Download Oceanic Crust

The theory of plate Tectonics
The Restless Earth
Plate Tectonics
Topic objectives
• Understand continental drift and how the theory
was discovered.
• Be able to site evidence for continental drift from
the works of Alfred Wegner.
• Identify the super-continent Pangaea and the large
sea Panthalassa.
• Understand the importance and Mid-Atlantic
Ocean ridge, its location and how the global
seafloor is renewed.
• Compare and contrast convergent & divergent
boundaries.
What is plate Tectonics?
A crash course.
• Tectonics- Greek
(tektonikos)–
construction.
• For eons, man has
wondered about the
inner workings of the
planet in which he
inhabits.
Serve it up on a plate.
Tectonic plates
• Blocks of Lithosphere
(crust) that consists of
the crust and the
outermost layer of the
mantle.
• Not all plates are the
same size.
• All plates fit together
like a puzzle.
The players of the game.
Types of crust found on Earth.
• Oceanic Crust-found
on the seafloor .
• Continental Crust-less
dense crust than
Oceanic crust. Forms
the continents.
• Both ride on the
Asthenosphere.
Bound by one another…
3 Types of plate boundaries
• Divergent- 2 plates
move away from one
another.
• Magma rises to the
surface and creates
new crust.
• Found on the ocean
floor
• Mid-Atlantic Ocean
Ridge.
Bound by one another…
3 Types of plate boundaries
• 3 types of collisions
can occur.
• Convergent- when one
plate collides into
another.
Going under…
Subduction Plates
• Subducting plates
Oceanic dense crust is
sunducted or pushed
under the lighter
Continental crust.
• An ocean trench forms
and coastal volcanoes
are created.
Head on Collision!!!
Converging plates
• Two Continental
plates collide into one
another.
• The edges push
upward and create
mountain ranges.
• Ex. Applachians,
Himalayas, Rocky
mountains.
Oceanic Collision
An Island is born.
• Convergent boundaries
occur between two
oceanic crust.
• A deep ocean trench is
created and lava is pushed
to the surface to form
islands.
• Known as “Hot Spots”.
Ex. Hawaiian Islands.
On shaky ground.
• Plate boundaries
known known as
Transform fault occur
when two plates grind
away at one another.
• The San Andreas fault
line is an example of a
transform fault.
Continental Drift
The theory of…
• 1912 German Alfred
Wegener proposed the
hypothesis called
continental drift.
• Said that all the continents
formed a single land mass
called Pangaea
• According Wegener, 200
million years ago Pangaea
began to break up.
What proof is there…
Putting the pieces together.
• Wegener based his theory
on fossil remains that were
found two different
continents. 270 m.y.a.
• Age and type of rocks in
the coastal regions of S.
America & Africa were
identical.
• Coal deposits in
N.America, Europe and
Siberia are very similar.
Sea-Floor Spreading
• 1947- Map of the
Mid0Atlantic Ocean
ridge, a mountain
chain underwater that
wraps around the
world.
• The age of the ocean
floor is very young
compared to the
continental crust.
Sea-floor Spreading
What proof is there?
• PALEOMAGNETISM OF
THE OCEAN FLOOR.
• When magma cools the
metallic materials in the
magma points to the
magnetic north.
• Sections of the ocean floor
on both sides of the ridge
orient in the opposite
directions that suggest that
there are paleo-shifts.
What fuels this process?
The Earth’s engine.
• Plate tectonics is driven by
convection currents that
are found within the
earth’s athenosphere.
• The athenosphere is the
layer under the crust that
consist of liquid like
magma that allows the
crust to float on top like
ice on a lake.
What fuels this process?
The Earth’s engine cont.
• Other possibilities to plate tectonics are;
• Ridge push- At the mid-atlantic ocean ridge the
lithosphere is higher than where it sinks into the
asthenosphere. It actually pushes the plates
downhill.
• Slab pull- Because oceanic lithosphere is denser
than continental lithosphere the edges of the
oceanic plates sink into the asthenosphere
pulling the rest of the tectonic plates.
Reviewing the “plate theory”
• Boundaries between tectonic plates include;
convergent, divergent and transform.
• Wegener hypothesized that continents drifted apart
from one another and did so in the past.
• As tectonic plates separate, the sea-floor spreads
apart and magma fills in the new gap.
• Magnetic reversals is one way to measure the age
and movement of the tectonic plates.