The Bonin Arc

The Bonin Arc is a well-developed island arc, associated with a deep trench, an active volcanic chain, and a back-arc basin. The Bonin Arc is approximately 1100 km long, extending north—south from latitude 35°N to 25°N within longitude 139°E and 145°E, facing the Pacific plate in front and the Shikoku Basin behind (Fig. 1). At its northern limit, the Bonin Arc forms part of a triple junction of trench—trench—transform fault or trench—trench—trench with the Tohoku and the Seinan (southwest) Japan arcs. The Mariana Arc continues the line of the Bonin Arc to the south. There is no marked morphological boundary between the Bonin and the Tohoku arcs, but one is inferred by the depression along the Sagami Trough (see Fig. 13). The southern boundary of the Bonin Arc is even less well defined than the northern margin. The Bonin Arc extends to the Mariana Arc as part of the same morphological sequence from north to south. These three arcs face the Pacific plate.