Spidergram for the calculated melt. The melt composition is normalized by the DMM composition, which is assumed as an initial mantle composition (before fluid flux is introduced) in our model. The green and orange lines correspond to the melt compositions produced in regions (A) and (B) of Figure 2d, respectively. Each line represents a local instantaneous melt composition. The red line represents the frontal arc basalt from NE Japan, and the blue line for the rear arc basalts (Kimura and Yoshida 2006; Kimura and Stern 2009). For comparison, an average melt composition corresponding to hypothetical pure DMM melting is shown as the purple line, with the same melting degrees and partition coefficients as in the model result.