Abstract Subduction at convergent margins introduces a range of sedimentary and crustal materials into the mantle, providing the most dominant form of heterogeneity in the source of oceanic basalts. Yet, the relationship between geochemical variability and lithologic heterogeneities in the Earth's mantle remains controversial. In this paper, we comprehensively review Zn, δ66Zn and Sr-Nd isotope systematics in near-primary basalts erupted at mid-ocean ridges (MORB) and ocean islands (OIB) to help constrain the nature and proportion of the carbon (C) bearing slab-derived component in their mantle sources. We show that Zn elemental and isotopic composition of oceanic basalts differs according to their tectonic settings, increasing from MORB (Zn = 62 ± 10 to 73 ± 11 ppm; δ66Zn = +0.24 ± 0.01 to +0.31 ± 0.02‰) to OIB (Zn = 74 ± 9 to 124 ± 7 ppm; δ66Zn = +0.21 ± 0.07 to +0.40 ± 0.04‰). Unlike MORB, the high Zn and δ66Zn recorded in OIB cannot be explained by partial melting of a fertile peridotite mantle source only. Importantly, global correlations between Zn content and Sr-Nd isotopes in oceanic basalts suggest that the Zn enrichment in OIB is inherited from a recycled component in their mantle source rather than melting processes. We demonstrate that involvement of neither typical MORB-like oceanic crust nor subducted sediments can achieve the whole range of Zn composition in OIB. Instead, addition of ≤6% C-bearing oceanic crust to a fertile peridotite mantle fully resolves the Zn heterogeneity of OIB, both in terms of magnitude of Zn enrichment and global trends with Sr-Nd isotopes. Such scenario is corroborated by the elevated δ66Zn of OIB relative to MORB and mantle peridotites, reflecting the contribution of isotopically heavy C-bearing phases (δ66Zn = +0.91 ± 0.24‰) to the mantle source (δ66Zn = +0.16 ± 0.06‰). Our study thus emphasizes the use of Zn and δ66Zn systematics to track the nature and origin of mantle carbon, highlighting the role of subduction in the deep carbon cycle. Finally, the positive correlation between Zn content and temperature of magma generation of oceanic basalts suggests that hotter mantle plumes are more likely to carry a higher proportion of dense C-bearing eclogite. Zinc systematics therefore may provide evidence that the presence of heterogeneous domains in the source of OIB is, at least partly, linked to plume thermal buoyancy, bringing new insights into mantle dynamics.

中文翻译：

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通过大洋玄武岩中锌系统学的地幔异质性：深层碳循环的证据

摘要 会聚边缘的俯冲将一系列沉积和地壳物质引入地幔，提供了大洋玄武岩来源中最主要的非均质性形式。然而，地球化学变异性与地幔岩性异质性之间的关系仍然存在争议。在本文中，我们全面回顾了大洋中脊 (MORB) 和海洋岛屿 (OIB) 喷发的近原生玄武岩的 Zn、δ66Zn 和 Sr-Nd 同位素系统学，以帮助限制含碳 (C) 的性质和比例。地幔来源中的板坯衍生成分。我们表明，大洋玄武岩的 Zn 元素和同位素组成根据它们的构造环境而不同，从 MORB（Zn = 62 ± 10 到 73 ± 11 ppm；δ66Zn = +0.24 ± 0.01 到 +0.31 ± 0.02‰）到 OIB（Zn = 74 ± 9 至 124 ± 7 ppm；δ66Zn = +0.21 ± 0.07 至 +0.40 ± 0.04‰）。与 MORB 不同，OIB 中记录的高 Zn 和 δ66Zn 不能仅通过肥沃的橄榄岩地幔源的部分熔化来解释。重要的是，大洋玄武岩中锌含量与 Sr-Nd 同位素之间的全球相关性表明，OIB 中的 Zn 富集是从其地幔源中的回收成分继承的，而不是熔化过程。我们证明，无论是典型的 MORB 类海洋地壳还是俯冲沉积物的参与，都不能实现 OIB 中锌成分的整个范围。相反，在富饶的橄榄岩地幔中添加≤6% 的含碳洋壳完全解决了 OIB 的 Zn 异质性，无论是在 Zn 富集程度还是 Sr-Nd 同位素的全球趋势方面。OIB 相对于 MORB 和地幔橄榄岩的 δ66Zn 升高​​证实了这种情况，反映了含同位素重 C 相（δ66Zn = +0.91 ± 0.24‰）对地幔源（δ66Zn = +0.16 ± 0.06‰）的贡献。因此，我们的研究强调使用 Zn 和 δ66Zn 系统学来追踪地幔碳的性质和起源，突出俯冲作用在深部碳循环中的作用。最后，锌含量与大洋玄武岩岩浆生成温度之间的正相关表明，较热的地幔柱更有可能携带更高比例的致密含碳榴辉岩。因此，锌系统学可能提供证据表明 OIB 源中异质域的存在至少部分与羽流热浮力有关，为地幔动力学带来了新的见解。16±0.06‰）。因此，我们的研究强调使用 Zn 和 δ66Zn 系统学来追踪地幔碳的性质和起源，突出俯冲作用在深部碳循环中的作用。最后，锌含量与大洋玄武岩岩浆生成温度之间的正相关表明，较热的地幔柱更有可能携带更高比例的致密含碳榴辉岩。因此，锌系统学可能提供证据表明 OIB 源中异质域的存在至少部分与羽流热浮力有关，为地幔动力学带来了新的见解。16±0.06‰）。因此，我们的研究强调使用 Zn 和 δ66Zn 系统学来追踪地幔碳的性质和起源，突出俯冲作用在深部碳循环中的作用。最后，锌含量与大洋玄武岩岩浆生成温度之间的正相关表明，较热的地幔柱更有可能携带更高比例的致密含碳榴辉岩。因此，锌系统学可能提供证据表明 OIB 源中异质域的存在至少部分与羽流热浮力有关，为地幔动力学带来了新的见解。Zn 含量与大洋玄武岩岩浆生成温度之间的正相关表明，较热的地幔柱更有可能携带更高比例的致密含碳榴辉岩。因此，锌系统学可能提供证据表明 OIB 源中异质域的存在至少部分与羽流热浮力有关，为地幔动力学带来了新的见解。Zn 含量与大洋玄武岩岩浆生成温度之间的正相关表明，较热的地幔柱更有可能携带更高比例的致密含碳榴辉岩。因此，锌系统学可能提供证据表明 OIB 源中异质域的存在至少部分与羽流热浮力有关，为地幔动力学带来了新的见解。