The solidus of carbonated, fertile peridotite

The solidus for a fertile peridotite composition (“Hawaiian pyrolite”) in the presence of CO₂ has been determined from 14 to 35 kbar. The solidus shape inP-T space is consistent with previous studies in the model system CaO—MgO—SiO₂—CO₂. The intersection of the decarbonation reaction Olivine + Diopside + CO₂ ⇌ Orthopyroxene + Dolomite with the pyrolite solidus defines the pointI₆, which is located at 20.5 kbar, 1050°C. At pressures less thanI₆ the solidus is only slightly (20–50°C) below that of the volatile-absent (C—H absent) solidus but at pressures greater thanI₆ the solidus curve is approximately 275°C below the volatile-absent solidus. The large depression of the solidus to lower temperatures with little change in pressure occurs at approximately 19 kbar, 1250°C. At 26 kbar the Hawaiian pyrolite-CO₂ solidus is approximately 100°C higher than the solidus for Hawaiian pyrolite-H₂O—CO₂ confirming that the primary sodic dolomitic carbonatite melt at the latter solidus does contain some dissolved water.