Plate Tectonics Flashcards
(32 cards)
Earth structure:
Describe the core
- 2900km down to the centre
- densest part of the planet
- made of rocks rich in iron and nickel
- semi-molten outer core and solid inner core
- can reach 5000*
- generates convection currents
Earth structure:
Mantle
- bottom of the crust down- 2900km
- surrounds core, silicate rocks rich in iron and magnesium
- most is semi-molten up to 3800*
- density increases as you go down
- generate convection currents
Earth structure:
Crust
- thinnest layer
- made of the coolest, less dense rocks
- rich in silicon, oxygen amd aluminium
- oceanic: thin, young basalt rocks and 5-10km in thickness
- continental: thick, old and up to 70km thick
Plate tectonic theory:
Who came up with it and describe it
1912 Alfred Wegener
- all continents were once joined together in a super continent called Pangea
- at some time the land masses had drifted apart until they occupied their current positions
What is some of the evidence for continental drift
- jigsaw fit: some continents seem to fit together if placed side by side eg. Africa and South America
-geological evidence: rocks of the same age and type found in SE Brazil and South Africa
_ trends in mountains like E Canada and NW Scotland are similar
-biological evidence: similar fossil formations found either side of Atlantic
How tectonic theory developed:
- W theory unable to explain how continents move
- 1940 improvements in rock and fossil dating
- 1950 nuclear submarines began monitoring and mapping ocean floors- mid Atlantic ridge was discovered
- 1962 Harry Hess updated w theory.
- studied rocks found youngest in the middle and oldest on the outside
- At,antic sea floor was spreading outwards from the centre- 5cm a year
Evidence for sea floor spreading
Issue of sea floor spreading
- implies the earth is getting bigger
- not the case- plates must be getting destroyed somewhere
- found this with huge ocean trenches
What is an ocean trench
- large areas of the ocean floor being pulled down
- subduction provides the mechanism
- denser oceanic crust is created in some areas and destroyed in others
- continental crust is not consumed
What are convection currents
- higher temperatures at the earths core and heat released by radioactive decay creates them
- more liquid magma which creates a continuous circulatory motion
- causes plates to move
Major plate boundaries
- seven major plates
- all moving at different speeds and at different directions
- over 50 plates
- move on average 5-10 cm a year
Tectonic plates:
Continental
-over 1500 million years old
-permanent
-will not sink
-low density
-
Tectonic plates:
Oceanic
- less than 200 million years old
- denser
- continually being formed sat ocean ridges
- and continually being destroyed
Tectonic plates:
Facts
- driven by slow moving convection currents within the mantle
- can move in any direction
- cannot overlap their boundaries so must either push past, be pushed upwards or downwards
- no gaps can occur
Landforms associated with constructive margins:
- Two plates separate to form a constructive margin
- Oceanic areas: sea floor spreading occurs on either side of mid-oceanic ridge: mid Atlantic ridge
- continental areas: stretching and collapsing the crust creates rift valleys: great African Rift Valley
Mid-oceanic ridges
- oceanic ridges are long continuous uplifted features
- total length of 60000km
- regular breaks are transform faults
- middle of ridges are deep valleys
What are rift valleys
-two plates pull apart Weaker zone in the crust and an increase in heat towards the surface Hotter expanded crust forms a ridge Central part may form a valley Great African Rift Valley
What is constructive margin
When two plates separate
What are submarine volcanoes
Split in the crust a lower pressure zone created where more liquid lava can erupt
Associated with constructive margins
What are transform faults
New crust forms and spreads causes transforms faults at a right angle to the plate boundary
Spreading plate on either side moves at different rates
Leading to friction and earthquakes
Three types of convergent margin
Oceanic and continental
Oceanic and oceanic
Continental and continental
What happens at a oceanic and continental plate boundary
Denser oceanic plate forced under lighter continental plate
Subduction deep trenches can be found
Fold mountains
What are deep trenches
Found along seaward edge of destructive margins
Marks where one plate begins to descend
Peru chile trench
Found at destructive plates
What are fold mountains
Sediments accumulate on the continental shelf
Where land mass are deformed from folding and faulting
Along edge of continental plate which are uplifted
Andes
Found at destructive margins
