近日，瑞士苏黎世联邦理工学院Cyril Chelle-Michou团队报道了深弧地壳中以硫酸盐为主的磷灰石表明，高氧化态促进了电弧中铜的熔化。相关论文于2025年11月13日发表在《地质学》杂志上。

在弧岩浆演化过程中，硫化物饱和会使上升的岩浆亏损亲铜元素（如铜），并促进金属再循环进入地幔。尽管有假说认为，弧深部地壳的高氧逸度（ƒO₂）会延迟硫化物饱和，但弧岩浆体系中硫化物饱和发生的时间及其控制因素仍存在争议。

研究组通过测定阿根廷Sierra Valle Fértil−La Huerta地区弧深部地壳堆晶岩中磷灰石内硫物种（S²⁻、S⁴⁺和S⁶⁺）的相对丰度，为弧深部地壳中硫的形态提供了新的约束。硫化物在原始堆晶岩中很罕见（<0.01%），仅在演化堆晶岩（镁指数 Mg# <0.65）中才变得丰富，这表明硫化物饱和在岩浆演化过程中被延迟了。磷灰石的S⁶⁺/总硫比值持续很高（0.8−1.0），表明其氧逸度（ƒO₂）比铁橄榄石-磁铁矿-石英（FMQ）氧逸度缓冲剂高1.4 ± 0.4个对数单位。因此，硫化物饱和的延迟，是由于母岩浆从其地幔源区获得了升高的ƒO₂所致。

研究组通过模拟表明，在FMQ+1.4的氧逸度条件下进行岩浆分异，足以延迟硫化物饱和，并产生铜浓度升高的镁铁质至中性熔体。因此，这种氧化的、含水的中性岩浆可能在向岩浆-热液系统和大气输送高硫通量和铜通量方面起着关键作用，从而导致现代大陆壳的铜亏损。

附：英文原文

Title: Sulfate-dominant apatite in the deep arc crust indicates that high oxidation state promotes copper fluxing in arcs

Author: Chetan Nathwani, Emanuel Giovanini, Olivier Bachmann, Paolo Sossi, Julien Allaz, Marine Cotte, Lorenzo Candioti, Cyril Chelle-Michou

Issue&Volume: 2025-11-13

Abstract: Sulfide saturation during arc magma evolution depletes ascending magmas in chalcophile elements (e.g., Cu) and promotes metal recycling into the mantle. Although sulfide saturation is posited to be delayed by high oxygen fugacity (O2) in the deep crust of arcs, the timing and controls on sulfide saturation in arcs remain disputed. Here, we report new constraints on S speciation in the deep crust of arcs using measurements of the relative abundance of S species (S2, S4+, and S6+) in apatite in deep crustal arc cumulates from the Sierra Valle FértilLa Huerta (Argentina). Sulfide is rare in primitive cumulates (<0.01%), only becoming abundant in evolved cumulates (Mg# <0.65), indicating that sulfide saturation was delayed in the magmatic evolution. Apatite yields consistently high S6+/ΣS (0.81.0), giving an fO2 of 1.4 ± 0.4 log units above the fayalite-magnetite-quartz (FMQ) redox buffer. Delayed sulfide saturation was therefore the result of the parental magma having elevated fO2 acquired from its mantle source. We use modeling to show that magma differentiation at FMQ+1.4 would be sufficient to delay sulfide saturation and produce mafic to intermediate melts with elevated Cu concentrations. Oxidized, hydrous intermediate magmas may therefore play a key role in delivering elevated sulfur and Cu fluxes to magmatic-hydrothermal systems and the atmosphere, contributing to the Cu deficit of modern continental crust.

DOI: 10.1130/G53549.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G53549.1/669297/Sulfate-dominant-apatite-in-the-deep-arc-crust