Plate boundaries are zones where the earth’s crust is both created and destroyed.
A constructive plate is where a new crust is created. This can be found beneath the middle of the Atlantic Ocean.
The convection currents of magma at this boundary causes the North and South American plates to move away from the Eurasian and African plates. This parting movement is called divergence. When these plates separate, molten magma from the mantle emerges steadily through the cracks and forms fissures. The hot magma cools quickly as it comes in contact with the Atlantic seawater, creating new crust. As the plates continue to separate, the new crust widens. The newest crust is at the center of the Mid-Atlantic Ridge and gradually becomes older towards the eastern and western edges of the Atlantic.
A destructive plate boundary is where the crust is destroyed. This can be found on the west margin of South America.
Convection currents of magma at this boundary causes the American plate and the Nazca plate to collide. As the Nazca plate is made up of oceanic crust which is heavier than the South American plate which is made up of continental crust, the Nazca plate sinks beneath the South American plate. The hot mantle melts and destroys the oceanic plate (Nazca plate) as it sinks. The molten plate material sometimes forms large underground bubbles of magma called batholiths which sometimes forces its way to the surface to eventually form volcanic mountains.