Download Plate Tectonics PPT

Document related concepts

Age of the Earth wikipedia , lookup

Nature wikipedia , lookup

History of geology wikipedia , lookup

Algoman orogeny wikipedia , lookup

Abyssal plain wikipedia , lookup

Geophysics wikipedia , lookup

Oceanic trench wikipedia , lookup

Geology wikipedia , lookup

Large igneous province wikipedia , lookup

Plate tectonics wikipedia , lookup

Transcript
Plate Tectonics
What is Plate Tectonics?
• The Earth’s crust and upper
mantle are broken into
sections called plates
• Plates move around on top of
the mantle like rafts
The Crust
• Outermost layer
• 5 – 100 km thick
• Made of Oxygen, Silicon,
The Mantle
• Layer of Earth
between the crust
and the core
• Contains most of
the Earth’s mass
• Has more
magnesium and
less aluminum and
silicon than the
crust
• Is denser than the
crust
The Core
• Below the mantle and
to the center of the
Earth
• Believed to be mostly
Iron, smaller amounts
of Nickel, almost no
Oxygen, Silicon,
Aluminum, or
Magnesium
Earth’s Layers
The Earth's rocky
outer crust solidified
billions of years ago,
soon after the Earth
formed.
This crust is not a
solid shell; it is broken
up into huge, thick
plates that drift atop
the soft, underlying
mantle.
Tectonic plates
What is the Lithosphere?
• The crust and part of the upper
mantle = lithosphere
–100 km thick
–Less dense than the material
below it so it “floats”
What is the Asthenoshere?
• The plastic layer below the
lithosphere = asthenosphere
• The plates of the lithosphere
float on the asthenosphere
2 Types of Plates
• Ocean plates - plates below
the oceans
• Continental plates - plates
below the continents
How Plates Move
Plates move because there is
slow movement of hot, softened mantle that lies below the rigid plates
http://pubs.usgs.gov/gip/dynamic/unanswered.html
Plate Boundaries
Divergent Boundaries
• Boundary between two plates
that are moving apart or rifting

• RIFTING causes SEAFLOOR
SPREADING
Divergent Boundaries
 Two tectonic plates separate (move
apart)
 Most happen on the sea floor
Sea-floor Spreading!
Features of Divergent
Boundaries
• Mid-ocean ridges
• rift valleys
• fissure volcanoes
Sea floor spreading
• Large continents
begin to crack and
split apart
• The gaps fill with
water
• Small seas become
oceans
• The mid ocean ridge
continues to produce
new crust
Sea Floor Spreading
Sea Floor Spreading
• Mid Ocean Ridges – underwater mountain
chains that run through the Earth’s Basins
• Magma rises to the surface and solidifies
and new crust forms
• Older Crust is pushed
farther away from the ridge
Divergent Boundary –
Arabian and African Plates
Plates move away from each other
Convergent Boundaries
• Boundaries between two
plates that are colliding
 
• There are 3 types…
Type 1
• Oceanic plate colliding with a
less dense continental plate
• Subduction Zone: where the
more dense plate slides under
the less dense plate
• VOLCANOES occur at
subduction zones
Convergent Boundaries
 Two tectonic plates collide
Continental-Oceanic
Collisions
Oceanic-Oceanic
Collisions
Continental-Continental
Collisions
Convergent Boundaries
• Continental-Oceanic Collisions:
– Continental plate collides with
oceanic plate
– The denser oceanic plate sinks
(subducts) beneath the less-dense
continental crust
Convergent Boundaries
 Continental-Oceanic Collisions:

Subduction may cause a chain of
volcanoes to form along the plate
boundary
Convergent Boundaries
• Oceanic-Oceanic Collisions:
– Oceanic plate collides with oceanic
plate
– The denser of the 2 oceanic plates
sinks (subducts)
Convergent Boundary – Indian and Eurasian
Plates
Andes Mountains,
South America
Type 2
• Ocean plate colliding with
another ocean plate
• The more dense plate slides
under the less dense plate
creating a subduction zone
called a TRENCH
Aleutian Islands, Alaska
Type 3
• A continental plate colliding
with another continental plate
• Have Collision Zones:
–a place where folded and thrust
faulted mountains form.
Transform Fault Boundaries
• Boundary between two plates
that are sliding past each other
• EARTHQUAKES along faults
Transform Boundaries
 Two tectonic plates slide past
one another
Building tension
Releases tension in a sudden, often
violent, jerk called an
EARTHQUAKE!!
Transform Boundaries
• The San Andreas fault is an example
of a transform boundary
◦ The Pacific plate
(west of fault) is
moving
northwest
◦ The North
American plate
(east of fault) is
moving
southeast
Pacific Plate
San Andreas Fault, CA
A fault is a break in a rock across which there is
observable movement.
When the break occurred an earthquake was
generated, whether or not anyone was there to
detect it.
Sometimes faults die at depth and do not break
the surface. Sometimes they do such as for the
Armenia 1988 earthquake.
Normal Fault
Normal Fault
Reverse Fault
Reverse Fault
Strike-Slip Fault
Strike-Slip Fault
Strike-Slip Fault
Strike Slip Fault
Causes of Plate
Tectonics
Convection Currents
• Hot magma in the Earth moves
toward the surface, cools, get
denser, and then sinks again with
the pull of gravity
• Creates convection currents in
asthenosphere beneath the plates
that cause the plates to move.
Continents Collide
• Eventually when plates
move together the
continental crust collides
• The heat and pressure
make metamorphic rock
• It also pushes and folds
the rocks into high
mountains
• The Himalayas rise to
8848m and are still
growing today
So the Earth must be growing?
• Dense heavy oceanic
crust can be subducted
below less denser
continental crust.
• The friction melts rock
• This magma rises
through the crust to form
new volcanoes
• This is happening in
South America (The
Andes)