Iron isotope evidence in continental intraplate basalts for mantle lithosphere imprint on heterogenous asthenospheric melts
Iron isotope evidence in continental intraplate basalts for mantle lithosphere imprint on heterogenous asthenospheric melts
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大陆板内玄武岩中的铁同位素证据：地幔岩石圈对不均一软流圈熔体的印记
DOI：
10.1016/j.epsl.2023.118499
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发表时间：
2024-01
影响因子：
5.3
通讯作者：
Rong Xu;S. Lambart;O. Nebel;Ming Li;Zhongjie Bai;Junbo Zhang;Ganglan Zhang;Jianfeng Gao;Hong Zhong;Yongsheng Liu
中科院分区：
文献类型：
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作者：
Rong Xu;S. Lambart;O. Nebel;Ming Li;Zhongjie Bai;Junbo Zhang;Ganglan Zhang;Jianfeng Gao;Hong Zhong;Yongsheng Liu
对洋岛玄武岩（OIB）和洋中脊玄武岩（MORB）的铁同位素研究揭示了辉石岩岩性在玄武岩岩浆生成中的贡献。大陆板内玄武岩的铁同位素组成是否可以用于追踪地幔源区的岩性异质性仍然缺乏研究。为了探索稳定铁同位素的系统学作为大陆板内玄武岩来源岩性非均质性的潜在探针，我们提供了来自中国东南部一组特征良好的新生代玄武岩的 24 种铁同位素数据。样品显示出大范围的 Fe 同位素值（δ56Fe=+0.09‰ 至 +0.20‰），与 SiO2、CaO/Al2O3、Ti/Eu、Hf/Hf*、Zr/Nb、Dy/Yb、La/Yb、Nb/Y、K/La、Sr/Ce、δ66Zn 和估计平衡压力相关。 δ56Fe 值最高的样品代表早期低硅玄武岩，具有中等富集的 Sr-Nd 同位素比和高 δ66Zn 值，而晚期高硅玄武岩则随着 87Sr/86Sr 的增加和 εNd 和 δ66Zn 的降低而表现出广泛的 δ56Fe 降低。我们证明最重的铁同位素特征不能来自纯橄榄岩源，并且需要源中含有辉石岩成分。结合其他地球化学指标，我们表明最重的玄武岩成分与含碳化辉石岩的软流圈地幔绝热减压产生的低度熔体一致。这些混合熔体与俯冲修正的次大陆岩石圈地幔（SCLM）原位熔融产生的熔体混合，再现了晚期玄武岩的铁同位素变异性。我们的研究结果证明了大陆板内玄武岩地幔源岩性非均质性的重要性，并强调了地幔岩石圈在其铁同位素组成演化中的后续印记。最后，这项研究例证了 Fe-Zn 稳定同位素对在地幔地球化学方面的潜力；与传统的放射性同位素以及主量和微量元素浓度相结合，它们形成了一种有效的工具来追踪地幔源成分在板内玄武岩形成中的性质和贡献。
Iron isotope studies on ocean island basalts (OIBs) and mid-ocean ridge basalts (MORBs) have disclosed the contribution of pyroxenite lithologies in the generation of basaltic magmas. Whether Fe isotopic compositions of continental intraplate basalts can be applied to trace lithological heterogeneity within the mantle source regions remains poorly investigated. To explore the systematics of stable Fe isotopes as a potential probe of lithological heterogeneity in the source of continental intraplate basalts, we present twenty-four Fe isotope data on a suite of well-characterized Cenozoic basalts from SE China. The samples show a large range of Fe isotope values (δ56Fe = +0.09‰ to +0.20‰), which correlate with SiO2, CaO/Al2O3, Ti/Eu, Hf/Hf*, Zr/Nb, Dy/Yb, La/Yb, Nb/Y, K/La, Sr/Ce, δ66Zn and estimated equilibrium pressures. The samples with the highest δ56Fe values represent early-stage low-silica basalts with moderately enriched Sr-Nd isotope ratios and high δ66Zn values, while the late-stage high-silica basalts display a broad δ56Fe decrease with increasing87Sr/86Sr and with decreasing εNdand δ66Zn. We demonstrate that the heaviest Fe isotope signatures cannot be derived from a pure peridotite source and require a pyroxenite component in the source. Combined with other geochemical proxies, we show that the heaviest basalt compositions are consistent with low-degree melts produced by the adiabatic decompression of a carbonated pyroxenite-bearing asthenospheric mantle. Mixing of these hybrid melts with melt produced from in-situ melting of the subduction-modified sub-continental lithospheric mantle (SCLM) reproduces the Fe-isotope variability of the late-stage basalts. Our results demonstrate the significance of lithological heterogeneity in the mantle source of continental intraplate basalts and highlight the subsequent imprint of mantle lithosphere in the evolution of their Fe isotope compositions. Finally, this study exemplifies the potential of the Fe-Zn stable isotope pair for mantle geochemistry; coupled with traditional radiogenic isotopes and major and trace element concentrations, they formed an efficient tool to trace the nature and contribution of the mantle source components in the formation of intraplate basalts.