Transcript File

2
Plate Tectonics
Chapter 2: Plate Tectonics
Theory 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.
Chapter 2: Plate Tectonics
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.
Red represents the
newest crust of the
earth. The further
from red the older
the crust. Where is
Ireland?
Chapter 2: Plate Tectonics
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
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 oceanic plate subducts
Magma rises to create volcanoes at the
continental plate
Continental plate is buckled and fold mountains
form
•
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•
Heavier, older plate dips
Subducted beneath lighter, younger plate
Deep sea trench may develop
•
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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?