Redox-Induced Destabilization of Dolomite at Earth’s Mantle Transition Zone

Carbonates are considered to be important hosts of oxidized carbon during subduction processes. Here we investigate the redox interactions between dolomite and metallic iron in laser-heated diamond anvil cells up to ∼20 GPa. The identification of recovered samples via in-situ synchrotron X-ray diffraction and ex-situ Raman spectroscopy shows that the reaction occurs with the formation of ferropericlase, graphite and hexagonal diamond, while CaCO3 remains stable. The experimental results indicate dolomite and metallic iron phases cannot coexist and demonstrate a possible formation mechanism of ultradeep diamonds via redox reaction between dolomite and iron under the mantle transition zone conditions. The results are significant for understanding carbon transportation during subduction processes and have further implications to the processes in the more complex systems regarding to carbonate-silicate-metal phase relations.