divergent margin

In plate tectonics, the boundary, or active zone between two lithospheric plates that are moving apart. Divergent margins are characterized by extensive normal faulting, low-magnitude earthquakes, and, in most cases, volcanic activity.

The most common type of divergent margin is the oceanic spreading centre, where two oceanic plates move apart. As they diverge, magma (molten rock) wells up to fill the open space, and solidifies, forming new oceanic crust. These boundaries are characterized by long, segmented volcanic ridges known as mid-ocean ridges. Mid-ocean ridges, which include the Mid-Atlantic Ridge and the East Pacific Rise, are found in all the world's oceans.

The second type of divergent margin occurs on the continents, in regions of incipient continental break-up. As the continent stretches, the crust breaks (faults) and thins. The most famous example is the Great Rift Valley in East Africa. Like their oceanic counterparts, continental rifts are characterized by normal faulting and volcanism. If rifting continues, the continent is broken in two, oceanic crust forms between the new continents, and the margin becomes a mid-ocean ridge.