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Unit 8
Plate Tectonics
Internal structure of the Earth
• The Earth has three concentric layers
Chapter 8: Plate Tectonics
1. Core
• Innermost layer
• About 3,500km thick in radius
• Divided into inner layer and
outer layer
• Has the highest tem...
Chapter 8: Plate Tectonics
3. Crust
• Outermost layer
• Ranges from 5 to 65 km thick
• Two types of crust – continental
an...
Chapter 8: Plate Tectonics
Tectonic plates and their boundaries
Before the Plate Tectonics Theory
• Idea that all the continents once formed a supercontinent
now called Pangaea (meaning ...
Chapter 8: Plate Tectonics
250 million years ago 180 million years ago
Evidence for Continental Drift Theory
• The west coast of Africa fitted with the east coast of
South America
• Matching re...
Chapter 8: Plate Tectonics
Evidence for Plate Tectonics Theory
1. Mid-oceanic ridges
• Presence underwater chains of mount...
Chapter 8: Plate Tectonics
Chapter 8: Plate Tectonics
2. Ocean trenches
• Long, narrow and deep depressions
along the sea floor
• Mark the boundaries...
Chapter 8: Plate Tectonics
Chapter 8: Plate Tectonics
4. Volcanoes
• Found where the sea floor is spreading or near subduction zones (i.e. where
one ...
Chapter 8: Plate Tectonics
5. Earthquakes
• Result from sudden movements of the Earth’s crust
• Often occur where there is...
Chapter 8: Plate Tectonics
Mechanism of plate tectonics
• Intense heat in the mantle leads to convection
currents which dr...
Chapter 8: Plate Tectonics
• The plates move very slowly with an average speed of
about 7cm per year
Chapter 8: Plate Tectonics
Types of Plate Movement
1. Divergent plate movement
• Plates move away from each other
• Heated...
Chapter 8: Plate Tectonics
• When only oceanic plates are involved, results in:
– Mid-oceanic ridges (e.g. Mid-Atlantic Ri...
Chapter 8: Plate Tectonics
2. Convergent plate movement
• Plates move towards each other
• Boundary is known as a destruct...
Chapter 8: Plate Tectonics
• When only oceanic plates are
involved, results in:
– Ocean trenches (e.g. Marianas
Trench)
– ...
Chapter 8: Plate Tectonics
• When the collision is between an oceanic plate and a
continental plate, it results in:
– Ocea...
Chapter 8: Plate Tectonics
3. Transform plate movement
• Plates slide past each other
• Boundary is known as a transform o...
Case study: Puerto Rico Trench and the Lesser
Antilles
Chapter 8: Plate Tectonics
• The Puerto Rico Trench lies to the nor...
Chapter 8: Plate Tectonics
Chapter 8: Plate Tectonics
• A transform fault is formed at the boundary, e.g. the San
Andreas Fault in California, USA
• ...
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Chapter 8 plate tectonics

