Influence of water and fluorine on melting of carbonated peridotite at 6 and 10 GPa

Experiments on partial melting of the garnet lherzolite–CO2–H2O and garnet wherlite–CO2–F systems were performed at 6 and 10 GPa and 1100–1600 °C using a multianvil apparatus. A comparison with previous experiments on peridotite–CO2 shows that the addition of H2O or F depresses the solidus of carbonated peridotite by almost 300 °C at 10 GPa and 150 °C at 6 GPa. Magnesite was stable near the solidus in both systems, and its stability field expanded with increasing pressure up to almost 300 °C above the solidus at 10 GPa. In the F-bearing system, F-clinohumite was found near the solidus. The compositions of melts in the hydrous system are similar to those in peridotite–CO2 experiments. The melts in equilibrium with F-clinohumite contain up to 16 wt.% F. F-bearing liquids are poorer in FeO and richer in MgO, CaO and SiO2 compared with those from the hydrous system. The compositions of partial melts were compared with the fields of kimberlites. It was found that, despite the strong depression of the carbonated peridotite solidus in presence of H2O and F, the formation of kimberlite-like melts (i.e. containing about 30 wt.% SiO2) requires very high temperatures (1600 °C at 6 GPa and 1700 °C at 10 GPa). It was also concluded that melts derived from a primitive or slightly depleted magnesite-bearing peridotite are different from possible primary kimberlite magmas.