Fig. 12
Model of global water circulation involving deep mantle melting. a A schematic diagram of water circulation. Excess regassing occurs associated with cold subduction (τ1: duration of excess regassing). This produces partial melting in the lower mantle (LVL-750). Due to the change in plate boundary geometry (associated with supercontinent cycle (Lithgow-Bertelloni and Richards 1998), the hydrated and buoyant materials will be transported to the MTZ, and when these materials reach to ~ 410 km, excess degassing starts (after τ2 since the beginning of the excess regassing (this is controlled largely by the time scale of change in plate boundary geometry)). b Definition of two functions:
Γ+(t) a function characterizing excess regassing pulse
Γ−(t) a function characterizing excess degassing