CHAPTER
8
Plate Tectonics
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8.1 What Is Plate Tectonics?
8.2 Types of Plate Boundaries
8.3 Causes of Plate Movement
8.4 Plate Movements and Continental Growth
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CHAPTER
8
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Plate Tectonics
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plate tectonics
continental drift
mid-ocean ridge
8.1 What is Plate Tectonics?
Alfred Wegner proposed the hypothesis of
continental drift to explain how a single land mass
had separated into separate continents, which
drifted apart.
Africa
South
America
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Areas in which mesosaurus
fossils have been found
Fossil evidence found in
South America and Africa
support the hypothesis that
the continents were once
joined.
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Plate Tectonics
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plate tectonics
continental drift
mid-ocean ridge
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8.1 What is Plate Tectonics?
Alfred Wegner proposed the hypothesis of
continental drift to explain how a single land mass
had separated into separate continents, which
drifted apart.
Later discoveries supported the idea that the
continents had been connected, but demonstrated
that the continents were not “drifting” but attached to
moving lithospheric, or tectonic, plates.
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8
Plate Tectonics
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plate tectonics
continental drift
mid-ocean ridge
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8.1 What is Plate Tectonics?
The theory of plate tectonics explains the
occurrence of volcanoes and earthquakes in
concentrated belts along plate boundaries.
Earthquakes
Volcanoes
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Plate Tectonics
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plate tectonics
continental drift
mid-ocean ridge
8.1 What is Plate Tectonics?
Plate tectonics also account for a distinctive pattern
in the age and magnetism of rocks that spread out
from mid-ocean ridges on the ocean floor.
Mid-Atlantic Ridge,
Atlantic Ocean
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East Pacific Rise,
Pacific Ocean
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divergent boundary
rift valley
rift
8.2 Types of Plate Boundaries
Plates move apart at divergent boundaries. A rift
valley is an example of a divergent boundary on
land.
convergent boundary
subduction boundary
deep-sea trench
Type of
Boundary
collision boundary
sea-floor
spreading
transform boundary
Divergent
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Process
Involved
Characteristic
Features
Current
Examples
•mid-ocean
ridges
•rift valleys
•earthquake
activity at
fracture zones
along mid-ocean
ridges
•volcanic activity
•Mid-Atlantic
Ridge
•East Pacific
Rise
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divergent boundary
rift valley
rift
convergent boundary
subduction boundary
deep-sea trench
8.2 Types of Plate Boundaries
Plates move toward each other at convergent
boundaries. One plate may subduct under the other,
as happens at deep-sea trenches, or the two plates
may collide.
Type of
Boundary
collision boundary
oceanocean
subduction
transform boundary
Convergent
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Process
Involved
Characteristic
Features
•deep-sea
trenches
•volcanic island
arcs
•earthquake
activity
Current
Examples
•islands of
Indonesia
•Mariana
Islands
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divergent boundary
rift valley
rift
convergent boundary
subduction boundary
deep-sea trench
8.2 Types of Plate Boundaries
Plates move toward each other at convergent
boundaries. One plate may subduct under the other,
as happens at deep-sea trenches, or the two plates
may collide.
Type of
Boundary
collision boundary
transform boundary
Convergent
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Process
Involved
Characteristic
Features
oceancontinent
subduction
•deep-sea trench
bordering
continent
•volcanoes along
coast of
continent
•earthquake
activity
Current
Examples
•western
coast of
South
America
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divergent boundary
rift valley
rift
convergent boundary
subduction boundary
deep-sea trench
8.2 Types of Plate Boundaries
Plates move toward each other at convergent
boundaries. One plate may subduct under the other,
as happens at deep-sea trenches, or the two plates
may collide.
Type of
Boundary
collision boundary
transform boundary
Convergent
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Process
Involved
Characteristic
Features
continentcontinent
collision
•high continental
mountain chains
•earthquake
activity
Current
Examples
•Himalayas
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divergent boundary
rift valley
8.2 Types of Plate Boundaries
Plates move past each other at transform
boundaries.
rift
convergent boundary
subduction boundary
deep-sea trench
Type of
Boundary
collision boundary
transform boundary
Transform
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Process
Involved
plates
sliding
past each
other
Characteristic
Features
•earthquake
activity
Current
Examples
•San Andreas
Fault
•North
Anatolian Fault
(Turkey)
•fracture zones
along midocean ridges
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mantle convection
ridge push
slab pull
8.3 Causes of Plate Movement
Mantle convection, ridge push, and slab pull are
hypothetical models for the causes of plate
movements.
Deep-sea
trench
Mid-ocean
ridge
Deep-sea
trench
Mantle convection
This image shows one model
of how mantle convection may
contribute to plate movement.
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This image shows
as section of the
East Pacific Rise, a
mid-ocean ridge.
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Pangaea
craton
terrane
8.4 Plate Movements and
Continental Growth
Plate movements have caused the positions of
Earth’s landmasses to shift over time. Scientists
think that all continents were once part of a single
landmass they call Pangaea.
Pathalassa
Ocean
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Tethys
Sea
200 million years ago
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Pangaea
craton
terrane
8.4 Plate Movements and
Continental Growth
Plate movements have caused the positions of
Earth’s landmasses to shift over time. Scientists
think that all continents were once part of a single
landmass they call Pangaea.
Laurasia
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180 million years ago
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Pangaea
craton
terrane
8.4 Plate Movements and
Continental Growth
Plate movements have caused the positions of
Earth’s landmasses to shift over time. Scientists
think that all continents were once part of a single
landmass they call Pangaea.
North
America
South
America
Asia
Africa
India
Australia
Antarctica
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65 million years ago
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Pangaea
craton
terrane
8.4 Plate Movements and
Continental Growth
Plate movements have caused the positions of
Earth’s landmasses to shift over time. Scientists
think that all continents were once part of a single
landmass they call Pangaea.
North
America
Europe
Asia
Africa
South
America
Australia
Antarctica
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Modern Day
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Pangaea
craton
terrane
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8.4 Plate Movements and
Continental Growth
Plate movements have caused the positions of
Earth’s landmasses to shift over time. Scientists
think that all continents were once part of a single
landmass they call Pangaea.
Scientists use fossils, the ages of rocks, and other
geologic evidence to reconstruct past land
movement.
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Pangaea
craton
terrane
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8.4 Plate Movements and
Continental Growth
The shapes of the landmasses have also changed.
At the core of each continent is a craton, the oldest
rock on the continent.
The North
American
craton
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Pangaea
craton
terrane
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8.4 Plate Movements and
Continental Growth
The shapes of the landmasses have also changed.
At the core of each continent is a craton, the oldest
rock on the continent.
Processes associated with plate tectonics add new
materials to a continent over time. For example,
terranes are blocks of lithospheric plates that
contribute to continental growth.
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Plate Tectonics
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