The density of carbonated peridotite magma was measured up to 3.8 GPa and 2100 K using an X-ray absorption method. A fit of the pressure-density-temperature data to the high-temperature Birch-Murnaghan equation of state yielded the isothermal bulk modulus, KT0 = 22.9 ± 1.4 GPa, its pressure derivative, K0′ = 7.4 ± 1.4, and the temperature derivative of the bulk modulus (∂KT/∂T)P = −0.006 ± 0.002 GPa/K at 1800 K. The bulk modulus of carbonated peridotite magma is larger than that of hydrous peridotite magma. The partial molar volume of CO2 in magma under high pressure and temperature conditions was calculated and fit using the Vinet equation of state. The isothermal bulk modulus was KT0 = 8.1 ± 1.7GPa, and its pressure derivative was K0′ = 7.2 ± 2.0 at 2000 K. Our results show that the partial molar volume of CO2 is less compressible than that of H2O, suggesting that, on an equal molar basis, CO2 is more effective than H2O in reducing peridotite melt density at high pressure.

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