Evolution of the Continents
Evolution of the Continents GEOL 101 001
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GEOL 101 001
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This 0 page Class Notes was uploaded by Madeline Wilson on Thursday February 25, 2016. The Class Notes belongs to GEOL 101 001 at University of South Carolina taught by Dr. Knapp in Spring 2016. Since its upload, it has received 14 views. For similar materials see Introduction to the Earth in Geology at University of South Carolina.
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Date Created: 02/25/16
Evolution of the Continents The Appalachian Mountains run along the eastern margin of North America Earth39s Tectonic Plates 0 The earth39s surface is a mosaic of 13 plates of several microplates that move slowly over the asthenosphere Group of rocks all moving in the same direction 0 Can have both oceanic and continental crust orjust one kind Nature of continents Continents are made and deformed by plate motions Continental rocks are generally older than oceanic rocks Lithosphere oats of a viscous layer below the continents the asthenosphere Continental Lithosphere Continental crust 1 Sedimentary cover 2 Crystalline basement igneous and metamorphic rocks Uppermost mantle Continental Components 0 Stable cratons 1 Shields 2 Platforms Folded mountain belts orogens Orogeny A general term for mountainbuilding processes 0 Folding and thrusting of rock layers Often accompanied by magmatic activity Continental Shields Central older portions of continents older rocks Low elevation and relatively at quotcrystalline basementquot of metamorphic and igneous rocks Composed of a series of zones that were once tectonically active Usually contain ore deposits Stable Platforms Shield covered with a sequence of horizontal sedimentary rocks Sandstones limestones and shales deposited in ancient shallow seas Many transgressions and regressions caused by changes in spreading rate Sedimentary rocks are now preserved in large basins Folded mountain belts Relatively narrow zones of folded rocks with associated magmatism Formed at convergent plate boundaries Two major active belt cordillera Rockies Andes and Alps Himalaya Older examples include Appalachians and the Urals The Appalachians Eastern North America from Newfoundland to Alabama Appalachian Plateau slightly uplifted with mildly deformed sediments Valley and Ridge province consists of long mountain ridges and valets and erosional features in a foldandthrust belt of sedimentary rocks Blue Ridge consists of mountains of Precambrian crystalline rocks Piedmont rough to gentle terrain of metamorphosed sedimentary and volcanic rocks Coastal Plain and continental shelf a terrain of low hills grading to at plains of sediments extending off shore Multiple plate collisions in the Paleozoic folded the sediments of the VampR province and transported them toward the interior of the continent Blue Ridge and Piedmont sheets were thrust westward over younger sediments Coastal Plain and Shelf developed after the Triassicjurassic splitting of North America from Africa and the opening of the modern North Atlantic Ocean Cretaceous and Tertiary sediments as much as 5 km thick lled the slowly subsiding through Tectonic Provinces of the North American Cordillera Complex geologic history from multiple episodes of deformation and magmatism Formed through convergence of the paci c the faralon and the north American plates over the past 200 mya The cordilleras are higher than the Appalachians because the main phase of mountain building was more recent 150 50 mya Rejuvenation melting of ice sheets 1520 mya Tectonic age is measured by the youngest major deformation event in the region How Continents Grow Magmatic differentiation magma transferred to continents at subduction zones Continental accretion buoyant fragments of crust attached to continents as the result of plate motions 1 Amalgamations or accretion of terranes 2 Exotic terranes seem out of place The volume of the continents has increased by about 2 kmquot3year for the past 4 billion years How Continents are Modi ed Orogeny mountainbuilding process of folding faulting magmatism and metamorphism Epeirogeny vertical motions of largely atlying rocks without faulting or signi cant folding The Wilson Cycle Rifting within a continent splits the continent Leading to the opening of a new ocean basin and creation of new oceanic crust starting the cycle As sea oor spreading continues and an ocean opens passive margin cooling occurs and sediment accumulates Convergence begins oceanic crust is subducted beneath a continent creating a volcanic mountain belt at the active margin Terrane accretion from the sedimentary accretionary wedge or fragments carried by the subducting plate welds material to the continent As continents collide orogeny thickens the crust and builds mountains forming a new supercontinent The continent erodes thinning the crust Eventually the process may begin again Continental rifting Continentcontinent collision Subduction Continental rifting Cratonic keels are thicker under continents than oceans
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