Thermal expansion measurements at very high pressure, systematics, and a case for a chemically homogeneous mantle

Abstract

New data on thermal expansivity, α, of iron to over 400 kbar in laser‐ and electrically‐heated diamond anvil cells and on MgO and forsterite from spectroscopic data to over 200 kbar and previously measured adiabats [Boehler, 1982], imply that α at high pressure may be described by a constant value of (∂1nα/∂1nV) T = 5.5 ± 0.5. This behavior is supported by previous α measurements at lower pressures on a large variety of materials. Densities of magnesio‐wüstite and silicate perovskite in a pyrolitic ratio calculated at lower mantle conditions using a finite strain equation and α at high pressures, using the above systematics, match those in PREM through the entire lower mantle, making a strong case for a uniform mantle.