Lunar apatite with terrestrial volatile abundances

Jeremy W. Boyce

Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California
Department of Earth and Space Sciences, University of California, Los Angeles, California

Yang Liu

Planetary Geosciences Institute, Department of Earth and Planetary Sciences
University of Tennessee, Knoxville, Tennessee

George R. Rossman, Yunbin Guan, John M. Eiler, Edward M. Stolper

Division of Geological and Planetary Sciences
California Institute of Technology, Pasadena, CA

Lawrence A. Taylor

Planetary Geosciences Institute, Department of Earth and Planetary Sciences
University of Tennessee, Knoxville, Tennessee

Abstract

The Moon is thought to be depleted relative to the Earth in volatile elements such as H, Cl and the alkalis. Nevertheless, evidence for lunar explosive volcanism has been used to infer that some lunar magmas exsolved a CO-rich and CO₂-rich vapour phase before or during eruption. Although there is also evidence for other volatile species on glass spherules, until recently there had been no unambiguous reports of indigenous H in lunar rocks. Here we report quantitative ion microprobe measurements of late-stage apatite from lunar basalt 14053 that document concentrations of H, Cl and S that are indistinguishable from apatites in common terrestrial igneous rocks. These volatile contents could reflect post-magmatic metamorphic volatile addition or growth from a late-stage, interstitial, sulphide-saturated melt that contained 1,600 parts per million H₂O and 3,500 parts per million Cl. Both metamorphic and igneous models of apatite formation suggest a volatile inventory for at least some lunar materials that is similar to comparable terrestrial materials. One possible implication is that portions of the lunar mantle or crust are more volatile-rich than previously thought.

Apatite (ap) in lunar sample 14053. Image courtesy of L.A. Taylor.

Nature Vol 466, p466-469, doi:10.1038/nature09274