title: The lunar apatite paradox.
abstract: Recent discoveries of water-rich lunar apatite are more consistent with the hydrous magmas of Earth than the otherwise volatile-depleted rocks of the Moon. Paradoxically, this requires H-rich minerals to form in rocks that are otherwise nearly anhydrous. We modeled existing data from the literature, finding that nominally anhydrous minerals do not sufficiently fractionate H from F and Cl to generate H-rich apatite. Hydrous apatites are explained as the products of apatite-induced low magmatic fluorine, which increases the H/F ratio in melt and apatite. Mare basalts may contain hydrogen-rich apatite, but lunar magmas were most likely poor in hydrogen, in agreement with the volatile depletion that is both observed in lunar rocks and required for canonical giant-impact models of the formation of the Moon.
authors.affiliation: Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095, USA.
authors.forename: J W
authors.initials: JW
authors.lastname: Boyce
authors.forename: S M
authors.initials: SM
authors.lastname: Tomlinson
authors.forename: F M
authors.initials: FM
authors.lastname: McCubbin
authors.forename: J P
authors.initials: JP
authors.lastname: Greenwood
authors.forename: A H
authors.initials: AH
authors.lastname: Treiman
mesh_terms: D001031:Apatites; D003460:Crystallization; D005118:Extraterrestrial Environment; D005461:Fluorine; D006859:Hydrogen; D016081:Moon; D017640:Silicates; D014867:Water
chemical_list: D001031:Apatites; D017640:Silicates; C060346:basalt; D014867:Water; D005461:Fluorine; D006859:Hydrogen