Water and melt distributions predicted in the model calculation. The upper right corner corresponds to the trench. The white solid lines indicate temperature contours with 200°C intervals (for 200°C, 400°C, 600°C, 800°C, 1,000°C, 1,200°C, and 1,400°C), and the white dotted lines indicate the streamline. The purple solid lines indicate the lower and upper boundaries of the subducting oceanic crust. (a) Water (in weight) in a local bulk system. (b) Aqueous fluid fraction (in volume). (c) Melt fraction (in weight). (d) A magnified view of the central part of (c). In (d), orange and green circles correspond to two different melting regimes, as explained in the main text.