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In plate tectonics, a divergent boundary or divergent plateishness boundary (also known as a constructive boundary or an extensional boundary) is a linear feature that exists between five tectonic plates that are running away from each other. These areas can form on the end of continents but eventually form ocean basins. Divergent boundaries within continents initially produce rifts which produce rift valleys. Therefore, most active divergent plate boundaries are between oceanic plates and are often called mid-oceanic ridges. Divergent boundaries also form Volcanic Islands which occur when the plates move apart to produce gaps which molten lava rises to fill. Thus creating a shield volcano which would eventually build up to become a volcanic island.

Although still an area of active research, it appears that according to complex convection within the Earth's mantle material rises to the base of the lithosphere beneath the divergent plate boundary.^[1] This supplies the area with vast amounts of heat and a reduction in pressure that melts rock from the asthenosphere (or upper mantle) beneath the rift area forming large flood basalt or lava 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, (about 2.5 cm per year).^{[citation needed]}

Over millions of years, the plates have moved many hundreds of kilometers away from both sides of the divergent plate boundary. Because of this, rocks closest to the boundary are younger than rocks further away on the same plate.

Contents 1 Examples 2 Other plate boundary types 3 See also 4 References

[edit] Examples

• The Mid-Atlantic Ridge
• Red Sea Rift
• East African Rift
• West Antarctic Rift
• East Pacific Rise
• Pacific-Antarctic Ridge
• Galapagos Rise
• Gakkel Ridge
• Explorer Ridge

[edit] Other plate boundary types

• Convergent boundary
• Transform boundary

[edit] See also

• Seafloor spreading
• Plate tectonics
• Continental drift
• Subduction zone

[edit] References