Download The Theory of Plate Tectonics

The Theory of Plate Tectonics
Background Information
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The lithosphere (Earth’s Crust and Upper
Mantle) is made of plates. When magma rises
from an ocean ridge (sea floor spreading) the
magma produces new crust, which pushes
plates apart.
As these plates are pushed apart, other plates
are pushed together.
Movement along any plate boundary
results in changes at other boundaries.
Major Plates of the Lithosphere
Types of Plate Boundaries
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Convergent Boundary – plates move
toward each other and collide
Divergent Boundary – plates move
away from each other
Transform Boundary - plates that slide
past one another. This causes many of the
features found on the Earth.
Continental Drift – No More
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The theory of continental drift was no
longer appropriate as scientists discovered
how plates were moving do a new name
was given.
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Theory of Plate Tectonics – proposes that
the plates of Earth’s lithosphere interact with
each other.
Tectonics – is the study of the movement of
large-scale structural features of Earth’s crust.
Convergent Boundaries
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are areas where the plates meet and
collide. Earth’s crust is subducted into the
mantle at these boundaries. ie India
converged into the Eurasian plate and
formed the Himalayas.
The area where a plate thrusts downward
under another is known as a subduction
zone.
3 Types of Convergent Boundaries
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1. Oceanic-Continental Convergence – When an oceanic
plate converges with a continental plate, the oceanic
plate sinks under the continental plate. Subduction zones
along an oceanic-continental boundary create a deepsea trench – a long, narrow, deep depression in the sea
floor.
Many of the trenches occur around the margin of the
Pacific Ocean because of subduction. High temperatures
cause rock to melt around the oceanic plate as it goes
under the continental plate. The newly formed magma is
forced upward through the upper plate, forming
volcanoes.
3 Types of Convergent Boundaries
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2. Oceanic-Oceanic Convergence – when an
oceanic plate meets another oceanic plate, the
older, colder, denser plate bends and sinks into
the mantle. New crust is then formed as the
magma rises to make volcanoes. Oceanicoceanic convergence also makes deep sea
trenches. The island of Japan and the Japan
Trench were formed by oceanic plates
converging.
3 Types of Convergent Boundaries
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3. Continental-Continental Convergence –
When two plates of continental crust
collide and crumple up, tall mountain
ranges may form. Earthquakes are
common at these convergent boundaries.
Volcanoes do not form, however, because
there is little or no subduction when two
continental plates collide.
Convergent Boundary
Divergent Boundaries
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Occurs when plates move away from each
other. Sea floor spreading occurs along a
divergent boundary. The Mid-Atlantic
Ridge in the Atlantic Ocean is an example
of a divergent boundary.
Divergent Boundary
Transform Boundary
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Transform boundaries occur where two
plates slide past one another. The plates
move in opposite directions or in the same
direction at different rates. When one
plate slips past another plate suddenly, an
earthquake occurs.
Transform Boundary
How do we measure Plate
Movement?
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Earthquakes, volcanoes and mountain ranges are
evidence of plate movement.
The theory of plate tectonics suggests that convection
currents inside Earth can affect the crust differently in
different locations. You have seen how the plates have
moved since Pangaea separated.
Scientists now use satellites and laser technology to
measure the exact movements of the plates, to the
nearest centimeter. Laser pulses are shot from the
ground to a satellite to determine an exact location on
the ground. New data confirm that parts of the crust are
moving from 1 – 12 centimeters each year.
Scientists are also using GPS by repeatedly measuring
distances between specific points.