Part 2. Younger Pacifics arcs and the eastern marginal seas: Rifting and seafloor spreading in marginal basins: Shikoku basin

Abstract

Marginal basins of the western Pacific Ocean comprise the small semi-enclosed seas which occur behind most island arc-trench systems. Seismic refraction measurements and petrology of dredged samples indicate that the crust of marginal basins is oceanic in type. Two hypotheses are currently held regarding the origin of these features. Karig, and Packham and Falvey have proposed that marginal basins are formed during episodes of extension behind island arcs. Sequential intervals of extension during the Cenozoic have caused the series of marginal basins and aseismic ridges (remnant portions of the island arc) to the west of the Izu- Bonin-Mariana and the Tonga-Kermadec island arc-trench systems. Crustal extension behind island arcs may not, however, explain the formation of all marginal basins. Magnetic lineations which trend at high angles to active or remnant island arcs in the West Philippine basin and the Aleutian basin have led to the suggestion that these marginal basins formed by entrapment of oceanic crust when an island-arc trench system developed in situ.