BackarcBecken

BackArcBecken, or back-arc basin, are elongated marine basins formed in the overriding plate behind a subduction-zone volcanic arc, where extension is driven by rollback of the subducting slab. As the slab descends and retreats, the hinge migrates trenchward, pulling on the overlying plate and causing it to stretch. This extensional regime may lead to rifting and, in many cases, back-arc spreading that creates new oceanic crust. The basins are typically bounded by normal faults, truncated by active arc volcanism, and filled with a thick sequence of sediments eroded from surrounding highs and volcanic deposits from the arc. In many basins, seafloor spreading centers or slow-spreading ridges develop within the basin, and hydrothermal systems are common along these axes.

The crust in back-arc basins ranges from oceanic to transitional, with thick sedimentary cover and, in some instances, serpentinized mantle rocks exposed in uplifted zones. The process of slab rollback can also induce complex mantle flow and changes in magma supply to the arc, influencing volcanic activity in both the arc and the basin.

Notable back-arc basins include the Mariana Trough, Lau Basin, Manus Basin, and North Fiji Basin in the western Pacific. These regions host active hydrothermal vent fields and are key to understanding subduction-zone dynamics and crust formation.

Back-arc basins are of interest for tectonics, magmatism, and mineral resources, but pose challenges for exploration due to deep-water environments and seismic activity.