Download U4-T2.6-Plate Boundaries

Earth Systems 3209
Unit: 4
The Forces Within Earth
Reference:
Chapters 4, 15, 16, 19; Appendix A & B
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Unit 4:
Topic 2.6
Plate Boundaries - Convergence
Focus on . . .
 describing and giving examples of the three types of
collision boundaries.
 demonstrating through a drawing the processes
associated with plate convergence.
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Plate Boundaries
 According to the Plate tectonic theory, three
boundaries exist at the edges of tectonic plates.
1) Divergent Boundary (Ridge)
2) Convergent Boundary (Trench)
3) Transform Boundary
Text Reference:
Pages 526-539
Figure 19.17, pg. 528
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Convergent Boundaries (3 Types):
1) Ocean – Ocean Convergent Boundary
 Ocean-ocean collisions involve
two oceanic plates.
 Compressional forces cause the
oceanic plates to move together,
causing one slab of lithosphere to be consumed into the mantle
initiating volcanic activity which creates volcanoes to form on the
ocean floor.
 The volcanoes produced at this collision boundary are island arc
volcanoes; they form a curved arc on the surface (map view).
 Features called ocean trenches are formed at these boundaries.
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Convergent Boundaries (3 Types):
1) Ocean – Ocean Convergent Boundary
 The composition of the molten
material is largely andesitic
(intermediate) since the melting
basaltic (mafic) oceanic crust
becomes mixed with melting
sediments that were located on top of the subducting plate
as a result of weathering and erosion from the nearest
continent (felsic).
 Lithosphere is destroyed as one oceanic slab descends
beneath another.
 Example include the Japan island arc and the Japan trench.
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Convergent Boundaries (3 Types):
2) Ocean – Continent Convergent Boundary
 Ocean-Continent collisions involve an
oceanic plate and a continental plate.
 Compressional forces cause an ocean plate and a continent plate
to move together, due to a greater density (basaltic vs. granitic), the
oceanic plate will most likely subduct beneath the continent forming
a trench and subduction zone.
 In a map view, a volcanic arc is created on the continent as a
result of the collision.
 Lithosphere is destroyed as one oceanic slab descends beneath
another.
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Convergent Boundaries (3 Types):
2) Ocean – Continent Convergent Boundary
 The composition of the molten material will
most likely be granitic (felsic) since the
upwelling magma created by the melting
oceanic crust has to burn through a granitic (felsic) continent.
 At depths of about 100 km the oceanic plate and parts of the
mantle partially melt producing viscous magmas. This molten rock
rises slowly where it cools and solidifies at depths producing
plutons. However, some magma may reach the surface and erupt
through composite volcanoes as violent volcanic eruptions.
 Example include the Rocky mountains in North America and the
Andes mountains in South America.
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Convergent Boundaries (3 Types):
3) Continent – Continent Convergent Boundary
 Continent-Continent collisions involve two
continental plates.
 Compressional forces cause two continental
plates to move together.
 Once the oceanic crust between the two
continents has been entirely subducted and
the continental shelves have nearly joined,
the process of subduction ceases.
 Lithosphere is destroyed as one oceanic slab
descends beneath another.
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Convergent Boundaries (3 Types):
3) Continent – Continent Convergent Boundary
 Because of the low density of continental crust
neither plate will subduct, both continental
shelves get uplifted and deformed, forming
folded mountains.
 Such a collision occurred when India collided
with Asia forming the Himalayan mountains
and also during the formation of the Appalachian
mountains
 Global examples of continental-continental
collisions include the Himalayan and
Appalachian mountains
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Plate Boundaries
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Example 1:
Collision at which plate boundary would result in the tallest
mountains?
(A) ocean - ocean
(C) ocean – continent
(B) ocean - fault
(D) continent - continent
Which is associated with an oceanic to oceanic collision?
(A) folded mountains
(B) island arc
(C) mid-oceanic ridge
(D) volcanic arc
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Example 2:
Based on the diagram below, what type of plate
collision formed the Himalaya mountain range?
(A) continent-continent
(B) ocean-continent
(C) ocean-ocean
(D) seafloor-ocean
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Your Turn . . .
Take the time and complete the following questions . . .
(Solutions to follow)
Question:
A range of mountains is found on
Australia’s east coast. With
reference to plate boundaries,
explain how this mountain range
may have been formed.
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Solutions . . .
Question:
A range of mountains is found on Australia’s east coast. With
reference to plate boundaries, explain how this mountain range may
have been formed.
Answer:
Mountain ranges are found along convergent plate
boundaries. At these boundaries one tectonic plate moves
toward and collides with another plate boundary. In the
above diagram, an oceanic plate (Pacific) collides with a
continental plate (Australian). This collision causes the
oceanic plate to subduct beneath the continental plate.
These compressional forces generally deform the tectonic
plates which result in the continental plate uplifting to form a
mountain chain along the length of the convergent boundary.
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Extra Practice Problems:
Which mountain ranges were formed by a collision
between continents?
(A) Andes and Rockies
(B) Andes and Himalayas
(C) Appalachians and Himalayas
(D) Appalachians and Rockies
Which feature is not associated with a convergent plate
boundary?
(A) deep-sea trench zone
(C) mid-ocean ridge
(B) earthquake
(D) volcanic activity
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Summary . . .
Overview of Points covered:
3 Types of Convergent Boundaries:
1) Ocean – Ocean
2) Ocean – Continent
3) Continent – Continent
All experience;
 Compressional forces
 Destruction of lithosphere
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