constructive plate margins

• Constructive (divergent) plate margins happen when plates move apart.
• At a constructive plate margin, where two sections of oceanic crust are separating, the lithosphere becomes thinner, leading to the upwelling of mantle rock. The reduced pressure exerted by the crust (because it is thinner) onto the mantle leads to mantle material melting (through a process called decompression melting), leading to diapirs, which feed magma chambers along the ridge. Magma can then rise to the surface in dykes, leading to surface eruptions and forming new crust, which drives the process of ridge push. The rising magma can form shield volcanoes
• Most constructive plate margins are under the oceans, where two sections of oceanic crustmove apart.
• Constructive boundaries are mainly located under the sea, e.g. the Mid-Atlantic Ridge. Here, chains of underwater volcanoes have formed along the plate boundary. One of these volcanoes may become so large that it erupts out of the sea to create a volcanic island, e.g. Surtsey and the Westman Islands near Iceland.
• constructive plate margin


  plates move apart and magma rises to fill the gap