Redox freezing and melting in the Earth’s deep mantle resulting from carbon–iron redox coupling

Rohrbach and Schmidt present an experimental study that defines how some of the deepest melts in Earth's mantle are generated. They show that carbonatite melts reduce to immobile diamond when recycled at depths greater than about 250 kilometres. They infer that when such carbon-enriched mantle heterogeneities become part of the upwelling mantle, diamond will inevitably react with Fe3+, leading to carbonatite 'redox melting' at depths of around 660 kilometres and 250 kilometres, to form deep-seated melts in Earth's mantle.