Phase diagram of iron, revised‐core temperatures

Shock‐wave experiments on iron preheated to 1573 K from 14 to 73 GPa, yield sound velocities of the γ‐ and liquid‐phases. Melting is observed in the highest pressure (∼71 ± 2 GPa) experiments at calculated shock temperatures of 2775 ± 160 K. This single crossing of the γ‐liquid boundary agrees with the γ‐iron melting line of Boehler [1993], Saxena et al. [1993], and Jephcoat and Besedin [1997]. This γ‐iron melting curve is ∼300°C lower than that of Shen et al. [1998] at 80 GPa. In agreement with Brown [2001] the discrepancy between the diamond cell melting data and the iron shock temperatures require the occurrence of yet another sub‐solidus phase along the principal Hugoniot at ∼200 GPa. This would reconcile the static and dynamic data for iron's melting curve. Upward pressure and temperature extrapolation of the γ‐iron melting curve to 330 GPa yields 5300 ± 400 K for the inner core‐outer core boundary temperature.