A lower-mantle water cycle component

Seismic Evidence for Subduction-Transported Water in the Lower Mantle

We use seismic attenuation tomography to identify a region at the top of the lower mantle that displays very high attenuation consistent with an elevated water content. Tomography inversions with >80,000 differential travel-time and attenuation measurements yield 3D whole-mantle models of shear velocity (VS) and shear quality factor (Q ). The global attenuation pattern is dominated by the locat...

Water distribution in the lower mantle: Implications for hydrolytic weakening

Transport of water into the lower mantle: Role of stishovite

[1] When subjected to lower-mantle pressures and temperatures, natural ‘‘anhydrous’’ basalt containing 0.2 wt.% H2O forms a phase assemblage in which SiO2 stishovite is a significant carrier of hydrogen (up to 500 ppm H2O by weight, as hydroxide), whereas the coexisting (Mg, Fe, Al, Ca)SiO3 perovskite appears to be not (upper bound of 50 ppm (wt) H2O). Contrary to the devolatilization character...

The incorporation of water into lower-mantle perovskites: A first-principles study

We have used first principles methods to calculate the partitioning of water between perovskite and ringwoodite under lower mantle and Fe-free conditions. We find that incorporation of water into ringwoodite is more favourable than into perovskite by about 0.25 eV per formula unit, or about 24 kJ/mol. This translates to a ringwoodite to perovskite partition coefficient of between 10 and 13, dep...

Spin transition zone in Earth's lower mantle.

Mineral properties in Earth's lower mantle are affected by iron electronic states, but representative pressures and temperatures have not yet been probed. Spin states of iron in lower-mantle ferropericlase have been measured up to 95 gigapascals and 2000 kelvin with x-ray emission in a laser-heated diamond cell. A gradual spin transition of iron occurs over a pressure-temperature range extendin...