Earth Chapter Plate Science 9 Tectonics Graphics by Tasa Graphic Arts. Inc. 1
I. Earth s surface is made up of lithospheric plates. A. Lithospheric plates are composed of the crust and part of the upper mantle. crust lithosphere asthenosphere lithospheric plate upper mantle lower mantle 2
1. The lithospheric plates are rigid and broken into pieces. 3
2. The plates are composed of basalt (very dense) except for the continents which are composed of granite (less dense) granite basalt Lithospheric basalt 4
3. Lithospheric plates float about on the asthenosphere. oceanic crust continental crust lithosphere asthenosphere 5
B. asthenosphere- partially melted, plastic-like, fluid-like, containing convection currents which rise upon heating and sink upon cooling. 6
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 7
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Eurasian Plate N. Am. Plate Eurasian Plate Pacific Plate African Plate Indian- Australian Plate S. Am Plate Philippine Cocos Plate Plate Nazca Plate Juan de Fuca Plate Antarctic Plate Caribbean Plate Arabian Plate 9
II. Wegnener s Theory- 1912- theory of continental drift. A. 1. 2. in the history of the earth, one or 2 supercontinents formed and broke up----the last supercontinent that formed was a C- shaped continent called Pangea, when it broke up, it formed the present day continents. Panthalassa the ocean surrounding Pangea Tethys Sea the sea inside Pangea 10
300 million years ago 11
200 million years ago 12
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50 million years ago 15
Present 16
B. Evidence 1. similar shape of the coasts of continents Africa and South America 17
2. similar fossils Mesosaurus 18
3. Rock Type and Structural Similarities mountain ranges that match up on different continents. 19
4. Paleoclimatic Evidence-evidence of similar climates on different continents, i.e. grooves on rock indicating glacial coverage, as well as glacial till. 20
5. Earthquakes and Volcanoes a. b. c. earthquakes & volcanoes occur close to the plate boundaries plate boundaries are active areas areas where one plate is moving relative to another plate. produces stress leads to fractures, earthquakes, heat and volcanoes. ring of fire largest active volcano belt surrounding the Pacific Ocean. 90% of the earthquakes and volcanoes. 21
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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. 24
Evidence shows our poles have reversed several times. 25
a. Used to compare new sea floor in the ocean on either side of the mid-atlantic ridge. N S Age in 26
b. Spreading centers where lithospheric plates are moving apart, new sea floor is forming 27
III. Three types of boundaries A. diverging boundaries 1. lithospheric plates are moving apart a. mid-oceanic ridge and the African Rift Valley 28
B. transform (sliding) boundaries 1. lithospheric plates are moving past each other a. San Andreas fault, California 29
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. b. Collision Subduction 30
a. collision 1) continental plates crash together and the plates weld together 31
2) features include: a) b) c) pushed up mountain ranges earthquakes Indian and Eurasian Himalayans Mts. Highest mountains in the world. 32
b. subduction 1) when one lithospheric plate plunges under another plate, which overrides the other 33
+ + + + + + + + + 2) features include: a) deep sea trench b) chain of volcanoes (volcano island arcs) c) mountain ranges d) deep earthquakes + + + + + + + + + + + 34
3) two subtypes a) convergence of 2 oceanic plates 1. Mariana trench; Philippine Plate over the Pacific Plate 35
b) convergence of an oceanic plate with a continental plate 1. Andes Mountains; Nazca under the South American Plate 36
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. 37
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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. 39
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 slabpush. 40
Slab push and slab pull 41
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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 molten material. 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. 45
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V. Continental Growth A. Craton-original or ancient continent core 1. usually smaller 47
2. material has been added from a. deep sea sediments. 48
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b. volcanic rock 50
c. sediments from rivers 51
B. thin skinned thrusting- 1. 2. the pushing of this horizontal sheets of rock along nearly level fault surfaces. Appalachian Mountains 52
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 53
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