1 Lab 506 ONLINE LESSON

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4 Do take notes as we peruse through this lesson…

5 Plate Tectonics

6 Plate Tectonics is a geologic idea that states the surface of the planet is covered by a series of rigid plates that move…

7 These plates move away each other

8 These plates move toward each other

9 These plates move past each other

10 Plate Tectonics is driven by heat within the interior of the planet…

11 A current theory suggests that radioactive materials are the source for the earth’s internal heat…

12 This heat melts the surrounding rock

13 Melted rock (magma) rises to the surface and pushes the plates…

14 There are three types of plate boundaries

15 Divergent, Convergent and Transform

16 Divergent boundary: the plates move away from each other

17 Convergent boundary: the plates move toward each other

18 Transform boundary: the plates move past each other

19 A transform boundary: cuts across a divergent boundary…

20 A divergent boundary is also referred to as a spreading center, such as the Mid Atlantic Ridge…

21 A divergent boundary is a part of the earth’s surface where new crust is formed…

22 A convergent boundary is also known as a subduction zone…

23 Subduction is the process of pushing seafloor crust into the interior of the planet…

24 A convergent boundary is where crust is destroyed and massive earthquakes occur…

25 A transform boundary is also known as a fracture zone or fault…

26 The San Andreas Fault is a well known transform fault in this area…

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28 Earthquakes occur at all of these boundaries because solid rock is moving against solid rock…

29 The bigger earthquakes occur at the convergent and transform boundaries…

30 But small and shallow earthquakes can occur at transform and divergent boundaries…

31 Shallow earthquakes occur at divergent boundaries because the crust is thin… km thick…

32 The following is a map of many divergent, convergent and transform boundaries…

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34 Plate Tectonics can be thought of as a grand unifying theory in geology…

35 Meaning that many geologic phenomena are associated with Plate Tectonics

36 And can be explained by Plate Tectonics

37 At convergent boundaries …volcanoes, earthquakes and mountains and deep sea trenches can be formed…

38 Right click to play

39 Also at convergent boundaries …the deepest earthquakes occur

40 Subducted seafloor is pushed into the interior of the planet….

41 As much as 650 kilometers

42 At divergent boundaries …heat, volcanoes, earthquakes and new seafloor can be formed…

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44 Since new seafloor is formed at the divergent boundaries…the notion of seafloor spreading can also be observed…

45 Seafloor crust is made primarily of iron rich (MAFIC) minerals

46 These MAFIC minerals are subject to the earth’s magnetic field…

47 Magma rises up from the interior of the planet…

48 And punches through the ocean crust to form new crust…

49 The newly formed MAFIC crust can record the prevailing magnetic field

50 The earth’s magnetic field has changed direction over the course of the life of the planet

51 North has become south and the other way around…

52 These magnetic reversals have been recorded in the seafloor crust

53 These records can tell us such things as the rate of movement of the plates…

54 Each recorded event is a time marker…

55 The newest crust is at the point where magma rises from the interior of our planet…

56 The older crust is further away…

57 Oceanic crust as old as 200,000,000 years old can be detected…

58 How can spreading rates be determined from magnetic reversals?

59 Here is a section of the ocean floor’s magnetic reversals…

60 Seafloor spreading begins here…

61 And ends up here…

62 The distance of seafloor movement is read here…in this case…1425 kilometers…

63 The time is read here…in this case…78,000,000 years…

64 Spreading rates are always noted in cm/year

km = 142,500,000 cm 142,500,000 cm 78,000,000 years

66 So the spreading rate is 1.83 cm/year

67 Hot Spots are places on the planet where magma rises up to produce pinpoint volcanic eruptions…

68 There are about 40 hotspots on the planet…

69 A hotspot can be described as a plume of magma rising up and punching through the crust…

70 The Hawaiian Islands are an example of a hotspot…

71 The hotspot plume is currently under the main island of Hawaii…

72 The Pacific Plate is moving northwest…

73 The plates move while the plume is stationary…

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76 END L506