Successive intrusions of mantle-derived mantle into the same area of the crust may cause further increases in temperature, and eventually cause the geothermal gradient to become higher than the wet solidus of the crustal material, resulting in a partial melt of the crust. From the discussion above it should be obvious that magmatism is closely related to plate tectonics. The diagram below summarizes melting mechanisms that occur as a result of plate tectonics and may be responsible for the generation of magmas in a variety of plate tectonic settings, such as oceanic ridges, near subduction zones, and at rift valleys. Diverging Plate Boundaries Diverging plate boundaries are where plates move away from each other. These include oceanic ridges or spreading centers, and rift valleys.
Oceanic Ridges are areas where mantle appears to ascend due to rising convection currents.
Decompression melting could result, generating magmas that intrude and erupt at the oceanic ridges to create new oceanic crust. Iceland is one of the few areas where the resulting magmatism has been voluminous enough to built the oceanic ridge above sea level. Continental Rift Valleys or Extensional Zones are areas, usually located in continental crust where extensional deformation is occurring. These areas may be incipient spreading centers and may eventually evolve into oceanic ridges, such as has occurred in the Red Sea region. Whether or not they develop into spreading centers, they are likely caused by mantle upwelling below the zone of extension.