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Plate Tectonics
The Plate Tectonic Theory
The plate tectonic
theory states that the
crust of the Earth is
broken into several
large sections known
as crustal or
lithospheric plates.
It is theorized that
these plates are
dynamic and move
continually. The
interaction between
plates produces
changes on Earth’s
surface such as,
volcanoes,
mountains, and
earthquakes.
The interface
between two or more
plates is known as a
boundary.
NOTE-- Divergent Boundaries are in blue,
Convergent Boundaries are in Red.
Why do the crustal plates move?
Crustal plates may move away from one another, towards one
another, or slide against one another. In addition, crustal plates may
rise above (uplift) or descend (subsidence) within the Earth.
It is theorized that crustal plates move due to the convection currents of heat
within the asthenosphere.
Tectonic Plates of the World
“Which tectonic
plate is located at
20˚N, 160˚W?”
PACIFIC PLATE
“What type of
boundary is the
Mid-Atlantic
Ridge?”
DIVERGENT
PLATE
BOUNDARY
RT = Pg. 5
Divergent Plate
Boundary
A divergent plate boundary is where two plates
separate from one another. This separation leads
to the rise of magma and igneous
intrusions/extrusions at the point of separation.
Young Crust
As the plates
diverge, magma and
lava are forced
upward due to
convection in the
asthenosphere.
Older Crust
When a divergent plate boundary occurs under an ocean, it is
also referred to as sea-floor spreading.
The molten rock will
cool to form new
crust.
Soon thereafter,
new magma will be
forced upward and
will force the new
crust to split and
diverge as well.
Divergent Plate
Boundary
Dynamic activity associated with a
divergent plate boundary includes:
1.
2.
3.
4.
When a divergent plate boundary occurs
under a continent, it is also referred to as
rift valley.
Many shallow earthquakes
Faulting (sudden uplift of
small portions of the crust)
Volcanic activity
The creation of a ridge of
volcanic mountains (ocean
only).
Convergent Plate
Boundary
A convergent plate boundary is where two
plates converge or collide with one
another. Convergent plate boundaries can
take place in three ways:
OCEANIC-OCEANIC CRUST
CONVERGENCE
CONTINENTAL-CONTINENTAL CRUST
CONVERGENCE
OCEANIC-CONTINENTAL CRUST
CONVERGENCE
OCEANIC-CONTINENTAL CRUST
CONVERGENCE
CONTINENTAL-CONTINENTAL CRUST
CONVERGENCE
OCEANIC-OCEANIC CRUST
CONVERGENCE
Convergent Plate Boundary:
SUBDUCTION ZONE
When two plates converge, the denser of
the two plates will move and sink under the
less dense plate. This process is known as
subduction.
A subduction zone is an area of
tremendous heat, pressure, and dynamic
activity. Many features are associated with
convergent plate boundaries including:
OCEANIC-CONTINENTAL CRUST
CONVERGENCE
CONTINENTAL-CONTINENTAL CRUST
CONVERGENCE
1.
2.
3.
4.
5.
6.
Volcanic activity
Deep earthquake activity
Regional metamorphism
Orogeny – Mountain-building forces
Deep ocean trenches
Deposition basins
OCEANIC-OCEANIC CRUST
CONVERGENCE
Transform Plate
Boundary
A transform plate boundary is
where two plates slide past one
another.
Dynamic activity associated
with a transform plate
boundary includes:
1.
2.
Many earthquakes
Faulting (sudden uplift
of small portions of the
crust)
San Andreas Fault, California: Transform
plate boundary between the North
American Plate and Pacific Plate
Evidence to Support the
Plate Tectonic Theory
Appearance of Continents
The outline of many
present day
continents seem to
fit together like
pieces of a puzzle.
Evidence to Support the
Plate Tectonic Theory
Landmass Features/Fossil Record
Fossil evidence supports the notion that
the continents were once connected.
Many rock assemblages are identical in
formation and age on different continents.
Evidence to Support the
Plate Tectonic Theory
Age and Heat Index of Ocean Rock
In a divergent plate boundary, molten rock
rises to the surface and cools to become
new crust.
This newly formed crust is continually
being replaced by new molten rock.
Older crust diverges and is forced to move
away from the area where new molten
rock will form into new crust.
This image is taken of the Mid-Atlantic Ridge –
a divergent plate boundary.
Each color represents rocks of similar age.
The red colored rock represents the youngest
rock (closest to the source of divergence). The
blue colored rock represents the oldest rock.
Evidence to Support the
Plate Tectonic Theory
Magnetic Polarity
Earth’s magnetic field has reversed its
polarity many times in Earth’s history.
Currently magnetic north is close to
Earth’s North Pole. Yet, in the past,
magnetic north was close to Earth’s
South Pole.
The nature and frequency of these
reversals of magnetic polarity are not
fully understood.
When molten rock cools at the site of
divergence, the minerals within the
molten rock begin to crystallize. Many
minerals found within igneous rock are
magnetic. These minerals will align
themselves in the direction of magnetic
north.
If there is a reversal in magnetic polarity
the minerals with igneous rock will align
in an opposite pattern.
These patterns suggest some plates are
moving away from one another.