Angrites originate from the early-formed differentiated angrite parent body. The pristine volcanic angrite D’Orbigny is devoid of brecciation, shock effects, or any evidence of secondary processes and is thus key for studying the early stages of planetary accretion and differentiation. However, chronometers used to establish the formation chronology of angrites (including D’Orbigny) yield discordant ages, either (i) suggesting that secondary processes could have disturbed the apparent formation ages or (ii) being taken as evidence of heterogeneous distribution of ²⁶Al in the early solar system. Yet spinel is minimally susceptible to secondary parent body processes and therefore a reliable target for establishing precise ²⁶Al–²⁶Mg ages. Here, we present the first in situ ²⁶Al–²⁶Mg analyses of spinel and plagioclase in D’Orbigny. Individual mineral assemblages provide distinct ages: olivine–spinel shows a well-defined isochron with an initial Al ratio ([²⁶Al/²⁷Al]_i) of (5.39 ± 0.85) × 10⁻⁶, indicating formation at 2.35 +0.25−0.22 Myr after the formation of calcium–aluminum-rich inclusions (CAIs), whereas plagioclase–olivine defines an isochron with [²⁶Al/²⁷Al]_i = (7.46 ± 1.87) × 10⁻⁷, implying formation at 4.40 +0.44−0.38 Myr after CAIs, consistent with previous MC-ICP-MS studies. This temporal gap can be attributed to secondary processes such as metamorphic or impact-generated diffusion. Thus, D’Orbigny and other angrites do not represent an immaculate anchor for chronometric comparison. This complexity should be considered in future studies, especially when using D’Orbigny as an anchor to discuss the chronology of the early solar system.

中文翻译：

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从不一致的 26Al 年龄推断出 D'Orbigny Angrite 的潜在年代学干扰


Angrites 起源于早期形成的分化 Angrite 母体。原始的火山长岩 D'Orbigny 没有角砾岩、激波效应或任何次生过程的证据，因此是研究行星吸积和分化早期阶段的关键。然而，用于确定安格石（包括 D'Orbigny）形成年代学的天文台表得出的年龄不一致，要么 （i） 表明次级过程可能扰乱了明显的形成年龄，要么 （ii） 被视为 ²⁶Al 在早期太阳系中异质分布的证据。然而，尖晶石对次生母体过程的敏感性最小，因此是建立精确的 ^{26 Al-26}Mg 年龄的可靠目标。在这里，我们首次对 D'Orbigny 的尖晶石和斜长石进行了原位 ^{26 Al-26}Mg 分析。单个矿物组合提供了不同的年龄：橄榄石-尖晶石显示出一个明确的等时线，初始铝比 （^[26Al/²⁷Al]）为 （5.39 ± 0.85） × 10⁻⁶，表明在形成富含钙-铝的内含物 （CAI） 后，在 2.35 +0.25-0.22 Myr 处形成，而斜长石-橄榄石定义了一个等时线，其 [²⁶Al/²⁷Al] = （7.46 ± 1.87） × 10⁻⁷，意味着 CAI 后在 4.40 +0.44-0.38 Myr 形成，与之前的 MC-ICP-MS 研究一致。这种时间差距可归因于次级过程，例如或冲击产生的扩散。因此，D'Orbigny 和其他 angrites 并不代表计时比较的完美锚点。在未来的研究中应该考虑这种复杂性，尤其是在使用 D'Orbigny 作为锚点来讨论早期太阳系的年代学时。