Trace element evidence for serial processing of the lunar flotation crust and a depleted bulk Moon

1Dian Ji,1Nicholas Dygert
Earth and Planetary Science Letters 602, 117958 Link to Article [https://doi.org/10.1016/j.epsl.2022.117958]
1Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996, United States of America
Copyright Elsevier

Plagioclase in lunar anorthositic crust have rare earth element (REE) patterns and Eu abundances which cannot be directly produced by lunar magma ocean (LMO) solidification. This is surprising as the LMO is invoked to explain the mineralogy of the crust, and other lunar surface and interior properties. We explored geological processes subsequent to LMO solidification that could reconcile anorthositic compositions with an LMO, finding that subsolidus reequilibration after addition of a minor KREEPy component successfully reproduces REE variations in natural samples. Monte-Carlo simulations used to constrain conditions of subsolidus reequilibration suggest the Moon has a light-REE depleted bulk composition. We propose a post-LMO serial processing model to reconcile the petrological, geochronological, and isotopic characteristics of lunar anorthosites and contemporaneous magmatism. If the bulk Earth is chondritic and the Moon accreted from material ejected from a depleted terrestrial reservoir, Earth underwent an early differentiation event prior to the Moon-forming giant impact.

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