Abstract Attention is now being given to Ni isotope systematics in hydrogenetic marine ferromanganese (Fe-Mn) crusts as paleoceanographic proxies. Previous work focused on identifying both mineralogy (post-depositional) and source effects (Gall et al. 2013; Gueguen et al. 2016), in particular regarding hydrothermal inputs in the oceans and the response of Ni isotope biogeochemical cycling through time. The most important sink for Ni in the oceans is the Fe-Mn oxides sink, but estimation of its Ni isotope composition is only based on hydrogenetic Fe-Mn crusts. In this study, we investigated a range of Fe-Mn deposits including Fe-Mn deposits variably affected by hydrothermal inputs, including hydrothermal deposits from the Lau back-arc basin (South West Pacific) and Lo'ihi seamount (Hawaii), hydrogenetic crust and nodules from the Bauer Basin (Pacific Ocean). Nickel isotope ratios were measured by multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) using a double-spike (61Ni and 62Ni) correction method. The combination of Ni isotopes and rare earth element (REE) geochemistry show that Ni isotope fractionation in Fe-Mn deposits is essentially controlled by formation processes of the deposits (such as the rate of formation, the initial Mn-phase and sorption processes) which are also related to the depositional environment. Consistent with previous studies, pure hydrogenetic crusts are characterized by isotopically heavy Ni isotope signatures (δ60/58Ni values range from ‰ 0.9 and 2.5‰) and well-developed positive Ce anomalies. In contrast, mixed hydrothermal‑hydrogenetic crust and nodules from the Bauer Basin (East Pacific) display negative Ce anomaly and lighter δ60/58Ni values (0.3‰ to 0.4‰), which are interpreted as the result of far-field hydrothermal inputs of Fe-Mn precipitates from the East Pacific Rise. Nickel in hydrothermal deposits from the Lau Basin (0.5 and 1.1‰) and Lo'ihi seamount (−0.8 to −1.5‰) is isotopically lighter than in hydrogenetic Fe-Mn crusts. Light δ60/58Ni values in Lo'ihi deposits is due to the removal of Ni during Ni adsorption from seawater and from the hydrothermal fluid (between 0 and 1.4‰) on Fe-oxides followed by isotope fractionation between the fluid and the mineral phase. Results suggest that Ni isotopes in hydrothermal Fe-rich deposits are strongly fractionated relative to the seawater/fluid source due to partial removal of Ni on Fe-phases. Hydrothermal Mn-oxides deposits from the Lau Basin acquired their Ni isotope signature through Ni adsorption and continuous exchange of Ni with seawater. We propose that the systematic difference in Ni isotope signatures between hydrogeneous and hydrothermal Fe-Mn deposits is related to the mechanisms of Ni uptake into oxide minerals (e.g., birnessite vs. todorokite; Fe-oxides vs. Mn-oxides) which depend on the rate of formation and the source of Mn and Fe to marine ferromanganese deposits (i.e., depositional environment) rather than Ni sources.

中文翻译：

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海洋氢化热液锰铁矿床镍同位素和稀土元素系统学

摘要 作为古海洋学指标的氢化海相铁锰 (Fe-Mn) 结壳中的 Ni 同位素系统学正受到关注。以前的工作侧重于确定矿物学（沉积后）和源效应（Gall 等人，2013 年；Gueguen 等人，2016 年），特别是关于海洋中的热液输入和 Ni 同位素生物地球化学循环随时间的响应。海洋中最重要的 Ni 汇是 Fe-Mn 氧化物汇，但其 Ni 同位素组成的估计仅基于氢化 Fe-Mn 结壳。在这项研究中，我们调查了一系列 Fe-Mn 矿床，包括受热液输入影响不同的 Fe-Mn 矿床，包括来自 Lau 弧后盆地（西南太平洋）和 Lo'ihi 海山（夏威夷）的热液矿床，来自鲍尔盆地（太平洋）的氢化地壳和结核。镍同位素比率通过多接收器电感耦合等离子体质谱仪 (MC-ICP-MS) 使用双尖峰（61Ni 和 62Ni）校正方法进行测量。Ni同位素和稀土元素（REE）地球化学的结合表明，Fe-Mn矿床中Ni同位素分馏主要受矿床形成过程（如形成速率、初始Mn相和吸附过程）的控制。还与沉积环境有关。与先前的研究一致，纯氢结壳的特征是同位素重 Ni 同位素特征（δ60/58Ni 值范围从 ‰ 0.9 到 2.5‰）和发育良好的 Ce 正异常。相比之下，Bauer盆地（东太平洋）的混合热液-水成壳和结核显示负Ce异常和较轻的δ60/58Ni值（0.3‰至0.4‰），这被解释为Fe-Mn沉淀物的远场热液输入的结果来自东太平洋海隆。来自 Lau 盆地（0.5 和 1.1‰）和 Lo'ihi 海山（-0.8 到 -1.5‰）的热液矿床中的镍同位素比氢化铁锰结壳中的镍轻。Lo'ihi 矿床中的轻 δ60/58Ni 值是由于在从海水和热液流体（0 到 1.4‰之间）中的 Ni 吸附过程中去除了 Ni，然后在流体和矿物相之间进行同位素分馏。结果表明，由于铁相上的镍被部分去除，热液富铁矿床中的镍同位素相对于海水/流体源有很强的分馏作用。Lau 盆地的热液锰氧化物矿床通过 Ni 吸附和 Ni 与海水的连续交换获得了它们的 Ni 同位素特征。我们提出，氢和热液 Fe-Mn 矿床之间 Ni 同位素特征的系统差异与 Ni 吸收到氧化物矿物（例如，水钠锰矿 vs. todorokite；Fe 氧化物 vs. Mn 氧化物）中的机制有关，这取决于海洋锰铁矿床（即沉积环境）的形成速率和锰和铁的来源，而不是镍的来源。Lau 盆地的热液锰氧化物矿床通过 Ni 吸附和 Ni 与海水的连续交换获得了它们的 Ni 同位素特征。我们提出，氢和热液 Fe-Mn 矿床之间 Ni 同位素特征的系统差异与 Ni 吸收到氧化物矿物（例如，水钠锰矿 vs. todorokite；Fe 氧化物 vs. Mn 氧化物）中的机制有关，这取决于海洋锰铁矿床（即沉积环境）的形成速率和锰和铁的来源，而不是镍的来源。Lau 盆地的热液锰氧化物矿床通过 Ni 吸附和 Ni 与海水的连续交换获得了它们的 Ni 同位素特征。我们提出，氢和热液 Fe-Mn 矿床之间 Ni 同位素特征的系统差异与 Ni 吸收到氧化物矿物（例如，水钠锰矿 vs. todorokite；Fe 氧化物 vs. Mn 氧化物）中的机制有关，这取决于海洋锰铁矿床（即沉积环境）的形成速率和锰和铁的来源，而不是镍的来源。