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22 Plate TectonicsPlate Tectonics22 Plate TectonicsPlate Tectonics
Chapter 2: Plate Tectonics
Theory of plate tectonicsTheory of plate tectonics
“Plate Tectonics” explains why the plates of the earth are moving.
The main idea (theory) was proposed by Alfred Wegener in 1912.
Earth’s crust consists of plates that move or float on the mantle
Movement is caused by convection currents in the mantle.
Plates diverge, converge or slide past each other.
Magma Convection currents Magma Convection currents
Causes the movement of plates
Magma heats; rises and moves towards the upper mantle
The magma flows sidewards, then cools and sinks.
Plate moves with sinking magma
Circular movement fuels plate movement
Chapter 2: Plate Tectonics
Sea floor spreading
New rock is formed where plates were split apart (Iceland!!)
Ocean floor widens; magma rises from within the mantle and fills the opening
Magma cools; new ocean floor formed
New sea floor youngest at the mid-ocean ridge
The rocks found further from the plate divide are older so older rocks are found closer towards continents.
Chapter 2: Plate Tectonics
Red represents the newest crust of the earth. The further from red the older the crust. Where is Ireland?
Theory of continental drift
Suggests that the continents are moved across the planet by convection currents
Drifting of the continents is still occurring today
Continents were once all joined together in one single landmass known as Pangaea. ……..a supercontinent.
Approximately 200 million years ago Pangaea began to break apart
The continents were fuelled by the convection currents and so they began to drift apart (pangea divided into Laurasia and Gondwanaland…until these broke further apart into todays continents.)
Chapter 2: Plate Tectonics
The process of subduction
Continents collide
Oceanic plate is heavier than the continental plate
Ocean floor pulled down into the mantle
Subduction occurs
Chapter 2: Plate Tectonics
Plate boundaries
There are three types of plate boundaries:
Divergent (boundaries of construction)
Convergent (boundaries of destruction)
Conservative (passive boundaries)
Chapter 2: Plate Tectonics
Chapter 2: Plate Tectonics
1. Divergent (constructive boundaries)
New crust is formed
Mid-ocean ridges created (Mid-Atlantic Ridge)
Plates separate and move away from each other
Example: American and Eurasian plates
Chapter 2: Plate Tectonics
2. Convergent (boundaries of destruction)
Three types of destructive boundaries:
I.Oceanic-continent: where an ocean and continental plate collide
II.Oceanic-oceanic: where two ocean plates collide
III.Continent-continent: where two continental plates collide
• Heavier, older plate dips • Subducted beneath lighter, younger plate• Deep sea trench may develop
• Heavier oceanic plate subducts • Magma rises to create volcanoes at the
continental plate• Continental plate is buckled and fold
mountains form
• Neither plates sink on collision• Lithosphere subducts • Continental crusts buckle • Formation of fold mountains
Chapter 2: Plate Tectonics
3. Conservative (passive boundaries)
crust is neither created nor destroyed
Plates slide past each other
The line along which the plates slide is known as a fault line
Known as transform faults
e.g. the San Andreas Fault in California
1. Who proposed the Theory of Plate Tectonics?
2. What is the main idea of this theory?3. What causes the plates of the earth
to move?4. What causes magma to move in the
mantle?5. What was Pangea?6. What proof do we have that the
continents of the earth were once all joined together?
7. What are the three types of plate boundary?8. Name examples of each plate boundary?9. What feature is generally found at each boundary?10. Can you name a famous world feature found at each of the main boundary types?