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The Theory of Plate Tectonics

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1 The Theory of Plate Tectonics
Terms: J. Tuzo Wilson Plate Scientific theory Plate tectonics Fault Divergent boundary Rift valley Convergent boundary Transform boundary Concepts: What is the theory of plate tectonics? What are the three types of plate boundaries?

2 J. Tuzo Wilson and Plates
A Canadian scientist, J. Tuzo Wilson, observed that there are cracks in the continent similar to those on the ocean floor. In 1965, Wilson proposed a new way of looking at these cracks. According to Wilson, the lithosphere is broken into separate sections called plates.

3 Lithospheric Plates The plates fit together along cracks in the lithosphere . The plates carry the continents or parts of the ocean floor or both. Wilson combined what geologists knew about sea-floor spreading, Earth plates, and continental drift into a single theory. What is a scientific theory? It is a well tested concept that explains a wide range of observations.

4 The Theory of Plate Tectonics
The theory of plate tectonics explain the formation, movement, and subduction of Earth’s plates.

5 How do the plates move? The theory of plate tectonics states that pieces of Earth’s lithosphere are driven by convection currents in the mantle. As the plates move, they collide, pull apart, or grind past each other producing spectacular changes in Earth’s surface. Volcanoes, mountain ranges, and deep ocean trenches The plates move very slow about 1-24 centimeters a year. About as fast as your fingernails grow. They have been moving for tens of millions of years.

6 The result of plate movements can result in catastrophic events.

7 Plate movement also creates beautiful landscapes
https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&docid=icN9y-7uTUhWrM&tbnid=aKKasg5R-vQHtM:&ved=0CAQQjB0&url=http%3A%2F%2Fwww.igf.fuw.edu.pl%2Fhill%2Fashima.html&ei=dJWBUtLQKsKqiQKL9YCgAw&bvm=bv ,d.cGE&psig=AFQjCNG1IWSWUDEdF1Vnur3ZQLCjtsEX-Q&ust=

8 What action occur at each location/type of plate boundary?
As we review each plate boundary, complete a tree map and include the following: Focus Questions: Plate Boundary Which direction are the plates moving at these boundaries in relationship to each other? What action occur at each location/type of plate boundary? What forms because of these actions? Examples

9 Tree Map Plate Boundary Plate Movement Location Location Arrows Action
Definition Examples Examples

10 Types of plate boundaries
Divergent plate boundary Ocean: Mid Oceanic Ridge Land: Continental Rift zone Convergent plate boundary Oceanic-oceanic convergence – Subduction Trench Continental-continental convergence – No Subduction - Mountains Oceanic - continental convergence – Subduction Trench Transform plate boundary Earthquakes Crust is neither created nor destroyed. The place where two plates move apart, or diverge, is called a divergent boundary. Most divergent boundaries occur along the mid-ocean ridges, where sea-floor spreading occurs. Divergent boundaries also occur on land, two of Earth’s plates slide apart. A deep valley called a rift valley forms along the divergent boundary. For example the Great Rift Valley in East Africa marks a deep crack in the African continent. Convergent boundary is the place where two plates come together, or converge. When two plates collide, the density of the plates determines which one comes out on top. Oceanic crust becomes cooler and denser as it spreads away from the mid ocean ridge. Where tow plates carrying ocreanic crust meet at a trench, the plate that ismore dense sinks under the other plate. Sometimes a plate carrying oceanic crust collides with a plate carrying continental crust. Oceanic crust is more dense than continental crust. The less dense continental crust can’t sink under the more dense oceanic crust. Instead subduction occurs as the oceanic plate sinks beneath the continenal plate. When two plates carrying continental crust collide, subduction doesn’t take place but mountains form. Transform boundaries is a place where tow plates slip past each other, moving in opposite directions. Earthquakes often occure along transform boundaries, but crust is neither created or destroyed.

11 Divergent plate boundaries
A place where two plates move apart, or diverge

12 Ocean Mid-Ocean Ridge E.g. Mid-Atlantic ridge is a result of sea floor spreading new basaltic magma rises to the surface along the ridge forming new oceanic crust.

13 Thingvellir Rift Valley
Slicing through the center of Iceland is the Mid-Atlantic Ridge. This is the boundary between theNorth American and Eurasian tectonic plates Thingvellir National Park, in southwestern Iceland, is one of the few spots in the world where an underwater ridge rises above the water surface. Iceland is one of the most geologically active places on Earth with more than 15 volcanoes that have erupted in the last century.

