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PLATE TECTONICS
The Earth’s Crust is in Motion
Relating Plate Tectonics to the
Rock Cycle and other Processes
http://earthsci.terc.edu/content/investigations/es0602/es0602page01.cfm
?chapter_no=investigation
Structure of the Earth
• Earth’s Layers Overhead Transparency and
Questions
4 Main Layers of the Earth

Crust – Made up of two types: Oceanic
and Continental. Contains mostly Silicon,
Oxygen, and Aluminum

Mantle – Divided into upper and lower
mantle; mostly Iron and magnesium

Outer Core – Liquid, mostly Iron and
Nickel

Inner Core – Solid, Mostly Iron and Nickel
Layers of the Earth
Comparison of Earth’s Two Types
of Crust

Oceanic

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Continental

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Thinner and more dense
Made up mostly of mafic
(basaltic) igneous rocks
basalt and gabbro
Thicker and less dense
Made up mostly of the
felsic (granitic) igneous
rocks granite and rhyolite
Theories Prior to Plate Tectonics

Continental Drift


Proposed by Alfred
Wegener
Says that the
continents have
moved horizontally
to their present
location
Evidence for Continental Drift


Continents fit
together
Fossils

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Continents fit like a puzzle
Wegener called this large
landmass Pangaea
Fossils of similar animals
such as mesosaurus and
plants like glossopteris
were found on different
continents.
(See fig. 2, p.273)
Movement of the Continents
Another View
Evidence for Continental Drift
(continued)

Climate

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Rock Type and
Structure

Warm-weather fossils
found in the Arctic
Evidence of glaciers
found in present-day
warm areas.
Same rock types and
structures on different
continents (example:
Eastern U.S. and
Western Europe
Why was Wegener’s Original
Proposal of Continental Drift not
Accepted?
Theories Prior to Plate Tectonics
(continued)
• Seafloor Spreading
• Proposed by Harry
Hess .
• The theory states
that hot, less dense
material in the mantle
is forced upward to
the surface at the
mid - ocean ridges.
Seafloor Spreading (continued)
• As magma is forced upward at mid-ocean
•
•
ridges, it flows in opposite directions away from
the ridge.
As it moves away from the ridge, the magma
cools, solidifies, gets thinner and becomes
______ dense.
Becoming more dense than the asthenosphere
below it, the oceanic crust sinks downward at
convergent boundaries, forming trenches
Evidence for Seafloor Spreading
• Age of the Seafloor
• Oceanic crust is younger
•
•
than continental crust
Oceanic crust is 160-180
million years old while
continental crust is
almost 4 billion years
old.
Rocks are younger at the
mid-ocean ridges and
get increasingly older
away from the ridge on
both sides
Evidence for Seafloor Spreading
(continued)
• Magnetic Clues
• Iron minerals in basaltic
•
•
rocks align with the
Earth’s magnetic field.
The magnetic field has
reversed several times.
The reversal creates an
alternating pattern of
normal and reversed
polarity that is the same
on both sides of the ridge
(see fig.7, p.278).
Theory of Plate Tectonics
• (Unifying theory that explains many complex
Earth systems);
• This theory helps explain continental _______,
seafloor ________, AND provides a cause
(mechanism) for these movements of the crust.
• The cause was what was lacking in the
previous theories.
Theory of Plate Tectonics (cont.)
• The theory of plate tectonics states that
the Earth’s continental and oceanic crust is
broken up into sections. These sections
are called tectonic or lithospheric plates,
and they move over the surface the Earth.
• The larger plates and their boundaries can
be seen in figure 9 on page 281.
Layers Related to Plate Tectonics
• Lithosphere
• Consists of the crust and
•
• Asthenosphere
rigid upper mantle
Broken into large pieces
called tectonic plates.
• Plastic-like part of the
•
upper mantle.
Is beneath the lithosphere
Tectonic Plate Boundaries
As the tectonic (lithospheric) plates move along
and above the asthenosphere, the plates meet
at three types of boundaries:
• 3 Types of Boundaries
• Divergent – plates
•
•
move away from each
other
Convergent – plates
move toward each
other
Transform – plates
slide past each other
horizontally
Divergent Boundaries
• The tectonic plates are moving away from
each other
• Characteristics of a divergent boundary are:
- Shallow-focus Earthquakes
- Volcanoes since molten material of
the mantle is so close to the surface.
• Examples of divergent boundaries are the
Mid-Atlantic _______ and the East-African
rift valley.
A plume of hot magma rises from deep within the mantle
pushing up the crust and causing pressure forcing the
continent to break and separate.
Lava flows and earthquakes would be seen.
As the rift valley expands two continental plates
have been constructed from the original one. The
molten rock continues to push the crust apart
creating new crust as it does.
As the rift valley expands, water collects
forming a sea.
The sea floor continues to spread and the
plates get bigger and bigger.
Convergent Boundaries
• Plates move away from each other
• There are three types of convergent boundaries:
1) Oceanic-to-Continental
2) Oceanic-to-Oceanic
3) Continental-to-Continental
Oceanic-to-Continental Convergent
Boundaries
• The more dense _______ crust subducts
under the less dense ___________ crust.
• Characteristics include:
- Trench at subduction zone
- Volcanoes
- Shallow- and deep-focus earthquakes
• An example is the ______ mountains on
the west coast of South America
Andes Mountains in South America
http://www.pbs.org/wnet/savageearth/animations/
Oceanic-to-Oceanic Convergent
Boundaries


