Shock compression of Fe-Ni-Si system to 280 GPa: Implications for the composition of the Earth's outer core

摘要

The shock Hugoniot of an Fe-9 wt %Ni-10 wt %Si system as a model of the Earth's core has been measured up to -280 GPa using a two-stage light-gas gun. The samples had an average density of 6.853 (±0.036) g/cm~3. The relationship between shock velocity (U_s) and particle velocity (u_p) can be described by U_s (km/s) = 3.95 (±0.15) + 1.53 (±0.05) u_p (km/s). The calculated Hugoniot temperatures and the melting curve indicate that the model composition melts above a shock pressure of ~168GPa, which is significantly lower than the shock-melting pressure of iron (-225 GPa). A comparison of the pressure-density (P-p) profiles between the model composition and the preliminary reference Earth model gives a silicon content close to 10wt %, necessary to compensate the density deficit in the Earth's outer core from seismological observations, if silicon is present as a major light element in the Fe-Ni core system.