14 Rift valleys may increase in size till water fills them to form a Sea
Land Rift valleys may increase in size till water fills them to form a Sea The Red Sea and the Gulf of Aden were once rift valleys. Mt. Kilimanjaro These rift valleys often have volcanoes lining them. Great African Rift Valley

15 The formation of the Atlantic Ocean
The Atlantic Ocean was also a result of a land rift!

16 Divergent Plate Boundaries
In the Ocean Ridge Action: oceanic plates move apart Sea floor spreading Mid-Ocean Ridge Example: Mid Atlantic Ridge Longest mountain Range On Land Rift Action: Continental crust pull apart Examples: Iceland, Great Rift Valley in East Africa Oceans and Seas form Example: Atlantic Ocean and Red Sea Volcanoes Example: Mt. Kilimanjaro In groups – compare and discuss peer maps. What’s the difference between a ridge and a rift?

17 Tree Map Divergent Plate Boundary Plate Movement Ocean: Ridge
Land: Rift Action: Sea-floor spreading Example: Mid Atlantic Ridge Oceans and Seas form: Examples: Atlantic Ocean and the Red Sea Action: Continental crust pull apart Examples: Iceland, Great Rift Valley in East Africa Oceans and Seas form Example: Atlantic Ocean and Red Sea Volcanoes Example: Mt. Kilimanjaro A place where to plates move apart, or diverge

18 Convergent Plate Boundaries
The place where two plates come together, or converge. Three types of convergent plate boundaries: Ocean crust to ocean crust collision Ocean crust to continental crust collision Continental crust to continental crust collision Make predictions as to what each of these collisions will form.

19 Tree Map Name of plate boundary
Draw arrows to indicate direction the plates move in relationship to each other. Create a Tree map of the 3 types of convergent boundaries, the events that occur there, and an example of each occurrence. i.e. action, formations, examples Compare the items in your map, which convergent boundary type does NOT result in volcanoes? Why?

20 Andes Mountains, Everest, Mt. Hood http://www. amazingplacesonearth

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22 Aleutian Islands Trench Island arc

23 Oceanic - continental convergence
E.g. Andes mountains The forces of plate tectonics are responsible for the formation of the Andes. The Nazca plate and a part of the Antarctic plate have been subducting beneath the South American plate, which is a process that continues today and causes earthquakes andvolcanic eruptions in the region

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25 Quick Review What is the cause of all of these plate movements?

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27 The sub-continent of India has collided with the Eurasian continent to form the Himalayas

28 Types Convergent plate boundaries
Oceanic-oceanic convergence Islands Japan, Aleutian Islands Volcanoes- Mt Pinatubo Trenches Earthquakes Oceanic - continental convergence Volcanoes - Andes, Cascades Continental-continental convergence No volcanoes Mountain building - Himalayas

29 Convergent Boundaries
3 types of convergent boundaries Ocean to ocean crust Crust melting forms volcanic island arc, ex Aleutian Islands Volcanoes – Philippines- Mt Pinatubo Subduction forms trench Ocean to continental crust Crust melting forms volcanic mountain ranges, ex Andes, cascade range, Mt Rainer, Mt Baker Subduction zones forms, trenches, Ocean crust denser than continental crust. Ocean crust slides/subducts under the continental crust Continental to continental crust No melting of crust = no volcanoes No subduction Folding of crust = Non-volcanic mountains are formed -Example Mt Everest

30 Tree Map Convergent Plate Boundaries Ocean to ocean crust
Continental to continental crust Ocean to ocean crust Ocean to continental crust Crust melting forms volcanic mountain ranges, ex Andes, cascade range, Mt Rainer, Mt Baker Subduction zones forms trenches Ocean crust denser than continental crust. Ocean crust slides/subducts under the continental crust Crust melting forms volcanic island arc, ex Aleutian Islands Volcanoes – Philippines- Mt Pinatubo Subduction forms trenches No melting of crust = no volcanoes No subduction Folding of crust = Non-volcanic mountains are formed -Example Mt Everest

31 Transform Boundary A place where two plates slip past each other, moving in opposite directions

32 North American plate Pacific plate

33 San Andres Fault

34 Earthquake in action

35 Transform plate boundary
Action: Earthquakes Forms: fault Example: San Andres fault No crustal melting = No volcanoes

36 Transform Boundary Draw arrows to indicate direction the plates move in relationship to each other. Name a location of a transform boundary. Name the event that occurs at transform boundaries. Could a volcano erupt in Los Angeles? Why or why?

37 No crustal melting = No volcanoes
Transform Boundary Crust is neither created nor destroyed Forms Direction Faults No crustal melting = No volcanoes Earthquakes Is a place where two plates slip past each other Example: San Andres fault


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