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Chapter 8 plate tectonics

  1. 1. Unit 8 Plate Tectonics
  2. 2. Internal structure of the Earth • The Earth has three concentric layers Chapter 8: Plate Tectonics
  3. 3. 1. Core • Innermost layer • About 3,500km thick in radius • Divided into inner layer and outer layer • Has the highest temperature • Consists mainly of iron and nickel 2. Mantle • About 2,900km thick • Rich in iron and magnesium • A mixture of solid rock and molten rock • The molten portion is known as magma • Convection currents occur here due to the heat from the core Chapter 8: Plate Tectonics
  4. 4. Chapter 8: Plate Tectonics 3. Crust • Outermost layer • Ranges from 5 to 65 km thick • Two types of crust – continental and oceanic • Continental crusts are: – less dense – composed mainly of granite – rocks are rich in silicates and aluminium (SIAL) • Oceanic crusts are: – denser – rocks are rich in silicates and magnesium (SIMA) • According to the generally accepted Plate Tectonics Theory, the crust is broken into several crustal or tectonic plates which are shifting due to convection currents in the mantle
  5. 5. Chapter 8: Plate Tectonics Tectonic plates and their boundaries
  6. 6. Before the Plate Tectonics Theory • Idea that all the continents once formed a supercontinent now called Pangaea (meaning ‘all land’) • The continents eventually drifted apart and this supercontinent was split up • In 1912, German geographer Alfred Wegener proposed the Theory of Continental Drift • According to his theory, the continents floated over denser rock Chapter 8: Plate Tectonics
  7. 7. Chapter 8: Plate Tectonics 250 million years ago 180 million years ago
  8. 8. Evidence for Continental Drift Theory • The west coast of Africa fitted with the east coast of South America • Matching reptile fossils in Africa and South America • Presence of coal, formed in warm wet conditions, under the Antarctic ice cap • Rocks of the same age and geological structure formed in southwest Africa and southeast Brazil • Presence of the same fossil fern in all the southern continents Chapter 8: Plate Tectonics
  9. 9. Chapter 8: Plate Tectonics Evidence for Plate Tectonics Theory 1. Mid-oceanic ridges • Presence underwater chains of mountains and volcanoes running along the central part of major oceans • Hot magma constantly rises through a gap in the crust called a rift and forms new crust upon cooling • Submarine volcanoes form occasionally • Rocks nearer the rift are newer while those further away are older • The sea floor is composed of rocks younger than the earth, an indication of sea floor renewal • The Atlantic Ocean is growing wider at a rate of 2cm per year
  10. 10. Chapter 8: Plate Tectonics
  11. 11. Chapter 8: Plate Tectonics 2. Ocean trenches • Long, narrow and deep depressions along the sea floor • Mark the boundaries where the sea floor suddenly plunges to great depths • Marianas Trench off the Philippines is the world’s deepest ocean trench with a depth of 11,033m 3. Island arcs • Chains of islands of volcanic origin • Develop along the margins of continents • Usually parallel to the coast Evidence for Plate Tectonics Theory Peru-Chile Trench
  12. 12. Chapter 8: Plate Tectonics
  13. 13. Chapter 8: Plate Tectonics 4. Volcanoes • Found where the sea floor is spreading or near subduction zones (i.e. where one plate moves under another one) • They can be in the oceans or on continental surfaces or at “hot spots” • Concentrated in the Pacific Ring of Fire which stretches from the Andes to California, Japan and New Zealand Evidence for Plate Tectonics Theory
  14. 14. Chapter 8: Plate Tectonics 5. Earthquakes • Result from sudden movements of the Earth’s crust • Often occur where there is frequent volcanic activity Evidence for Plate Tectonics Theory
  15. 15. Chapter 8: Plate Tectonics Mechanism of plate tectonics • Intense heat in the mantle leads to convection currents which drive the movement of the plates above Continent Continent Mid-oceanic ridge
  16. 16. Chapter 8: Plate Tectonics • The plates move very slowly with an average speed of about 7cm per year
  17. 17. Chapter 8: Plate Tectonics Types of Plate Movement 1. Divergent plate movement • Plates move away from each other • Heated magma rises at the rift and cools to form new crust • Boundary where the new crust is created is called a constructive plate boundary
  18. 18. Chapter 8: Plate Tectonics • When only oceanic plates are involved, results in: – Mid-oceanic ridges (e.g. Mid-Atlantic Ridge) – Earthquakes • When only continental plates are involved, results in: – Rift valleys (e.g. Great Rift Valley) – Earthquakes A view of the Great African Rift Valley
  19. 19. Chapter 8: Plate Tectonics 2. Convergent plate movement • Plates move towards each other • Boundary is known as a destructive plate boundary • The denser crust dips under the lighter crust and is destroyed in the magma • Magma rises through breaks in the plates to form volcanoes • Folding of plates results in the formation of mountains
  20. 20. Chapter 8: Plate Tectonics • When only oceanic plates are involved, results in: – Ocean trenches (e.g. Marianas Trench) – Island arcs – Earthquakes – Volcanoes The Himalayas • When only continental plates are involved, results in: – Fold mountains (e.g. Himalayas) – Earthquakes
  21. 21. Chapter 8: Plate Tectonics • When the collision is between an oceanic plate and a continental plate, it results in: – Ocean trenches (e.g. Peru-Chile Trench, Java Trench) – Fold mountains (e.g. Andes) – Earthquakes – Volcanoes World distribution of fold mountains
  22. 22. Chapter 8: Plate Tectonics 3. Transform plate movement • Plates slide past each other • Boundary is known as a transform or conservative plate boundary
  23. 23. Case study: Puerto Rico Trench and the Lesser Antilles Chapter 8: Plate Tectonics • The Puerto Rico Trench lies to the north of Puerto Rico • It is located at a boundary where there is sliding as well as convergence of plates • The rising of the eastern border of the Caribbean Plate forms the Lesser Antilles • The Caribbean Plate slides eastwards at its northern boundary with the North American Plate • At its eastern border, the Caribbean Plate overrides parts of the North American and South American Plates • This subduction zone explains the formation of the island arc of the Lesser Antilles with its active volcanoes • The trench is the deepest part of the Atlantic Ocean (9,219m) and is poorly studied because of its depth
  24. 24. Chapter 8: Plate Tectonics
  25. 25. Chapter 8: Plate Tectonics • A transform fault is formed at the boundary, e.g. the San Andreas Fault in California, USA • Earthquakes are a common occurrence along transform boundaries San Andreas Fault

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