plate tectonics plate tectonics plateoceanography.asu.edu/oc_sept14_pos.pdf · c. linear sea. the...
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1)The plate tectonic system2)A theory is born3)Early evidence for continental drift4)Continental drift and paleomagnetism5)Plate boundaries6)History and future of plate motions 7)Mantle convection system
Plate Tectonics
Plate boundaries define the major lithospheric plates.Blue: Seafloor spreading; Green: Transform faulting; Red: Subduction
Plate boundariesPlate boundaries5) Plate boundaries5) Plate boundariesPLATEPLATETECTONICSTECTONICS
See 3-14 b
Plate boundariesPlate boundaries
Earthquake occurrence coincides with plate boundaries,reflecting the energy released during subduction, seafloor spreadingor plates sliding past each other (transform).
See Fig. 3-14a
5) Plate boundaries5) Plate boundariesPLATEPLATETECTONICSTECTONICS
Divergent (constructive)
Transform (shear)
New material isadded to the platesat spreading center
Lithospheric plates are destroyed when they converge at trenches .
Plates slide past each other.
Plate boundariesPlate boundaries5) Plate boundaries5) Plate boundariesPLATEPLATETECTONICSTECTONICS
Divergent(constructive)
Convergent(destructive)
See Fig. 3-20 and Table 3-3
5) Plate boundaries5) Plate boundariesPLATEPLATETECTONICSTECTONICS
Transform (shear)
Transform faults and fracture zones. In transform faultsthe 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.
Transform boundaryTransform boundary
Fig.4-18
Mid-ocean ridgesform a continuous mountainchain winding around the globe throughall ocean basins.
They resemble the seams of a baseball.
Divergent plate boundariesDivergent plate boundaries
5) Plate boundaries5) Plate boundariesPLATEPLATETECTONICSTECTONICS 5) Plate boundaries5) Plate boundariesPLATEPLATE
TECTONICSTECTONICS
Oceanic type
Continental type
Divergent plate boundariesDivergent plate boundaries
5) Plate boundaries5) Plate boundariesPLATEPLATETECTONICSTECTONICS
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) Plate boundaries5) Plate boundariesPLATEPLATETECTONICSTECTONICS
The mid-Atlantic ridge surfaces in Iceland. New volcanic material fills the rift valley as plates are pulled apart.
4. Growth of ocean basins4. Growth of ocean basinsThe breakup of Pangaea: A)
Upwarping, stretchingMolten basalt movesthrough the cracks ofthe lithosphere
B)Formation of a riftvalley. Two continentsare separated by a valley that downdropsand eventually floods
C. Linear sea. The high density basaltsinks below sea level, a new ocean basin forms.
D. After millionsof years, the rift becomesthe new mid-ocean ridge.Continental margins form.
5) Plate boundaries5) Plate boundariesPLATEPLATETECTONICSTECTONICS
Fig. 3-24 See movie! 3-26
Oceanic rises and ridges
16 cm/yr
2-3 cm/yr
ocean-ocean
ocean-continent
continent-continent
5) Plate boundaries5) Plate boundariesPLATEPLATETECTONICSTECTONICS
Convergent boundaries
Continental arc trench systemAndes mountains (Peru-Chile trench), Cascade mountains (Juan de Fuca plate subduction)
Island arc trench system
Japan (Japan trench)
Mariana (Mariana's trench)
Himalayas, Alps, Appalachians
Convergent boundariesConvergent boundariesExample of ocean-continent convergent boundary is the subduction of theJuan de Fuca plate off Washingtonunter the North-American Plate
Trench
Eruption of Mount St. Helens 1980.
5) Plate boundaries5) Plate boundariesPLATEPLATETECTONICSTECTONICS
Fig. 3-28
Tectonic features off the coast of Washington and the CascadiaMountain range, including convergent, divergent and transform boundaries
Fig. 3-30
5) Plate boundaries5) Plate boundariesPLATEPLATETECTONICSTECTONICS
Fig. 3-12
4) Continental drift and paleomagnetism4) Continental drift and paleomagnetism
Age of sea-floor measured from magnetic reversals and deep sea drilling.
PeruPeru--Chile trench and the Andes mountainsChile trench and the Andes mountains(continental arc). Change in elevation across a distance of (continental arc). Change in elevation across a distance of 200 km is more than 15,000 m. 200 km is more than 15,000 m.
Fig. 4-12Marianas trench
•Open ocean convergence zones are called trenches
•Open ocean convergence zones are called trenches
Example of ocean-ocean convergent plate boundary.Example of ocean-ocean convergent plate boundary.5) Plate boundaries5) Plate boundariesPLATEPLATETECTONICSTECTONICS
1)The plate tectonic system2)A theory is born3)Early evidence for continental drift4)Continental drift and paleomagnetism5)Plate boundaries6)History and future of plate motions 7)Mantle convection system
Plate Tectonics 6) History and future of plate motionsPLATEPLATETECTONICSTECTONICS
750 Ma Late Proterozoic supercontinent Rodinia458 Ma Middle Ordovician Gondwana forms390 Ma Early Devonian Euramerica forms237 Ma Early Triassic supercontinent Pangaea195 Ma Early Jurassic Breakup of Pangaea152 Ma Late Cretaceous N and S Atlantic opened
Future plate motions…see Oc webpage and movie!
See Fig. 3-38!
PLATEPLATETECTONICSTECTONICS 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.
PLATEPLATETECTONICSTECTONICS 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.
PLATEPLATETECTONICSTECTONICS 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.
See Fig. 3-32
HotspotsHawaiian islands and Emperor seamounts result from the movement of the Pacific plate over the ‘Hawaiian’ hotspot.
Fig. 4.23
Hot spots are plumes originating from the coreHot spots are plumes originating from the core--mantle boundarymantle boundaryPLATETECTONICSPLATEPLATETECTONICSTECTONICS
Distribution of ‘Hot Spots’
PLATEPLATETECTONICSTECTONICS 7) Mantle convection
See Fig. 3-31
PLATETECTONICSPLATEPLATETECTONICSTECTONICS Summary: Modern supporting evidenceSummary: Modern supporting evidencePLATEPLATE
TECTONICSTECTONICS
Geomagnetism
Earthquakes
Deep Sea Ocean Drilling
Hot spots
Modern measurements
Deep earthquakes line up along plate boundaries
Confirmed ocean floor age increases away from mid-ocean ridge
Linear island chains in direction of plate motion
Using satellites to measure current movement of continents
Earth’s magnetic field reversals are recorded parallel to mid-ocean ridges
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