Fig. 1. The division between the outer zone (OZ) and inner zone (IZ). Blue droplets denote H₂O in hydrous minerals subducting with a sinking plate into the IZ, and reacting with Fe in the deep lower mantle [reaction (1)] to form FeO₂H_x and release hydrogen (green droplets).

Fig. 2. The OZ–IZ interaction processes. (a) A steady-state process of reaction (1) brings H₂O in the sinking plate to react with Fe, form oxygen-rich patches (ORPs), and release hydrogen. (b) The ORPs accumulate, partially melt, and form oxygen-rich magma (ORM) chambers (red). (c) A catastrophic event of ORM eruption, forming superplumes, perturbing thermal convections, generating chemical convections, and causing large-scale melting in the lithosphere.