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Plate Tectonics and the Ocean Floor. Continental Drift Theory proposed by Alfred Wegener in 1912 Continents once formed a single landmass.

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Presentation on theme: "Plate Tectonics and the Ocean Floor. Continental Drift Theory proposed by Alfred Wegener in 1912 Continents once formed a single landmass."— Presentation transcript:

1 Plate Tectonics and the Ocean Floor

2 Continental Drift Theory proposed by Alfred Wegener in 1912 Continents once formed a single landmass

3 Early Evidence

4 Age of Oceanic Crust Courtesy of

5 Paleomagnetism

6 Plate Tectonics – 1960’s Explains HOW the plates moved

7 The Crust Continental Crust - thick (10-70km) - buoyant (less dense than oceanic crust) - mostly old Oceanic Crust - thin (~7 km) - dense (sinks under continental crust) - young

8 Plate Movement “Plates” of lithosphere are moved around by the underlying hot mantle convection cells

9 Divergent Convergent Transform Three types of plate boundary

10 Spreading ridges – As plates move apart new material is erupted to fill the gap Divergent Boundaries

11 Mid-Ocean Ridge Underwater mountain ranges Due to plates pulling away from each other A Rift Valley forms in the middle where magma comes out Have many fracture zones which break the ridge up

12 Black smoker at a mid- ocean ridge hydrothermal vent in the Atlantic.

13 Close up at the mid-ocean ridge

14 Iceland has a divergent plate boundary running through its middle Iceland: An example of continental rifting

15 There are three styles of convergent plate boundaries – Continent-continent collision – Continent-oceanic crust collision – Ocean-ocean collision Convergent Boundaries

16 Forms mountains, e.g. European Alps, Himalayas Continent-Continent Collision

17 Himalayas

18 Called SUBDUCTION Continent-Oceanic Crust Collision TRENCH

19 Oceanic lithosphere subducts underneath the continental lithosphere Oceanic lithosphere heats and dehydrates as it subsides The melt rises forming volcanism E.g. The Andes Subduction

20 Trenches Due to one plate subducting (going below) another plate Earthquakes Many volcanoes and volcanic island arcs form here

21 When two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone. The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench. The worlds deepest parts of the ocean are found along trenches. – E.g. The Mariana Trench is 11 km deep! Ocean-Ocean Plate Collision

22

23 Where plates slide past each other Transform Boundaries Above: View of the San Andreas transform fault

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25 Volcanism is mostly focused at plate margins Pacific Ring of Fire

26 Other Ocean Features

27 Continental Shelf Part of a continent covered by water Gentle slope Average depth is 60 m Amount exposed changes with sea level

28 Continental Slope Steep May be cut by submarine canyons Sediment piles up at the bottom and forms continental rise

29 Abyssal Plains Flattest area on earth Cover ½ of deep ocean Covered with fine sediment

30 Seamounts Submerged volcanic mountains Called oceanic island if they rise above water

31 Guyot Seamounts that have been eroded and are now flat on top


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