The study of Howardite-Eucrite-Diogenite (HED) meteorites provides unique insights into early planet formation and the impact events that shaped the early Solar System. However, unraveling the complex history of the HED parent body (hypothesized to be the asteroid 4 Vesta) from whole-rock samples is challenging since most HEDs are impact-related breccias comprising mixed lithic and mineral fragments that experienced variable deformation and alteration. Combining U-Pb geochronology, trace element geochemistry, and microstructural analysis of zircon can unravel magmatic, metamorphic and impact processes through time to decipher the HED parent body evolution. Here we present textural (EBSD), geochronological (Pb/Pb SIMS dating) and geochemical data (Th/U, REE, Ti-in-zircon thermometry) on 61 zircon grains from melt breccia eucrites, unbrecciated/monomict/polymict eucrites, howardites and diogenites. Diverse textures indicate variable histories of impact deformation and high-temperature recrystallization. Undeformed, fractured zircons preserve primary zoning (CL, Th/U, REE) indicating magmatic and metamorphic origins. At least three magmatic zircon grains (Th/U > 0.3) give Pb/Pb ages of 4558–4565 Ma, suggesting primary differentiation in the parent body first million years. Twenty metamorphic zircon grains (Th/U < 0.3) date to 4420–4568 Ma, indicating prolonged thermal metamorphism from impact heating and/or crustal cooling. Impact-recrystallized granular zircon grains reveal major impacts during and just after the parent body differentiation (4500–4560 Ma), plus later events potentially linked to synchronous impacts in the Solar System (e.g. the Moon). Similarity of metamorphic and shocked zircon ages (circa 4550–4450 Ma) suggests impacts occurred for ≥100 million years after the parent body formed.

中文翻译：

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HED 锆石作为了解太阳系第一地壳的窗口：通过结构和化学研究解耦原始分化、变质作用和撞击事件


对霍华德-锂辉石-闪长石 (HED) 陨石的研究为了解早期行星形成以及塑造早期太阳系的撞击事件提供了独特的见解。然而，从全岩石样本中解开 HED 母体（假设是小行星 4 灶神星）的复杂历史具有挑战性，因为大多数 HED 是与撞击相关的角砾岩，由经历了可变变形和蚀变的混合岩屑和矿物碎片组成。结合 U-Pb 地质年代学、微量元素地球化学和锆石微观结构分析，可以揭示随时间变化的岩浆、变质和撞击过程，从而破译 HED 母体的演化。在这里，我们展示了来自熔体角砾锂辉石、非角砾岩/单晶/多晶锂辉石、菱镁矿的 61 颗锆石晶粒的结构 (EBSD)、地质年代学（Pb/Pb SIMS 测年）和地球化学数据（Th/U、REE、Ti-in-zircon 测温）和闪长岩。不同的织构表明冲击变形和高温再结晶的不同历史。未变形、断裂的锆石保留了原生分带（CL、Th/U、REE），表明岩浆和变质起源。至少三个岩浆锆石颗粒 (Th/U > 0.3) 给出的 Pb/Pb 年龄为 4558–4565 Ma，表明母体在前百万年发生了初级分化。二十颗变质锆石颗粒 (Th/U < 0.3) 的年代可追溯到 4420–4568 Ma，表明冲击加热和/或地壳冷却导致了长期的热变质作用。撞击再结晶的粒状锆石颗粒揭示了母体分化期间和之后的重大撞击（4500-4560 Ma），以及可能与太阳系同步撞击（例如月球）相关的后续事件。 变质和冲击锆石年龄（约 4550–4450 Ma）的相似性表明，母体形成后 ≥1 亿年发生了影响。