subducted

Subducted is a geological term describing rock, oceanic crust, or sediments that have been forced downward into the mantle at a subduction zone, typically at convergent plate boundaries. In most cases, an oceanic plate sinks beneath either another oceanic plate or a continental plate because it is denser and cooler than the surrounding mantle.

Subduction begins when two tectonic plates collide; the older, cooler plate becomes the downgoing slab that sinks into the mantle. The descending slab can penetrate to depths of hundreds of kilometers; fluids released from hydrous minerals lower the melting point of the overlying mantle and contribute to arc volcanism on the overriding plate. The geometry of subduction zones varies, with steep or shallow angles influencing surface deformation and volcanic activity.

Subducted material undergoes high-pressure metamorphism, producing rocks such as blueschist and eclogite, and forms features like accretionary prisms and deep-sea trenches. The process also is a major mechanism for recycling crustal material, returning it to the mantle where it may later melt or mix with other mantle reservoirs. Seismic activity is a hallmark, including shallow and deep focus earthquakes within the slab.

Notable subduction zones include the Pacific Ring of Fire, where the Pacific Plate subducts beneath many surrounding plates; the Nazca plate subducting beneath South America; and the Java-Sumatra and Japan subduction systems. Studying subducted material through seismic imaging and xenoliths helps scientists understand mantle dynamics and the long-term evolution of Earth’s crust.