3.1 Plate tectonics Flashcards
What are the types of crust, direction of movement and example of a constructive plate boundary
Oceanic - oceanic
Divergent
Mid-Atlantic ridge (Eurasian + North American plate)
What are the types of crust, direction of movement and example of a destructive plate boundary (under continent)
Oceanic - continental
Convergent
Nazca + South American plates - creates Peru/chile trench and and Andes mountains
What are the types of crust, direction of movement and example of a destructive plate boundary (island arc)
Oceanic - oceanic
Convergent
Lesser Antilles (Caribbean + North American plates)
What are the types of crust, direction of movement and example of a collision (fold mountains)
Continental - continental
Convergent
Himalayas (Indian and Eurasian plates)
What are the types of crust, direction of movement and example of a conservative plate boundary
Continental - continental (or oceanic - oceanic)
Passive/transform
San Andreas (North American + Pacific)
Draw a labelled divergent (constructive plate) boundary
See notes page
Draw a labelled conservative plate boundary
See notes page
Draw a labelled convergent (destructive plate) boundary
See notes page
Explain sea floor spreading
- Sea floor spreading occurs at divergent plate boudaries between two oceanic plates
- As the plates move apart, due to convection currents and slab pull, magma rises in the gaps produced pushing the plates apart, which causes them to move as well - ridge push
- The is causes the sea floor to spread as older rock moves away from the boudary and new rock forms
- The rocks of the mid atlantic ridge were magnetised in alternate directions and symmetrical on either side of the ridge
Explain subduction
- Subduction zones form where an oceanic plate collides with another plate (either continental or oceanic)
- This occurs at destructive (convergent) plate boundaries
- The oceanic plate is more dense so is pushed below the other plate
- Slab pull occurs - the subducted oceanic plate remains cooler and therefore denser than surrounding mantle, so subduction carries on
Explain fold mountain building
- Fold mountains are formed in convergent plate boundaries and on land
- When a continental plate collides with an oceanic plate, compressional forces cause it to fold or buckle into mountains
- E.g. Andes - Nazca and S.American plates
- In some cases, two continental plates converge, which causes immense amounts of force, folding and deforming the rock into steep mountains
- E.g. Himalayas - Indian and Eurasian plates
Explain ocean ridges
- Ocean ridges form at a divergent/constructive plate boundary between two oceanic plates
- The plates are pulled apart due to process of convection currents and slab pull
- The spreading of the sea floor causes gaps to appear in the boundary
- Hot non-dense magma rises through these cracks as it is less dense than surrounding material
- It causes submarine volcanoes as well as crestal mountains
Explain ocean trenches
- At a subduction zone, deep-sea ocean trenches are found
- They are long, narrow depressions in the ocean floow with depths from 6000-11000 metres
- As the denser oceanic plate subducts beneath the continental plate, the pressure causes the plates to buckle and fold to form a steep v shaped trench
Explain volcanic island arcs
- Volcanic island arcs are a chain of volcanic islands that for parallel or close to a boundary between two converging tectonic plates
Explain hotspots
- A hotspot is a plume of lava that rises vertically throught the mantle
- Most are found near plate margins and they may be responsible for the original rifting of the crust
- They can cause movement - the outward flow of viscous rock from the centre may create a drag force on the plates and cause them to move
