Edmund, Eric ; Morard, Guillaume ; Baron, Marzena Anna ; Rivoldini, Attilio ; Yokoo, Shunpei ; Boccato, Silvia ; Hirose, Kei ; Pakhomova, Anna ; Antonangeli, Daniele

Talk presented at AGU Fall Meeting 2021, New Orleans, online on 2021-12-16

Abstract: Mercury’s iron core is expected to contain some quantity of silicon, with estimated Si abundances spanning nearly the entire Fe-FeSi phase diagram. However, at present it is not understood how this phase diagram evolves over the P-T conditions of Mercury’s core. Consequently, the effect of silicon alloying on Mercury’s core crystallization regime, thermal and structural evolution are not well constrained. Here we present an investigation of the Fe-FeSi system over a wide range of Si concentrations (7-30 wt% Si), using laser-heated diamond anvil cells, and combining in situ and ex situ diagnostics. We present a new phase diagram for this system at Mercury’s core conditions – providing new constraints on melting temperatures, solid/liquid partitioning and solid phase relations. In doing so, we show that the unique behaviour of this system can stabilize new mechanisms for structural evolution and crystallization, with no current analogues among terrestrial planets.

Keyword(s): Mercury, core, Fe-Si
Funding: 3PRODPLANINT/3PRODPLANINT/3PRODPLANINT