Abstract Lithological heterogeneity is a widely accepted feature of the Earth’s mantle, with recycled crustal material accounting for a significant part of heterogeneity in ocean island basalt (OIB) geochemistry. Fe isotopes have been used to link geochemical heterogeneity in OIB sources to distinct mantle lithologies due to their mineral-specific equilibrium fractionation effects, or their composition, such as incorporation of kinetically-fractionated core liquids entrained from the core-mantle boundary. Here we present Fe isotope data for Samoan shield, and Azores volcanoes, together with a combined phase-equilibria and equilibrium mineral-melt isotope fractionation model. These OIB lavas allow us to study the roles of core-derived and recycled mantle components in generating heavy δ 57Fe melts. Heavy δ 57Fe correlates with radiogenic isotope signatures of enrichment by a crustal component and not with Fe/Mn or any indicator of core involvement. However, single-stage melting of a MORB-like eclogitic pyroxenite cannot generate the heavy δ 57Fe seen in Pitcairn, Azores, and rejuvenated Samoa lavas. Melts of a reaction-zone pyroxenite (commonly suggested to form part of the OIB source), derived from eclogite melts hybridised with peridotite, also fail to generate the heaviest Fe isotopic compositions seen in OIB. Instead, the generation of heavy δ 57Fe melts in OIB requires: (1) processes that make subducted eclogite isotopically heavier than its pristine precursor MORB (e.g., hydrothermal alteration, metamorphism, sediment input); (2) lithospheric processing, such as remobilisation of previously frozen small-degree melts, or a contribution from lithospheric material metasomatised by silicate melts; and/or (3) melting conditions that limit the dilution of melts with heavy δ 57Fe by ambient lower δ 57Fe materials. No single process we consider can generate the heavy δ 57Fe seen in the Azores, Pitcairn, and rejuvenated Samoan lavas. Therefore, it cannot be assumed that a pyroxenite lithology derived from recycled crustal material is the sole producer of heavy δ 57Fe melts in OIB, nor can these signatures be related to contributions from the Earth’s core. Instead, the observation of heavy δ 57Fe OIB melts cannot be ascribed to a unique source or process. This ambiguity reflects the multitude of processes operating from the generation of recycled lithologies through to their mantle melting: from MORB generation, its low temperature alteration, through mantle heterogeneity development and lithospheric processing, to eruption at ocean islands.

中文翻译：

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海岛玄武岩中的重δ57Fe：地幔过程和源岩性的非独特特征

摘要 岩性非均质性是地幔的一个被广泛接受的特征，在海岛玄武岩 (OIB) 地球化学中，回收的地壳物质占非均质性的重要组成部分。铁同位素已被用于将 OIB 源中的地球化学异质性与不同的地幔岩性联系起来，因为它们具有特定于矿物的平衡分馏效应，或其组成，例如从核 - 地幔边界夹带的动力学分馏核心液体的结合。在这里，我们提供了萨摩亚地盾和亚速尔群岛火山的 Fe 同位素数据，以及相平衡和平衡矿物熔体同位素分馏模型的组合。这些 OIB 熔岩使我们能够研究核心衍生和回收的地幔成分在产生重 δ 57Fe 熔体中的作用。重 δ 57Fe 与地壳成分富集的放射性同位素特征相关，而不与 Fe/Mn 或任何核参与指标相关。然而，类似 MORB 的榴辉岩辉石岩的单阶段熔化不能产生在皮特凯恩、亚速尔群岛和恢复活力的萨摩亚熔岩中看到的重 δ 57Fe。来自榴辉岩熔体与橄榄岩杂化的反应区辉石岩（通常建议形成 OIB 源的一部分）的熔体也无法产生 OIB 中看到的最重的 Fe 同位素组成。相反，OIB 中重 δ 57Fe 熔体的产生需要： (1) 使俯冲榴辉岩同位素比其原始前体 MORB 重的过程（例如，热液蚀变、变质作用、沉积物输入）；(2) 岩石圈处理，如先前冻结的小程度熔体的再流动，或由硅酸盐熔体交代的岩石圈材料的贡献；和/或 (3) 限制环境中低 δ 57Fe 材料稀释重 δ 57Fe 熔体的熔化条件。我们考虑的任何单一过程都不能产生在亚速尔群岛、皮特凯恩和恢复活力的萨摩亚熔岩中看到的重 δ 57Fe。因此，不能假设源自回收地壳材料的辉石岩岩性是 OIB 中重 δ 57Fe 熔体的唯一生产者，这些特征也不能与地核的贡献有关。相反，对重 δ 57Fe OIB 熔体的观察不能归因于独特的来源或过程。这种模糊性反映了从再生岩性的产生到地幔熔融的多种过程：从 MORB 的产生、其低温变化、