Formation of the Lunar Primary Crust From a Long-Lived Slushy Magma Ocean

Chloé Michaut (1, 2) , Jerome A. Neufeld

1 LGL-TPE - Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement
2 IUF - Institut universitaire de France

Classical fractional crystallization scenarios of early lunar evolution suggest crustal formation by the flotation of light anorthite minerals from a liquid magma ocean. However, this model is challenged by the >200$ > 200$ Myr age range of primitive ferroan anorthosites, their concordance with Mg-suite magmatism and by the compositional diversity observed in lunar anorthosites. Here, we propose a new model of slushy magma ocean crystallization in which crystals remain suspended in the lunar interior and crust formation only begins once a critical crystal content is reached. Thereafter crustal formation occurs by buoyant melt extraction and magmatism. The mixture viscosity strongly depends on temperature and solid fraction driving the development of a surface stagnant lid where enhanced solidification and buoyant ascent of melt lead to an anorthite-enriched crust. This model explains lunar anorthosites heterogeneity and suggests a crustal formation timescale of 100s Ma, reconciling anorthosite ages with an early age of the Moon.

Mots clés: magma ocean; lunar anorthosite; lunar crust; suspension

Domaines: Planète et Univers [physics]; Sciences de la Terre

Chloé Michaut, Jerome A. Neufeld. Formation of the Lunar Primary Crust From a Long-Lived Slushy Magma Ocean. Geophysical Research Letters, 2022, 49, ⟨10.1029/2021GL095408⟩. ⟨insu-03710174⟩