Partial melting of a Pb-Sn mushy layer due to heating from above, and implications for regional melting of Earth's directionally solidified inner core

James Yu , Michael I. Bergman , Ludovic Huguet (1) , Thierry Alboussiere (1)

1 LGL-TPE - Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement

Superimposed on the radial solidification of Earth's inner core may be hemispherical and/or regional patches of melting at the inner-outer core boundary. Little work has been carried out on partial melting of a dendritic mushy layer due to heating from above. Here we study directional solidification, annealing, and partial melting from above of Pb-rich Sn alloy ingots. We find that partial melting from above results in convection in the mushy layer, with dense, melted Pb sinking and resolidifying at a lower height, yielding a different density profile than for those ingots that are just directionally solidified, irrespective of annealing. Partial melting from above causes a greater density deeper down and a corresponding steeper density decrease nearer the top. There is also a change in microstructure. These observations may be in accordance with inferences of east-west and perhaps smaller-scale variations in seismic properties near the top of the inner core.

Domaines: Planète et Univers [physics]

James Yu, Michael I. Bergman, Ludovic Huguet, Thierry Alboussiere. Partial melting of a Pb-Sn mushy layer due to heating from above, and implications for regional melting of Earth's directionally solidified inner core. Geophysical Research Letters, 2015, 42 (17), pp.7046-7053. ⟨10.1002/2015GL064908⟩. ⟨hal-02341074⟩