Thermal equation of state of lower-mantle ferropericlase across the spin crossover

摘要: The thermal equation of state ferropericlase [(Mg{sub 0.75}Fe{sub 0.25})O] has been investigated by synchrotron X-ray diffraction up to 140 GPa and 2000 K in a laser-heated diamond anvil cell. Based on results at high pressure-temperature conditions, the derived phase diagram shows that spin crossover widens elevated temperatures. Along lower-mantle geotherm, occurs between 1700 km 2700 depth. Compared high-spin state, thermoelastic modeling data {approx}1.2% increase density, factor two expansion coefficient over range 1000 km, maximum decrease 37% 13% bulk modulus sound velocity, respectively, {approx}2180 depth across crossover. These anomalous behaviors properties must be taken into account order understand seismic signatures geodynamics lower mantle.