Immiscible hydrocarbon fluids in the deep carbon cycle

Area of Science:

• Geochemistry
• Geology
• Planetary Science

Background:

• The deep carbon cycle is crucial for Earth's long-term habitability.
• Understanding carbon migration in the deep Earth is essential.
• The role of hydrocarbon fluids in this cycle remains controversial.

Purpose of the Study:

• To investigate the formation and stability of hydrocarbon fluids under deep Earth conditions.
• To assess the potential for immiscible hydrocarbon fluids in deep carbon migration.

Main Methods:

• Experimental synthesis of isobutane from aqueous sodium acetate at high pressures (2.4-3.5 GPa) and temperatures (300°C).
• Theoretical predictions on isobutane stability across a range of pressures and temperatures.
• Integration with existing experimental data on methane-rich fluids and fluid inclusions.

Main Results:

• Immiscible isobutane was formed in situ from sodium acetate transformation under experimental conditions.
• High pressure was found to oppose isobutane decomposition.
• Isobutane may coexist with silicate mineral assemblages in the deep Earth.

Conclusions:

• Hydrocarbon fluids, including isobutane and methane, can form and persist under deep Earth conditions.
• These immiscible hydrocarbon fluids likely contribute to carbon transfer within the deep carbon cycle.
• The presence of diverse hydrocarbon fluids influences the understanding of planetary habitability.