That's mostly incorrect.
When someone speaks of ocean trenches, they're referring to the deep ocean trenches formed by subduction zones, which are convergent boundaries, not divergent boundaries.
When oceanic-continental or oceanic-oceanic convergent collisions occur, one plate will subduct. This subducting plate dives down into the mantle, and the overriding plate catches its leading edge, causing it to bow down. This combination forms a deep ocean trench. Examples are the subduction of the Nazca plate beneath the South American plate creating the Peru-Chile Trench. The North American plate subducting beneath the Caribbean plate and forming the Puerto Rico Trench. Or... most spectacularly, the Pacific plate subducting beneath the Philippine plate creating the Marianas Trench, the deepest point on the surface of the Earth.
· 9 years ago