Carbonate melts in the hydrous upper mantle

Carbonatite compositions resulting from melting of magnesian calcite + olivine + clinopyroxene were experimentally determined in the system CaO–MgO–SiO 2 –CO 2 –H 2 O as a function of temperature and bulk H 2 O contents at 1.0 and 1.5 GPa. The melting reaction and melt compositions were found to be highly sensitive to H-loss or -gain during experiments. We hence designed a new hydrogen-trap technique, which provided sufficient control to obtain consistent results. The nominally dry solidus temperatures at 1.0 and 1.5 GPa are 1225–1250 °C and 1275–1300 °C, respectively. At 1.0 GPa, the solidus temperature decreases with H 2 O increasing to 3.5 wt