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Unformatted text preview: Evolution of Continents Continents o Middle= older; outer= younger Cratons o Old, stable interior parts of continental lithosphere o Comprised of shields and platforms Shields: crystalline, metamorphic rocks that form the upper crust Interior Platforms: sediment-covered region surrounding the crystalline shield rocks How do continents grow? o Magmatic Addition Building up continent by adding magma to it through volcanic activity; makes new mountains=adds to size of continent o Continental Accretion Accretion of buoyant fragments Buoyant continental/oceanic fragment is carried into a plate collision zone Fragment is more buoyant so is not subducted Fragment is welded into the overriding plate Accretion of Islan.,d Arcs Plates are slowly getting closer together When finally meet, subduction zone shuts off Island arc crust becomes embedded into the continent Accretion by Continental Collision A plate carrying a continent subducts beneath another continental plate Continent isnt subducted so the two continents are smashed together...
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- Spring '11