Download plate tectonics

Plate Tectonics (Part II)
1) The plate tectonic system
2) A theory is born
3) Early evidence for continental drift
4) Continental drift and paleomagnetism
5) Plate boundaries
6) History and future of plate motions
7) Mantle convection system
5) Plate boundaries
PLATE
Plate boundaries
TECTONICS
Plate boundaries define the major lithospheric plates.
Blue: Seafloor spreading; Green: Transform faulting; Red: Subduction
5) Plate boundaries
PLATE
Plate boundaries
TECTONICS
See
Fig. 2.4
Earthquake occurrence coincides with plate boundaries,
reflecting the energy released during subduction, seafloor spreading
or plates sliding past each other (transform).
PLATE
Plate
boundaries5) Plate boundaries
TECTONICS
Transform (shear)
Divergent
(constructive)
Convergent
(destructive)
Divergent (constructive)
Plates slide past
each other.
New material is
added to the plates
at spreading center
Lithospheric plates
are destroyed when
they converge at
trenches .
2.5
PLATE
TECTONICS
5) Plate boundaries
Transform (shear)
2.10
PLATE
TECTONICS
5) Plate boundaries
Divergent plate boundaries
Mid-ocean ridges
form a continuous mountain
chain winding around the globe through
all ocean basins.
They resemble the seams of a baseball.
PLATE
TECTONICS
5) Plate boundaries
Divergent plate boundaries
Oceanic type
Continental type
PLATE
TECTONICS
5) Plate boundaries
Rifts opening by the divergence of the
Arabian plate from the African Plate formed
the Gulf of Suez and Gulf of Aqaba.
Rift opening by the divergence
of Baja California from the
Mexican mainland creates the
Gulf of California.
PLATE
TECTONICS
5) Plate boundaries
The mid-Atlantic ridge surfaces
in Iceland. New volcanic
material fills the rift valley as
plates are pulled apart.
PLATE
TECTONICS
5) Plate boundaries
 Convergent boundaries
ocean-ocean
Island arc trench system
Japan (Japan trench)
Mariana (Mariana's trench)
ocean-continent
Continental arc trench system
Andes mountains (Peru-Chile trench),
Cascade mountains
(Juan de Fuca plate subduction)
continent-continent
Himalayas, Alps, Appalachians
PLATE
TECTONICS
5) Plate boundaries
Convergent boundaries
Example of ocean-continent convergent
boundary is the subduction of the
Juan de Fuca plate off Washington
unter the North-American Plate
Trench
Eruption of Mount St. Helens 1980.
5)of Plate
boundaries
ocean basins
PLATE
4. Growth
TECTONICS
The breakup of Pangaea:
A)
Upwarping, stretching
Molten basalt moves
through the cracks of
the lithosphere
B)
Formation of a rift
valley. Two continents
are separated by a valley that downdrops
and eventually floods
C. Linear sea. The high density basalt
sinks below sea level, a new ocean basin
forms.
D. After millions
of years, the rift becomes
the new mid-ocean ridge.
Continental margins form.
PLATE
TECTONICS
6) History and future of plate motions
750 Ma Late Proterozoic supercontinent Rodinia
458 Ma Middle Ordovician Gondwana forms
390 Ma Early Devonian Euramerica forms
237 Ma Early Triassic supercontinent Pangaea
195 Ma Early Jurassic Breakup of Pangaea
152 Ma Late Cretaceous N and S Atlantic opened
Future plate motions…
PLATE
TECTONICS
7) Mantle convection
There are likely two convection cells in the mantle, separated by a
boundary at about 700 km depth, a whole mantle convection and a
shallow convection.
PLATE
TECTONICS
7) Mantle convection
One support of deep mantle convection are plumes
“Hotspots” of lava that might originate at the core-mantle
boundary and that give rise to island chains such as Hawaii.
PLATE
PLATE
TECTONICS
TECTONICS
7) Mantle convection
Distribution of ‘Hot Spots’
PLATE
TECTONICS Summary:
Modern supporting evidence
Geomagnetism
Earth’s magnetic field reversals are recorded parallel to mid-ocean ridges
Earthquakes
Deep earthquakes line up along plate boundaries
Deep Sea Ocean Drilling
Confirmed ocean floor age increases away from mid-ocean ridge
Hot spots
Linear island chains in direction of plate motion
Modern measurements
Using satellites to measure current movement of continents (Fig. 2.13)