Subducting

Subducting is the process by which a tectonic plate descends into the Earth's mantle at a convergent plate boundary. The plate that sinks is known as the subducting or descending slab; the plate it moves beneath is the overriding plate. Subduction zones are characterized by oceanic trenches, a surrounding accretionary wedge, and often a volcanic arc on the overriding plate. They are major sites of earthquakes, including deep-focus events that occur within the subducting slab.

Mechanism and consequences: Subduction is driven by gravity acting on cool, dense oceanic lithosphere, a force known as slab pull, and by mantle convection. The descending slab interacts with the surrounding mantle, releasing fluids from minerals as it dehydrates, which lowers the mantle wedge melting point and fuels arc volcanism. The geometry of subduction can be steep or shallow and may undergo rollback or tearing, influencing back-arc basin formation and tectonic deformation. Subduction recycles oceanic lithosphere into the mantle and plays a key role in continental growth and mountain building.

Common features include Wadati-Benioff seismic zones, where earthquakes trace the path of the sinking slab, and metamorphism of rocks at high pressures and low temperatures. Volcanic arcs, whether continental (andesitic) or island arcs, form above the subduction zone due to the flux melting of the mantle.

Examples: the Pacific subduction under the surrounding continents; the Nazca plate subducting beneath South America; the Juan de Fuca plate subducting beneath North America; the Japan Trench region.