In plate tectonics, a divergent boundary (divergent fault boundary or divergent plate boundary) is a linear feature that exists between two tectonic plates where the plates are moving away from each other. These areas can form in the middle of continents but eventually form ocean basins. Divergent boundaries within continents initially produce rifts which produce rift valleys. If the rifting process stops, a failed rift results. Therefore most active divergent plate boundaries exist between oceanic plates and are often called oceanic rifts as a result.
It is thought that convection currents in the Earth's mantle rise to the base of the lithosphere where the divergent plate boundary exists. This supplies the area with copious amounts of heat and pressure that melts rock from the asthenosphere (or upper mantle) that then travels to the rift area forming large flood basalt flows. Each eruption occurs in only a part of the plate boundary at any one time, but when it does occur, it fills in the opening gap as the two opposing plates move away from each other. The average rate of movement is comparable to how fast human fingernails grow.
Over millions of years the plates grow many hundreds of kilometers away from both sides of the divergent plate boundary. Because of this, rock closest to the boundary is younger than rock further away on the same plate.
Divergentboundaries on land cause rifting, in which broad areas of land are uplifted, or moved upward.
Early in the plate tectonic revolution, geologists proposed that transform faults were a new class of fault because they “transformed” plate motions from one plateboundary to another.
As a transform plateboundary cuts perpendicularly across the edges of the continental crust near the borders of the continental and oceanic crust, the result is a system such as the San Andreas transform fault system in California.
It might be possible for a plate to be a continent alone, but for this to occur all edges of the continent would have to be a plateboundary (very rare, perhaps not practically possible).
Two divergent margins (plateboundaries) are present in the cross section: one labeled as such to the right of the continental craton, and the other on the left side.
Divergentplateboundaries always create new ocean floor (that is, new mafic oceanic lithosphere, called the ophiolite suite) when magma oozes into the crack as plates separate.
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