Stress-induced percolative core formation through a bridgmanite
mantle
Lin Wang1,*, Yingwei Fei1
1 Earth and Planets Laboratory, Carnegie Institution
for Science, U.S.
Corresponding author: Lin Wang
(liwang@carnegiescience.edu)
Key Points:
- A new method of determining melt connectivity in silicate matrix was
developed.
- Core-forming melts can form an interconnected network in a deformed
bridgmanite matrix.
- Stress-induced percolation is a viable core formation mechanism in
planets.
- The stranded melt in the Earth mantle left by core formation could
explain its abundance of highly siderophile elements.
Abstract
Segregation of liquid metal from solid silicate is a necessary pathway
for core formation in a large rocky planetary body during the planet
growth. The mechanism and extent of such process have an important
effect on the geophysical and geochemical properties of the planetary
body. Percolative flow of core forming melts through a silicate mantle
has been ruled out as a possible mechanism of core formation by
hydrostatic annealing experiments at pressures less than 50 GPa.
However, an evolving mantle is not static, but continually deforming.
Here, using element migration in the melts as an effective indicator for
melt connectivity, we conclusively demonstrated that iron alloy melts
could form an interconnected network in a solid bridgmanite matrix under
deformation, even at a small total strain of ~0.1.
Depending on the grain size of bridgmanite, percolation as a core
formation mechanism could leave mantle disequilibrium/equilibrium with
the core. The result showed that ~0.4 vol.% liquid
metal was trapped in the silicate mantle and the stranded metal alloy
could explain the highly siderophile elements (HSE) chondritic abundance
in the Earth’s mantle without late veneer.