Fig. 10
A schematic phase diagram at ~ 410 km. A green region represents temperature distribution. TH, C is temperature in the hot (H) or the cold (C) regions respectively. TCr is temperature at which the melt has high enough water content and is buoyant. \( {X}_S^{H,C},{X}_L^{H,C} \) are the water content at the solidus and liquidus in the hot or the cold region respectively. XC1 is the minimum water content in the transition zone where the melt will ascend (~ 0.2%). XC2 is the water content above which hydrated materials above the MTZ are buoyant to form a plume (~ 1%; Supplementary Material)