Carbonate-Metal Reactions in the Lower Mantle

TL;DR

This study explores how carbonates react with metals in Earth's lower mantle under extreme conditions, revealing insights into carbon stability.

Contribution

The paper presents new experimental data on carbonate-metal reactions at high pressures and temperatures relevant to the lower mantle.

Findings

Carbonates react with iron alloys to form silicates, iron carbides, and oxides.

Reaction temperatures increase with pressure, stabilizing carbonates in the lowermost mantle.

Carbon is less siderophilic than silicon at high pressures.

Abstract

Carbonates are important carbon-bearing phases in the
mantle. While
their role in upper mantle petrologic processes has been well studied,
their effect on phase relations, melting, and transport properties
in the lower mantle is less understood. The stability of carbonates
in the mantle depends on a host of factors, including pressure, temperature,
oxygen fugacity, and reactions with surrounding mantle phases. To
understand the stability of carbonates in the presence of metal in
the lower mantle, carbonate-metal reaction experiments on the Fe–Si–Ca–Mg–C–O
system were conducted up to 124 GPa and 3200 K. We find that carbonates
react with iron alloys to form silicates, iron carbides, and oxides.
However, the temperature at which these reactions occur increases
with pressure, indicating that along a geotherm in the lowermost mantle
carbonates are the stable carbon-bearing phase. Carbon is found to
be less siderophilic at high-pressure compared to silicon.

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