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Plate Tectonics
Overview:
• The Lithosphere and the Crust
• Basic Concepts of Plate Tectonics
• Plate Movements and Boundaries
Inside the Earth:
The Lithosphere:
The Basic Concepts:
- the earth is covered by several large lithospheric plates
These plates move slowly (about a few
cm./yr)
• Due to convection cells in the asthenosphere
Convection movement driven by heat from the core:
Mantle convection produces lateral
forces at the boundary between the
mantle and the crust
Theory of Plate Tectonics:
Plate Movement and Boundaries
• Divergent Boundaries
o
o
o
o
Plates move apart
Volcanic activity
Earthquakes shallow
Two types of boundaries
 Oceanic
 Continental
Oceanic divergent boundary
• Sea-floor spreading of ocean plates
Mid-Atlantic Ridge
Page 43, Worrall
Continental Divergent Boundary
• Continental Rifting,
eventually oceanic
crust is formed
 Modern example ;
 East African Rift
Convergent Boundaries
•
•
•
•
Plates move towards each other
Volcanic activity common
Deep, medium and shallow earthquakes
Three types;
Ocean to ocean
Ocean to continent
Continent to continent
Ocean to Ocean- convergence
• Subduction - process which one plate
slides under the other (subducts)
• Volcanic arc islands are formed
Ocean to Continent Convergence
• Ocean lithophere subducts under
continent
•Most tectonic activity occurs at or near these boundaries
Continent to Continent - Convergence
• Subduction does not
occur
• Mountain building
occurs without
volcanic activity
• Collision of India
with Eurasia
• Height is still
increasing
Transform Boundaries
• Plates slide past
each other
• Little or no volcanic
activity
• Shallow but strong
earthquakes
• Example: San
Andreas Fault
West Coast: unstable -subduction zone and transform fault zone
A
Divergent
•plates are
moving apart
•new crust is
created
•Magma is
coming to the
surface
B
Convergent
•plates are coming
together
•crust is returning
to the mantle
C
Transform
•plates are
slipping past
each other
•crust is not
created or
destroyed
A
Divergent
Continental crust
 rift valley
B
Convergent
2 continental plates 
mountain range
C
Transform
Plates move
against each
other
Stress builds up
Oceanic crust  midocean ridge
2 oceanic plates or
oceanic + continental
subduction
Stress is released
earthquake
The Big Picture