P–V–T equation of state of Na-majorite to 21 GPa and 1673 K

Abstract

The P–V–T equation of state (EoS) for Na-majorite at pressures to 21GPa and temperatures to 1673K was obtained from in situ X-ray diffraction experiments using a Kawai-type multi-anvil apparatus. Analyses of the room-temperature P–V data to a third-order Birch–Murnaghan EoS yielded ambient unit cell volume, V0=1476 (1) (Å3); isothermal bulk modulus, K0,300=181 (9) GPa; and its pressure derivative, K0,300′=4.4 (1.2). When fitting a high-temperature Birch–Murnaghan EoS using entire P–V–T data at a fixed V0=1475.88Å3, K0,300=184 (4) GPa, K0,300′=3.8 (6), (∂K0,T/∂ T)P=−0.023 (5) (GPaK−1), and a=3.17 (16)×10−5K−1, b=0.16 (26)×10−8K−2, where α=a+bT is the volumetric thermal expansion coefficient. Fitting the Mie–Grüneisen–Debye EoS with the present data to Debye temperature fixed at θ0=890K yielded Grüneisen parameter, γ0=1.35 at q=1.0 (fixed). The new data on Na-majorite were compared with the previous data on majorite type garnets. The compression mechanism of majoritic garnets was described in detail. The entire dataset enabled to examine the thermoelastic properties of important mantle garnets and these data will have further applications for modeling P–T conditions in the transition zone of the Earth’s mantle using ultradeep mineral assemblages.