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