How does subduction occur at convergent plate boundaries?

Subduction occurs at convergent plate boundaries when a denser tectonic plate descends into the Earth's mantle beneath a less dense plate. Because the Earth maintains a constant volume, the continuous creation of new crust at mid-oceanic ridges necessitates the destruction of older crust at these margins.12

As oceanic lithosphere ages, it cools and becomes denser than the underlying asthenosphere, eventually causing it to sink. When two oceanic plates meet, the older, denser plate is subducted; when an oceanic plate meets a continental plate, the greater buoyancy of the continent forces the oceanic plate downward.2

The process is characterized by several key features:
* Deep-sea trenches: Formed by the frictional drag and bending of the descending plate.3
* Wadati-Benioff zones: A planar zone of earthquakes that marks the path of the subducting slab as it descends into the mantle.3
* Metamorphism: High-pressure, low-temperature conditions transform rocks into blueschists and, at greater depths, eclogites, which further increase density and facilitate continued subduction.3