Effects of P₂O₅ and TiO₂ on the partial melting of spinel Lherzolite in the system CaO-MgO-Al₂ O₃-SiO₂ at 1.1 GPa

The effects of small amounts of P₂O₅ on the partial melting of model spinel lherzolite in the system CaO-MgO- Al₂O₃- SiO₂ + P₂O₅ have been investigated at 1.1 GPa in piston-cylinder experiments, in order to constrain the influence of this minor component on mantle melting. A concentration of 1 wt% P₂O₅ in the melt depresses the solidus of spinel lherzolite by only 2°C, reduces SiO₂ in melts by 1 wt% and Al₂O₃ by 0.44 wt%, but increases CaO by 0.3 wt% and MgO by 0.14 wt%. A preliminary investigation of the effect of TiO₂ in the system CaO- MgO-Al₂ O₃-SiO₂ + TiO₂ shows that it decreases the solidus by ∼1°C/wt%, and its effect on the melt composition is small, being mainly one of dilution.