Density of carbonated peridotite magma at high pressure using an X-ray absorption method

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, K_T0 = 22.9 ± 1.4 GPa, its pressure derivative, K₀' = 7.4 ± 1.4, and the temperature derivative of the bulk modulus (∂K_T∂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 K_T0 = 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 H ₂O, suggesting that, on an equal molar basis, CO₂ is more effective than H₂O in reducing peridotite melt density at high pressure.