Hypsographic Curve Chapter 10 Evolution of Continental Crust Continental Crust Terms Orogeny Epeirogeny Terrane Accreted Terrane Mantle Plume Hot Spot Volcanism Wilson Cycle Basin Dome Accretion Craton Shield Continental Crust It s thick 30 60km It s old 250 4000 my It s light 2 75 g cm3 It s silicic dioritic to granitic in composition It has a stable interior called the craton It grows at active margins It does not subduct Continental Crust Because continental crust is thick and old it has experienced and recorded many orogenic events It is extremely heterogeneous Oldest continental rocks are about 4 billion years old The oldest oceanic rocks are only 200 million years old 1 Cratons and Shields The craton is the stable interior part of the continent The craton may be covered by a thin 2km veneer of sedimentary rocks The shield is that portion of the craton that is free of sedimentary cover Shields occur in Canada Southern Africa Western Australia and Scandinavia Terranes A terrane is a co genetic block of crust Continents are composed of terranes or blocks of similar age and origin The terrane we are on gives a metamorphic age of 1800 my The CO WY border is also a terrane boundary The Wyoming terrane is Archean Growth of Continents Continents grow at active margins They grow by addition of accreted or exotic terranes A exotic terrane accreted terrane is a small block of crust scraped off a subducting plate Much of SE Alaska and British Columbia is composed of accreted terranes 2 Mountain Belts An orogeny is an episode of mountain building An orogenic belt is a co genetic belt of mountain ranges e g Alps Himalayas Rocky Mountains Mountain belts tend to have thicker sedimentary cover 2 10 km Wilson Cycle The cycle of opening and closing of ocean basins is called the Wilson Cycle Continents can be rifted by the formation of new ocean crust Continents can fuse or collide as in the Alpine Himalaya orogeny Plate tectonic movements and ocean basins Rifting splits the continent Earth System Figure 10 18 page 232 Go to next slide to begin 3 leading to the creation of new oceanic crust Passive margin cooling occurs and sediment accumulates Convergence begins an oceanic plate subducts beneath a continental plate creating a volcanic chain Terrane accretion welds material to the continent Orogeny thickens the crust and builds mountains forming a new supercontinent The continent erodes thinning the crust Rifting may begin the process again 4 Plumes and Hot Spots Plume Hypothesis A Plume is a small convective upwelling from the mantle Plumes may cause hot spot volcanism Yellowstone Hawaii Orogeny and Epeirogeny Orogeny is an episode of mountain building Himalayas Rocky Mtns Alps Appalachians Epeirogeny is regional vertical movement of continental crust Glacial rebound in NE US Rocky Mountains Epeirogeny example Glacial Rebound Epeirogeny 1 mm y 1000 m My 5 Continental Crust Western US has several terranes Coast Ranges Cascades Sierra Nevada Columbia Plateau Snake River Hot spot track Basin and Range Colorado Plateau Rocky Mountains Great Plains Continental Crust Terms Clicker Question A small block of crust added on to the active margin of a continent is called a n A B C D E Accreted Terrane Shield Craton Mantle Plume Epeirogeny Orogeny Epeirogeny Terrane Accreted Terrane Mantle Plume Hot Spot Volcanism Hypsographic Curve Wilson Cycle Basin Accretion Craton Shield The stable interior portion of a continent is the A B C D E Accreted Terrane Shield Craton Mantle Plume Epeirogeny 6 An episode of mountain building is called a n A B C D E Accreted Terrane Shield Craton Orogeny Epeirogeny Upward or downward movement of a region of continental crust is called a n A B C D E Accreted Terrane Shield Craton Orogeny Epeirogeny The stable interior portion of a continent that is not covered by sediments is the A B C D E Accreted Terrane Shield Craton Mantle Plume Epeirogeny 7
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