Download Chapter 10-3 - Theory of Plate Tectonics

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Chapter 10-3 – Theory of Plate Tectonics Study Guide Part 1
Plate Tectonics
Wegener had suggested the idea of seafloor spreading.
His idea showed more than just continents were moving.
It was now clear to scientists that sections of the seafloor and continents
move in relation to one another.
Plate Movements
In the 1960’s, scientists came up with a new theory. This theory combined
both continental drift and seafloor spreading. This theory is called Plate
Tectonics.
Theory of Plate Tectonics =
 Earth’s crust and part of the upper mantle are broken into irregularly
shaped sections.
 These sections are called plates.
 The plates move on a plastic like layer called the mantle.
 You can think of the plates as a raft that floats and moves on this
layer.
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Composition of Earth’s Plates
 Plates are made up of crust and a part of the upper mantle.
 These 2 parts combined (put together) are called the lithosphere (LiH
thuh sfihr).
 The lithosphere is rigid (unbending, set, firm) and about 100 km thick.
The rigid plates on the
lithosphere float and move
around on the asthenosphere.
Composition of Earth’s Plates…
 The plastic layer below the lithosphere is known as the asthenosphere
(as the nuh sfhr).
 The asthenosphere is made of hot molten material that has the property
of plasticity (flexibility, softness, elasticity) and so it can flow easily.
 The plates move on the hot molten material that forms the
asthenosphere.
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Ocean Crust
 Oceanic crust = Crust beneath (below) the oceans
 It is less than 10 km thick.
 Oceanic crust is made mostly of silicon, oxygen, iron, and magnesium.
 These elements form the igneous rock, basalt.
Continental Crust
 Continental Crust = The crust beneath the continental. It has an
average thickness of about 32 km.
 Beneath (under) mountains, the crust is much thicker.
 Continental crust is made mostly of silicon, oxygen, aluminum, calcium,
sodium and potassium.
 These elements for the igneous rock, granite.
Seven Main Lithospheric Plates
The Pacific plate covers 1/5 of the Earth’s surface.
The other major plates are:
 North American
 South American
 Eurasian
 African
 Indian-Australian
 Antarctic
There are also smaller plates such as:
 The Caribbean Plates
 Arabian Plates
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Plate Boundaries (When the plates interact you can see the result of their
movement in the picture below).
 When plates move, they can interact (act together or work together)
in a few ways.
 They can move toward each
 They can pull apart of slide
other and converge, or
alongside one another.
collide.
 Plates move at different speeds and in different directions.
 Smaller landmasses move more quickly.
 In a few cases, the edges of the continents are the boundaries of
plates.
This picture shows the major plates of the lithosphere. It shows the direction of
movement. Your book shows another diagram on page 281 which shows the types of
boundaries between the plates.↓
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Types of Plate Boundaries – There are 3 types of plate boundaries.
Turn to page 283 in your text to help you see more of the
Divergent Boundaries↓
Convergent Boundaries↓
“Constructive”
“Destructive”
Boundary between 2 plates 2 plates get together and
that are moving apart.
the older lithosphere is
Ex. Seafloor spreading
destroyed.



Because the plates
move apart, the ridges
are called divergent.
Divergent boundaries
occur at the midocean ridges.
Sometimes rift valley
or continental rifting
3 types of convergent
plate boundaries:
1) Ocean-Ocean trenches-volcanic island
arc
2) Ocean-Continenttrenches-volcanic mountain
arc
3) Continent–continentregular mountains on edge
of continent
(this does not produce a
trench but some land is
destroyed)


Ex. East African rift
(South America + Africa
separated by the Atlantic
Ocean)Africa +Arabian
Peninsula (separated by
the Red Sea)
None of the ocean floor
is older than 180 million
years.
The East Pacific Rise is
spreading more quickly
than the Mid-Atlantic
Ridge.
plate boundary pictures.
Transform Boundaries↓
Plates horizontally sliding past
each other.
What could happen as a result?
Earthquakes
Ex. The Pacific Plate is sliding
past the North American plate
forming the San Andreas Fault in
California.
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