The effect of network-formers (Si, Ti, Al and P) on ferric/ferrous ratio in silicate melts: experimental study and improvement of existing models.

岩浆系统中发生的地球化学过程强烈地依赖于氧逸度和硅酸盐熔体中的Fe3/Fe2比值。可以使用现有的热力学模型从理论上预测这一比例。现有的热力学模型考虑了组成参数，但主要考虑网络修饰的阳离子(Ca、Mg、Na、K)。很少有系统的研究允许我们考虑形成网络的阳离子(Si，Al，Ti，P)的影响。在本项目中，将在1bar的条件下实验研究Al对硅酸盐熔体中Fe3/Fe2比值的影响。这一结果将与最近有关硅、磷和钛对硅酸盐熔体中Fe3/Fe2比值影响的数据相结合，以提供一个一致的热力学模型，准确地预测熔体组成，特别是SiO_2、Al_2O_3、TiO_2和P_2O_5对镁铁质熔体中Fe_3/Fe_2比值的影响。这一结果不仅对地球上形成的镁铁质熔体及其分异产物(硅质熔体)有重要意义，而且对解释月球或其他行星系玄武岩的形成和演化也有重要意义，这些玄武岩与地球玄武岩的Al/Si比值不同。

Geochemical processes occurring in magmatic systems depend strongly on oxygen fugacity and on the Fe3+/Fe2+ ratio in silicate melts. This ratio can be theoretically predicted using available thermodynamic models. The available thermodynamic models take compositional parameters into account, but mainly for network modifying cations (Ca, Mg, Na, K). There are few systematic studies allowing us to take the effects of network forming cations into account (Si, Al, Ti, P). In this project, the effect of Al on the Fe3+/Fe2+ ratio in silicate melts will be investigated experimentally at 1 bar. The results will be combined with recent previous datasets on the effects of Si, P und Ti on the Fe3+/Fe2+ ratio in silicate melts to provide a consistent thermodynamic model predicting accurately the effect of melt composition, in particular SiO2, Al2O3, TiO2 and P2O5, on the Fe3+/Fe2+ ratio of mafic melts. The results are of importance for mafic melts generated in the Earth and for their differentiation products (silicic melts) but also for the interpretation of the formation and evolution of basalts from the Moon or other planetary systems, which differ from Earth basalts by their Al/Si ratio.