Crustal Movement

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Chapter 4-1

• Crustal Movement

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The EGG Model of the Earth

• Shell Crust
• Very thin compared to entire egg
• Slimy Skin Moho
• Keeps the white from leaking out
• White Outer Core
• Soft mushy, but still a solid
• Yolk Inner Core
• Denser
• Needs to be divided into 2 layers

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Layers of the Earth
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Layers of the Earth

• Think about the Egg model
• Always start at the stick person to find the
  location in the Earth, before you look for data
• Be careful when reading the graphs
• All rocks are found in the GREEN layer
• Different crusts have different densities

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Crust

• Oceanic

• Continental

• High-density rocks (like basalt)
• Rich in Iron Magnesium (Mafic)
• Average thickness is 10 km
• NOT thinner or denser because of the ocean on it
  because of the rock properties

• Low-density rocks (like granite)
• Rich in Aluminum (Felsic)
• Average thickness is 20-40 km
• Collisions cause sediments at rivers to uplift
  (creating met. possibly igneous rocks in the
  process)

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Crustal Boundaries

• Located along the edge of the plates
• Interaction depends on plate movement
• Land formations are the result of the crustal
  movement
• There are 3 types
• Convergent
• Divergent
• Transform

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Convergent
Boundaries

• Plates are moving towards each other
• Resulting landforms depend on plate types due to
  density differences
• Same Type of Plates (Cont Cont)
• Neither plate will give in
• Mountains will form

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Convergent Boundaries

• Different type of plates (Cont Oceanic)
• The denser one (Oceanic) will go under the less
  dense one (subduction) melt into magma
• Intersection will form a deep trench under water
• As this plate moves, earthquakes will occur along
  the interface between the plates
• The less dense one (Cont) will get bent due to
  the collision form mountains (possibly
  volcanoes if magma gets through)

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Divergent
Boundaries

• Plates are moving away from each other causing a
  rift valley to form
• This valley will then fill with magma/lava form
  new crust
• This new crust is still very warm, so it will be
  elevated form a mountain chain
• As the crust cools, it will contract
• Most of these boundaries are under water

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Divergent Boundary ABOVE Water
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Transform Boundaries

• Plates are rubbing against each other, cause lots
  of earthquakes
• There is little or no lava involved
• Having many frequent small earthquakes is better
• otherwise there will be less, but they will be
  stronger cause more damage
• the end result will still be the same amount of
  movement
• San Andreas Fault (California)

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San Andreas Fault
Pacific Plate
North American Plate
http//www.youtube.com/watch?vZxPTLmg0ZCw
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Cause of Plate Movement

• Convection of the Magma in the Plastic Mantle
• Look at the arrows on page 10 of the ESRT

http//www.youtube.com/watch?featureendscreenNR
1vryrXAGY1dmE
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Pattern of Boundaries

• Most Earthquakes Volcanoes are concentrated in
  narrow belts
• These belts help indicate where plate boundaries
  occur
• See ESRT page 5

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Theories of Crustal Movement

• 1910
• Professor Al Wegener
• Continental Drift Theory
• Pieces fit like a puzzle
• Rocks match (NJ Africa)
• Fossils match
• Fossil Fuel Deposits
• (PA. Alaska, Antarctica)
• Couldnt explain HOW

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Sea-floor Spreading

• 1960
• Harry Hess
• Hypothesis that the sea floor forms out of the
  mid-ocean ridges
• Moves away from the ridge like a conveyor belt
  due to the magma underneath (what Prof Al
  couldnt explain)
• Age of rocks are older as you move away from the
  ridge on both sides

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Reversed Polarity

• If there is magnetic material in molten rock, it
  will be aligned by the magnetic field of the
  Earth
• When it cools hardens, a record of the Earths
  polarity at that time is preserved in the rock
• Across the Atlantic ocean, there is a pattern

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Plate Tectonic Theory

• Put together
• Continental Drift
• Sea-floor Spreading
• Convection of the plastic mantle
• Reversed polarity
• Some plates are all oceanic crust
• Some plates have continental chunks on them
• The plates are separating, colliding, or sliding
  past each other (plate boundaries)
• The plates rest on the athenosphere (plastic
  mantle) which is moving in slow, powerful
  convection cells

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Just a Theory

• There are still places that cannot be explained
  by these concepts
• 3 possible driving forces for plate movement are
• Plates are pushed from the rear
• Convection of the magma drag the plates
• Descending denser plates pull the plate as it
  sinks into the plastic mantle
• Keep an open mindlike Professor Al

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Hot Spots

• Hole in the Moho that the plate slides over
• Creates an active volcano
• Once the plate moves the volcano becomes extinct
  because it has lost its source of magma
• The Hawaiian Island chain is a great example

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Strata

• Horizontal layers of sedimentary rock
• If the layers are NOT horizontal then they are
  evidence of crustal movement

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Deformed Strata

• The most common deformed strata are
• Tilting
• Folding
• Faulting