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Fig. 18-2, p. 419. Fig. 18-2a, p. 419 Fig. 18-2b, p. 419.

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Presentation on theme: "Fig. 18-2, p. 419. Fig. 18-2a, p. 419 Fig. 18-2b, p. 419."— Presentation transcript:

1 Fig. 18-2, p. 419

2 Fig. 18-2a, p. 419

3 Fig. 18-2b, p. 419

4 Fig. 18-2c, p. 419




8 PLATE TECTONICS The unifying theory of geology Plate Tectonics explains many geologic phenomena, such as volcanism, earthquakes, mountain building, changes in climate, flora and fauna distributions, and the distributions of natural resources.

9 Basics of Plate Tectonics Earth ’ s surface is broken into numerous tectonic plates (8 larger plates and several smaller pieces) Tectonic plates are moving (variable rates from 1 cm to 18 cm per year) Tectonic plates interact at their boundaries Moving tectonic plates cause the simultaneous renewal and destruction of the Earth ’ s surface. Heat-transfer mechanism known as convection in the mantle is thought to be the mechanism for the movement of tectonic plates.

10 Plate Tectonics Continental Drift + Sea Floor Spreading = Plate Tectonics The continents are carried with the moving sea floor as the lithospheric plates travel.

11 The Lithospheric Plates

12 Fig. 2-14, p. 38 Tectonic Plates

13 The Earth’s Layers The layers of the Earth result from density differences between the layers caused by variations in composition, temperature, and pressure. Continental Crust: SiAl (rock) Oceanic Crust: SiMa (ferromagnesian rock — basalt--mafic) Mantle: FeMg (Peridotite — ultramafic) (rock) Core: Fe and a small amount of Ni (metal)

14 Fig. 1-10c, p. 14

15 Lithosphere and Asthenosphere Lithosphere is the solid, brittle outer layer of the Earth composed of: Oceanic and continental crust Top part of the mantle Asthenosphere is the plastic layer of the mantle directly below the lithosphere over which the lithospheric plates move. The lithosphere is broken into many pieces called plates.

16 Fig. 1-11, p. 15

17 Plate Tectonics and Surface Features Trench Ridge Fault Volcanoes Mountain Ranges Islands or Island Arcs

18 Mantle Plumes and Hot Spots The Hawaiian Islands

19 Fig. 1-12, p. 15 The Mechanism for Plate Motion is Convection in the Mantle

20 Fig. 1-17, p. 20

21 Fig. 1-14, p. 18 Three types of plate boundaries 1.Divergent plate boundary2. Convergent Plate Boundary3. Transform Plate boundary

22 Table 2-2, p. 39

23 Table 1-3, p. 16

24 Fig. 2-15, p. 40

25 Plate Boundary Structures Oceanic Ridges (MOR and Iceland) Rift zones (East African Rift Zone) Trenches (Marianas Trench) Island Arcs (Japan, Indonesia) Mountain Ranges (Alps, Andes, Himalayans) Faults (San Andreas Fault) Volcanoes (Mount St. Helens, Mont Pelee, Vesuvius)

26 Mid-Oceanic Ridge: Divergent Plate Boundary

27 Mid-Oceanic Ridge: Divergent Plate Boundary: formation of an ocean

28 Mid-Oceanic Ridge: worldwide distribution

29 Iceland

30 Iceland

31 Iceland and the Mid-Oceanic Ridge (MOR)

32 Iceland and the MOR

33 Fig. 2-16, p. 41 East African Rift Zone Spreading center activity leading to separation of continental crust

34 Fig. 2-17, p. 42 Volcanic Island Arc Convergent Zone: oceanic crust melts and volcanoes develop Convergent Plate Boundaries Subduction zone

35 Fig. 2-19, p. 43 Convergent Plate Boundary: Himalayan Mountains or Alps form as a result of the collision of two continental masses

36 The Alps

37 The Marianas Trench

38 San Andreas Fault, California

39 Fig. 2-20, p. 44



42 Vesuvius and Pompeii

43 Fig. 2-23, p. 46

44 Fig. 2-24, p. 47

45 Catch all Explains how rocks now present in one climatic region of the Earth actually formed in another. Explains that the continents and sea floor are in motion.

46 Table 2-1, p. 28

47 Plate tectonics is evidenced by continental drift and by seafloor spreading

48 CONTINENTAL DRIFT Based upon geologic, paleontologic and climatologic evidence. The continents were one united in to a single supercontinent called Pangaea.

