Abstract
Metallic melt containing iron (Fe) and carbon (C) may be present at depths greater than 250 km inside the Earth. Depending on its wetting behavior, such dense melt may be trapped locally or drain into deep mantle and core. Here, we report experimental data on the wetting behavior of Fe-C melt in silicates at the conditions of Earth’s mid-mantle between 10 and 23 GPa and 1600 and 1800 ˚C. The measured dihedral angles of Fe-C melt in olivine, ringwoodite or bridgmanite and ferropericlase matrixes are 117±14°, 120±14° and 107±16° respectively, well above the critical value of 60° for complete wetting. The estimated percolation thresholds are at least 7% in volume, far exceeding the amount of metal in the mantle. Consequently, slab-derived Fe-C melt in the mid-mantle is expected to occur as isolated pockets and would not percolate through its silicate matrix.
Highlights
Iron–carbon alloys represent reduced forms of carbon and are important components of Earth’s long-term carbon cycle
Our results show that the measured dihedral angles of Fe–C melt in silicates remained near 120◦, indicating that the Fe–C melt does not wet major silicate phases in the mantle
The measure dihedral angles and estimated percolation thresholds are applied to assess the behavior of Fe–C alloys at deep Earth conditions
Summary
Iron–carbon alloys represent reduced forms of carbon and are important components of Earth’s long-term carbon cycle. At depths greater than ∼250 km, metallic iron may reduce subducted carbonates to produce elemental carbon or carbide (MgCO3 + 2 Fe0 = 3 (Fe, Mg)O + C, e.g., Rohrbach and Schmidt, 2011). It has been proposed that slab-derived Fe–C melt in isolated patches can match seismically observed density and velocity features of some ultralow velocity zones (ULVZs) (Liu et al, 2016). For these reasons, knowledge of the wetting behavior of Fe–C is crucial for assessing the fate of slab-derived metallic liquid in deep Earth
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