Abstract The potential for the mobilization of Fe from secondary phases within subsurface basaltic rocks of the Hawaii Scientific Drilling Project Phase2 (HSDP2) drill core was investigated to elucidate the possible contribution of volcanic islands to the Fe budget of nearby ocean surface waters. Rock specific parameters governing Fe mobilization, such as Fe redox state, specific surface area (SSA), and connected porosity were determined. A four-step sequential extraction procedure using solutions with increasing strength of the extractants was applied to characterize different states of chemical bonding of Fe in secondary phases of the basaltic rocks, a controlling parameter for its release to oceanic water. The sequential extraction results were then used as a measure for the reactivity of secondary Fe-bearing phases and the mobilizable Fe from these rocks. Basaltic rocks with different degrees of weathering showed elevated Fe(III) contents up to 58% total Fe as Fe(III), compared to 11–18% in fresh basalts. SSAs increased with depth, with maximum values of 70 m2/g observed for hyaloclastites. Both parameters depended mainly on the alteration state of the basalt, which was more strongly affected by the fluid chemistry (freshwater ↔ seawater) than by the age of the rocks. The sequential extractions revealed the presence of highly reactive secondary Fe-bearing phases in submarine rocks exposed to seawater whereas observations for rocks altered in freshwater point to better crystallized phases with lower mobilizable Fe contents. In seawater, aging of secondary Fe-bearing phases was most probably suppressed by the adsorption of silica and multivalent anions. Comparing different types of rock, hyaloclastites and pillow basalts showed the highest mobilizable Fe with up to 19% and 16%, respectively, of the total Fe of the bulk rock. The potential for high amounts of mobilizable Fe from basaltic rocks altered under seawater dominated conditions suggests that the submarine part of volcanic ocean islands represent an underestimated source of Fe supply to ocean surface waters.

中文翻译：

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来自不同蚀变地下玄武岩第二相的潜在可迁移铁——对 ICDP 站点夏威夷的连续提取研究

摘要 研究了夏威夷科学钻探项目第 2 阶段 (HSDP2) 钻芯的次表层玄武岩内次生相中 Fe 的动员潜力，以阐明火山岛对附近海洋表层水的 Fe 收支可能的贡献。确定了控制铁迁移的岩石特定参数，例如铁氧化还原状态、比表面积 (SSA) 和连通孔隙率。使用具有增加萃取剂强度的溶液的四步顺序萃取程序被应用于表征玄武岩第二相中 Fe 化学键的不同状态，这是其释放到海洋水中的控制参数。然后将连续提取结果用作衡量次生含铁相和这些岩石中可迁移铁的反应性的量度。具有不同风化程度的玄武岩表现出较高的 Fe(III) 含量，高达 58% 的 Fe(III) 总 Fe，而新鲜玄武岩为 11-18%。SSAs 随着深度的增加而增加，对于透明碎屑岩观察到的最大值为 70 m2/g。这两个参数主要取决于玄武岩的蚀变状态，其受流体化学（淡水↔ 海水）的影响比受岩石年龄的影响更大。连续提取揭示了暴露于海水的海底岩石中存在高反应性的次生含铁相，而对淡水中发生变化的岩石的观察表明，具有较低可迁移铁含量的更好结晶相。在海水中，二次含铁相的老化很可能被二氧化硅和多价阴离子的吸附所抑制。比较不同类型的岩石，透明碎屑岩和枕状玄武岩显示出最高的可迁移 Fe，分别高达大块岩石总 Fe 的 19% 和 16%。在以海水为主的条件下，玄武岩可能会产生大量可迁移的铁，这表明火山海洋岛屿的海底部分代表了被低估的海洋表水铁供应来源。