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Plate Tectonics
Oceans 11
PANGEA
• In 1912 Alfred Wegener
thought that all of the
continents were
connected as one
supercontinent called
PANGEA.
• This was about 300
million years ago and
over time they drifted
apart.
Continental Drift Theory
http://www.suu.edu/faculty/colberg/Hazards/PlateTectonics/18_Pangaea.htm
The Structure of Earth
• The Earth is made up
different types of
layers.
• The Lithosphere is
divided into large
plates.
• Convection currents
in the asthenosphere
move the plates.
LAYERS OF THE EARTH
I. Crust:
•
Rigid surface of the Earth.
It can be between 0-100 km
thick, depending on where
it is.
•
2 Types:
– Continental Crust: Thicker parts of the crust;
above the ocean
– Oceanic Crust: Thinner parts of the crust;
under the ocean
LAYERS OF THE EARTH
II. Mantle:
•
•
•
•
•
Between the crust and the
core.
Largest volume of the earth. Mg, Fe, O,
Si
Upper Mantle: Solid part of the mantle
Lithosphere: Crust and upper mantle.
Lower mantle: Loose moving due to
heat from the core.
LAYERS OF THE EARTH
III. Core:
• Outer part is liquid and about 2300km thick.
• Inner is solid and mostly nickle and iron.
**Believed to control the Earth’s magnetic field.**
Tectonic Plates
• The lithosphere is
broken into 9 large,
rigid pieces called
plates.
• The plates are all
moving in different
directions and at
different speeds (from 2
cm to10 cm per year)
Plates meet at Plate Boundaries
• There are 3 main
plate boundaries:
• 1) Convergent Boundary
• 2) Divergent Boundary
• 3) Transform Boundary
1. Convergent Boundaries
• Occurs when 2 plates
collide.
• Oceanic plate is more
dense and is forced
under the continental
plate.
• Some of the rock in the Oceanic plate melts as the
plate sinks. The melted rock rises up causing
earthquakes and volcanic eruptions.
• Where they collide is called a SUBDUCTION
ZONE.
When a continental plate has crashed
into a continental plate:
• The 2 continental plates are the same density.
• This causes folding and bending of the plates as
well as earthquakes.
• Continental plates are folded into mountains.
Example of a Convergent Plate Boundary
South America:
• Oceanic Nazca Plate collides
into the South America plate.
• Formed the Andes Mountains
(volcanoes along the mountain
crest)
• Formed a deep trench off the
coast in the Pacific Ocean.
Divergent Plate Boundaries
• Plates are being pulled apart by
convection currents in the mantle.
• As the plates separate along the
boundary, the block between the
faults cracks .
• Magma from the mantle rises
through the cracks.
• This cools and new crust is
formed along the boundary.
• Earthquakes occur along the
faults, and volcanoes form where
the magma reaches the surface.
Mid Atlantic Ridge
• Mid-Atlantic Ridge is a
Divergent Plate Boundary.
• Over 15000 km long.
• Average height of 3km.
• Mid Atlantic Ridge Video
• http://www.youtube.co
m/watch?feature=endscr
een&v=GyMLlLxbfa4
&NR=1
Transform Boundary
• Places where plates slide past
each other.
• Transform boundaries are not
marked by spectacular surface
features, their sliding motion
causes lots of earthquakes.
• Example: San Andreas Fault
http://www.youtube.com/watc
h?v=ZxPTLmg0ZCw
• The slice of California to the
west of the fault is slowly
moving north relative to the rest
of California.
• http://www.youtube.com/watch?
v=hReS4Fm94L4