Submarine hydrothermal venting leads to the formation of black smoker chimneys with complex internal zoning. These emerge through mineral precipitation under changing fluid conditions caused by variable degrees of fluid-seawater mixing. This study explores the potential of selenium (Se) isotopes as a novel tool to understand the enrichment processes and identify the sources of chalcophile elements in seafloor hydrothermal systems. In-situ trace element analysis of hydrothermal sulfides combined with high-precision Se and S isotope analysis of micro-domains through the wall of black smoker chimneys from the Nifonea vent field (New Hebrides back-arc, SW Pacific) revealed variations in sulfide chemistry at small spatial resolution. The δSe values (deviation of Se/Se relative to NIST SRM 3149) of the sulfide micro-domains range from +0.6 to −3.7 ‰ ± 0.2 ‰ (2 s.d.) with a general decrease from the inner chalcopyrite lining towards the outer chimney wall. The highest δSe values overlap with the mean value of fresh basaltic glass from Nifonea caldera (+0.6 ± 0.4 ‰, n = 4), indicating that Se is primarily leached from the surrounding back-arc basalts. The trace element contents of sulfides revealed systematic variations between vent sites, linked to differences in fluid vapor content induced by sub-seafloor boiling, which did not cause any Se isotope fractionation. Instead, decreasing Se/Tl ratios of pyrite together with decreasing δSe values of sulfide micro-domains and calculated δS fluid values towards the outer chimney wall are indicative of temperature-dependent Se and S isotope fractionation at 370 to <200 °C during fluid-seawater mixing within the chimney wall. This study presents Se isotopes as a new robust instrument to unravel the sources of chalcophile elements and related fluid processes in seawater-diluted hydrothermal systems, enhancing our understanding of their geochemical complexities.

中文翻译：

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海水混合过程中的温度控制 Se-S 同位素分馏和黑烟囱中的硫化物沉淀

海底热液排放导致形成具有复杂内部分区的黑烟囱。这些是在流体与海水不同程度混合引起的流体条件变化下通过矿物质沉淀而出现的。这项研究探讨了硒 (Se) 同位素作为了解富集过程和识别海底热液系统中亲铜元素来源的新工具的潜力。对热液硫化物进行原位痕量元素分析，结合对 Nifonea 喷口场（新赫布里底群岛弧后，西南太平洋）黑烟囱壁微区的高精度 Se 和 S 同位素分析，揭示了硫化物化学的变化在小空间分辨率下。硫化物微域的 δSe 值（Se/Se 相对于 NIST SRM 3149 的偏差）范围为 +0.6 至 -3.7 ‰ ± 0.2 ‰ (2 sd)，从内黄铜矿衬里到外烟囱壁普遍减小。最高的 δSe 值与 Nifonea 火山口新鲜玄武岩玻璃的平均值重叠（+0.6 ± 0.4 ‰，n = 4），表明 Se 主要从周围的弧后玄武岩中浸出。硫化物的微量元素含量揭示了喷口位置之间的系统变化，这与海底沸腾引起的流体蒸气含量的差异有关，这不会引起任何硒同位素分馏。相反，黄铁矿 Se/Tl 比率的降低以及硫化物微域 δSe 值的降低以及朝向外烟囱壁计算的 δS 流体值表明在流体-过程中在 370 至 <200 °C 温度依赖性 Se 和 S 同位素分馏。海水在烟囱壁内混合。这项研究将硒同位素作为一种新的强大工具来揭示海水稀释热液系统中亲铜元素的来源和相关流体过程，从而增强我们对其地球化学复杂性的理解。