The relative enrichment of sulfur (S) observed in arc magmas when compared to MORB, reflects the addition of slab-derived S to the mantle wedge source region. However, the mechanisms and efficiency of such S recycling remain poorly constrained. In this study, sediment melting experiments have been conducted using a synthetic pelite starting composition containing ∼7 wt% H₂O and ∼1.9 wt% S, at 3 GPa, 1050°C and variable oxygen fugacity (fO₂)_, to investigate the effect of fO₂ on S solubility in sediment melts. To assess temperature and concentration effects, selected experiments were repeated either at lower temperatures of 950°C and 1000°C, or with a higher bulk S content of ∼4 wt%. All experiments produced hydrous rhyolitic melts, saturated with either pyrrhotite under reduced conditions or anhydrite under oxidized conditions. For 3 GPa, 1050°C experiments, the sulfur content at sulfide saturation (SCSS) in melt is found to increase with decreasing fO_2, from ∼200 ppm at FMQ-0.5 to ∼1900 ppm at FMQ-7.5. The highest S solubility is achieved at FMQ+1.6 where melt is saturated with both anhydrite and pyrrhotite. The sulfur content at sulfate saturation (SCAS) decreases from ∼2600 ppm at FMQ+1.6 to ∼2000 ppm at FMQ+7. Increasing either bulk S content or temperature produces a positive effect on SCSS and SCAS. Raman spectra of our experimental melts show that S exists as H₂S/HS^- under reduced conditions and as SO₄^2- under oxidized conditions. The solubility minimum, i.e., the onset of transition from S^2- to S⁶⁺ is estimated to occur at ∼FMQ, with full transition to S⁶⁺ by ∼FMQ+2. While the SCAS values are in good agreement with previous reports, the distinct increase of SCSS with decreasing fO₂ (when fO₂<FMQ) has not been observed in previous slab melting experiments. Furthermore, we report for the first time that dissolution of H₂S and SO₂ in hydrous rhyolitic melt follows the Fincham-Richardson relationship; and propose the definition of a hydro-sulfide capacity as C_HS = [HS]*(fO₂/fS₂)^1/2; where [HS] is the concentration of S in melt (in ppm) dissolved as HS^- and H₂S. SCSS for H₂S dissolution can therefore be modeled using C_HS in an analogous fashion to modeling SCSS for anhydrous melts using the sulfide capacity (C_S^2-), with the relation $ln{[\text{HS}]}_{\text{SCSS}}=-\mathrm{\Delta }{G}_{\text{Fes - FeO}}^{°}/RT+\text{ln}{C}_{\text{HS}}-\text{ln}{a}_{\text{FeO}}^{\text{melt}}+\text{ln}{a}_{\text{FeS}}^{\text{sulfide}}$. As predicted by such a model framework, we indeed observe a linear correlation between logSCSS and logX_FeO (the mole fraction of FeO in melt) with a slope close to -1, i.e., SCSS experiences a sharp increase when FeO in melt falls below 1 wt%. Therefore, both our experimental results and model predictions suggest hydrous low-Fe rhyolitic melt produced by sediment melting under reduced conditions has the required S solubility to account for the relative enrichment of S observed in arc magmas.

与MORB相比，在弧岩浆中观察到的硫（S）的相对富集反映了板坯衍生的S添加到地幔楔源区。但是，这种硫回收的机理和效率仍然受到限制。在这项研究中，沉积物熔化实验已经使用合成泥质起始含~7重量％H组合物已进行₂ O和〜1.9％（重量）S，在为3GPa，1050℃和可变氧逸度（˚F Ò ₂）_，调查的效果˚F Ò ₂S在沉积物熔体中的溶解度。为了评估温度和浓度的影响，在较低的950°C和1000°C的温度下，或在〜4 wt％的较高体积S含量下重复了选定的实验。所有实验均产生含水流变质熔体，在还原条件下用黄铁矿或在氧化条件下用无水铁矿饱和。对于1050°C，3 GPa的实验，发现熔体中硫化物饱和（SCSS）时的硫含量随着f O _2的降低而增加_。从FMQ-0.5时约200 ppm到FMQ-7.5时约1900 ppm。最高的S溶解度在FMQ + 1.6时达到，熔体同时被硬石膏和黄铁矿饱和。硫酸盐饱和度（SCAS）下的硫含量从FMQ + 1.6时的〜2600 ppm降至FMQ + 7时的〜2000 ppm。增加大量S含量或温度都会对SCSS和SCAS产生积极影响。我们的实验熔体的拉曼光谱显示该S存在以H ₂ S / HS ^-还原条件下和作为SO ₄ ^2-氧化条件下进行。溶解度最小值，即从S ^2-过渡到S ^6+的开始时间估计在〜FMQ发生，并完全过渡到S ⁶⁺〜FMQ + 2。虽然SCAS值与以前的报告非常吻合，但在以前的板坯熔化实验中，未观察到SCSS随着f O _2的降低而明显增加（当f O ₂ <FMQ时）。此外，我们首次报道了H ₂ S和SO ₂在含水流纹岩熔体中的溶解遵循Fincham-Richardson关系。并提出了硫化氢容量的定义为C _HS = [HS] *（f O ₂ / f S ₂）^1/2；其中[HS]是溶解为HS的熔体中S的浓度（以ppm为单位）^-和H ₂ S. SCSS用于h ₂小号溶解，因此可以使用建模Ç _HS以类似的方式来建模使用硫化物容量（无水熔体SCSS Ç_小号^2-），与所述关系$ln{[\text{HS}]}_{\text{SCSS}}=--\mathrm{\Delta }{G}_{\text{Fes-FeO}}^{°}/\mathrm{[R}Ť+\text{ln}{C}_{\text{HS}}--\text{ln}{\mathrm{一种}}_{\text{氧化铁}}^{\text{熔化}}+\text{ln}{\mathrm{一种}}_{\text{硫化铁}}^{\text{硫化物}}$。正如该模型框架所预测的，我们确实观察到logSCSS与log X _FeO（熔体中FeO的摩尔分数）之间的线性相关，其斜率接近-1，即，当熔体中FeO降至以下时，SCSS急剧增加。 1重量％。因此，我们的实验结果和模型预测均表明，在还原条件下通过沉积物熔融产生的含水低铁流纹熔体具有所需的S溶解度，以解决弧岩浆中S的相对富集问题。