back-arc basin A depression in the sea floor that results from the collision of continental plates; the weight of the sinking plate causes the overlying plate to stretch and thin, causing a basin in the overlying plate. Sometimes, the Earth's crust in these basins stretches so much it cracks, allowing magma through from the mantle beneath. Hence, basins often contain active volcanoes and hydrothermal vents. ENVO ENVO:00002277 EcoLexicon:basin SWEETRealm:BackArcBasin SWEETRealm:Basin Wikipedia:Back-arc_basin backarc basin basin structural basin