Stability Of Hydrous Minerals And Water Reservoirs In The Deep Earth Interior

Water storage capacities in hydrous phases and nominally anhydrous minerals in the deep mantle are summarized. There are several controversies on the water contents in the lower mantle minerals, such as periclase, stishovite, and MgSiO3 perovskite, and we need more studies to clarify the effect of pressure, temperature, and compositions on the H2O activity of these high-pressure minerals. The transition zone has a water storage capacity of approximately 0.5-1 wt % due to a high water solubility of about 1-3 wt % in wadsleyite and ring-woodite, which are the major constituents in the transition zone. Water has significant effects on the phase boundaries of the phase transformations of the mantle minerals and can explain some topography of the 410 and 660 km seismic discontinuities. Recent discovery of hydrous ringwoodite and phase Egg as inclusions in diamond strongly suggests existence of the hydrous transition zone, a major water reservoir in the Earth's-interior. Discovery of a new hydrous phase H, MgSiO2(OH)(2) and its solid solution with isostructural phase d-AlOOH suggests that water can be stored in this phase in the lower mantle. Water may be transported into the bottom of the lower mantle by this phase in descending slabs.