PLATE TECTONICS review

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PLATE TECTONICSreview

• REVIEW

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Plate Tectonics

• Plates are made up of the crust and top part of
  the mantle
• They move due to convection currents that occur
  in the asthenosphere
• Plates can converge, diverge, or slide past
  eachother

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Diverging Plates

• Where plates diverge, a rift valley is formed
• Magma rises up to fill the space
• Younger rock is closest to the boundary, older
  rock is farther away
• Ridges occur as the sea floor spreads

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Converging Plates

• Oceanic crust is more dense than continental
  crust, so it subducts (plunges under)
• The result is volcanic mountains or islands above
  the subduction zone (lots of melting and pressure)

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Converging Plates

• Once there is no longer any oceanic crust (and
  subduction stops), two continental plates will
  collide and the rock will crumple (deform and
  uplift) forming mountain ranges

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Transform (Sliding) Boundaries

• plates slide horizontally past each other
• Friction of rock causes stress to build, which
  can result in an earthquake

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Volcanoes

• Volcanic activity can take place in many
  locations on the crust (shown below), due to hot
  magma rising to the surface

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Types of Eruptions and Volcanoes Formed

• Rift (quiet) eruptions occur at spreading
  boundaries and release lava
• They result in broad cones called shield
  volcanoes

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Types of Eruptions and Volcanoes Formed

• Subduction (explosive) eruptions occur at
  subduction zones
• They result in steeper cone shaped volcanoes
  (strata or cinder cone) and release ash and other
  pyroclastics

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Igneous Intrusions

• When magma solidifies in the crust in various
  locations, batholiths, sills, dikes, laccoliths,
  stocks result

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Earthquakes

• Earthquakes are common at subduction zones and
  transform boundaries (friction, stress!)
• They occur when stress builds and then is
  suddenly released
• Tsunamis can be caused by underwater earthquakes

Elastic-rebound theory
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Earthquake Waves

• There are three wave types released during an
  earthquake primary, secondary and body (L) waves

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Recording Earthquakes

• P waves travel fastest and through all materials
• S waves travel slower and do not pass through
  liquids
• The difference in the arrival of the p and s
  waves helps geologists determine how far away the
  earthquake is

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Recording Earthquakes

• A minimum of 3 seismograph stations are required
  to pinpoint the epicenter of an earthquake
  (triangulation)

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Magnitude and Intensity

• The energy released by an earthquake (magnitude)
  is measured on the Richter Scale
• Intensity (how much damage caused) is measured on
  the Mercalli scale (subjective!)

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Continental Margins

• Active continental margins occur at plate
  boundaries and have lots of tectonic activity
  (earthquakes, volcanoes)
• Passive continental margins do not occur at plate
  boundaries, and mostly consist of the
  accumulation of sediment.

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Faults-Three Types

• Strike-Slip sides move horizontally past
  eachother (shearing force)
• Normal one side drops with respect to the other
  (tension force)
• Reverse one side is pushed up with respect to
  the other (compression force)

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Fault Block Mountains

• When whole blocks of crust have been faulted and
  thrust upwards, fault block mountains result

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Folding of Rock Layers

• When compressional forces act on sedimentary rock
  layers, folding occurs
• Anticline-upfold, syncline-downfold
• Folding causes the tilting of rock layers
• Layers can also be overturned

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Plate Tectonics-A Summary
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