Download Theory of Plate Tectonics

Plate Tectonics
Causes of Plate Tectonics
Plate Boundaries
The lithosphere is broken into separate sections called
plates. These plates “float” on top of the Asthenosphere.
The theory of plate tectonics explains the formation,
movement, and subduction of Earth’s plates.
The
crust and part of the
upper mantle = lithosphere
• 100 km thick
• Less dense than the material
below it so it “floats”
The
semi-molten layer below the
lithosphere =Asthenosphere
The
plates of the lithosphere
float on the Asthenosphere
Ocean
plates – lithospheric
plates below the oceans
Continental
plates –
lithospheric plates below the
continents
Hot
magma in the Earth
moves toward the surface,
cools, then sinks again. This
creates convection currents
beneath the plates that cause
the plates to move.
At the locations where two tectonic plates
interact, a boundary between these plates
exist.
There are three types of boundaries: divergent
boundaries, convergent boundaries, and
transform boundaries.
Boundary
between two plates
that are moving apart or
rifting

RIFTING
causes SEAFLOOR
SPREADING
Mid-ocean
ridges (2 oceanic
plates pulling apart)
Rift valleys (2 continental
plates pulling apart)
Fissure volcanoes (either
type)
In sea-floor spreading, the two oceanic plates spread
apart. Magma reaches the surface, cooling to form
new crust. As a result, the ocean floors move like
conveyor belts, carrying the continents along with
them.
Evidence includes:
eruptions of molten material, magnetic stripes
in the rock of the ocean floor, and the ages of
the rocks themselves (youngest closest to
the mid-ocean ridge).
Boundaries
between two
plates that are colliding
 
There
are 3 types…
Ocean
–Continental Convergent
More
dense oceanic plate
colliding with a less dense
continental plate
Subduction
Zone: where the
more dense plate (oceanic)
slides under the less dense
plate (continental)
 Mountains
and possibly volcanoes
Examples: Cascade Mtns in Oregon,
Washington and Andes Mtns in South
America.
 Trenches
(underwater canyons) on ocean
floor
Examples: Marianas Trench in Pacific
Ocean
Ocean-Ocean
The
Convergent
less dense ocean plate
slides under the more dense
ocean plate creating a
subduction zone.
 Island
Arcs may form due to volcanic
activity at this boundary. Examples:
Caribbean Islands, Japan, Indonesia,
Philippines, Aleutian Islands.
 Trenches
also form on ocean floor
Continent-Continent
Convergent
Continental plate colliding
with another continental
plate.
Plates have similar density so
both plates thrust (push) up.
 Fault
Block and Folded Mountain Ranges
are formed.
 Examples: Himalayan
Mtns.
Mtns, Appalachian
Boundary
between two plates
that are sliding past each
other
EARTHQUAKES occur along
these type of boundaries
Examples: San Andreas Fault
in California