In terms of plate tectonics, divergent boundaries are areas under tension where lithospheric plates are pushed apart by magma upwelling from the mantle. Lithospheric plates are regions of Earth's crust and upper mantle that are fractured into plates that move across a deeper plasticine mantle. At divergent boundaries, lithospheric plates move apart and crust is created.

Earth's crust is fractured into approximately 20 lithospheric plates. Each lithospheric plate is composed of a layer of oceanic crust or continental crust superficial to an outer layer of the mantle. Oceanic crust comprises the outer layer of the lithosphere lying beneath the oceans. Oceanic crust is composed of high-density rocks, such as olivine and basalt. Continental crust comprises the outer layer of the lithospheric plates containing the existing continents and some undersea features near the continents. Continental crust is composed of lower density rocks such as granite and...