Plate Tectonics Flashcards
What’s The Theory of Plate Tectonics?
Plate tectonics states that the earths lithosphere is broken into a number of slabs called plates
These plates float on top of the mantle and are constantly in motion
Who proved scientifically the theory of plate tectonics in 1963
Fredrick Vine and Drummond Matthews
Earlier theories that helped form the theory of plate tectonics were?
Continental drift, Alfred Wegner in 1912
Conventional currents, Arthur Holmes in 1928
Mid ocean ridges, Maurice Ewing 1947
Sea floor spreading, Harry Ness 1962
What is continental drift
Suggests that the continents are constantly moving across the planet by convection currents
Who originally discovered the idea of pangea
Wegner
Evidence of continental drift
Continental fit, S.america and west coast of Africa fit together. A bit less obvious due to erosion
Matching plant fossils eg fern in s.America and India, Antarctica
Matching animal fossils eg mesosaurus (fresh water) in s.america and Africa
Matching rock folds and mountains of same era in USA and British isles
Matching Glacial deposit materials in Africa and Australia which are currently too hot to have ice fixtures
What’s the reason continents have drifted
Convection currents
What are convection currents
How do they occur
Magma deep in mantle becomes superheated by 6000* core, magma becomes hotter and rises (heat rises)
When reached upper mantle it cools and becomes semi molten. It then moves laterally (sideways) before sinking again.
As it moves sideways it rubs off lithosphere and moves plates, causing friction
What’s slab-pull force
When the edge of a plate begins to sink into a mantle it then pulls the rest of the plate with it (subduction)
Which sinks into mantle? Continental or oceanic? Why?
Oceanic is heavier so will sink
What happens at a divergent plate boundary
Two plates separate
Example of a diverting plate boundary feature
Mid ocean ridge
Example of a diverging plate boundary on earth, in terms of which plates
American plate diverging from Eurasian plate to form mid Atlantic ridge
Arabian and African plate are diverging to cause East African Rift Valley
How are mid ocean ridges formed and give an example
Convection currents cause plates to pull apart
Magma rises up through gap and cools as it reaches the surface creating new oceanic crust. Plates move further and further apart as new crust forms
Magma that has risen and cooled forms a mid ocean Rigde (mid Atlantic ridge) which is mostly below sea level. But some has risen to form islands such as Iceland
Some magma rises more violently causing volcanic mountains
What are transform plates
Plates that are passing by each other either in opposite directions or along side each other but at different speeds
Give an example of plates that are transverse
Pacific plate and North American plate at San Andreas fault
Give a feature that is at transform plates
Transverse faults
Explain the San Andreas fault line
It’s where the North American plate and the Pacific plate move past each other.
Both move in a north western,y direction but at different speeds. Pacific plate moves x6 faster than North American plate. This causes cracks in earths crust. Tension builds up as rocks continue to jam against eachoter before slipping away.
Slips cause plates to jerk releasing shock waves which cause tremors and earthquakes
SAN Francisco is on the fault line so suffered from earthquakes
What are convergent plate boundaries
What happens at them
Plates collide
Example of converging plates
South American and nazca plate
Explain what happens at the south America and nazca plate collision
Heavier nazca plate pushes under South American plate (subduction)
Where oceanic crust descends a deep ocean trench (Peru-chile trench)is formed. Trenches are the deepest parts of our oceans.
Oceanic crust is destroyed and melted in earths mantle. Melted crust material forms batholiths (magma reservoirs), huge underground masses of molten magma. Some magma my make it’s way to the surface to form volcanic mountains
Friction between plates causes underground rock to bend and snap causing earthquakes eg great Chilean earthquake.
South American plate is lighter and buckled up to form fold mountains Andes
As heavier layer sinks, parts if it are scraped off by other plate. Scraped off crust is called terranes and they pile up at the end of fold mountains
What is the name for colliding plates
Covering
What is the name for separating plates
Divergent
What’s the name for passive plates
Transform
Example of an oceanic and continual convergent plate
Nazca plate and South American plate form oceanic trench
Example of oceanic and oceanic plate converging
Pacific plate and Philippine plate forming Mariana Trench
Example of continental and continental plate converging
Indo- Australian and Eurasian plate forming Himalayas
Constructive plate boundaries
Divergent (separating)
Constructive as new crust is formed
Destructive plate boundaries
Convergent (colliding)
Length of mid Atlantic ridge
1500km
Example of volcanic mountain on mid Atlantic ridge
Mount Helka
Iceland
Length of San Andreas fault
1300km
Earthquake example on San Andreas fault
San Francisco 1906
Depth of Mariana Trench , worlds largest ocean trench
1100km
Plates diverging at East African Rift Valley
African
Arabian
Forming Red Sea
Rate East African Rift Valley is widening by
4mm a year
