Figure F2. Evolution of IBM arc and adjacent Philippine Sea (from Ishizuka et al., 2011). A. ~40–35 Ma arc rocks are shown as the Eocene arc and the Kyushu-Palau arc. Also shown: Cretaceous crust in the north and seafloor spreading (West Philippine Basin) and mantle plume magmatism (Oki-Daito) in the south. B. 35–25 Ma: arc magmatism continues along the front and rear of the Kyushu-Palau arc, whereas seafloor spreading in the West Philippine Basin wanes but Oki-Daito plume influence extends to the southern part of the Kyushu-Palau arc. C. Kyushu-Palau arc is rifted penecontemporaneously along its length, and seafloor spreading begins in the Shikoku and Parece Vela Basins by ~25 Ma, separating the rear arc from the arc front and producing the Kyushu-Palau Ridge remnant arc. D. ~22–17 Ma: spreading of Shikoku and Parece Vela Basins. E. 17–6 Ma: Neogene IBM arc front roughly coincides with the Paleogene arc front with the active rear arc behind it.
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