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2
upper
mantle
lithospheric plate
asthenosphere
lithosphere
crust
lower
mantle
•
• I. Earth’s surface is made up of lithospheric plates.
• A. Lithospheric plates are composed of the crust
and part of the upper mantle.
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• 2. The plates are composed of basalt (very dense) except for
the continents which are composed of granite (less dense)
basalt
granite
Lithospheric
basalt
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• 3. Lithospheric plates float about on the asthenosphere.
continental crust
lithosphere
asthenosphere
oceanic
crust
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• B. asthenosphere- partially melted, plastic-like, fluid-like,
containing convection currents which rise upon heating and
sink upon cooling.
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• C. there are 12 major plates:
• 1. African
• 2. Antarctic
• 3. Arabian
• 4. Caribbean
• 5. Cocos
• 6. Eurasian
• 7. Indian
• 8. Nazca
• 9. North American
• 10. Pacific
• 11. Philippine
• 12. South American
• 13. Juan de Fuca
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Pacific Plate
N. Am. Plate
S. Am
Plate
Antarctic Plate
Eurasian Plate
African Plate
Indian-
Australian Plate
Caribbean
Plate
Cocos Plate Arabian
PlatePhilippine
PlateNazca Plate
Juan de Fuca Plate
Eurasian Plate
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• II. Wegnener’s Theory- 1912- theory of continental drift.
• A. in the history of the earth, one or 2 supercontinents formed
and broke up----the last supercontinent that formed was a C-
• 1. Panthalassa the
ocean surrounding
Pangea
• 2. Tethys Sea the
sea inside Pangea
•shaped continent called Pangea,
when it broke up, it formed
•the present day
•continents.
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• 3. Rock Type and Structural Similarities—mountain
ranges that match up on different continents.
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• 4. Paleoclimatic Evidence-evidence of similar climates on
different continents, i.e. grooves on rock indicating
glacial coverage, as well as glacial till.
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• 5. Earthquakes and Volcanoes
• a. earthquakes & volcanoes occur close to the plate
boundaries
• b. plate boundaries are active areas—areas where one
plate is moving relative to another plate. produces
stress—leads to fractures, earthquakes, heat and
volcanoes.
• c. ring of fire—largest active volcano belt
surrounding the Pacific Ocean. 90% of the
earthquakes and volcanoes.
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• 6. Paleomagnetism—some igneous minerals contain iron
minerals that are magnetic. When these minerals form and
hardened they preserve a record of the magnetic poles at the
time the rock was formed.
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Age in
N
S
•a. Used to compare new sea floor in the ocean on
either side of the mid-Atlantic ridge.
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• III. Three types of boundaries
• A. diverging boundaries
• 1. lithospheric plates
are moving apart
• a. mid-oceanic ridge
and the African Rift
Valley
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• B. transform (sliding) boundaries
• 1. lithospheric plates are
moving past each other
• a. San Andreas fault,
California
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• C. converging boundaries: lithospheric plates are
moving toward each other. NOTE: generally, oceanic
plates (basaltic) are more dense than continental plates
(granitic).
• 1. 2 main types
• a. Collision
• b. Subduction
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• 2) features include:
• a) pushed up mountain ranges
• b) earthquakes
• c) Indian and Eurasian –Himalayans Mts.
Highest mountains in the world.
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• b. subduction
• 1) when one lithospheric plate plunges under another
plate, which overrides the other
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• 2) features include:
• a) deep sea trench
• b) chain of volcanoes (volcano island arcs)
• c) mountain ranges
• d) deep earthquakes
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• 3) two subtypes
• a) convergence of 2 oceanic plates
• 1. Mariana trench; Philippine Plate over the Pacific Plate
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• b) convergence of an oceanic plate with a continental
plate
• 1. Andes Mountains; Nazca under the South American
Plate
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• IV. Driving Mechanism
• A. Convection currents-
• 1. heat from the interior of the earth warms up the asthenosphere.
• 2. This causes expansion of the rock material making it less dense and causing the semi-fluid material to rise.
• 3. As it reached the upper level of the asthenosphere it loses its heat and cools down.
• 4. This causes it to contract and become more dense.
• 5. Now the material sinks back down to the lower level where it once again heats up.
• 6. The cycle repeats.
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• B. Slab-Push and Slab-Pull—
• 1. Cold, dense oceanic slabs are descending in the oceanic trenches. These are heavy, moving plates that pull the trailing lithosphere with it. Hence, slab-pull.
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• 2. Where spreading centers occur, the hot material produces an uplifted ridge. New material is being produced and pushes the material on either side away from the ridge. Therefore it is known as slab-push.
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• C. Hot Plumes-
• 1. Thermal plumes may exist that contribute to plate motion. Deep in the mantle there appear to be areas that consistently produce extremely hot moltenmaterial. This may be due to radioactive elements that are breaking down producing heat or some other as of yet unexplained heat source. “Hot spots”exist through out the world,
• a) example: Hawaiian Islands.
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• B. thin skinned thrusting-
• 1. the pushing of this horizontal sheets of rock along
nearly level fault surfaces.
• 2. Appalachian Mountains
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• C. terrane
• 1. a large block of lithospheric plate that has been moved and attached to the edge of a continent.
• 2. identified by
• a. terrane block is bounded on all sides by major faults
• b. fossils do not match surrounding area
• c. magnetic polarity does not match area surrounding it.
• 3. Example: India
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