The solidus of carbonated eclogite in the system CaO-Al 2O 3-MgO-SiO 2-Na 2O-CO 2 to 32 GPa and carbonatite liquid in the deep mantle
Melting phase relations have been determined in a model carbonated eclogite (5 wt.% CO2) at 10.5-32.0 GPa and 1300-1850 °C. The assemblage of silicate minerals coexisting with partial melts changes with pressure from garnet-omphacite-kyanite-stishovite at 10 GPa via garnet-corundum-stishovite at 16-20 GPa to Mg-perovskite-Ca-perovskite-CF phase-stishovite at 27-32 GPa. Magnesite is the only carbonate stable in this system through the studied pressure range. The solidus temperature was defined by the appearance of partial melt. The solidus of carbonated eclogite is bracketed at 1380-1460 °C at 10.5 GPa, 1460-1560 °C at 16.5 GPa, 1530-1630 °C at 20 GPa, and 1600-1790 °C at 27 and 32 GPa. The slope of solidus curve is less steep at 10-32 GPa than at lower pressures. The solidus curve of Fe-free carbonated eclogite roughly coincides with an average mantle geotherm. Partial melts formed by melting of carbonated eclogite at 10.5-32.0 GPa have magnesiocarbonatite compositions with Ca/Mg ratios higher than in similar melts in peridotite assemblages, and contain high Na2O-contents. It has been demonstrated that carbonatite-like melt can be generated by partial melting of carbonated eclogites at pressure up to at least 32 GPa, i.e. to lower mantle depths.