Density of jadeite melts under high pressure and high temperature conditions

Abstract

The density of the jadeite (NaAlSi₂O₆) melt has been measured up to 6.5 GPa and 2273 K using the X–ray absorption technique at beamline 13–BM–D of the Advanced Photon Source. A fit of the pressure–density–temperature data to the high temperature Birch–Murnaghan equation of state yielded the following thermoelastic parameters: density, ρ₀ = 2.36 g/cm³, isothermal bulk modulus, K_T0 = 21.5 ± 0.8 GPa, its pressure derivative, K₀′ = 8.9 ± 1.2, and the temperature derivative (∂K_T/∂T)_P = −0.0021 ± 0.0011 GPa/K at a reference temperature T₀ = 1473 K. The densification of jadeite melt at low pressures is primarily dominated by topological changes in the structure, including a decrease in T–O–T angle and breaking and reforming of the T–O bond (T = Si⁴⁺, Al³⁺). Compressibilities of jadeite, albite, diopside, phonolite and peridotite melts display a systematic trend: the K₀–K₀′ plot of these silicate melts exhibits an inverse linear relation.