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Continental Margins

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Volcanoes Present at subduction boundaries Ocean / Ocean Ocean / Continent Plutonic intrusions core of mountains in Andes and Sierra Nevada Volcanic mountain ranges ... – PowerPoint PPT presentation

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Title: Continental Margins


1
Continental Margins
  • Boundary that occurs between the continental
    crust and the oceanic crust
  • Boundary occurs at continental slope, not the
    shoreline
  • Two basic types of continental margins
  • Active and passive

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Active Continental Margins
  • Occur along plate boundaries
  • Earthquakes, volcanoes and mountain building
    result
  • Example west coast of South America where the
    Nazca Plate is subducting beneath the South
    American Plate forming the Andes Mountains

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Passive Continental Margin
  • Do not occur at plate boundaries
  • Stable areas of shallow water
  • Major activity is the buildup of sediment
    received from rivers and the skeletons and shells
    of marine organisms
  • Example Atlantic Coast of N. A.

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Ocean/Continent Collisions
  • Ocean crust subducts under continent
  • Magma is generated and rises to the surface to
    form volcanoes
  • Deep earthquakes occur here
  • Obduction and accretion also occurs Scraping of
    oceanic crust and attaching to continent/Terranes

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Continent/ Continent Collision
  • Second type of mountain building occurs when two
    continents collide
  • Examples are the Alps and Himalaya mountains

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  • Features of Collision Mountains
  • 1. Faults- break in the Earths crust where
    movement has occurred
  • Normal- rocks on one side drop down, caused by
    tension (Baikal)
  • Reverse- one side pushed up, caused by stresses
    pushing together
  • Strike-slip- rocks move horizontally (San Andreas
    Fault)

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Footwall Up Normal Fault FUN
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2. Folds
  • Anticline-an upfold in the Earth layers, oldest
    layers in the center
  • Syncline-a downfold in the Earths layers,
    youngest in the center
  • Limbs-the sides of the folds
  • Dip-steepness of limbs intensity
  • Strike-compass direction of fold

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  • 3. Volcanoes
  • Present at subduction boundaries
  • Ocean / Ocean
  • Ocean / Continent
  • Plutonic intrusions core of mountains in Andes
    and Sierra Nevada
  • Volcanic mountain ranges as in the Cascades of
    North America

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  • Evidence of Mountain Building
  • Uplifting
  • Areas raised to higher elevations with little
    deformation
  • Determined by
  • 1. Fossils found above sea level
  • 2. Raised beaches above sea level
  • 3. Regular measurements

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Tilting
  • Sedimentary rocks form in level layers-originally
    horizontal
  • Layers can be tilted several ways
  • Folding
  • Thrusting of layers
  • Uplifting
  • Faulting

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Overturning
  • Determined by
  • Ripple Marks
  • Cross-bedding
  • Mudcracks
  • Shells

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Tectonic Features
  • Joints-a crack or break in the bedrock along
    which no movement has occurred
  • Groups called sets, can be filled with minerals
    called vein deposits

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  • Dome Mountains are circular folded mountains
    formed by uplifting forces - two types
  • Plutonic Dome Mtns.- pushed up by the intrusion
    of an igneous mass
  • Tectonic Domes-result from uplifting forces

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