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Physical Geography: Plate Tectonics - Coggle Diagram
Physical Geography: Plate Tectonics
Earth's Internal Structure
Crust
Lithosphere
Earth’s crust and rigid upper mantle
Mantle
Asthenosphere
Molten state
The lower mantle and the lithosphere floats on top
Outer core
Inner core
Crusts
Continental crust
Thick, averaging between 30 km and 70 km in thickness
Made up of light rocks, e.g. granite
Made from silica and alumina (SIAL)
Oceanic crust
Thinner than the continental crust, averaging between 3 km and 10 km
Made up of heavy rocks, e.g. basalt
Made from silica and magnesium (SIMA)
Plate Tectonics
Continental drift
Sea-floor spreading
Harry Hess 1960s
New rock is formed where plates were split apart
Ocean floor widens; magma rises from within the mantle and fills the opening
Magma cools; new ocean floor formed
New ocean floor is youngest at the mid-ocean ridge
Older crust moves away towards continents
Continental drift: Alfred Wegener 1912
Looked like continents once fitted together
Supercontinent Pangaea
Laurasia and Gondwanaland
Proof of continental drift
Continental fit
Fossil distribution
Common rock types
Matching glacial deposits
Theory of continental drift
Suggests that the continents are transported 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. It was effectively 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
Plate Boundaries
There are three types of plate boundaries:
Divergent (constructive boundaries)
Fissure: new rock is formed
Rift valleys, volcanic islands, mid-ocean ridges created
Plates separate and move away from each other (sea-floor spreading)
Convergent (destructive boundaries):
Three types of destructive boundaries
Oceanic-oceanic: where two ocean plates collide
Heavier, older plate dips
Subducted beneath lighter, younger plate
Deep sea trench may develop
Subducted plate melts as it moves down the mantle
Volcanic activity
Island arc, active volcanoes, e.g. Japan
Earthquakes
Oceanic-continental: where an ocean and continental plate collide
Heavier oceanic plate subducts
Ocean trench forms
Oceanic plate melts
Magma rises to create volcanoes at the continental plate
Continental plate is buckled
Fold mountain range formed
Faulting
Explosive volcanoes
Earthquakes
e.g. The Andes in South America
Continent-continental: where two continental plates collide
Neither plates sink on collision
Lithosphere subducts
Continental crust buckles upwards
Formation of fold mountains, e.g. Himalayas
Earthquake activity, e.g. Nepal 2015
Transform (conservative/passive boundaries)
Rock is neither created nor destroyed
Plates slide past each other
Fissure or fault line
Also known as transverse or tear faults
Example: San Andreas Fault in California
Ireland’s geological past
850 MYA divided into two sections
400 MYA plates collided, forming Ireland
380 MYA Ireland covered in a hot desert south of the equator
350 MYA Ireland under warm tropical sea, limestone laid down
250 MYA Armorican fold mountain period
200–140 MYA continental drift, Ireland moving northwards
65 MYA Atlantic Ocean formed