Plate TectonicsPlate Tectonics

What is 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 CrustThe Crust• This is where we live!

• The Earth’s crust is made of:

Continental Crust

- thick (10-70km)- buoyant (less dense than oceanic crust) - mostly old

Oceanic Crust

- thin (~7 km)- dense (sinks under continental crust)- young

World PlatesWorld Plates

What are tectonic plates made of?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?What lies beneath the tectonic plates?

• Below the lithosphere (which makes up the tectonic plates) is the asthenosphere.

Plate MovementPlate Movement• “Plates” of lithosphere are moved around by

the underlying mantle convection currents.– Also, gravity pulls harder on the more dense

oceanic plates.

Questions...Questions...

• What causes plates to move?• How is a convection current

formed?

Questions...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 BoundariesPlate Boundaries

• Divergent

• Convergent

• Transform

Three types of plate boundary

• Seafloor Spreading– As plates move apart new material is erupted to

fill the gap

Divergent Boundaries

Age of Oceanic Crust

Courtesy of www.ngdc.noaa.gov

• Iceland has a divergent plate boundary running through its middle

Iceland: An example of continental rifting

• Two plate that are colliding • There are three styles of convergent

plate boundaries– Continent-continent collision– Continent-oceanic crust collision– Ocean-ocean collision

Convergent Boundaries

• Forms mountains, e.g. European Alps, Himalayas

1. Continent-Continent Collision

Himalayas

• Called SUBDUCTION

2. Continent-Oceanic Collision

• Oceanic lithosphere subducts underneath the continental lithosphere

• Oceanic lithosphere heats and dehydrates as it subsides

• The melt rises forming volcanism

• E.g. The Andes

Subduction

• 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!

3. Ocean-Ocean Collision

• Where plates slide past each otherTransform Boundaries

Above: View of the San Andreas transform fault

Questions...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 EffectsSide Effects• Earthquakes and

volcanoes transfer energy from Earth’s interior to the surface.• Earthquakes –

mechanical energy• Volcanoes – thermal

and mechanical energy