1. Plate Tectonics—part 2 Alfred Wegener did not know the earth’s composition, but by the 1960’s scientists were able to revise Wegener’s hypothesis into a theory now known as Plate Tectonics. Alfred Wegener did not know the earth’s composition, but by the 1960’s scientists were able to revise Wegener’s hypothesis into a theory now known as Plate Tectonics.

2. Post 1950’s evidence Convection currents Convection currents Mid-ocean ridge & trenches Mid-ocean ridge & trenches Age of continent rocks vs. seafloor rocks Age of continent rocks vs. seafloor rocks Earthquake/volcano and satellite data Earthquake/volcano and satellite data

7. Directions and rates of plate motions

8. Plate Tectonics The lithosphere is composed of 7 major and 13 minor plates. The lithosphere is composed of 7 major and 13 minor plates. A plate can be composed of continental and/or oceanic crust. A plate can be composed of continental and/or oceanic crust. Continental crust- felsic Continental crust- felsic Oceanic crust-mafic Oceanic crust-mafic

9. 14.3 Differences Between Continental & Oceanic Lithosphere Oceanic – Oceanic –  younger (180 million years or less)  more dense  ~7 km thick Continental – Continental –  older (4 billion years old)  less dense  ~35-40 km thick

10. Plate Tectonics The areas where plates are in contact with each other are called plate boundaries. There are three types of plate boundaries.

11. Plate Boundaries (type 1) Divergent-two plates are moving away from each other. New crust is formed. Most divergent boundaries are on the ocean floor. These are marked by mid-ocean ridges. Divergent-two plates are moving away from each other. New crust is formed. Most divergent boundaries are on the ocean floor. These are marked by mid-ocean ridges. Tensional force is applied to rocks at a divergent boundary. (tension is what pulls them apart) Tensional force is applied to rocks at a divergent boundary. (tension is what pulls them apart)

12. Geographic Examples

13. The East African rift – a divergent boundary on land

14. Plate Boundaries (type 2) Convergent- two plates are moving towards each other. (which applies a “compressional force”)  Oceanic/continental oceanic crust has a higher density than Continental crust, therefore it sinks below the continental crust. This is called a subuction zone.  Volcanoes, mountains and trenches form.

16. Plate Boundaries (type 2)  Continental/continental neither plate is subducted. In this case, both edges are crumpled and uplifted producing large mountain ranges.  Himalayan Mountains (India is colliding with Asia)

18. Plate Boundaries (type 2)  Oceanic/oceanic These are rare and create deep trenches.  Marianas Trench deepest trench in the world.

19. Plate Boundaries (type 3) Transform Fault Boundaries- two plates grind past each other. (which applies a “shearing” force) Transform Fault Boundaries- two plates grind past each other. (which applies a “shearing” force)  They do not slide easily-they stick and slip.  When these plates slip they create earthquakes.  San Andreas Fault in California

21. MOUNTAIN BUILDING

22. Deformation Deformation  The bending, tilting and breaking of Earth’s Crust. MOUNTAIN BUILDING

23. Stress Stress  Force applied to rock material from Isostasy. Strain Strain  Change in shape or volume of rocks from rocks being squeezed, twisted or pulled apart. MOUNTAIN BUILDING

24. Folding Folding  Permanent deformation or bending of a rock under stress. Faulting Faulting  Break in rock along which rocks on either side of the break have moved. MOUNTAIN BUILDING

25. Faulted Faulted  Faulting breaks Earth’s crust into large blocks and those blocks become tilted.  Ex. Sierra Nevada Mountains

27. MOUNTAIN BUILDING Folded Folded  Plates collide (Convergent boundary)  Ex. Appalachian Mtns, Himalayas

30. MOUNTAIN BUILDING Dome Dome  Molten rock pushes up rock layers on Earth’s surface creating a dome. Over time this top layer erodes away leaving the igneous rock exposed.  Ex. Black Hills, South Dakota

32. MOUNTAIN BUILDING Volcanic Volcanic  Molten rock that has erupted onto Earth’s Surface.  Cascade Mtns., Mid-Atlantic Ridge