title: The chlorine isotope fingerprint of the lunar magma ocean.
abstract: The Moon contains chlorine that is isotopically unlike that of any other body yet studied in the Solar System, an observation that has been interpreted to support traditional models of the formation of a nominally hydrogen-free ("dry") Moon. We have analyzed abundances and isotopic compositions of Cl and H in lunar mare basalts, and find little evidence that anhydrous lava outgassing was important in generating chlorine isotope anomalies, because (37)Cl/(35)Cl ratios are not related to Cl abundance, H abundance, or D/H ratios in a manner consistent with the lava-outgassing hypothesis. Instead, (37)Cl/(35)Cl correlates positively with Cl abundance in apatite, as well as with whole-rock Th abundances and La/Lu ratios, suggesting that the high (37)Cl/(35)Cl in lunar basalts is inherited from urKREEP, the last dregs of the lunar magma ocean. These new data suggest that the high chlorine isotope ratios of lunar basalts result not from the degassing of their lavas but from degassing of the lunar magma ocean early in the Moon's history. Chlorine isotope variability is therefore an indicator of planetary magma ocean degassing, an important stage in the formation of terrestrial planets.
authors.affiliation: Division of Geological and Planetary Sciences, Caltech, 1200 East California Boulevard, Pasadena, CA 91125, USA. ; Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095-1567, USA.
authors.forename: Jeremy W
authors.initials: JW
authors.lastname: Boyce
authors.affiliation: Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, TX 77058, USA.
authors.forename: Allan H
authors.initials: AH
authors.lastname: Treiman
authors.affiliation: Division of Geological and Planetary Sciences, Caltech, 1200 East California Boulevard, Pasadena, CA 91125, USA.
authors.forename: Yunbin
authors.initials: Y
authors.lastname: Guan
authors.affiliation: Division of Geological and Planetary Sciences, Caltech, 1200 East California Boulevard, Pasadena, CA 91125, USA.
authors.forename: Chi
authors.initials: C
authors.lastname: Ma
authors.affiliation: Division of Geological and Planetary Sciences, Caltech, 1200 East California Boulevard, Pasadena, CA 91125, USA.
authors.forename: John M
authors.initials: JM
authors.lastname: Eiler
authors.affiliation: Department of Earth and Planetary Sciences, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024, USA.
authors.forename: Juliane
authors.initials: J
authors.lastname: Gross
authors.affiliation: Department of Earth and Environmental Sciences, Wesleyan University, Middletown, CT 06459, USA.
authors.forename: James P
authors.initials: JP
authors.lastname: Greenwood
authors.affiliation: Division of Geological and Planetary Sciences, Caltech, 1200 East California Boulevard, Pasadena, CA 91125, USA.
authors.forename: Edward M
authors.initials: EM
authors.lastname: Stolper
keywords: Lunar; Moon; apatite; basalt; chlorine; magma ocean; volatiles; water