that Kalahari 009 is one of the oldest lunar basalts and ought to have been derived from very early-formed mantle cumulates, a heavy Cl isotopic signature is likely not related to its mantle source, but more likely to magmatic or secondary alteration processes, perhaps via impact-driven vapor metasomatism of the lunar crust.
KW - Apatite
KW - Apollo samples
KW - Isotope fractionation
KW - Lunar meteorites
KW - NanoSIMS
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U2 - 10.1016/j.gca.2018.12.032
DO - 10.1016/j.gca.2018.12.032
M3 - Article
SN - 0016-7037
VL - 266
SP - 144
EP - 162
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
ER -