Microstructures of Fe-16wt%S-2wt%Si in Partial and Complete Melt Regions at High Pressures: Implications for Dynamics in Small Planetary Cores

Regions of partial melt of Fe-S-Si alloys at high pressures may arise during planetary formation or at the boundary of the inner and outer cores of small terrestrial planetary bodies. Melting experiments were performed on Fe-16wt%S-2wt%Si samples in a multi-anvil apparatus across the range 2–13 GPa with quench temperatures in partial and complete melt regions. A phase diagram is constructed from electron microprobe analyses, back-scattered electron imaging, and electrical resistivity measurements. Microstructures arising in post-quench samples include Turing patterns of Fe and FeS in the partial melt, dendritic Fe structures with tertiary arms in the partial and complete melt, and Fe-S-Si miscible regions in the complete melt. These melt structures may arise broadly or locally in small Fe-S planetary cores with consequences for the energetics of the core.