Carbonate-Metal Reactions in the Lower Mantle

Area of Science:

• Geochemistry
• Mineral Physics
• High-Pressure Science

Background:

• Carbonates are crucial carbon reservoirs in the Earth's mantle.
• Their behavior in the lower mantle, particularly phase relations and transport properties, is poorly understood.
• Understanding carbonate stability is key to comprehending deep carbon cycles.

Purpose of the Study:

• To investigate the stability of carbonates under lower mantle conditions.
• To determine the reaction products between carbonates and iron alloys at high pressures and temperatures.
• To assess the role of carbonates as carbon-bearing phases in the deep Earth.

Main Methods:

• High-pressure, high-temperature experimental studies were conducted on the Fe-Si-Ca-Mg-C-O system.
• Experiments reached pressures up to 124 GPa and temperatures up to 3200 K.
• Analysis of reaction products to determine phase stability.

Main Results:

• Carbonates react with iron alloys to form silicates, iron carbides, and oxides.
• The reaction temperature increases with pressure, shifting stability fields.
• Carbon exhibits lower siderophilicity than silicon at high pressures.

Conclusions:

• Along a geotherm, carbonates are the stable carbon-bearing phase in the lowermost mantle.
• These findings impact models of deep carbon cycling and mantle composition.
• Carbonate stability is pressure-dependent, influencing carbon's fate in the deep Earth.