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CHAPTER 4
PLAT E T E C T O N I C S
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Highest pt=Mt
Everest, 29029 ft,
8848 m
Lowest pt.
Marianas trench,
-11,000 m
© 2008, John Wiley and Sons, Inc.
Plate Tectonics
A Revolution in Geology
The Plate Tectonic Model
© 2008, John Wiley and Sons, Inc.
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A Revolution in Geology
• Continental drift
• Proposed by Alfred
Wegener
• Slow, lateral movement
of continents along
Earth’s surface
• The puzzle piece
argument
• Pangaea
• Continental shelf
• Continental slope
Wegener proposed a supercontinent
named Pangaea that split apart with
continents moving to current positions.
Main evidence was the match of
coastlines. Hypothesis was ridiculed by
geologists of the day.
Plate Tectonics
A Revolution in Geology
The Puzzle-Piece Argument
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Evidence of Continental Drift: What
is the “true” edge of a continent?
Figure 4.2
Continent match gets better if you use continental
shelves instead of modern coasts.
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Evidence of Continental Drift:
How well do the continents fit?
Figure 4.2
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Plate Tectonics
A Revolution in Geology
Matching Geology and fossils
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Evidence of Continental Drift:
How well do ages match?
Figure 4.3
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Evidence of Continental Drift: What
evidence did glaciers leave?
Figure 4.3
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a
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Glossopteris
a
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How well do the fossil records match?
Figure 4.4
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Plate Tectonics
A Revolution in Geology
Apparent Polar
Wandering Paths
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Wandering poles?
Positions of N pole for N. America and Europe.
Since the pole really doesn’t move, it means
the continents did. If you rotate NA and Europe
back together, the paths overlap. Evidence for
the movement of the continents.
Figure 4.5
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The color bands represent volcanic rocks of the same magnetic polarity and
age. They are symmetrical on either side of the mid-Atlantic ridge. This shows
new crust is formed at the ridge and moves in opposite directions.
Figure 4.6
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Sea floor spreading
Seafloor spreading
Each side is a
tectonic plate.
Figure 4.7
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The mid-ocean ridge is a line of
volcanoes. This is a vent from one
of them spewing gas into the
ocean.
a
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Direction and velocity of plate movement by GPS measurements
a
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The Plate Tectonic Model
• Plate tectonic
– The movement and interactions of large fragments of
Earth’s lithosphere (i.e. plates)
– Below lithosphere- asthenosphere
• Weak due to hot temperature (near melting point)
• Fault
– A fracture in Earth’s crust along which movement has
occurred
The Plate Tectonic Model
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Types of plate margins
• Divergent margins
– A boundary along
which two plates
move apart from
one another
Types of plate margins
• Convergent margin
– A boundary along which two plates come together
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Types of plate margins
• Subduction zone
– A boundary along which one lithosphere plate plunges into
the mantle beneath another plate
• “Collision zone” between continents
– Deep oceanic trenches
– Arcs of volcanoes
Types of plate margins
• Transform vault
– A fracture in the
lithosphere where
two plates slide past
each other
Earthquakes and plate margins
• Earthquake
– Tectonic movement produce pressure and friction.
– Friction is overcome, the block slips and pent up energy releases with a
huge “snap”
– Focus
• Where earthquake begins
– Epicenter
• Point on earth’s center directly over the focus
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The search for a mechanism
• Earth’s internal heat
– Conduction
• Slow release of heat
– Convection
• A form of heat transfer in
which hot material
circulates from hotter to
colder regions, looses its
heat, and then repeats the
cycle
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Hawaiian Islands
Amazing Places: The Hawaiian Islands
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