The effect of titanium and phosphorus on ferric/ferrous ratio in silicate melts: an experimental study
The effect of titanium and phosphorus on ferric/ferrous ratio in silicate melts: an experimental study
复制标题
DOI：
10.1007/s00410-013-0943-9
复制
发表时间：
2013-12-01
影响因子：
3.5
通讯作者：
Holtz, Francois
中科院分区：
文献类型：
--
作者：
Borisov, Alexander;Behrens, Harald;Holtz, Francois
在模拟的硅酸盐熔体中，研究了二氧化钛和五氧化二磷对硅酸盐熔体中铁/铁比的影响。用10wt%的Fe2O3和不同量的二氧化钛(高达30wt%)或五氧化二磷(高达20wt%)对钙长石-透辉石共晶化合物的基础成分进行了改性。有些成分还含有较高的二氧化硅浓度，以比较二氧化硅、二氧化钛和五氧化二磷对Fe3+/Fe2+比率的影响。采用湿化学比色法测定亚铁，分析了实验玻璃中的铁/铁比。结果表明，在恒温条件下，随着SiO_2、TiO_2和P_2O_5含量的增加，铁/铁比降低。二氧化钛和二氧化硅对Fe~(3+)/Fe~(2+)比值的影响基本相同。相反，添加P_2O_5比添加SiO_2更有效地降低铁/铁比。将结果与已发表的预测Fe3+/Fe2+比值的经验公式的预测值进行了比较。结果表明，二氧化钛的影响很小，但为了更好地描述含磷硅酸盐熔体中的铁/铁比，模型中应考虑P2O5的影响。在此基础上，讨论了用迄今发表的经验公式从天然玻璃中的Fe3+/Fe2+比值确定岩浆中的普遍fO(2)。
The effect of TiO2 and P2O5 on the ferric/ferrous ratio in silicate melts was investigated in model silicate melts at air conditions in the temperature range 1,400-1,550 degrees C at 1-atm total pressure. The base composition of the anorthite-diopside eutectic composition was modified with 10 wt % Fe2O3 and variable amounts of TiO2 (up to 30 wt %) or P2O5 (up to 20 wt %). Some compositions also contained higher SiO2 concentrations to compare the role of SiO2, TiO2, and P2O5 on the Fe3+/Fe2+ ratio. The ferric/ferrous ratio in experimental glasses was analyzed using a wet chemical technique with colorimetric detection of ferrous iron. It is shown that at constant temperature, an increase in SiO2, TiO2, and P2O5 content results in a decrease in the ferric/ferrous ratio. The effects of TiO2 and SiO2 on the Fe3+/Fe2+ ratio was found to be almost identical. In contrast, adding P2O5 was found to decrease ferric/ferrous ratio much more effectively than adding silica. The results were compared with the predictions from the published empirical equations forecasting Fe3+/Fe2+ ratio. It was demonstrated that the effects of TiO2 are minor but that the effects of P2O5 should be included in models to better describe ferric/ferrous ratio in phosphorus-bearing silicate melts. Based on our observations, the determination of the prevailing fO(2) in magmas from the Fe3+/Fe2+ ratio in natural glasses using empirical equations published so far is discussed critically.