Density of jadeite melts under high pressure and high temperature conditions

摘要

The density of the jadeite (NaAlSi_2O_6) 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 thermo-elastic parameters: density, p_0 = 2.36 g/cm~3, isothermal bulk modulus, K_(T0) = 21.5 ± 0.8 GPa, its pressure derivative, K_o′ = 8.9 ± 1.2, and the temperature derivative (∂K_T/∂T)_P = -0.0021 ± 0.0011 GPa/K at a reference temperature T_0 = 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 = Si~(4+), Al~(3+)). Compressibilities of jadeite, albite, diopside, phonolite and peridotite melts display a systematic trend: the K_0-K_0′ plot of these silicate melts exhibits an inverse linear relation.