Effect of pressure on the melting of diopside, CaMgSi2O6, and albite, NaAlSi3O8, in the range up to 50 kilobars

The melting curves of albite and diopside have been determined in the pressure range 5 to 50 kb by means of single-stage apparatus. Data are given for NaAlSi3O8 composition only at pressures below 33 kb, where albite is the phase stable at the liquidus. Simon equations have been calculated for both curves, and they fit the data well. The melting curves have a pronounced curvature, and the slopes at pressures above 25 kb are only about half the initial slopes. These results suggest that the effect of pressure on the melting of rocks in the mantle will decrease notably with depth. Extrapolation of the diopside curve to a pressure of 1400 kb, equivalent to that present at the core-mantle boundary, gives a melting temperature of 3750°C. Experience with single-stage apparatus has shown that the friction correction of −8 per cent that we previously applied is probably too large. Results of this study are given as load pressures and are believed to be accurate within ±5 per cent.