The Ti4+/Ti3+ ratio of magmatic melts: Application to the problem of the reduction of lunar basalts

Using published experimental data an expression was derived for the Ti4+/Ti3+ ratio as a function of temperature, oxygen fugacity, and melt composition. The equation can be used to estimate Ti3+ content in lunar basaltic melts. It was shown that the Ti3+ content in melts is probably no higher than the Fe3+ content even under the reduced conditions typical of lunar magmas. Trivalent Ti can lead to some decrease in fO₂ during melt cooling under closed-system conditions, but it cannot reduce Fe2+ in melt to metal, because it will be completely consumed by Fe3+ reduction to Fe2+. The presence of additional reducers, such as Cr2+, can be favorable for the formation of metal during melt cooling.