EXPERIMENTAL-DETERMINATION OF THE REACTION DOLOMITE PLUS 2 COESITE EQUALS DIOPSIDE PLUS 2 CO2 TO 6 GPA

The carbonation reaction CaMg(CO3)(2) (dolomite) + 2SiO(2) (coesite) = CaMgSi2O6 (diopside) + 2 CO2 (vapor) has been determined experimental ly between 3.5 and 6 GPa in a multiple-anvil, solid-media apparatus. T his reaction, a candidate for carbonation of eclogites (garnet + clino pyroxene) in the Earth's mantle, lies at higher pressure for a given t emperature than do the carbonation reactions for peridotites (olivine + orthopyroxene +/- clinopyroxene). A depth interval may exist within the Earth's mantle under either 'normal' or 'subduction' thermal regim es where carbonated peridotite could coexist with carbonate-free, CO2- bearing eclogite.