Iron Isotope Fractionation on Vesta Driven by Magma Ocean Process

Abstract

Magma oceans represent a pivotal stage in the early evolution of terrestrial planets. Early‐formed asteroids, driven by the decay of ²⁶ Al, may have also experienced such magma ocean processes. To investigate potential magma ocean differentiation on asteroid 4 asteroids, we reported high‐precision iron isotope data for 25 eucrites and 13 diogenites. Eucrites exhibit a δ ⁵⁶ Fe range of approximately 0.1‰, varying from −0.044 to 0.073‰, with a mean value of 0.020 ± 0.013‰ (2SE, N  = 25). Diogenites display δ ⁵⁶ Fe ranging from −0.051 to 0.018‰, yielding an average of −0.004 ± 0.011‰ (2SE, N  = 13). The observed Fe isotope variation and offset between eucrites and diogenites cannot be produced by terrestrial weathering, impacts, and core formation. Combined with MELTS modeling using two different initial compositions for Vesta, the isotope variation can be explained by magma ocean differentiation. A cross‐planetary comparison is made with the Moon, where magma ocean differentiation and associated Fe isotope variations have been extensively studied. Vestan samples exhibit remarkably limited δ ⁵⁶ Fe variation (∼0.1‰) compared to lunar basalts (∼0.3‰). This dichotomy may reflect distinct magma ocean evolution pathways across planetary bodies: later pyroxene crystallization, the absence of ilmenite‐driven mantle overturn, and rapid cooling in the case of Vesta. Thus, planetary geochemical diversity is fundamentally shaped by magma ocean dynamics modulated by body size, composition, and thermal history.