Fig. 3: Schematic diagram of ULVZ formation through iron–water exchange.
From: Extensive iron–water exchange at Earth’s core–mantle boundary can explain seismic anomalies
Deep mantle convection may deliver some quantity of water to the CMB. During prolonged heating at the CMB, the water diffuses to the outer core because of its siderophile nature and active diffusivity, resulting in an increase in the FeO component at the CMB. FeO-enriched ULVZs are formed by the partitioning of excess FeO into the core and mantle after heating and are detectable locally.
