Siderophile volatile element inventory in lunar magmatic rocks and mantle sources

The volatile element inventory of the Moon and the processes of volatile loss and/or gain (e.g., degassing and late accretion) are key aspects for our understanding of the Earth-Moon system. Elevated concentrations of volatile elements and water in lunar rocks have recently invigorated the discussion on the volatile content of the lunar interior and on the extent to which the volatile element inventory of lunar magmatic rocks is controlled by degassing. Here we report mass fractions of the siderophile volatile elements Cu, Se, Ag, S, Te, Cd, In, and Tl in lunar magmatic rocks, analyzed isotope dilution ICP-MS techniques. Similar mass fractions of Cu, S, Se, and Ag and fractional crystallization trends in mare basalts and magnesian suite norites indicate that these elements are less prone to magmatic degassing than proposed previously. Disturbed fractional crystallization trends of more volatile elements (e.g., Tl, Cd) and enrichments of the latter in brecciated ferroan anorthosites indicate their redistribution and vapor deposition. Differences in element ratios between lunar magmatic rock suites suggest a predominant control of S, Se, Cu, and Ag by mantle source compositions. New estimates of mantle source compositions of low-Ti mare basalt suites reveal low mass fractions of Cu, S, Se, and Ag and element ratios in the lunar mantle that are significantly different from the terrestrial mantle. Our new data support the hypothesis of volatile loss prior to formation of the lunar mantle sources and indicate limited degassing of mare basalts.