The ferric/ferrous ratio in silicic melts: experimental investigation and modelling

岩浆系统中的地球化学过程强烈地依赖于氧逸度和硅酸盐熔体中的Fe ~（3+）/Fe ~（2+）比值。现在可以使用Borisov等人最近提出的改进模型充分预测镁铁质熔体的这一比例（2018年，对矿物学和岩石学的贡献），但到目前为止提出的所有模型都不适合或不满足富二氧化硅成分（SiO2 > 65-68重量%）。在这个建议中，它计划通过测试网络形成和网络改性阳离子在各种流纹岩组合物中的作用，包含高达10重量%的Fe 2 O3 tot，以改善模型预测Fe 3 +/Fe 2+的比率。在大气压下进行的实验工作将包括在各种温度和氧逸度下平衡铝硅酸盐熔体。将通过湿化学法测定Fe 3 +/Fe 2+比。结果将与以前的数据集相结合，以提供一个一致的热力学模型，准确预测温度的影响，fO 2和熔体组成的Fe 3 +/Fe 2+比在很宽的组成范围内（镁铁质到镁铁质熔体），特别注意富硅熔体。

Geochemical processes occurring in magmatic systems depend strongly on oxygen fugacity and on the Fe3+/Fe2+ ratio in silicate melts. This ratio can now be predicted adequately for mafic melts using the refined model proposed recently by Borisov et al. (2018, Contributions to Mineralogy and Petrology), but all models proposed so far are not suitable or satisfying for silica-rich compositions (SiO2 > 65-68 wt%). In this proposal, it is planned to improve the models predicting Fe3+/Fe2+ ratios by testing the role of network-forming and network-modifying cations in various rhyolitic compositions containing up to 10 wt% Fe2O3tot. The experimental work, conducted at atmospheric pressure, will consist in equilibrating aluminosilicate melts at various temperatures and oxygen fugacities. The Fe3+/Fe2+ ratio will be determined by wet chemistry. The results will be combined with previous datasets to provide a consistent thermodynamic model predicting accurately the effect of temperature, fO2 and melt composition on the Fe3+/Fe2+ ratio over a wide compositional range (mafic to silicic melts), with particular attention to silica-rich melts.