49 Early Ideas For Continental Drift Edward Suess (1885) Recognized the presence of Glossopteris flora on five southern “ continents ” (Antarctica, Asia, Africa, India and South America) Called this collection Gondwanaland. Explains this similarity among fossils by the appearance and disappearance of land bridges

50 Fig. 2-3, p. 29 Alfred Wegener (A German meteorologist developed the hypothesis of continental drift in 1915)

51 Alfred Wegener (1915) Credited with the development of the hypothesis of Continental Drift (1915) Proposed that all land masses were originally united into a single supercontinent called Pangaea. Pangaea subsequently separated in a series of breakups. Based his conclusions upon geologic, paleontologic and climatologic evidence. He did not put forth a convincing mechanism for the drift of the continents

52 Alexander du Toit (1937) Placed the five southern “ continents ”— Gondwanaland--at the south pole to explain the presence of glacial deposits Placed the northern continents — Laurasia — near the equator to explain the presence of coal deposits.

53 Evidence for Continental Drift Continental Fit Similarity of Rock Sequences and Mountain Ranges Rocks of the Appalachians end abruptly and appear again in Greenland, Ireland, Great Britain and Norway (figure 2.5) Glacial Evidence Glacial till Glacial striations in exposed rock (figure 2.6)

54 Fig. 2-4, p. 30 Pangea (the supercontinent)

55 Fig. 2-5, p. 31 Appalachian and Caledonian Mountains are same age, but have been separated by moving plates.

56 Fig. 2-6, p. 31 Glacial Striations formed when great thickness of ice moved over the rock. Direction of striations associated with this rock formation agrees with the configuration of these continents.

57 Evidence for Continental Drift Fossil Evidence Glossopteris flora of Late Paleozoic Mesosaurus of Late Permian Lystrosaurus and Cynognathus of Early Triassic (figure 2.7)

58 Fig. 2-2, p. 29 Glossopeteris leaves from upper Permian Period. Found on all five Gondwanaland landmasses.

59 Fig. 2-7, p. 32 Paleontological and Paleobiological Evidence for Pangea

60 Evidence for Continental Drift --Paleomagnetism and Polar Wandering Remnant magnetism in ancient rocks Iron-bearing minerals atoms in magma or lava aligns with the Earth ’ s magnetic pole Record both direction and strength of the magnetic field The iron-bearing minerals are “ frozen ” into place at the Curie point, when the magma or lava cools. The movement of the crust away from the ridge or spreading zone shows a pattern of magnetic pole reversals (figure 2.10) Arrangement of continents in Pangaea based upon paleomagnetic mapping is supportive of Continental Drift

61 Fig. 2-8a, p. 34 Earth’s Magnetic Field: Today

62 Fig. 2-8b, p. 34 Magnetic field lines show the position of the magnetic north and south poles.

63 Fig. 2-10, p. 35

64 Fig. 2-11, p. 36 The iron in the lava is aligned with the current magnetic configuration and is frozen in place when the lava cools.

65 Fig. 2-9, p. 35 Pole paths actually indicate the motion of the plates leading up to Pangea when both continents were adjacent to each other

66 Fig. 2-13, p. 37 Relative ages of sea floor rocks are oldest away from the ridge. This supports the idea that the sea floor is spreading away from the ridge.

67 Fig. 2-6a, p. 31

68 Fig. 2-6b, p. 31

69 Fig. 2-12, p. 36

70 Fig. 2-14, p. 38

71 Plate Tectonic Theory Provides a framework for interpreting the composition, structure and internal processes of the Earth (see Table 1.3). Explains that Earth is broken into lithospheric plates that move over the asthenosphere. Shows relationship between plate boundaries and zones of major geologic activity. Establishes a basis for explaining cyclical and systematic destruction and renewal of the crust. Based upon Alfred Wegener ’ s Continental Drift hypothesis, which was later revised and improved upon by Harry Hess ’ s theory of sea-floor spreading.

72 Fig. 2-15a, p. 40

73 Fig. 2-15b, p. 40

74 Fig. 2-15c, p. 40

75 Fig. 2-15d, p. 40

76 Fig. 2-17a, p. 42

77 Plate Tectonic Theory Provides a framework for interpreting the composition, structure and internal processes of the Earth (see Table 1.3). Explains that Earth is broken into lithospheric plates that move over the asthenosphere. Shows relationship between plate boundaries and zones of major geologic activity. Establishes a basis for explaining cyclical and systematic destruction and renewal of the crust. Based upon Alfred Wegener ’ s Continental Drift hypothesis, which was later revised and improved upon by Harry Hess ’ s theory of sea-floor spreading.

