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

Abstract

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, K 0 ′ = 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 CO 2 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 K 0 ′ = 7.2 ± 2.0 at 2000 K. Our results show that the partial molar volume of CO 2 is less compressible than that of H 2 O, suggesting that, on an equal molar basis, CO 2 is more effective than H 2 O in reducing peridotite melt density at high pressure.