Subduction hinge migration

Abstract

It has been argued that back-arc tectonics is controlled principally by the “absolute” motion of the overriding plate and the migration of the hinge of the downgoing plate. Thus, hinge migration (rollback) is fundamentally important to understanding the geodynamics of back-arc regions, but even rates of hinge migration are unknown. The rate of hinge migration can be estimated if the rate of back-arc extension and the motion of the overriding plate are known. Rates of rollback in a hotspot reference frame range from near zero in the case of the New Hebrides Arc, to 50–70 mm/a at the South Sandwich Arc, and may be as high as 100 mm/a at the Tonga Trench, but the hinge is actually advancing along the Izu-Bonin Trench, as evidenced by the fact that there is no significant active extension behind the Izu-Bonin Arc. The rate of hinge advance increases from north to south along the Izu-Bonin Trench, and correlates well with the dip of the subducted slab. Active spreading in the Mariana Trough may be attributed to a rate of hinge advance which is lower than the rate of retreat of the Philippine plate. All of the possible motions of overriding plates and subduction hinges which might give rise to back-arc opening are represented among the examples considered. Thus, there is no unique circumstance in which back-arc extension occurs. Finally, there appears to be no clear correlation between hinge motion and the age of the subducted lithosphere.