Passive Margin

A passive margin is a continental margin that lies within a single tectonic plate, far from any active boundary, so it is tectonically quiet. It forms when a continent rifts apart and a new ocean basin opens, leaving the rifted edge to subside and accumulate sediment as the lithosphere cools, the classic Atlantic-type margin. The full profile develops: a wide continental shelf, a continental slope, and a thick continental rise built by downslope sediment, with no trench to intercept it. Seismicity is low. Contrast the active margin, which tracks a plate boundary and carries a trench and volcanic arc.