The Theory of Plate Tectonics
Concepts:
• What is the theory of
plate tectonics?
• What are the three
types of plate
boundaries?
Terms:
• J. Tuzo Wilson
• Plate
• Scientific theory
• Plate tectonics
• Fault
• Divergent boundary
• Rift valley
• Convergent boundary
• Transform boundary
J. Tuzo Wilson and Plates
• A Canadian scientist,
J. Tuzo Wilson,
observed that there
are cracks in the
continent similar to
those on the ocean
floor.
• In 1965, Wilson
proposed a new way
of looking at these
cracks.
• According to Wilson,
the lithosphere is
broken into separate
sections called
plates.
Lithospheric Plates
The Theory of Plate Tectonics
• The theory of plate tectonics explain
the formation, movement, and
subduction of Earth’s plates.
How do the plates move?
• The theory of plate tectonics states that pieces of Earth’s
lithosphere are driven by convection currents in the mantle.
• As the plates move, they collide, pull apart, or grind past
each other producing spectacular changes in Earth’s
surface.
• Volcanoes, mountain ranges, and deep ocean trenches
• The plates move very slow about 1-24 centimeters a year.
• About as fast as your fingernails grow.
• They have been moving for tens of millions of years.
As we review each plate boundary, complete a tree map and
include the following:
•
Focus Questions:
1. Plate Boundary
2. Which direction are the plates moving at
these boundaries in relationship to each
other?
3. What action occur at each location/type of
plate boundary?
4. What forms because of these actions?
1. Examples
Tree Map
Plate Boundary
Plate Movement
Location
Location
Arrows
Action
Action
Definition
Examples
Examples
Types of plate boundaries
•
Divergent plate boundary
1. Ocean: Mid Oceanic Ridge
2. Land: Continental Rift zone
•
Convergent plate boundary
1. Oceanic-oceanic convergence – Subduction
Trench
2. Continental-continental convergence – No
Subduction - Mountains
3. Oceanic - continental convergence – Subduction
Trench
•
Transform plate boundary
• Earthquakes
• Crust is neither created nor destroyed.
Divergent plate boundaries
A place where two plates move apart, or diverge
Ocean
Mid-Ocean Ridge E.g. Mid-Atlantic ridge is a result of
sea floor spreading
new basaltic magma
rises to the surface
along the ridge
forming new oceanic
crust.
Thingvellir Rift Valley
http://epod.usra.edu/blog/2010/08/mid-atlantic-ridge-in-iceland.html
Slicing through the center of Iceland is
the Mid-Atlantic Ridge. This is the
boundary between theNorth
American and Eurasian tectonic plates
Thingvellir National Park, in southwestern Iceland, is
one of the few spots in the world where an underwater
ridge rises above the water surface.
Iceland is one of the most geologically active places on Earth with
more than 15 volcanoes that have erupted in the last century.
Land
•Rift valleys may increase in
size till water fills them to form
a Sea
•The Red Sea and the Gulf of
Aden were once rift valleys.
Mt. Kilimanjaro
These rift valleys often
have volcanoes lining them.
Great African Rift Valley
The formation of the Atlantic
Ocean
Divergent Plate Boundaries
In the Ocean
• Ridge
• Action: oceanic plates
move apart
• Sea floor spreading
• Mid-Ocean Ridge
• Example: Mid Atlantic
Ridge
• Longest mountain Range
On Land
• Rift
• Action: Continental crust
pull apart
• Examples: Iceland, Great
Rift Valley in East Africa
• Oceans and Seas form
• Example: Atlantic Ocean
and Red Sea
• Volcanoes
• Example: Mt. Kilimanjaro
Tree Map
Divergent Plate Boundary
Plate Movement
A place where to plates
move apart, or diverge
Ocean: Ridge
Land: Rift
Action: Sea-floor
spreading
Action: Continental crust
pull apart
Example: Mid
Atlantic Ridge
Examples: Iceland, Great
Rift Valley in East Africa
Oceans and Seas
form:
Examples: Atlantic
Ocean and the Red
Sea
Oceans and Seas form
Example: Atlantic Ocean
and Red Sea
Volcanoes
Example: Mt. Kilimanjaro
Convergent Plate Boundaries
The place where two plates come together, or converge.
