Plate Tectonics
Tectonic Plates of the Earth
Plate tectonics
Today we will explore….
Different type of Plates
Different types of Plate Boundary (where the
two plates are touching)
Different directions of plate movement
Results of what is created by all three of
these items
Plate tectonics
Types of plates….(2)
Oceanic Plate and Continental Plate
mainly defined along the boundary where the two plates touch, for
example…while most plates are comprised of both continental and oceanic crust
the giant Pacific Plate is almost entirely oceanic, and the tiny Turkish-Aegean
Plate is entirely land.
Plate Boundary…..(3)
Ocean to Ocean
Ocean to Continental
Continental to Continental
Plate tectonics
Direction of Movement (3)
Plates are either…….
Convergent
Colliding….there are 2 different types of convergent
Divergent
Pulling apart (spreading)
Transgressional/Transformational
Sliding past one another
Plate tectonics
What happens when plates move, collide,
etc
Mountains, Trenches, Volcanoes, Islands, rift valley,
earthquakes, etc, etc, etc
Plate tectonics
Convergent Movement
Two plates colliding….one usually goes down.
Subduction –usually when an ocean plate collides with a
continental plate the Ocean plate “subducts” under the
continental plate.
Over-riding –usually when a continental plate collides with
another continental plate. One of the plates usually
subducts, but the other plate will also Over-ride the other
plate.
Plate tectonics
Convergent Movement
Convergent plate boundaries have the following characteristics:
1. plate motion is toward plate boundary,
2. oceanic lithosphere sinks back into Earth and is recycled,
3. the volcanic arc is region of highly explosive volcanoes, like Mt. St. Helens and
Mt. Rainer in Washington,
4. The plate boundary is marked on the seafloor by a deep-sea trench, or just trench,
the deepest areas of the ocean,
5. These types of plate boundaries have the strongest earthquakes and most
explosive volcanic eruptions!
Ocean-to-continent subduction - An oceanic plate is subducted
beneath a continental plate, forming a trench adjacent to a continent, and volcanic
mountains along the edge of the continent.
Example: Peru-Chile Trench adjacent to the western coast of South America and the
Andes Mountains.
Note that the volcanic rocks in this setting tend to be andesite (named for Andes
Mountains) - coming from a mixture of basaltic and granitic magmas.
Ocean-to-ocean subduction - An oceanic plate is subducted
beneath another oceanic plate, forming a deep-sea trench, with an associated basaltic
volcanic island arc.
Examples: Marianas Trench adjacent to Mariana Islands, Aleutian Trench adjacent to
Aleutian Islands, Java Trench adjacent to Java, Sumatra, and Sunda Islands in the
Indonesian region.
A second type of convergent plate boundary involves the sinking of oceanic
lithosphere beneath another plate of oceanic lithosphere -- these regions have the
very deepest trenches along the seafloor and a line of volcanic islands, called an
island arc. Once again these regions have explosive volcanoes.
Continental collisions (convergent movement also
called Over-riding) form mountain belts with folded
sedimentary rocks, and a central area of metamorphic
rocks. and granitic igneous intrusions.
Examples: Himalaya Mountains, Ural
Mountains, Appalachian Mountains
* Non-volcanic
Continental to Continental Convergent
Converging
3 types
A. Oceanic-Continental  volcanic ranges
e.g. Andes
B. Oceanic-Oceanic
 volcanic island arcs
e.g. Japan, Aleutian islands
C. Continental-Continental  mountain ranges
e.g. Alps, Himalayas
Plate tectonics
Divergent Movement
Two plates pulling apart or spreading….they are “diverging” from
each other.
Most common when two oceanic plates are diverging, but can
occur on land between two continental plates
Divergent/Spreading boundaries
When a divergent boundary occurs beneath oceanic lithosphere, the rising
convection current below lifts the lithosphere producing a mid-ocean ridge.
Extensional forces stretch the lithosphere and produce a deep fissure
Examples - Mid-Atlantic ridge (two ocean plates),
Great Rift Valley (two continental plates)
Major Divergent Boundry
Animation
Plate tectonics
Transformational Movement
Two plates sliding past one another….usually involves one plate
doing most of the moving, the other being stationary
Ocean to continental plate - San Andreas
Ocean and Ocean – Steps on the Mid Atlantic Ridge
Transform boundaries, in many places, form steps in the mid-ocean ridges.
These boundaries mark regions where one oceanic plate slips horizontally by another
oceanic plate -- lithosphere is neither created or recycled, but it is conserved.
Plate motion is parallel to the plate boundary and can result in very large earthquakes.
With a few exceptions, transform plate boundaries do not exhibit volcanoes, but can
right along the boundary (Calif does have volcanoes but eruptions are very rare)
Steps on Mid Atlantic Ridge
Ocean and Continental transformation
Transform boundaries
• associated w/ major seismic activity
How is it all connected?
Earthquakes, faults, volcanoes, etc
We will do an activity that allows you to make connections with all types of movements
and what the produce.
Plate tectonics in the future: 50 my
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Australia will straddle the equator
E. Africa will form new continent
Mediterranean will close off
Atlantic Ocean will grow
Pacific Ocean will shrink