Fig. 9
Processes of water transport across the 410 km with heterogeneous temperature. In the hot region (area SH (a majority of regions)), melts are dense and spread on the 410-km boundary and eventually be entrained into the transition zone (Bercovici and Karato 2003; Karato et al. 2006). Only a small amount of water is transported upward by the residual solids to define the composition of the asthenosphere (Karato 2012). In the cool region (area SC), melt is buoyant and if there is enough amount of buoyant melt present (a caseXMTZ ≥ XC2 (shown here)), substantial degassing from the MTZ will occur