Continental Growth

Continental Growth

•Most continents used to be smaller.

•Through tectonic processes, rock has been added to continents.

Continental Growth•A craton is the

ancient core of a continent.•They are older and more altered than the rest of the continent.•There are two types of craton: shields and platforms.

Cratons•Shield–made of igneous and metamorphic rock– are in geologically stable areas– are from the Precambrian time period

•Platform–made of sedimentary rock–generally flat or very slightly tilted– sits on top of the shield (and is younger)

Two types of craton:

CratonsThe Canadian Shield is the only part of the North American craton that is still exposed.

Continental Growth

•Continents grow by adding land to their cratons.•Land is added from:–Oceanic Sediment–Volcanoes–Collisions with

other land masses (terranes)

Continental GrowthOceanic Sediment

• When an oceanic plate is subducted under a continental plate, some of the ocean floor is scraped up.

• This deep-sea sediment is pushed onto the continental plate.

Continental Growth•Volcanoes

•Volcanic chains at subduction zones.•Lava can harden into rock on the edges of a continent.•Weathering of volcanoes produces sediment.