Transcript Plate Tectonics PowerPoint

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
• This is where we live!
• The Earth’s crust is made
of:
Continental Crust
Oceanic Crust
- thick (10-70km)
- buoyant (less dense
than oceanic crust)
- mostly old
- thin (~7 km)
- dense (sinks under
continental crust)
- young
World Plates
What are tectonic plates made of?
• Plates are
made of rigid
lithosphere.
The lithosphere is
made up of the
crust and the upper
part of the mantle.
What lies beneath the tectonic plates?
• Below the
lithosphere
(which makes
up the tectonic
plates) is the
asthenosphere.
Plate Movement
• “Plates” of lithosphere are moved around by
the underlying mantle convection currents.
– Also, gravity pulls harder on the more dense
oceanic plates.
Questions...
• What causes plates to move?
• How is a convection current
formed?
Questions...
• What is the theory of plate
tectonics?
• What is the lithosphere?
• What is the asthenosphere?
• What is the connection between
the two?
• What are the two types of plates?
Plate Boundaries
Three types of plate boundary
• Divergent
• Convergent
• Transform
Divergent Boundaries
• Seafloor Spreading
– As plates move apart new material is erupted to
fill the gap
Age of Oceanic Crust
Courtesy of www.ngdc.noaa.gov
Iceland: An example of continental rifting
• Iceland has a divergent
plate boundary running
through its middle
Convergent Boundaries
• Two plate that are colliding  
• There are three styles of convergent
plate boundaries
– Continent-continent collision
– Continent-oceanic crust collision
– Ocean-ocean collision
1. Continent-Continent Collision
• Forms mountains, e.g. European Alps, Himalayas
Himalayas
2. Continent-Oceanic Collision
• Called SUBDUCTION
Subduction
• Oceanic lithosphere
subducts underneath the
continental lithosphere
• Oceanic lithosphere heats
and dehydrates as it
subsides
• The melt rises forming
volcanism
• E.g. The Andes
3. Ocean-Ocean Collision
• When two oceanic plates collide, one runs over the other
causing it to sink into the mantle forming a subduction zone.
• The subducting plate is bent downward to form a very deep
depression in the ocean floor called a deep-sea trench.
• The deepest parts of the ocean are found along trenches.
– The Mariana Trench is 11 km deep!
Transform Boundaries
• Where plates slide past each other
Above: View of the San Andreas
transform fault
Questions...
• What are the three types of
boundaries?
• What direction do plates go for
each?
• Which boundary has a subduction
zone…what occurs at a
subduction zone?
Side Effects
• Earthquakes and
volcanoes transfer
energy from Earth’s
interior to the surface.
• Earthquakes –
mechanical energy
• Volcanoes – thermal
and mechanical energy