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Plate Tectonics

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Travel-time versus Distance. 12/24/09. M=6.7, =25 Magnitude 6.8 CAYMAN ISLANDS, December 14, 2004 at 23:20 UTC ... Magnitude 7.8 TARAPACA, CHILE, June 13, 2005 ... – PowerPoint PPT presentation

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Title: Plate Tectonics


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 1900s
  • 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 1600s, 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.
  • Wegeners 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
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19
According to Wegeners hypothesis, South America
and Africa began to drift apart about 70 million
years ago.
20
Breakup of Pangaea
21
Geophysicists countered Wegeners argument They
argued that physical properties of Earth
materials would not permit that much horizontal
motion.
22
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

23
Wegeners 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

24
Glacial Ice
18,000 years ago
Today
25
Pangaea - Glacial Ice
26
Reconstruction of Ancient Climates
27
Climate Zones
28
Similar Fossils
29
Fossil Distribution
30
Explanation of Fossil Evidence
31
Similar Rock Structures
32
Fig. 3.06a
  • W. W. Norton. Modified from Hurley.

33
  • W. W. Norton

34
Reconstruction of Pangaea
35
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

36
Fossil Distribution
37
Wegeners Mechanism forContinental Drift
38
The Earths Crust
39
By the early 1900s, seismologists had already
discerned the general structure and physical
properties of the Earths interior.
40
P and S Wave Paths
41
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42
M7.6, ?97
Magnitude 7.6 PAKISTAN, October 08, 2005 at 0351
UTC
Boston, Massachusetts - First Wave Arrives 404
(13 minutes)
43
Travel-time versus Distance
D
Distanced measured in degrees from epicenter.
44
M6.7, ?25
Magnitude 6.8 CAYMAN ISLANDS, December 14, 2004
at 2320 UTC
Boston, Massachusetts - First Wave Arrives 2326
(6 minutes)
45
M7.8, ?62
Magnitude 7.8 TARAPACA, CHILE, June 13, 2005
2245 UTC
Boston, Massachusetts - First Wave Arrives 2255
(10 minutes)
46
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47
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
48
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
49
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
50
Composition of Earths Interior
Crust Granite/Basalt
Mantle Peridotite
Outer Core Liquid Iron
Inner Core Solid Iron
51
1909 - Andrija Mohorovicic analysed records of an
earthquake in Croatia - discovered the existence
of the mantle underneath the continental
crust.
52
Basalt
Granite
Peridotite
53
Wegeners Mechanism forContinental Drift
54
Mechanism of Plate Tectonics
55
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

56
(No Transcript)
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