Continental Margins

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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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