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Plate Tectonics

Plate Tectonics. Plate Tectonics. Mechanism of Plate Tectonics. Cross-section of Atlantic Ocean. Directions and Rates of Plate Motion. Geology in the Early 1900’s. By about 1900, advances in geology, biology and geochemistry (primarily radioactivity) Earth is billions of years old .

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Plate Tectonics

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  1. Plate Tectonics

  2. Plate Tectonics

  3. Mechanism of Plate Tectonics

  4. Cross-section of Atlantic Ocean

  5. Directions and Rates of Plate Motion

  6. Geology in the Early 1900’s • By about 1900, advances in geology, biology and geochemistry (primarily radioactivity) • Earth is billions of years old. • Earth is dynamic - The rocks and landforms that we see today evolved over a very long history, including: • mountain building • erosion • sedimentation • metamorphism • etc.

  7. Geologic Time Scale 540 Million 4.5 Billion 540 Million (= 0.540 Billion)

  8. Age of the Earth 4.6 Billion Years Oldest Rocks on Earth (3.9-4.0) 10 billion 1 billion 100 million 20 million years 10,000,000 1,000,000 100,000 10,000 6,000 years 1,000

  9. Continental Drift ?? • By about 1900, advances in geology, biology and geochemistry (primarily radioactivity) • Earth is billions of years old. • Earth is dynamic - The rocks and landforms that we see today evolved over a very long history, including: • mountain building • erosion • sedimentation • metamorphism • etc. • However, until the second half of the 20th century, most models of the evolution of the Earth involved: • Vertical Tectonics • Very few geologists believed that large scale horizontal motions could occur. • It was thought that the physical properties of Earth materials could not permit such motions.

  10. Continental Drift ?? Until the second half of the 20th century, most models of the evolution of the Earth involved: Vertical Tectonics Very few geologists believed that large scale horizontal motions could occur. It was thought that the physical properties of Earth materials could not permit such motions.

  11. Rock Cycle

  12. Mountain Building and Erosion

  13. Alfred Wegener

  14. Stages in the Development of Plate Tectonics • 1912-1915: Continental drift proposed by Alfred Wegener • 1915-1930: Continental drift debated • 1930-1950: Stalemate • 1950-1960: Revival of interest in continental drift • Paleomagnetism • Ocean Floor Exploration (Mid-ocean ridges/young age of oceanic crust) • 1962: High heat flow over mid-ocean ridges/convection (H. Hess) • 1963: Magnetic anomalies parallel to mid-ocean ridges (F. Vine and D. • Matthews) • 1965: Transform faults and earthquake locations in ocean basins (J.T. Wilson) • 1968: Earthquake locations and direction of earthquake motion consistent • with plate motion (J. Oliver, B. Isacks and L. Sykes) • 1970-?: Plate tectonics accepted by most geoscientists

  15. Alfred Wegener and Continental Drift • Although several people had proposed continental drift as far back as the 1600’s, such an hypothesis was not generally accepted. • In 1912, a German climatologist named Afred Wegener published a book entitled Origin of Continents and Oceans in which he proposed an hypothesis of continental drift and listed supporting evidence for it. • Wegener’s evidence came from: • Reconstruction of ancient climates • Similar fossils on widely separated continents • Matching rock structures across ocean basins • Geometrical fit of continental margins

  16. Directions and Rates of Plate Motion

  17. Wegener proposed that an original super-continent that he called Pangaea (“all land”) existed before continental drift began about 180 million years ago.

  18. According to Wegener’s hypothesis, South America and Africa began to drift apart about 70 million years ago.

  19. Breakup of Pangaea

  20. Geophysicists countered Wegener’s argument: They argued that physical properties of Earth materials would not permit that much horizontal motion.

