1. The Structure of the Earth and Plate Tectonics

2. How do we know what the Earth is made of? Geophysical surveys: seismic, gravity, magnetics, electrical, geodesy –Acquisition: land, air, sea and satellite –Geological surveys: fieldwork, boreholes, mines

3. Structure of the Earth The Earth is made up of 3 main layers: –Core –Mantle –Crust Inner core Outer core Mantle Crust

4. The Crust The crust is composed of two rocks. The continental crust is mostly granite. The oceanic crust is basalt. Basalt is much denser than the granite. Because of this the less dense continents ride on the denser oceanic plates.

5. The Crust This is where we live! The Earth’s crust is made of: Continental Crust - thick (10-70km) - buoyant (less dense than oceanic crust) - mostly old Oceanic Crust - thin (~7 km) - dense (sinks under continental crust) - young

6. The Mantle The Mantle is the largest layer of the Earth. is composed of very hot dense rock that flows like asphalt under a heavy weight. The movement of the middle mantle (asthenosphere) is the reason that the crustal plates of the Earth move.

7. The Outer Core The core of the Earth is like a ball of very hot metals. The outer core is so hot that the metals in it are all in the liquid state. The outer core is composed of the melted metals of nickel and iron.

8. The Lithosphere The crust and the upper layer of the mantle together make up a zone of rigid, brittle rock called the Lithosphere.

9. The Inner Core The inner core of the Earth has temperatures and pressures so great that the metals are squeezed together and are not able to move about like a liquid, but are forced to vibrate in place like a solid.

10. The Asthenosphere The asthenosphere is the semi-rigid part of the middle mantle that flows like hot asphalt under a heavy weight.

11. What is Plate Tectonics?

12. If you look at a map of the world, you may notice that some of the continents could fit together like pieces of a puzzle.

13. Plate Tectonics The Earth’s crust is divided into 12 major plates which are moved in various directions. This plate motion causes them to collide, pull apart, or scrape against each other. Each type of interaction causes a characteristic set of Earth structures or “tectonic” features. The word, tectonic, refers to the deformation of the crust as a consequence of plate interaction.

14. What are tectonic plates made of? Plates are made of rigid lithosphere. The lithosphere is made up of the crust and the upper part of the mantle.

15. The Lithospheric Plates The crust of the Earth is broken into many pieces called plates. The plates "float" on the soft, semi-rigid asthenosphere.

16. What lies beneath the tectonic plates? Below the lithosphere (which makes up the tectonic plates) is the asthenosphere.

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

18. Practical Exercise 1 Supercontinents!

19. Convection Currents The middle mantle "flows" because of convection currents. Convection currents are caused by the very hot material at the deepest part of the mantle rising, then cooling and sinking again --repeating this cycle over and over.

20. Convection Currents The next time you heat anything like soup or water in a pan you can watch the convection currents move in the liquid. When the convection currents flow in the asthenosphere they also move the crust. The crust gets a free ride with these currents, like the cork in this illustration. Safety Caution: Don’t get your face too close to the boiling water!

21. What happens at tectonic plate boundaries?

22. Divergent Convergent Transform Three types of plate boundary

23. Rift or Spreading ridges –As plates move apart causing a gap or break and new material erupts to fill the gap Divergent Boundaries

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

25. Plates move towards each other There are three styles of convergent plate boundaries –Continent-continent collision –Continent-oceanic crust collision –Ocean-ocean collision Convergent Boundaries

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

27. Himalayas

28. Called SUBDUCTION Continent-Oceanic Crust Collision

29. 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

30. 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

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

34. …what’s the connection? Volcanoes and Plate Tectonics…

35. Volcanism is mostly focused at plate margins Pacific Ring of Fire

36. - Subduction - Rifting - Hotspots Volcanoes are formed by:

37. Pacific Ring of Fire Hotspot volcanoes

38. Hot mantle plumes breaching the surface in the middle of a tectonic plate What are Hotspot Volcanoes? Photo: Tom Pfeiffer / www.volcanodiscovery.com The Hawaiian island chain are examples of hotspot volcanoes.

39. The tectonic plate moves over a fixed hotspot forming a chain of volcanoes. The volcanoes get younger from one end to the other.

40. …what’s the connection? Earthquakes and Plate Tectonics…

41. As with volcanoes, earthquakes are not randomly distributed over the globe At the boundaries between plates, friction causes them to stick together. When built up energy causes them to break, earthquakes occur. Figure showing the distribution of earthquakes around the globe

42. Where do earthquakes form? Figure showing the tectonic setting of earthquakes

43. Plate Tectonics Summary The Earth is made up of 3 main layers (core, mantle, crust) On the surface of the Earth are tectonic plates that slowly move around the globe Plates are made of crust and upper mantle (lithosphere) There are 2 types of plate There are 3 types of plate boundaries Volcanoes and Earthquakes are closely linked to the margins of the tectonic plates