摘要：AbstractThe fate of subducted carbonates in the lower mantle and at the core-mantle boundary was modelled via experiments in the MgCO3-Fe0system at 70–150 GPa and 800–2600 K in a laser-heated diamond anvil cell. Usingin situsynchrotron X-ray diffraction andex situtransmission electron microscopy we show that the reduction of Mg-carbonate can be exemplified by: 6MgCO3 + 19Fe = 8FeO +10(Mg0.6Fe0.4)O + Fe7C3 + 3C. The presented results suggest that the interaction of carbonates with Fe0or Fe0-bearing rocks can produce Fe-carbide and diamond, which can accumulate in the D’’ region, depending on its carbon to Fe ratio. Due to the sluggish kinetics of the transformation, diamond can remain metastable at the core-mantle boundary (CMB) unless it is in a direct contact with Fe-metal. In addition, it can be remobilized by redox melting accompanying the generation of mantle plumes.Graphical abstractDisplay OmittedHighlights•We investigated redox reaction in the MgCO3–Fe0system at 70-150 GPa and 800–2600 K.•Wüstite, ferropericlase, carbide, and diamond form at lower mantle P-T conditions.•The reaction is defined as: 6 MgCO3 + 19 Fe = 8 FeO +10 (Mg0.6Fe0.4)O + Fe7C3 + 3 С.•Wüstite and (Mg0.6Fe0.4)O ferropericlase are immiscible at depth below ∼1600 km.•Diamond and Fe7C3are stable hosts of carbon in the reduced lower mantle.
