Compositional effect on the pressure derivatives of bulk modulus of silicate melts

Abstract

Although the bulk moduli ( K T 0) of silicate melts have a relatively narrow range of values, the pressure derivatives of the isothermal bulk modulus ( K T 0 ′) can assume a broad range of values and have an important influence on the compositional dependence of the melt compressibility at high pressure. Based on the melt density data from sink/float experiments at high pressures in the literature, we calculate K T 0 ′ using an isothermal equation of state (EOS) (e.g., Birch–Murnaghan EOS and Vinet EOS) with the previously determined values of room-pressure density ( ρ 0) and room-pressure bulk modulus ( K T 0). The results show that best estimates of K T 0 ′ vary considerably from ~ 3 to ~ 7 for different compositions. K T 0 ′ is nearly independent of Mg # (molar Mg/(Mg + Fe)), but decreases with SiO 2 content. Hydrous melts have anomalously small K T 0 ′ leading to a high degree of compression at high pressures. For anhydrous melts, K T 0 ′ is ~ 7 for peridotitic melts, ~ 6 for picritic melts, ~ 5 for komatiitic melts, and ~ 4 for basaltic melts.