High-energy impact and vapor recondensation history of the angrite parent body revealed by nickel isotopes

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Zhu, Ke ; Yamaguchi, Akira ; Sossi, Paolo A. ; Bouvier, Audrey ; Chen, Lu ; Ni, Peng:
High-energy impact and vapor recondensation history of the angrite parent body revealed by nickel isotopes.
In: Proceedings of the National Academy of Sciences of the United States of America. Bd. 122 (2025) Heft 46 . - e2519759122.
ISSN 1091-6490
DOI: https://doi.org/10.1073/pnas.2519759122

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Abstract

Angrites are the most volatile-depleted planetary materials known, yet the processes driving such extreme depletion remain uncertain. Using high-precision nickel isotope measurements, this study reveals that the angrite parent body (APB) experienced a complex, multistage volatile evolution. While plutonic angrites preserve chondritic Ni isotopic compositions indicative of an undisturbed core, mantle-derived olivine-rich samples display heavy Ni isotopic signatures, pointing to evaporation from high-energy impacts after core formation. In contrast, isotopically light Ni in volcanic crustal materials suggests partial recondensation of Ni vapor. Together, these data provide direct isotopic evidence for impact-induced vapor loss and atmospheric recondensation on a differentiated asteroid, offering a framework to understand volatile depletion and redistribution on early planetary bodies. The angrite parent body (APB) is the most volatile-depleted among known differentiated bodies in the Solar System, yet the mechanisms responsible remain poorly constrained. Here, we present high-precision nickel (Ni) isotope data from a suite of angrite samples to reconstruct the APB’s volatile depletion history. Plutonic angrites contain unusually high proportions of metallic iron and exhibit chondritic δ60/58Ni values (0.202 ± 0.028‰; per mille mass-dependent 60Ni/58Ni deviation relative to National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 986). These observations are consistent with a homogeneous Ni isotope composition of the APB after core formation and the subsequent incorporation of endogenous core material in plutonic angrites. In contrast, a dunite and megacrystic olivines from volcanic angrites, derived from the mantle, display suprachondritic δ60/58Ni values (0.4 to 0.7‰). We argue that these values are consistent with Ni loss via evaporation during a high-energy impact that follows an initial stage of volatile loss from a magma ocean generated by 26Al heating. Thermodynamic modeling confirms Ni to be more volatile than Mn, Fe, Si, and Mg during evaporation from silicate liquids, in agreement with the observed relative magnitude of isotopic fractionation. Volcanic angrite matrices show variable and often subchondritic δ60/58Ni values (down to −0.5‰), reflecting mixing with isotopically heavy megacrystic olivines and recondensation of light Ni vapor onto the crust. These findings imply that volatile elements are stratified (core–mantle–crust) in the APB and provide direct isotopic evidence for impact-driven vapor loss and recondensation on a differentiated planetary body.