Transcript PlateTectonics03

Plate Tectonics
Overview
I. The Theory of Plate Tectonics

The Earth’s surface is divided into plates that move and interact with
one another.
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The plates include Continental Crust and Oceanic Crust.
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The plates are made up of brittle slabs called the Lithosphere.
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This includes the crust and the uppermost region of the upper
mantle
The lithospheric plates slide around on top of a plastic-like layer of
the upper mantle, called the Asthenosphere.
II. The Mechanism that Drives Plate Tectonics
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Convection
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Material moves from regions of high heat (low density) to
regions of low heat (high density).
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This creates convection currents in the mantle
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This movement causes the overlying lithospheric plates to
move!
III. Plate Boundary Interactions
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Divergent
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Lithospheric plates are moving apart
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New crust and lithosphere is “created”
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Associated with ocean ridges, volcanism, earthquakes and
high heat flow
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Most commonly found on the seafloor
Examples found on Earth: Mid-Atlantic Ridge, African Rift Valley, Iceland
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Convergent
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Plates are moving towards each other
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Associated with trenches, island arcs and mountains
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Old crust and lithosphere is “recycled”
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Three types of convergent boundaries exist:
1. Continental - Continental (colliding)
2. Continental - Oceanic (subducting)
3. Oceanic - Oceanic (subducting)
Examples found on Earth: Himalayas, Ring of Fire, Andes Mountains,
Marianas Trench
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Sliding
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Lithospheric plates slide horizontally past each other
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Crust is deformed or fractured
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Characterized by long faults and earthquakes
Examples found on Earth: San Andreas Fault
Plate Interactions Overview
IV. Evidence For Plate Tectonics
A. Continental Drift
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In 1912, Alfred Wegener proposed
that the Earth’s continents had
once been joined as a large
landmass called Pangaea.
•
Continents fit together like a
puzzle.
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Fossil remains of Mesosaurus
(lived 270 million years ago)
are found in Brazil and in
South Africa, but nowhere else
in the world.
This hypothesis was rejected because he
could not propose an explanation for how
this happened!
B. Earthquakes
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Do not occur randomly throughout the world
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Occur in the same regions as volcanoes
C. Volcanoes and Hot Spots
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Do not occur randomly
throughout the world
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80% occur at convergent
plate boundaries
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15% occur at divergent
plate boundaries
The remaining 5% do not
occur at a plate boundary and
form as the result of hot
spots.
D. Magnetism
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The Earth’s magnetic poles
have often been reversed.
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Rocks in the Earth’s crust
contain magnetic minerals
that provide a record of the
direction of Earth’s magnetic
poles at the time the rock was
formed.
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Magnetic reversals reveal
themselves in symmetrical
banding patterns in the rocks
on the ocean floor.
What do you notice about the age of the
rocks?
E. Age of the Ocean Floor
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Further analysis of rocks on the sea floor revealed that the
ages of the rocks vary.
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The rocks are youngest near ocean ridges and get older
as you move away in opposite directions
F. Heat Flow
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Heat flow is a measure of the amount of heat leaving the
rocks of the lithosphere.
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The values are unusually high near ocean ridges and
decrease as you move away from the centers in either
direction.
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The values are unusaully high in the subduction zone
where plates converge.
What conclusions can be drawn from this
evidence?
The Theory of Seafloor Spreading
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Harry Hess compiled all the evidence together and proposed the
theory of Seafloor Spreading in 1962.
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The theory states that new ocean crust is formed at ocean
ridges and is destroyed at deep-sea trenches.
A compilation of all this evidence and past theories has lead
scientists to develop the current theory of Plate Tectonics.
V. Examples of Land Formation due to Plate Tectonics
A. Formation of the Andes Mountains
Nazca plate subducts beneath
the South American plate
B. Formation of Japan
Pacific Plate subducts
beneath the Eurasian Plate
C. Formation of Iceland
North American plate and Eurasian plate diverge
D. Formation of the Galapagos Islands
Nazca plate and Cocos Plate
diverge
Is the Geology of the Galapagos
more similar to Iceland or
Hawaii?