The lithospheric plates move relative to each other. They
are created at mid-oceanic ridges and destroyed at subduction zones.
A mid-ocean ridge is an underwater mountain system
formed by plate tectonics. It consists of various mountains linked in chains,
typically having a valley known as a rift running along its spine. This type of
oceanic mountain ridge is characteristic of what is known as an oceanic
spreading center, which is responsible for seafloor spreading. The
production of new seafloor results from mantle upwelling in response to plate
spreading; this isentropic upwelling solid mantle material eventually exceeds
the solidus and melts. The buoyant melt rises as magma at a linear weakness in
the oceanic crust, and emerge as lava, creating new crust upon cooling. A
mid-ocean ridge demarcates the boundary between two tectonic plates, and
consequently is termed a divergent plate boundary.
