Iron oxyhydroxide as water carrier to the deep mantle

The discovery of new mineral phases capable of transporting water into the Earth’s mantle via subduction zones is essential for understanding the deep Earth water cycle and its influence on mantle dynamics. Recent experimental and computational studies have proposed that certain hydrated oxyhydroxides may remain stable under lower mantle conditions, particularly within cold subducting slabs. Here, we report on an advanced synchrotron multi-technique study on a natural complex iron oxyhydroxide mineral preserved within a super-deep diamond. This finding provides direct evidence that specific hydrous minerals survive at approximately ~ 900 to 1,250 km depths at the lower mantle. Moreover, it offers new evidence on water transport via cold subducted slabs and highlights the potential role of iron oxyhydroxides as carriers of volatiles into Earth’s deep interior.