Experiments on CaCO3-MgCO3 solid solutions at high pressure and temperature

Multi-anvil experiments have been performed ill the system CaCO3-MgCO3 at pressures of 5.0-7.0 GPa and temperatures of 800-1600 degrees C. The reaction dolomite = aragonite + magnesite has been reversed and located near 750 degrees C at 5.0 GPa, 900 degrees C at 6.0 GPa,and 1000 degrees C at 7.0 GPa. Between 5 and 6 GPa, the reaction boundary is strongly curved and its dP/dT slope increases from 2 to 12 MPa/degrees C, expanding the stability field of dolomite. This increase is attributed to increasing Ca-Mg disorder in the dolomite. In addition to the reaction boundary, in isobaric section of CaCo3-MgCO3 has been determined at 6.0 GPa. There is a two-phase field of aragonite + dolomite on the Ca-rich side, which closes before minimum melting temperatures of: 1350 degrees C Life reached. The two-phase field oil the Mg-rich side, where dolomite + magnesite coexist, intersects with the solidus. Inferred minimum melts Lire close to dolomite composition Suggesting congruent melting of dolomite at 6 GPa. The melt compositions and temperatures in the pure carbonate system Lire surprisingly similar to solidus phase relations in the CMAS-CO2 system. implying that minimum melting conditions in carbonated peridotite at high pressures Lire dominated and controlled by the carbonate component.