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Plate Tectonics

Plate Tectonics. Ch-8. History of plate tectonics. Map makers shapes of Africa and South America 1912 Alfred Wegener introduces continental drift His proof was 1.      similar fossils (Mesosaurus SA & A) 2.      similar rock types (SA & A) 3.      climatic change (SA & A)

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Plate Tectonics

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  1. Plate Tectonics Ch-8

  2. History of plate tectonics • Map makers • shapes of Africa and South America • 1912 Alfred Wegener introduces continental drift • His proof was • 1.      similar fossils (Mesosaurus SA & A) • 2.      similar rock types (SA & A) • 3.      climatic change (SA & A) • Was not accepted because he could not explain how they move

  3. The theory of Plate Tectonics • Earth’s Lithosphere is broken into plates that move on the Asthenosphere. This movement creates and destroys new landforms as well as supplies the energy for several geologic events. • Divided into about a dozen plates • Moving in different directions • Some together • Some apart • Some slide past each other

  4. Evidence for Plate Tectonics • Location of Earthquakes and volcanoes • mostly on plate boundaries • Ring of fire • volcanoes around the pacific • Magnetism in rocks • When new igneous rock cools the minerals line up with the north pole • When all continents are back together all mineral line up

  5. More Evidence • Strips of reversed polarity • When new igneous rocks harden the magnetic minerals in the will align themselves with the poles. As you move away from the mid-ocean ridge the minerals reverse repeatedly from north to south. • Shows movement

  6. More Evidence • Age of rocks • Rocks get older as you move away from the mid-ocean ridge • Continent shapes • South America and Africa

  7. Types of Plates • Continental Plate • Less dense • Oceanic Plate • More dense

  8. How the plates move • Mantle convection • Core supplies heat to mantle • Warm mantle expands and pushes up • Turns under weight of crust • Cools and shrinks • Rising = divergent • Sinking = convergent • Slab pull • The denser plate that is diving under the other plate hangs down into the mantle pulling along the plate

  9. How the plates move cont. • Ridge push • The molten rock that comes to the surface heats the rocks around the causing them to expand and push up as well as out. • The rock becomes denser as it cools and moves down and away

  10. Types of plate boundaries • Diverging plate boundaries (Also known as spreading centers) • Plates moving apart • Most are along the ocean floor • Called ridges (Mid-Atlantic, East Pacific rise) • Have a rift valley in middle which isa deep valley broken into segments along fracture zones • New material is brought to the surface here creating new crust

  11. Transform boundaries (Also known as Sliding boundaries) • When two plates slide past each other • Faults occur at the boundary • Earthquakes happen here • Movement is not uniform • San Andreas fault averages 5 cm of movement a year

  12. Convergent Boundaries (2 types) • Subduction boundaries • When one plate dives under the other plate • Diving plate melts away while destroying the crust • Could be • Continental/Oceanic • Oceanic/Oceanic • Collision Boundary • Two continental plates collide but neither dives • Land is pushed up • Ex) Himalayas

  13. oceanic crust to oceanic crust Creates a deep-sea trench Creates volcanic island arc oceanic crust to continental crust Oceanic crust is denser so it always dives Creates a deep-sea trench Creates volcanoes on the landmass Creates mountains on the landmass Types of subduction boundaries

  14. How the continents grow • Continents were not always this large • Craton – the old smaller continent that got added on to • Where material comes from • Deep-sea sediments • As one plate subducts under another plate the sediments get scrapped off one and put onto the other • Igneous rock • plutons brought to the surface • lava, ash and other volcanic debri

  15. River sediments • Rivers deposit new soil at the mouth extending the shoreline • Terranes • plates that are added onto continents due to movement • How do we know they don’t belong there? • A)They are surrounded by faults • B) fossils do not match other rock • C)magnetism does not match

  16. Use today’s landforms to figure out the past Appalachian mts North America and Africa collided Thin skinned thrusting When material caught between the continents gets pushed up onto one Boundary no longer exists Ural mts. In middle of a plate Europe and Asia collided Now called Eurasia boundary no longer exists    Plate movements in the past

  17. pre 200 mill. years ago all continents moving towards each other 200 million years ago Pangea one large land mass Appalachian mts formed now 180 million years ago Pangea breaks up forms Laurasia & Gondwana up to today Keeps moving apart North America & Europe move apart 2.5 cm per year Hawaii moving at 7 cm per year Plate movement history

  18. Future movement • We continue to move • Africa collides with Europe • New mts instead of Med sea • Antartica & Australia collide • New mountains and change of climate • Collide to form a great continent again • Whole system goes in patterns

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