Oceanic plate diving beneath continental plate — Wadati-Benioff zone
Subduction occurs when dense oceanic lithosphere (basalt/gabbro, ~3.0 g/cm³) sinks beneath lighter continental crust (~2.7 g/cm³). Slab pull (gravity on the cold dense slab) is the dominant driving force, contributing ~90% of plate motion energy. The Wadati-Benioff zone marks seismicity along the slab, reaching depths of 660–700 km. Fluids released from the subducting slab lower the mantle wedge melting point, generating arc volcanoes 100–150 km above the slab surface.