MOVE - Mid-Ocean Volcanoes and Earthquakes

Ocean basins are formed by seafloor spreading at active mid-ocean ridges, the boundary between two divergent lithospheric plates. Mantle material is upwelling under the ridges and melts to produce magma which erupts onto the sea floor and crystallises at depth to produce new oceanic crust. Crustal generation and plate separation rate keep pace over a wide range of spreading rates and produce oceanic crust with a uniform thickness of about 7 km. Models predict that at spreading rates below about 20 mm/y, the mantle looses heat by conduction and only small amounts of melt are produced at large depths. Consequently, magmatism and crustal thickness should decrease with decreasing spreading rate. Volcanic eruptions should be unlikely at ultraslow spreading ridges (<20 mm/y). Until recently, very little data from ultraslow-spreading ridges were available to verify this theory because these ridges are located in remote ocean basins, the ice covered Arctic Ocean and the rough ocean between Africa and Antarctica.