Iron diapirs entrain silicates to the core and initiate thermochemical plumes

J R Fleck,C L Rains,D S Weeraratne,J M Rincon,C Martinez,C T Nguyen,D M Brand,P L Olson,S M Klein,J M Mcgehee

doi:10.1038/s41467-017-02503-2

J R Fleck, C L Rains + Show 8 more

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https://doi.org/10.1038/s41467-017-02503-2

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Abstract

Segregation of the iron core from rocky silicates is a massive evolutionary event in planetary accretion, yet the process of metal segregation remains obscure, due to obstacles in simulating the extreme physical properties of liquid iron and silicates at finite length scales. We present new experimental results studying gravitational instability of an emulsified liquid gallium layer, initially at rest at the interface between two glucose solutions. Metal settling coats liquid metal drops with a film of low density material. The emulsified metal pond descends as a coherent Rayleigh−Taylor instability with a trailing fluid-filled conduit. Scaling to planetary interiors and high pressure mineral experiments indicates that molten silicates and volatiles are entrained toward the iron core and initiate buoyant thermochemical plumes that later oxidize and hydrate the upper mantle. Surface volcanism from thermochemical plumes releases oxygen and volatiles linking atmospheric growth to the Earth’s mantle and core processes.

Highlights

Segregation of the iron core from rocky silicates is a massive evolutionary event in planetary accretion, yet the process of metal segregation remains obscure, due to obstacles in simulating the extreme physical properties of liquid iron and silicates at finite length scales
Our experiments model the evolution of an emulsified metal pond that settles within a magma ocean during or following a moderate-sized impact
We measure interfacial tension (IFT) in our experiments, which causes S1 fluid to adhere to metal droplets and we obtain IFT = 642 mN/m

Summary

Introduction

Segregation of the iron core from rocky silicates is a massive evolutionary event in planetary accretion, yet the process of metal segregation remains obscure, due to obstacles in simulating the extreme physical properties of liquid iron and silicates at finite length scales. Particles began to collide and clumped together forming kilometer-sized meteorites and small planetesimals Differentiation began at this early stage by decay of radio nuclides, 26Al and 60Fe7. The iron droplets will settle and accumulate in a metal pond at the base of the magma ocean[23], at a depth where the silicate mantle is significantly more viscous[14] due to growth of planetary radii and increasing mantle pressures. Large metal diapirs that form from Rayleigh−Taylor instabilities[1, 27] are consistent with rapid core formation, but large metal diapirs would have residence times too short and surface area too small for wide spread metal−silicate equilibration in the upper mantle[29]. We consider the descent of metal diapirs consisting of emulsified liquid metal which simultaneously provides rapid core formation times and ample residence time for chemical equilibration at high pressures

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