Fig. 11
Cartoons showing how water is transported across the cool regions of 410 km (SC in Fig. 9). In a cool region, when water-rich buoyant materials (XMTZ ≥ XC0) move up to ~ 410 km, a buoyant melt is formed. a Regime I: If XMTZ is small (XC1 > XMTZ ≥ XC0), water in the melt is removed to surrounding minerals immediately and melt does not ascend. b Regime II: When XMTZ exceeds a critical value (XMTZ ≥ XC1), melt does not lose its buoyancy immediately. However, if XMTZ is not very high (XC2 > XMTZ ≥ XC1 (XC1~0.2%, XC2~1%)), then surrounding minerals remain dry and heavy, and only melt ascend (regime II). In this case, ascending melt will lose most water to the surroundings, and not much water is transported to the shallow region. c Regime III: When XMTZ is high (XMTZ ≥ XC2(~ 1%)), then wet melt hydrates surrounding minerals extensively, and melt and minerals together become buoyant. They ascend together to transport water to the shallow regions. Wet materials migrate up in the MTZ as well, but the velocity of transportation of wet materials is much faster in the upper mantle than in the MTZ due to the difference in solid viscosity between these regions