Transcript I-4 Dynamic Planet Notes

I-4 Dynamic Planet
Notes
The Earth’s Lithosphere
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The boundary between the lithosphere and the
asthenosphere is a temperature boundary
Below the boundary the rocks are hot enough to
flow
Above the boundary they are cooler and rigid
Two types of lithospheric plates
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Oceanic crust
Continental crust
Oceanic Crust
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Thickens as it moves away from the hot midocean ridge
Thinner
More dense
Newer crust
Continental Crust
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Less dense
Thicker
Older crust
Lithospheric plates
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The lithosphere is not one continuous piece
Made of very large pieces as well as a lot of
smaller pieces
These pieces are called lithospheric plates
Plate Boundary
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Where two plates are in contact with each other
Plate Movement
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3 Types
Plates are in motion relative to one another
Divergent Boundary
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Plates are moving away from each other
Mid-ocean ridges
New plate material produced on either side of
ridge
Convergent Boundaries
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Plates are moving towards one another
Transform Boundary
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Plates slide past one another
Example – the San Andreas Fault
The Pacific Plate is moving northwest relative to
the North American Plate
Transform boundaries are sometimes called
conservative (lithosphere is neither created nor
destroyed)
Subduction
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Surface area of the Earth is not changing
Must be a place where plates are consumed and
created
Subduction Zone
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Plate boundaries where one plate dives underneath
another plate
The down going plate is an oceanic plate
The plate that stays at the surface can be an oceanic
plate or a continental plate
The place where the down going plate bends downward
is marked by a deep trench on the ocean floor
Earthquakes and volcanoes are very common
Copy Diagram
Continent-Continent Collision
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Subduction zones can make an ocean basin
close up
Two continents may meet at a subduction zone
Continents are less dense than the mantle, so
they do not go down a subduction zone
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When two continents meet, one of the
continents is pushed horizontally beneath the
other continent
The movement eventually stops, when the force
of friction between the continents becomes
large enough
Continent-continent collision zones are where
the continent is the thickest
Example
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India is slowly being pushed under southern
Asia
Produces the Himalayas – the highest mountain
chain
Also produces the Tibetan Plateau
AYR Questions
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1. What is the difference between crust and
lithosphere?
What is the difference between oceanic crust
and the continental crust?
What is the difference between a subduction
zone and a continent-continent collision zone?
Why do continents not go down subduction
zones?
Review and Reflect Questions
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What type of plate boundaries are found in or
along the continental United States?
Why does the surface of a thicker continent
stand higher above sea level than the surface of
a thinner continent?
Answers to I-4 AYR Questions
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The curst is the outermost shell of the Earth. The
lithosphere consists of the crust and the upper, rigid
part of the mantle (the part that does not take part in
the mantle convection).
Continental crust is thicker, less dense, and generally
much older than oceanic crust.
A subduction zone occurs where oceanic lithosphere
is subducted under another oceanic lithospheric
plate). A trench forms on the sea floor as one
lithospheric plate descends below the other.
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In a continent-continent collision, one of the
two continental plates slides horizontally under
the other for some distance. That thickens the
continental crust and forms high mountain
ranges.
4. Continents cannot go down subduction zones
because continental lithosphere is less dense
than the mantle.