Plate Tectonics and Seafloor Spreading

Discovery of Subsea mountain ranges led to theories of: Plate Tectonics and Seafloor Spreading

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Development of Plate Tectonics Theory Francois Placet: showed how the continental coastlines matched Antonio Snider showed how similar fossils appear on different continents

continents broke apart along plate boundaries Alfred Wegener 1912-1922 Developed the theory of Plate tectonics or Continental Drift Proposed that the continents broke apart along plate boundaries

Permian 225 mya See Fig. 3-1b Triassic 200 mya

Jurassic 135 mya Cretaceous 65 mya See Fig 3-1b Present Day

Plate Movement See Fig. 3-7a

See Fig 3- 6a

Types of Plate Boundaries • Divergent (moving apart) • Convergent (moving together) • Transform (sliding past )

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)

Arabian Plate African Plate See Fig B3-4a

2.Convergent Boundary Types: • Type I: Subduction- Ocean Crust slips below Continental Crust • Type II: Collision: 2 areas of continental crust meet each other and push together

Convergent Plate Boundaries

Island Arc: Mariana Islands See Fig. 3-6b

Oceanic- Continental Peru-Chili Nazca See Fig. 3-6a

Characteristics of Subduction Zones • Crust destroyed or deformed • Frequent earthquakes • Deep trenches Major source of oil

Occurs when 2 continental plates meet- Convergent Boundary Types • Type II: Collision Occurs when 2 continental plates meet- Mountains formed

Eurasian and Indian Plates Crunch Collision = 62 mya

Himalayan Mountain Formation See Fig 3-11b India China

Type II: Continental-Continental Convergent Zone

Himalayan Mountains See Fig. 3-11c

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

Transform Plate Boundary

San Andreas Fault: See Fig. B3-2a

See Fig. 3-9a

See Fig. 3-9b

Hawaiian Island Chain

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

ACTIVE CONTINENTAL MARGINS PASSIVE CONTINENTAL MARGINS

Passive Continental Margins: East Coast of Canada shelf Margin characteristics: slope •Few earthquakes rise • Wide continental shelf (20-200km wide) • Economically rich- oil, gas, fisheries

Example: West coast of North and South America Active Continental Margins mountains Example: West coast of North and South America Margin characteristics: shelf slope • Frequent earthquakes (steep) • Active volcanoes in convergent zones) No rise! • Narrow continental shelf trench • Troughs • Trenches, Island arcs

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