Shock Melting Curve of Iron: A Consensus on the Temperature at the Earth's Inner Core Boundary

Abstract

Abstract The Earth's core consists of iron as the major component. The melting point of iron at the inner core boundary constrains the thermal structure and solidification of the Earth's core. However, the current estimation of the melting temperature of iron under the core conditions has significant variations. Here, we measured the temperatures of iron shocked up to ~256 GPa using precise pyrometer and velocimeter diagnostics via a two‐stage light‐gas gun. Our results indicated that the melting temperatures of iron at the core‐mantle and inner core boundaries are 4300(250) and 5950(400) K, respectively. These temperatures are significantly lower than some previous shock experiments but are overall consistent with the recent results determined by fast X‐ray diffraction techniques, X‐ray absorption experiments in laser‐heated diamond anvil cells, and by ab initio computations. Our iron melting curve indicates a relatively small Clapeyron slope and supports thermal models for a young inner core.