Download Theory of Plate Tectonics

Plate Tectonics
What is Plate Tectonics
• The Earth’s crust and upper
mantle are broken into
sections called plates
• These plates move around on
top of the asthenosphere like
rafts
Lithosphere
• The crust and part of the upper
mantle = lithosphere
–Less dense than the material
below it so it “floats”
Asthenosphere
• The “plastic” layer below the
lithosphere
• The plates of the lithosphere
float on the asthenosphere
2 Types of Plates
• Ocean plates - plates below
the oceans
• Continental plates - plates
below the continents
Plate Boundaries
Divergent Boundaries
• Boundary between two plates
that are moving apart or rifting

Examples of Divergent
Boundaries
• Mid-ocean ridges
• rift valleys
Convergent Boundaries
• Boundaries between two
plates that are colliding
 
• There are 3 types…
Type 1
• Ocean plate colliding with a
less dense continental plate
• Subduction : occurs where the
more dense plate slides under
the less dense plate
Subduction Zones occur here
Deep ocean trenches may occur here
Mountains and volcanoes may occur
Andes Mountains,
South America
Type 2
• Ocean plate colliding with
another ocean plate
• The more dense plate slides
under the less dense plate
creating a subduction zone
called a TRENCH
Aleutian Islands, Alaska
Type 3
• A continental plate colliding
with another continental plate
–a place where folded and thrust
faulted mountains form.
Transform Fault Boundaries
• Boundary between two plates
that are sliding past each other
• EARTHQUAKES along faults
San Andreas Fault, CA
Questions...
• What are the three types of
boundaries?
• What direction do plates go for
each?
• Which boundary has a subduction
zone…what occurs at a
subduction zone?
Causes of Plate
Tectonics
Convection Currents
• Hot magma in the Earth
moves toward the surface,
cools, then sinks again.
• Creates convection currents
beneath the plates that cause
the plates to move.
Questions...
• What causes plates to move?
• How is a convection current
formed?
New sea-floor is produced at what
type of boundary?
A. convergent
B. divergent
C. transform
D. I don’t know
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Mt. Everest was produced by this
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A. convergent
B. divergent
C. transform
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D. I Don’t Know