High precision Al-Mg dating of NWA 15118 challenges a primary anorthositic crust on VestaOPEN ACCESS 

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H. Ren, L. Fang, J.-A. Barrat, T.-H. Luu, J. Siebert, Y. Li, S. Li, Y. Liu, F. Moynier

Geochemical Perspectives Letters, Version 38, Published 24 November 2025

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“A lunar-like magma ocean model has been proposed for the asteroid 4 Vesta, where a global primary anorthositic crust formed from buoyant plagioclase floating above complementary diogenitic cumulates. In this hypothesis, the crystallization of the anorthosite should predate the formation of eucrites that are thought to reflect secondary magmatism at the surface of Vesta. To test this model, we present the first 26Al-26Mg age of the anorthosite Northwest Africa (NWA) 15118. The NWA 15118 yields a model 26Al-26Mg age younger than 4.35 ± 0.03 Myr after CAIs formation. However, eucritic crust formation initiated at ∼2.88 Myr after CAIs, and predating NWA 15118 by over 1.5 Myr, contradicting the proposed global primary anorthositic crust of Vesta formed from a magma ocean. Instead, anorthosite NWA 15118 more plausibly represents a fragment of regional crust formed after the primary crustal differentiation of Vesta, potentially related to late stage basaltic eucrites with negative Eu anomalies or derived from a chemically distinct source.”

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