Back-arc basin

A seafloor basin behind a volcanic arc, formed as the overriding plate extends and thins. It may contain oceanic crust produced by seafloor spreading.

Slab rollback: The retreat of a subducting plate hinge relative to the overriding plate. Retreat can stretch the overriding plate and promote opening behind the arc.
Subduction zone: A tectonic boundary where one lithospheric plate descends beneath another. Back-arc basins form within the overriding plate above a subducting slab.
Mariana Trough: An actively spreading back-arc basin west of the Mariana volcanic arc. It is a well-studied example of extension linked to retreat of the Mariana slab.
Forearc basin: A sedimentary basin between a subduction trench and its volcanic arc. It lies in front of the arc, opposite the position of a back-arc basin.
Back-arc extension: Crustal stretching and thinning in the region behind a volcanic arc. It is the tectonic deformation that creates space for the basin.
Volcanic arc: A chain of volcanoes formed on an overriding plate above a subduction zone. The basin's position is defined relative to this chain of volcanoes.
Lau Basin: An actively spreading basin between the Tonga volcanic arc and the Lau Ridge. Its rapid evolution records changing subduction and spreading conditions.
Rift basin: A basin formed where continental or oceanic lithosphere is pulled apart. Rifting describes extension broadly, while back-arc basins require a subduction-arc setting.
Seafloor spreading: The formation of new oceanic crust as magma rises at a spreading center. Sustained extension can develop into spreading that forms new basin crust.
Overriding plate: The tectonic plate that lies above a subducting plate at a convergent boundary. Its extension and thinning make room for the basin to develop.

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