Title: Plate Tectonics
1Plate Tectonics
2Plate Tectonics
3Mechanism of Plate Tectonics
4Cross-section of Atlantic Ocean
5Directions and Rates of Plate Motion
6Geology 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.
7Geologic Time Scale
540 Million
4.5 Billion
540 Million ( 0.540 Billion)
8Age 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
9Continental 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.
10Continental 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.
11Rock Cycle
12Mountain Building and Erosion
13 14Stages 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
15Alfred 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
16Directions and Rates of Plate Motion
17Wegener proposed that an original super-continent
that he called Pangaea (all land) existed
before continental drift began about 180 million
years ago.
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19According to Wegeners hypothesis, South America
and Africa began to drift apart about 70 million
years ago.
20Breakup of Pangaea
21Geophysicists countered Wegeners argument They
argued that physical properties of Earth
materials would not permit that much horizontal
motion.
22Stages 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
23Wegeners 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
24Glacial Ice
18,000 years ago
Today
25Pangaea - Glacial Ice
26Reconstruction of Ancient Climates
27Climate Zones
28Similar Fossils
29Fossil Distribution
30Explanation of Fossil Evidence
31Similar Rock Structures
32Fig. 3.06a
- W. W. Norton. Modified from Hurley.
33 34Reconstruction of Pangaea
35Stages 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
36Fossil Distribution
37Wegeners Mechanism forContinental Drift
38The Earths Crust
39By the early 1900s, seismologists had already
discerned the general structure and physical
properties of the Earths interior.
40P and S Wave Paths
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42M7.6, ?97
Magnitude 7.6 PAKISTAN, October 08, 2005 at 0351
UTC
Boston, Massachusetts - First Wave Arrives 404
(13 minutes)
43Travel-time versus Distance
D
Distanced measured in degrees from epicenter.
44M6.7, ?25
Magnitude 6.8 CAYMAN ISLANDS, December 14, 2004
at 2320 UTC
Boston, Massachusetts - First Wave Arrives 2326
(6 minutes)
45M7.8, ?62
Magnitude 7.8 TARAPACA, CHILE, June 13, 2005
2245 UTC
Boston, Massachusetts - First Wave Arrives 2255
(10 minutes)
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471
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
48P-wave Velocities
Crust 6-7 km/sec
Mantle 8-13 km/sec
Outer Core 8-10 km/sec
Inner Core 10-11 km/sec
49P-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
50Composition of Earths Interior
Crust Granite/Basalt
Mantle Peridotite
Outer Core Liquid Iron
Inner Core Solid Iron
511909 - Andrija Mohorovicic analysed records of an
earthquake in Croatia - discovered the existence
of the mantle underneath the continental
crust.
52Basalt
Granite
Peridotite
53Wegeners Mechanism forContinental Drift
54Mechanism of Plate Tectonics
55Stages 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
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