Back-arc basins are geologic features, submarine basins associated with
island arcs and
subduction zones. They are found at some
convergent plate boundaries, presently concentrated in the Western
Pacific ocean. Most of them result from
tensional forces caused by
oceanic trench rollback (the oceanic trench is wandering in the seafloor direction) and the collapse of the edge of the continent. The arc crust is under
extension/ rifting as a result of the sinking of the subducting slab. Back-arc basins were initially a surprising result for
plate tectonics theorists, who expected convergent boundaries to be zones of compression, rather than major extension. However, they are now recognized as consistent with this model in explaining how the
Earth loses heat.