Velocity-Density Systematics of Fe-5wt%Si: Constraints on Si Content in the Earth's Inner Core

摘要

The elasticity of hcp-Fe-5wt%Si has been investigated by synchrotron X-ray diffraction up to 110GPa and 2,100K and by picosecond acoustics measurements at ambient temperature up to 115GPa. The established Pressure-Volume-Temperature equation of state shows that the density of the Earth's inner core can be matched by an Fe-Si alloy with 5wt% Si for all reasonable core temperatures, but that its compressional and shear velocities remain too high with respect to seismological observations. On the other hand, Fe-Si alloys whose velocities are expected to get close to seismological observations are too dense at relevant temperatures. Thus, based on these combined velocity-density measurements, silicon is not likely to be the sole light element in the inner core.