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Transcript
5) Plate boundaries
PLATE
Plate boundaries
TECTONICS
Plate Tectonics
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
Plate boundaries define the major lithospheric plates.
Blue: Seafloor spreading; Green: Transform faulting; Red: Subduction
5) Plate boundaries
See 3-14 b
PLATE
5) Plate boundaries
Plate
boundaries5)
TECTONICS
PLATE
Plate boundaries
TECTONICS
Transform (shear)
Divergent
(constructive)
Convergent
(destructive)
Divergent (constructive)
See
Fig. 3-14a
Plates slide past
each other.
Earthquake occurrence coincides with plate boundaries,
reflecting the energy released during subduction, seafloor spreading
or plates sliding past each other (transform).
New material is
added to the plates
at spreading center
Lithospheric plates
are destroyed when
they converge at
trenches .
See Fig. 3-20 and Table 3-3
PLATE
TECTONICS
5) Plate boundaries
Transform boundary
Transform (shear)
Transform faults and fracture zones. In transform faults
the plate movement is opposite, at fracture zones it is in
the same direction. Transform faults are always between
two mid-ocean ridges. Earthquakes are frequent but
generally shallow.
PLATE
TECTONICS
5) Plate boundaries
Divergent plate boundaries
PLATE
TECTONICS
5) Plate boundaries
Divergent plate boundaries
Oceanic type
‰Mid-ocean ridges
form a continuous mountain
chain winding around the globe through
all ocean basins.
‰They resemble the seams of a baseball.
Continental type
Fig.4-18
PLATE
TECTONICS
5) Plate boundaries
PLATE
TECTONICS
5) Plate boundaries
The mid-Atlantic ridge surfaces
in Iceland. New volcanic
material fills the rift valley as
plates are pulled apart.
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.
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
2-3 cm/yr
Oceanic rises and ridges
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
Fig. 3-24
See movie!
of years, the rift becomes
the new mid-ocean ridge.
Continental margins form.
16 cm/yr
3-26
PLATE
TECTONICS
5) Plate boundaries
PLATE
TECTONICS
z Convergent boundaries
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
ocean-ocean
Island arc trench system
Trench
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)
Eruption of Mount St. Helens 1980.
continent-continent
Himalayas, Alps, Appalachians
PLATE
TECTONICS
Fig. 3-28
5) Plate boundaries
4) Continental drift and paleomagnetism
Tectonic features off the coast of Washington and the Cascadia
Mountain range, including convergent, divergent and transform
boundaries
Fig. 3-12
Fig. 3-30
Age of sea-floor measured from magnetic reversals and deep sea drilling.
PLATE
Example of
TECTONICS
Peru-Chile trench and the Andes mountains
(continental arc). Change in elevation across a distance of
200 km is more than 15,000 m.
Fig. 4-12
Plate Tectonics
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
ocean-ocean
plate boundary.
5) Plateconvergent
boundaries
•Open ocean
convergence
zones are
called trenches
Marianas trench
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…see
Oc webpage and movie!
See Fig. 3-38!
PLATE
TECTONICS
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
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.
Hotspots
7) Mantle convection
Hawaiian islands and Emperor seamounts result from the
movement of the Pacific plate over the ‘Hawaiian’ hotspot.
See Fig. 3-32
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.
Fig. 4.23
Hot spots are plumes originating from the corecore-mantle boundary
PLATE
PLATE
PLATE
TECTONICS
TECTONICS
TECTONICS
See Fig. 3-31
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