Solubility of CO2 in olivine melilitite at high pressures and role of CO2 in the earth's upper mantle

The positions of the liquidi and the near-liquidus phases of olivine-melilitite+CO₂ have been determined under MH-buffered and furnace-buffered conditions up to 40 kb. It is found that CO₂ alone lowers the liquidus compared to dry conditions, yet its influence is minor compared to H₂O. The major role of CO₂ is to favour the growth of orthopyroxene and garnet over that of olivine at least at high pressures. CO₂-contents of glasses from experiments just above the liquidus (MH-buffered) were determined as 5.1 % at 10kb; 7.5 % at 20kb, 9.3 % at 30kb and 10–11 % (estimated) at 40 kb. Experiments on (pyrolite –40 % olivine)+H₂O+CO₂ show that CO₂ occurs under mantle conditions as carbonate under subsolidus conditions and dissolved in a melt above the solidus. At 30kb, the solidus lies between 1,000 ° C and 1,050 ° C for vapour-saturated conditions, at and at .