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Plate Tectonics Earth Science
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Continental Drift The theory of Continental Drift was created by Alfred Wegener in ~ 1915 His theory stated that the continents were one large land mass called Pangea and drifted to their present locations
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Evidence For Pangea Jig-Saw Puzzle Fit Of Continents
PANGAEA Jig-Saw Puzzle Fit Of Continents B) Similar Rocks and Fossils C) Glacial evidence D) Coal Deposits E) Mountain Ranges 225 million years ago 135 million years ago 65 million years ago Present
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Theory of Plate Tectonics
The Theory of Plate Tectonics states that Earth’s crust is made up of a number of solid pieces called plates, and these plates move in relation to each other. The term tectonics refers to the forces that deform Earth’s Crust.
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INDIAN-AUSTRLIAN PLATE
Reykjanes Ridge EURASIAN PLATE EURASIAN PLATE Mid- Atlantic Ocean Ridge ANATOLIAN PLATE JUAN DE FUCA PLATE NORTH AMERICAN PLATE CHINA SUBPLATE CARIBBEAN PLATE Transform fault PHILIPPINE PLATE ARABIAN PLATE PACIFIC PLATE COCOS PLATE AFRICAN PLATE Mid- Indian Ocean Ridge Transform fault SOUTH AMERICAN PLATE Carlsberg Ridge East Pacific Rise SOMALIAN SUBPLATE INDIAN-AUSTRLIAN PLATE Southeast Indian Ocean Ridge Transform fault Southwest Indian Ocean Ridge ANTARCTIC PLATE Plate motion at convergent plate boundaries Divergent ( ) and transform fault ( ) boundaries Plate motion at divergent plate boundaries Convergent plate boundaries
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Oceanic vs. Continental Crust
Oceanic Crust (predominately igneous basalt) Mafic – rich in iron High density, thin Continental crust (predominately granite) Felsic – rich in feldspars and Al Low density, thick
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What is the Driving Force?
The driving force to move the plates comes from convection cells in the mantle
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Spreading center Oceanic tectonic plate Oceanic tectonic plate Ocean trench Collision between two continents Plate movement Plate movement Tectonic plate Oceanic crust Oceanic crust Subduction zone Continental crust Continental crust Material cools as it reaches the outer mantle Cold dense material falls back through mantle Mantle convection cell Hot material rising through the mantle Two plates move towards each other. One is subducted back into the mantle on falling convection current. Mantle Hot outer core Inner core
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Divergent Boundary 2 plates separate Example: Mid-Atlantic Ridge
Features Formed: Mountains Volcanoes Ridges Rift Valleys
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Convergent Boundary 2 plates come together
Example: land/land (Collisional Boundary) India/Asia Features Formed: Mountains - Himalayas
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Convergent Boundary 2 plates come together Features Formed:
Example: ocean/land Nazca plate/S. American plate Features Formed: Subduction Zones Ocean Trenches Mountains Volcanoes
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Transform (lateral) Boundary
2 plates slide past each other Example: San Andreas Fault Features Formed Fault Line
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San Andreas Fault
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Plate Tectonics
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Evidence for Sea Floor Spreading
Igneous Ocean Rock – evidence shows that igneous material along the center of the mid-ocean ridge is younger (it formed most recently) than the igneous material farther from the ridges. As new crust is generated at the mid-ocean ridges, the ocean floor widens.
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Sea Floor Spreading
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Reversal of Magnetic Polarity
The strips of basaltic igneous rock which lie parallel to the mid-ocean ridges show matched patterns of magnetic reversals Over thousands of years, the magnetic poles of Earth reverse their polarities, the north magnetic pole becomes the south magnetic pole and vice versa
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Magnetic Polarity Cont.
When basaltic magma flows up into the ridge and cools, crystals of magnetic minerals align themselves with Earth’s magnetic field like tiny compass needles, thus recording the magnetic polarity at the time of formation.
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Magnetic Reversals
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Hot Spots
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Hot Spots
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Hot Spots Hot Spots: Places on Earth’s surface found
within the plates, with unusually high heat flow. The cause of these hot spots are plumes of magma rising up from the mantle producing active volcanoes.
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Hot Spots Continued As the plate passes over a hot spot, a chain of
volcanic mountains form. The only mountain that remains active is the mountain located directly over the hot spot.
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Hot Spots
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Crustal Activity Normal Deposition of Rock Layers (Strata):
Horizontal layers show no movement (crustal activity) Sedimentary Rock Lava Flows
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Folding Caused by strata (layers) bending due to mountain building.
Example: Appalachian Mountains
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Tilting Layers of rock that have moved from a horizontal position to
an angular position Example: Any fault or an area uplifted by an intrusion
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Faulting A zone of weakness or a crack in the crust
along which rocks have moved. If there is no movement it is called a fracture. Examples: Teton Mountains San Andreas Fault
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Fault-block Mountains
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Evidence of Crustal Activity
Displaced Fossils: Marine fossils found in layers of sedimentary rock thousands of feet above sea level Suggests that layers rock (strata), have been uplifted.
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Evidence of Crustal Activity
Subsidence: The sinking of rock strata. Shallow water organisms have been found as fossils deep within the ocean, indicating the land is sinking
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