Subduct

Subduct is a term used in plate tectonics to describe the process by which one lithospheric plate sinks beneath another into the mantle at a subduction zone. The downgoing slab, typically oceanic lithosphere, moves beneath the overriding plate, which can be continental or another oceanic plate. The interaction creates a deep ocean trench at the surface and a seismic zone that traces the angle of descent, known as the Wadati–Benioff zone.

Mechanisms and consequences: Subduction is driven by slab pull and gravity. As the slab descends, it undergoes dehydration, releasing fluids into the overlying mantle. This lowers melting temperatures and generates magma that rises to form volcanic arcs on the overriding plate. The subducting plate often causes strong earthquakes, including megathrust events, and penetrates deep into the mantle. The process also leads to crustal recycling and mountain building at margins.

Types and regional variation: Oceanic-continental subduction occurs where oceanic lithosphere sinks beneath continental lithosphere, creating mountain belts such as the Andes. Oceanic-oceanic subduction involves one oceanic plate subducting beneath another, forming island arcs like Japan and the Aleutians. Slab geometry can vary from steep to shallow, and in some regions the slab may rollback or flatten, leading to back-arc basins and changes in volcanic activity.

Distinctions: Subduction is distinct from obduction, where oceanic crust is thrust above another plate. Subduction zones are central to the recycling of crustal material and the geologic activity that shapes many of Earth’s margins. Etymology: from Latin subducere, to lead under.