Measurement of hydrous peridotite magma density at high pressure using the X-ray absorption method

The density of hydrous peridotite magma containing 5 wt.% H2O was measured at pressures and temperatures up to 4.3 GPa and 2073 K, respectively, using the X-ray absorption method. A fit of pressure–density–temperature data to the high-temperature Birch–Murnaghan equation of state yields isothermal bulk modulus KT = 8.8 ± 1.9 GPa, its pressure derivative K′ = 9.9 ± 3.6 and the temperature derivative of the bulk modulus (∂KT/∂T)P = − 0.0022 ± 0.0015 GPa/K at 1773 K. The small bulk modulus of the hydrous peridotite magma compared with that of the dry peridotite magma reflects the effect of water, which is more compressible than the silicate melt. The partial molar volume of H2O in magma under high pressure conditions was calculated and fitted using the Vinet equation of state. The isothermal bulk modulus was KT = 2.4 ± 1.0 GPa, and its pressure derivative was K′ = 5.7 ± 1.5 at 1973 K.