Chapter 4, Section 2 Objectives:

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• Chapter 4, Section 2 Objectives
• 1. Summarize the theory of plate tectonics.
• 2. Compare the characteristic geologic activities
  that occur along the three types of plate
  boundaries.
• 3. Explain the possible role of convection
  currents in plate movement.
• 4. Summarize the theory of suspect terranes.

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• Theory of Plate Tectonics describes continental
  movement and proposes a possible explanation of
  why and how continents move.
• From Greek word tektonikos, meaning construction
• Tectonics the study of the formation of features
  in the Earths crust
• Earths surface consists of a number of rigid,
  but moving pieces called plates

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• 2 Types of Earths crust
• Oceanic Crust material on the ocean floor.
• Continental Crust makes up the continental
  landmasses.

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• Lithosphere made up of the crust and the rigid
  upper mantle.
• Forms the thin outer shell of the Earth
• Rigid but broken into plates that move with
  respect to one another
• Asthenosphere a layer of plastic rock
• Solid rock that slowly flows (like putty)
• Layer within the mantle that the lithospheric
  plates rest on

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• According to the Theory of Plate Tectonics
• Lithosphere is broken into separate plates
• Plates ride on denser asthenosphere
• Most plates composed of both continental and
  oceanic crust
• To date about 30 lithospheric plates have been
  identified

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• Plate Boundaries
• Place where one plate is moving relative to
  another plate
• 3 types
• Each associated with a characteristic type of
  geological activity
• Differs according to the way the plates move in
  relation to each other

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Kinds of Plate Boundaries
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• Transform Fault Boundries plates are grinding
  past one another
• Move in a series of sudden spurts of activity
• Earthquakes
• Ex San Andreas fault

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Example San Andreas Fault
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• Divergent boundaries where two lithospheric
  plates are moving apart (spreading centers)
• As plates move apart, molten rock rises and fills
  space between plates
• cools and hardens creating new oceanic crust
• Most divergent boundaries are found on the ocean
  floor

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Mid-Atlantic Ridge
Spreading Center
New ocean floor is being created
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• Rift Valley narrow valley formed as the plates
  separate.

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• Convergent Boundary the place where one plate
  directly collides with another plate.
• 3 types of convergent boundries

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• Oceanic crust collides with continental crust
  since oceanic crust is denser it is forced under
  the continental crust (subducted)
• Subduction Zone region along a plate boundary
  where one plate moves under another

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• Deep Ocean Trench usually forms along a
  subduction zone.
• Oceanic crust moves down
• Melts and becomes part of the mantle material
• Some magma rises through the continental crust
• Produces volcanic mountains

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• Continental crust collides with continental
  crust neither plate is subducted
• Colliding edges are crumpled and uplifted
• Produces large mountain ranges
• Himalayas

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• Oceanic crust collides with oceanic crust
• Island Arc is formed when
• One plate is subducted, forming a trench
• Subducted plate melts
• Molten rock rises to surface along trench
• Forms volcanic islands

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• Convection the transfer of heat through the
  movement of heated fluid material.
• Convection Current the cycle of warm less dense
  material rising and cooler denser material sinking

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Lets go to this website and review!
CLICK HERE
http//www.pbs.org/wgbh/aso/tryit/tectonics/
Click on Plate Tectonics Activity (with a yellow
arrow) when you get there!
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Here it is all in one big picture
Can you pick out the types of Plate Boundaries?
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Were you right?
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• Terranes pieces of lithoshpere
• Each with its own distinct geologic history
• Theory of Suspect Terranes suggests that the
  continents are actually a patchwork of terranes
• As oceanic crust is subducted, terranes are
  scraped off and become part of the continental
  crust