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An older, cooler, and _____ dense oceanic
plate subducts under another oceanic plate
Characteristics include:
- Volcanic island arcs
- Earthquakes and volcanoes
- Ocean or sea on both sides of the boundary
Examples of this type of boundary are Japan
and the Aleutian Islands in Alaska
Aleutian Island Chain, Alaska
Aleutian Mountains
Pavlof Volcano
Continental-to-Continental Convergent
Boundary




This occurs when less –dense continental-crust
plates collide.
Being less dense, these plates can only move
upward during collision.
Characteristics include:
- Tall mountains
- Earthquakes (Shallow- and medium-focus)
- Absence of __________ since there is no
subduction.
The Himalaya mountains where _____ and
____ collided are an example.
Continental-to-Continental
Convergent Boundary
Collision of India and Asia
Himalaya Mountains
Transform Plate Boundaries


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At this boundary, the tectonic plates slide past
each other with little or no vertical movement
or subduction.
Characteristics of a transform boundary:
- Shallow-focus Earthquakes
- An Absence of volcanoes since there is
no subduction.
An example of a transform boundary is the
___ _______ fault in California
Transform Boundary Example
Diagram of Transform Boundary
Example of Transform Boundary
Plate Boundary Summary
Plate Boundary Summary
Other Characteristics Related to
Plate Tectonics


Volcanoes and Earthquakes are
concentrated along plate
boundaries
An example is the “ring of ____”
around the Pacific Ocean
(See figures 2 on page 301 and 5 on
page 333)
Earthquakes are Also Concentrated Along Plate
Boundaries
Other Characteristics of the Plate
Tectonics Theory (continued)
• An EXCEPTION to earthquakes and
volcanoes being along plate boundaries is
the occurrence of hot spots.
• These occur where the mantle material is
very close to the surface in isolated areas
within a plate (See fig.8 on p.335)
• An example of a hot spot is ________
Plate Moves over Hot Spot,
Creating an Island Chain
Map of Island Chain Created by the
Hawaiian Hot Spot
What Causes the Plates to Move?
• The cause of tectonic (lithospheric) plate
movement is __________ currents in the
plastic-like mantle, or the _____________
• There are different models made to
explain these __________ currents
(See figure 12 on page 285)
Now, Repeat Everything
Comprehensive Review
http://www.glencoe.com/sec/science/lep_science/
earth_science/tutor/quizzes/test11.html
http://www.geocities.com/Athens/Agora/3006/ge
ogpb/tectonicprocessesreview.htm
http://www.harlan.k12.ky.us/ges/7th%20online
%20tests/ch._14_plate_tectonics.htm
(Also see links on volcano power point presentation)
Va. Tectonic landforms link
http://filebox.vt.edu/users/shamner/EPortfolio/Lessonplans/PlateTectonics/Day%205.pdf