Three types of convergent plate boundaries:
1. Ocean crust to ocean crust collision
2. Ocean crust to continental crust
collision
3. Continental crust to continental
crust collision
Tree Map
•
•
•
•
Name of plate boundary
Draw arrows to indicate direction the plates
move in relationship to each other.
Create a Tree map of the 3 types of
convergent boundaries, the events that occur
there, and an example of each occurrence. i.e.
action, formations, examples
Compare the items in your map, which
convergent boundary type does NOT result in
volcanoes? Why?
Mt. Hood
Aleutian Islands
Trench
Island arc
Oceanic continental
convergence
E.g. Andes mountains
The forces of plate tectonics are
responsible for the formation of the
Andes. The Nazca plate and a part of
the Antarctic plate have
been subducting beneath the South
American plate, which is a process
that continues today and
causes earthquakes andvolcanic
eruptions in the region
http://www.windows2universe.org/geography/andes.html
Quick Review
The sub-continent of India has
collided with the Eurasian
continent to form the Himalayas
•Types Convergent plate boundaries
Oceanic-oceanic convergence
Islands
Japan, Aleutian Islands
Volcanoes- Mt Pinatubo
Trenches
Earthquakes
Oceanic - continental convergence
Volcanoes - Andes, Cascades
Trenches
Earthquakes
Continental-continental convergence
No volcanoes
Mountain building - Himalayas
Convergent Boundaries
• 3 types of convergent boundaries
• Ocean to ocean crust
• Crust melting forms volcanic island arc, ex Aleutian Islands
• Volcanoes – Philippines- Mt Pinatubo
• Subduction forms trench
• Ocean to continental crust
• Crust melting forms volcanic mountain ranges, ex Andes, cascade
range, Mt Rainer, Mt Baker
• Subduction zones forms, trenches,
• Ocean crust denser than continental crust.
• Ocean crust slides/subducts under the continental crust
• Continental to continental crust
• No melting of crust = no volcanoes
• No subduction
• Folding of crust = Non-volcanic mountains are formed -Example
Mt Everest
Tree Map
Convergent Plate Boundaries
Ocean to ocean crust
Crust melting forms
volcanic island arc, ex
Aleutian Islands
Volcanoes –
Philippines- Mt
Pinatubo
Subduction forms
trenches
Ocean to continental crust
Continental to
continental crust
Crust melting forms volcanic
mountain ranges, ex Andes,
cascade range, Mt Rainer, Mt
Baker
No melting of crust = no
volcanoes
Subduction zones forms
trenches
No subduction
Ocean crust denser than
continental crust.
Folding of crust = Non-volcanic
mountains are formed
Ocean crust slides/subducts
under the continental crust
-Example Mt Everest
Transform Boundary
A place where two plates slip past each other,
moving in opposite directions
North American plate
Pacific plate
San Andres Fault
Earthquake in action
• http://www.classzone.com/books/earth_science/terc/conte
nt/visualizations/es1005/es1005page01.cfm?chapter_no=
visualization
Transform plate boundary
• Action: Earthquakes
• Forms: fault
• Example: San Andres fault
• No crustal melting = No volcanoes
Transform Boundary
•
•
•
•
Draw arrows to indicate direction the
plates move in relationship to each
other.
Name a location of a transform
boundary.
Name the event that occurs at
transform boundaries.
Could a volcano erupt in Los Angeles?
Why or why?
Transform Boundary
Direction
Forms
Faults
Earthquakes
Is a place where
two plates slip
past each other
Example: San Andres fault
Crust is neither created
nor destroyed
No crustal
melting = No
volcanoes