78 Fig. 2-17b, p. 42

79 Fig. 2-18, p. 42

80 Fig. 2-18a, p. 42

81 Fig. 2-18b, p. 42

82 Fig. 2-19a, p. 43

83 Fig. 2-19b, p. 43

84 Fig. 2-20a, p. 44

85 Fig. 2-20b, p. 44

86 Fig. 2-20c, p. 44

87 Fig. 2-21, p. 44

88 Fig. 2-22, p. 45

89 Fig. 2-22a, p. 45

90 Fig. 2-22b, p. 45

91 Fig. 2-24a, p. 47

92 Fig. 2-24b, p. 47

93 Fig. 2-25, p. 47

94 CHAPTER OBJECTIVES 1 Plate tectonics is the unifying theory of geology and has revolutionized geology. 2 The hypothesis of continental drift is based on considerable geologic, paleontologic, and climatologic evidence. 3 The hypothesis of seafloor spreading accounts for continental movement, and thermal convection cells provide a mechanism for plate movement. 4 The three types of plate boundaries are divergent, convergent, and transform, and along these boundaries new plates are formed, consumed, or slide past one another. 5 The interaction of plates along their boundaries accounts for most of Earth’s earthquake and volcanic activity. 6 The rate of movement and motion of plates can be calculated in several ways. 7 Some type of convective heat system is involved in plate movement. 8 Plate movement affects the distribution of natural resources.

95 CHAPTER OUTLINE Introduction Early Ideas about Continental Drift Evidence for Continental Drift CULTURAL CONNECTIONS: The Struggle toward Scientific Progress Magnetic Reversals Related to Seafloor Spreading Plate Tectonic Theory Three Types of Plate Boundaries Plate Movement and Motion The Driving Mechanism of Plate Tectonics Tectonics and Natural Resources GEO-FOCUS 2.1: Oil, Plate Tectonics, and Politics GEO-RECAP

96 Fig. 2-CO, p. 26

97 Fig. 2-1, p. 28

98 CHAPTER SUMMARY The concept of continental movement is not new. The earliest maps showing the similarity between the east coast of South America and the west coast of Africa provided the first evidence that continents might once have been united and subsequently separated. Alfred Wegener is generally credited with developing the hypothesis of continental drift. He provided abundant geologic and paleontologic evidence to show that the continents were once united into one supercontinent he named Pangaea. Unfortunately, Wegener could not explain how the continents moved, and most geologists ignored his ideas. The hypothesis of continental drift was revived during the 1950s when paleomagnetic studies indicated the presence of multiple magnetic north poles instead of just one as there is today. This paradox was resolved by constructing a hypothetical map and moving the continents into different positions, making the paleomagnetic data consistent with a single magnetic north pole. Magnetic surveys of the oceanic crust revealed magnetic anomalies in the rocks, indicating that Earth’s magnetic field has reversed itself in the past. Because the anomalies are parallel and form symmetric belts adjacent to the oceanic ridges, new oceanic crust must have formed as the seafloor was spreading.

99 CHAPTER SUMMARY Seafloor spreading has been confirmed by radiometric dating of rocks on oceanic islands. Such dating reveals that the oceanic crust becomes older with distance from spreading ridges. Plate tectonic theory became widely accepted by the 1970s because of the overwhelming evidence supporting it and because it provides geologists with a powerful theory for explaining such phenomena as volcanism, earthquake activity, mountain building, global climatic changes, the distribution of the world’s biota, and the distribution of some mineral resources. The supercontinent cycle indicates that all or most of Earth’s landmasses form, break up, and re-form in a cycle spanning about 500 million years. The three types of plate boundaries are divergent boundaries, where plates move away from each other; convergent boundaries, where two plates collide; and transform boundaries, where two plates slide past each other. The average rate of movement and relative motion of plates can be calculated in several ways. The results of these different methods all agree and indicate that the plates move at different average velocities.

100 CHAPTER SUMMARY The absolute motion of plates can be determined by the movement of plates over mantle plumes. A mantle plume is an apparently stationary column of magma that rises to the surface where it becomes a hot spot and forms a volcano. Although a comprehensive theory of plate movement has yet to be developed, geologists think that some type of convective heat system is the major driving force. A close relationship exists between the formation of some mineral deposits and petroleum and plate boundaries. Furthermore, the formation and distribution of some natural resources are related to plate movements.

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