Absolute Primary Pressure Scale to 120 GPa: Toward a Pressure Benchmark for Earth's Lower Mantle

Abstract

Self-consistent absolute primary pressure scale available to whole Earth's lower mantle pressure regime was established by the simultaneous measurement of densities and acoustic wave velocities of NaCl-B2 phase up to ~120 GPa without any use of prior pressure standards. While our pressure scale shows excellent agreement with the theoretical predictions, some of the previous secondary pressure scales constructed based on the prior pressure standard by the shock wave data significantly deviate from our primary scale reaching above 12 GPa at most within lower mantle pressure regime, which corresponds to ~120-km difference in depth. Our newly established pressure scale would thus be a new benchmark to deal with the controversy on the depth of the boundaries of Earth's layered structure, such as magnesium-silicate postperovskite phase transition boundary at the bottom of the Earth's mantle which might represent the D″ seismic discontinuity.