Download Plate Tectonics

Plate Tectonics
Theory of Plate Tectonics

A combination of two other
theories:
1. Continental Drift
2. Sea Floor Spreading
Convection

Process by which currents are driven
by temperature differences within
fluid bodies.
 When a fluid is heated, it expands,
lowering the density of the heated
material, causing it to rise through
the cooler fluid.
 As it rises it will cool, becoming
more dense (because it is cooler) than
the surrounding fluid. It will then
begin to sink.
Convection Currents

This behavior sets up convection currents in
the mantle that cause plate movement.
Convection Video
Plate Tectonics

States that Earth’s lithosphere is broken into
slabs called plates, that move in different
directions and rates.

Plate edges can be drawn by connecting the
dots that mark earthquakes’ epicenters.

Plates can be made of :
– All Oceanic Lithosphere
– All Continental Lithosphere
– Nearly all are made of a combination of both.
Plate Boundaries
 Are
the edges where two plates meet.
 Most Geologic activity (volcanoes,
earthquakes, mountain building) take
place on plate boundaries.
3 Types of Plate Boundaries:
1. Divergent
2. Convergent
3. Transform

The type of plate boundary and type of
crust for each side determines the
geologic activity that will be found there.
Divergent Boundaries



Plates move away from each other.
Most occur at mid-ocean ridges
Primarily responsible for
sea-floor spreading
Rift valley –
divergent plate movement that occurs on land
by the pulling apart of a continent

Convergent Boundaries
 Plates
move towards each other.
 3 types
1. Oceanic + Oceanic
2. Oceanic + Continental
3. Continental + Continental
Oceanic + Oceanic

Subduction: One plate is pushed under the other
plate.
Subduction Video
 Can form a deep sea trench: plate descends to mantle
& melts.
 Can form Island Arc if formed magma is pushed back
to surface.
 Ex. Aleutian
Islands of Alaska

Ex. Aleutian
Islands of Alaska
Oceanic + Continental
 Subduction
of oceanic crust forms
mountain ranges with volcanoes.
 Trenches, Volcanoes, Earthquakes
Oceanic + Continental

Ex. Peru-Chile Trench
Continental + Continental

Forms high mountain ranges.
 No Volcanoes because of thick crust.
 Large Earthquakes
Continental + Continental

Ex. Himalayas
Continental + Continental
Transform Boundaries
 Plates
move past
each other in
opposite
directions
 Crust is deformed
or fractured
 Massive
earthquakes
Transform Boundaries

Ex. San Andreas Fault
Intraplate Activity

Geologic activity that takes place within a plate
rather than at plate boundaries.
 A mantle plume of hot rock rises up from near the
core-mantle boundary through the crust to the
surface to form a hotspot.
Ex. Hawaiian Islands
The tectonic plate moves over a fixed hotspot forming a
chain of volcanoes.
The volcanoes get younger from one end to the other.
Hotspot Volcano Video
Past locations of the hotspot in millions of years.
Review

What are the 3 Types of Plate Boundaries?
 What are the 3 Types of Convergent
Boundaries?
 What intraplate activity is responsible for
the Hawiian islands?
Review

Give an example of:
– a Divergent Boundary.
– a Transform Boundary.
– Oceanic-Oceanic Convergent.
– Oceanic-Continental Convergent.
– Continental-Continental Convergent.