Sea-floor Spreading

A divergent margins with a spheric plates move in opposite directions. The plates, which include crusts and part of the upper mantle, ride over the asthenosphere. As hot mantle rock rises to shallow depths. It begins to melt to a lower pressure. This forms Magnum. Dense plutonic rock is created as the magma is injected into the crust. Small mega chambers form low in the crust. Less than one quarter of a magnet ever reaches the surface to erupt as pillow lavas. As it moves away from the ridge, the cooling rock sits progressively lower than the hotter more buoyant rock at the ridge. By two giant conveyor belts, the plates transport newly formed oceanic crust away from the ridgecrest at three to ten centimeters per year.