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What is plate tectonics?
Plate tectonics is the theory explaining the motions of the Earth's lithosphere. Plates move on the mantle, fuelled by convection currents
How do convection currents fuel the movement of plates
Crust is divided into plates. Magma is heated it moves and rises towards the upper mantle. It flows sidewards, cools and sinks, bringing with it a plate. Circular movement-convection currents fuel the movement of the plates
What is sea-floor spreading?
- Ocean floors widen as new rock is formed where plates have split apart.Convection currents fuel the separation of plates.
- As they separate,magma rises and fills the opening made.It cools to form a new crust.New ocean floor is formed
- Older crust moves away from the centre
- Suggests that continents are transported by convection currents.
- Single landmass-Pangea
- Single ocean-Panthalassa
- 200 million years ago, broke apart
- Laurasia and Gondwanaland
- Continents collide when they are carried across the globe by convection currents.
- Ocean floor is pulled down into the mantle by subduction. Oceanic plate heavier than continental ones.
Proof of continental drift?
- Edges of continents fit together- S.America and AfricaSame fossils found in S America and Africa
- Same kind of rocks in S America and Africa
- Ice sheets and glacial deposits found in Oz, Africa and India are of same age
Rocks are either created or destroyed
What are the three types of plate boundary?
- Divergent (construction)Convergent ( destruction)
- Conservative (passive)
- New rock is formed
- Mid-ocean ridges
- Plates separate and move away from each other
- Rock is changed or destroyed as plates collide
- Rock is neither created nor destroyed
- Plates slide past each other
Divergent plate boundaries
Seafloor spreading results in 2 plates moving apart. eg Mid-Atlantic Ridge
Plates split apart creating a rift valley East African Rift Valley
Provides route for magma, creates new sea floor, cools and forms volcanic mts over time. Further eruptions, volcanoes apear above water and are known as volcanic islands eg Iceland
North American plate and Eurasian plate
Convergent plate boundaries
Destructive.Plates collide and rock is changed or destroyed. Subduction occurs when a plate dips beneath another plate. Oceanic-oceanic. Oceanic-continent. Continent-Continent.
- Oceanic-Oceanic plate boundary:
- Heavier older plate subducts, deep sea trench may form. Subducted plate melts. Volcanic activity occurs. Magma rises and forms islands eg island arc. Japan is an eg- Pacific Plate and Eurasian Plate. Earthquakes
Convergent plate boundaries
Heavier oceanic plate subducts, ocean trench is formed, oceanic plate melts. Magma creates volcanoes at continental plate. Continental plate is buckled, compression causes the plate to rise forming a mountain belt. FOLD MTS. Andes - Nazca and S American plate
Faulting may occur- stress in earths crust. Earthquakes
Convergent :Oceanic oceanic boundaries
Neither plate sinks. Lighter plate will subduct (was previously a continental one)while the continental plate remains intact. Collision continues. Buckle and form fold mountains
Indian and Eurasian - Himalayas
Conservative plate boundaries
Rock is neither created nor destroyed
Plates slide past each other
Fault line - transform faults
The San Andreas Fault Line in Cali
Pacific and N American
Earthquake activity as they often get stuck , pressure builds up and releases causing earthquakes
The position of Ireland
850 million years ago, One section of Ire was part of NAmerican plate, other England and Wales
400 million years ago, plates collided forming Ireland, sea closed
380 mill Ireland moved to south of Equator, north above sea level, south submerged
350 mill sea levels rose, formed limestone as Ireland was closed
200 mill Ireland moved North
Atlantic ocean was formed 65 mill years ago as American and Eurasian plates moved apart