Whether and how subduction increases the oxidation state of Earth's mantle are two of the most important unresolved questions in solid Earth geochemistry. Using data from the southern Cascade arc (California, USA), we show quantitatively for the first time that increases in arc magma oxidation state are fundamentally linked to mass transfer of isotopically heavy sulfate from the subducted plate into the mantle wedge. We investigate multiple hypotheses related to plate dehydration and melting and the rise and reaction of slab melts with mantle peridotite in the wedge, focusing on electron balance between redox-sensitive iron and sulfur during these processes. These results show that unless slab-derived silicic melts contain much higher dissolved sulfur than is indicated by currently available experimental data, arc magma generation by mantle wedge melting must involve multiple stages of mantle metasomatism by slab-derived oxidized and sulfur-bearing hydrous components.

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板坯衍生的硫酸盐在南喀斯喀特弧（美国加利福尼亚州）产生氧化玄武质岩浆

俯冲是否以及如何增加地幔的氧化态是固体地球化学中两个最重要的未解决的问题。使用来自南喀斯喀特弧（美国加利福尼亚州）的数据，我们首次定量地表明弧岩浆氧化态的增加与同位素重硫酸盐从俯冲板块向地幔楔的质量转移有根本的联系。我们研究了与板块脱水和熔化以及板坯熔体与楔形地幔橄榄岩的上升和反应相关的多种假设，重点研究了这些过程中氧化还原敏感铁和硫之间的电子平衡。这些结果表明，除非板坯衍生的硅熔体含有比目前可用的实验数据表明的高得多的溶解硫，