Download Plate Tectonics

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Plate Tectonics and
Seafloor Spreading
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Discovery of Subsea mountain ranges
led to theories of:
Plate
Tectonics
and
Seafloor
Spreading
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• http://www.classzone.com/books/earth_scie
nce/terc/navigation/chapter08.cfm
Development of Plate Tectonics Theory
1666 Francois Placet: showed how the
continental coastlines matched
1858 Antonio Snider showed how similar
fossils appear on different continents
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Alfred Wegener
1912-1922
Developed the theory of
Plate tectonics or Continental
Drift
Proposed that the
continents broke apart
along plate boundaries
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Permian
225 mya
See Fig. 3-1b
Triassic
200 mya
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See Fig 3-1b
Jurassic
135 mya
Cretaceous
65 mya
Present Day
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Plate Movement
See Fig. 3-7a
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See Fig 3- 6a
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Types of Plate Boundaries
• Divergent
(moving apart)
• Convergent
• Transform
(moving together)
(sliding past )
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1.Characteristics of Divergent or
Spreading Zones
• New oceanic crust is being made
• This creates undersea mountain chains
• Spreading rates:
1-2 cm/yr (slow)
6-15 cm/yr (fast)
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Arabian Plate
African
Plate
See Fig B3-4a
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2.Convergent Boundary Types:
2 Types
• Type I: Subduction- Ocean
Crust slips below Continental
Crust
• Type II: Collision: 2 areas of continental
crust meet each other and push together
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Convergent Plate Boundaries
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Island Arc: Mariana Islands
See Fig. 3-6b
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Oceanic- Continental
Nazca
See Fig.
3-6a
PeruChili
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Characteristics of Subduction
Zones
• Crust destroyed or deformed
• Frequent earthquakes
• Deep trenches
• Major source of oil
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Convergent Boundary Types
• Type II: Collision
•Occurs when 2 continental plates meet•Mountains formed
Eurasian and Indian Plates Crunch
Collision = 62 mya
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Himalayan Mountain Formation
See Fig 3-11b
India
China
Type II: Continental-Continental
Convergent Zone
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Himalayan Mountains
See Fig. 3-11c
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3. Transform Plate Boundaries
Plates Sliding past each other
Transform boundary zones
have many earthquakes both
on land and under the ocean
as well as volcanic islands .
This part of the Plate Tectonics Theory was
developed by John Tuzo Wilson, a Canadian
scientist
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Transform Plate Boundary
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San
Andreas
Fault:
See
Fig.
B3-2a
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See Fig. 3-9a
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See Fig. 3-9b
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Hawaiian Island Chain
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Continental Margins
• These are the areas where the
continents meet the oceans
• There are two types:
– Active: where 2 plates meet
– Passive: where one plate
continues out under the water to
form a continental shelf
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ACTIVE CONTINENTAL MARGINS
PASSIVE CONTINENTAL MARGINS
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Passive Continental Margins:
East Coast of Canada
Margin characteristics:
•Few earthquakes
shelf
slope
rise
• Wide continental shelf (20-200km wide)
• Economically rich- oil, gas, fisheries
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Active Continental Margins
mountains
Example: West coast of
North and South America
Margin characteristics:
• Frequent earthquakes
• Active volcanoes in
convergent zones)
• Narrow continental shelf
• Troughs
• Trenches, Island arcs
slope
shelf
(steep)
No rise!
trench
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• http://www.windows.ucar.edu/tour/link=/ear
th/interior/cooling_history_2.html