Calculated distribution of Pb. (a) Pb concentration in solid. (b) Pb concentration in aqueous fluid. The Pb concentration in aqueous fluid is color-coded only where the fluid phase is present in respective grid cells and is shown everywhere else with a ‘background zero ppm’ concentration (i.e., the dark blue region). The white solid and dotted lines correspond to the temperature contours (with 200°C intervals) and the streamline, respectively, as in Figure 2. The purple solid lines indicate the lower and upper boundaries of the subducting oceanic crust (as in Figure 2), and the boundary conditions of mass and energy conservation are the same as in Figure 2.