Cryptic metasomatism during late-stage lunar magmatism implicated by sulfur in apatite

Abstract

The use of volatile-bearing (H 2 O-Cl-F-C-S) minerals as proxies for constraining the volatile content of lunar magmas remains controversial. In this study, we apply published F-Cl-S signature trends in apatite from lunar mare basalts, new experimentally determined apatitemelt partition coefficients for S, and thermodynamic modeling to demonstrate unequivocally that fractional crystallization of lunar silicate melt could not have produced the observed S signatures of lunar apatite. Instead, metasomatic (cryptic) alteration by a S-Cl–bearing, F-poor volatile phase plausibly explains the volatile element zoning in lunar apatite, consistent with some lunar magmas being more volatile rich than previously suggested.