Carbon Cycle in the Subduction Zone and Deep Mantle: Constraints from Equilibrium Experiments at High Pressure and Temperature (Invited)

Carbon recycles in convergent boundaries through subduction and eruption. A subducting slab descends into the Earth’s interior along certain pressure-temperature trajectory, releasing fluids through dehydration of hydrous minerals in the slab. The slab also contains carbon-bearing materials such as carbonates and organic compounds in sediment, which are expected to undergo phase transformations and decarbonation reactions during deep subduction. In this presentation, we review experimental results on the stability fields of carbonates and the carbonate-silicate reactions at high pressure and temperature. We also assess the effect of fluids on these reactions particularly under oxidized and reduced conditions. The experimental results show that carbon can be liberated from carbonates to form either CO₂ free phase or C-rich melt at mantle P-T conditions. The formation of the reduced carbon compounds including iron carbides and diamond is observed through carbonate reduction under reduced conditions. Along low-temperature subduction trajectory, significant amount of carbonates in the slab could survive, descending into deep mantle. This could lead to imbalance of CO₂ flux between the subducted carbon and that released by arc magmatism through geological time.