  21. Stages in the Development of Plate Tectonics • 1912-1915: Continental drift proposed by Alfred Wegener • 1915-1930: Continental drift debated • 1930-1950: Stalemate • 1950-1960: Revival of interest in continental drift • Paleomagnetism • Ocean Floor Exploration (Mid-ocean ridges/young age of oceanic crust) • 1962: High heat flow over mid-ocean ridges/convection (H. Hess) • 1963: Magnetic anomalies parallel to mid-ocean ridges (F. Vine and D. • Matthews) • 1965: Transform faults and earthquake locations in ocean basins (J.T. Wilson) • 1968: Earthquake locations and direction of earthquake motion consistent • with plate motion (J. Oliver, B. Isacks and L. Sykes) • 1970-?: Plate tectonics accepted by most geoscientists

  22. Wegener’s Evidence for Continental Drift • Reconstruction of ancient climates • Similar fossils on widely separated continents • Matching rock structures across ocean basins • Geometrical fit of continental margins

  23. Glacial Ice 18,000 years ago Today

  24. Pangaea - Glacial Ice

  25. Reconstruction of Ancient Climates

  26. Climate Zones

  27. Similar Fossils

  28. Fossil Distribution

  29. Explanation of Fossil Evidence

  30. Similar Rock Structures

  31. Fig. 3.06a W. W. Norton. Modified from Hurley.

  32. W. W. Norton

  33. Reconstruction of Pangaea

  34. Stages in the Development of Plate Tectonics • 1912-1915: Continental drift proposed by Alfred Wegener • 1915-1930: Continental drift debated • 1930-1950: Stalemate • 1950-1960: Revival of interest in continental drift • Paleomagnetism • Ocean Floor Exploration (Mid-ocean ridges/young age of oceanic crust) • 1962: High heat flow over mid-ocean ridges/convection (H. Hess) • 1963: Magnetic anomalies parallel to mid-ocean ridges (F. Vine and D. • Matthews) • 1965: Transform faults and earthquake locations in ocean basins (J.T. Wilson) • 1968: Earthquake locations and direction of earthquake motion consistent • with plate motion (J. Oliver, B. Isacks and L. Sykes) • 1970-?: Plate tectonics accepted by most geoscientists

  35. Fossil Distribution

  36. Wegener’s Mechanism forContinental Drift

  37. The Earth’s Crust

  38. By the early 1900’s, seismologists had already discerned the general structure and physical properties of the Earth’s interior.

  39. P and S Wave Paths

  40. M=7.6, ∆=97° Magnitude 7.6 PAKISTAN, October 08, 2005 at 03:51 UTC Boston, Massachusetts - First Wave Arrives 4:04 (13 minutes)

  41. Travel-time versus Distance D Distanced measured in degrees from epicenter.

  42. M=6.7, ∆=25° Magnitude 6.8 CAYMAN ISLANDS, December 14, 2004 at 23:20 UTC Boston, Massachusetts - First Wave Arrives 23:26 (6 minutes)

  43. M=7.8, ∆=62° Magnitude 7.8 TARAPACA, CHILE, June 13, 2005 22:45 UTC Boston, Massachusetts - First Wave Arrives 22:55 (10 minutes)

  44. 1 Path Distance (km) Time (sec) Velocity 1 2,758 360 7.7 km/sec 2 6,563 600 10.9 km/sec 3 9,543 780 12.2 km/sec 2 3 6371 km

  45. P-wave Velocities Crust 6-7 km/sec Mantle 8-13 km/sec Outer Core 8-10 km/sec Inner Core 10-11 km/sec

  46. P-wave Velocities Air: 0.3 Water: 1.4 Concrete: 3.6 Granite: 5.5-6.0 Iron: 5.8 Aluminum: 6.6 Crust 6-7 km/sec Mantle 8-13 km/sec Outer Core 8-10 km/sec Inner Core 10-11 km/sec

  47. Composition of Earth’s Interior Crust: Granite/Basalt Mantle: Peridotite Outer Core: Liquid Iron Inner Core: Solid Iron

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