Plate tectonics Flashcards
(26 cards)
Inner core
Solid dense ball of metal, composed of iron and nickel Radius of 1200km
6000 degrees Celsius
Outer core
Semi molten, composed of iron and nickel
Radius of 2200km
Temperatures reach 5000 degrees Celsius
Mantle
The part nearest the core is quite rigid, the layer above this (the asthenosphere) is semi molten and the very top layer is rigid.
It is made up of silicate rocks, iron and magnesium.
Radius of 2900km
Average temperature of 3000 degrees Celsius
The Crust
Upper most layer
Oceanic crust
Dense and relatively thin (6-10km)
Composed of basalt and gabbro.
Continental crust
Less dense and thicker (30-70km)
Composed of granite.
Lithosphere
The rigid top part of the mantle and the crust.
Ocean ridges
A landform created
Tectonic plates
Huge slabs in which the lithosphere is broken up into.
Convection Currents
Lower parts of the asthenosphere heat up due to the heat of the core, they become less dense and slowly rise.
As they move towards the top of the asthenosphere they cool down and slowly sink.
These circular motions create drag on the base of tectonic plates, causing them to move.
Ridge push
Another theory about how tectonic plates move, also known as gravitational sliding.
At constructive boundaries, magma rises to the surface at mid-ocean ridges.
|t is very hot so heats surrounding rocks, causing them to expand and rise above the surrounding crust, forming a slope.
The new rock cools and becomes denser.
Gravity causes dense rock to move downslope and away from the margin.
This puts pressure on the plates, causing them to move apart.
Slab pull
Another theory about how tectonic plates move.
At destructive boundaries, the denser crust is forced under the less dense one.
The sinking of the plate edge pulls the rest of the plate towards the boundary.
Sea-floor spreading
As plates move apart, magma rises to fill the gaps created, and then cools to form new crust.
Overtime, the crust is dragged apart and more new crust forms between it.
When this happens at a plate margin under the sea the seafloor gets wider, creating mid ocean ridges.
Constructive margins
Plates move apart and new crust is created.
The mantle is under pressure from the plates above so when they move, pressure is released, causing the mantle to melt, producing magma.
The magma is less dense than the plate above, and it can form a volcano.
Plates don’t move in a uniform way so pressure builds up. It eventually becomes too much so the plate cracks, making a fault line and causing an earthquake.
Once the fault line has been created, further earthquakes are likely to occur.
Ocean ridges
Formed at constructive margins where diverging plates are underwater.
e.g. the Mid-Atlantic ridge. The North American and Eurasian plates are moving away from each other, it rises 2-3km above the ocean floor.
Underwater volcanoes
They erupt along mid-ocean ridges and can build up to be above sea level.
e.g. Iceland was formed by the build up of underwater volcanoes along the Mid-Atlantic ridge.
Rift Valleys
Formed at constructive margins where plates diverge within a continent.
Rising magma causes the continental crust to bulge and fracture.
They form when the plates keep moving apart and the crust between the parallel faults drop down.
e.g. East African Rift system - a series of rift valleys that stretch 4000km from Mozambique to the Red Sea.
It is formed by the Nubian and Somalian plates diverging.
Volcanoes can also be found here, such as Mount Kilimanjaro.
Destructive margins: Oceanic-oceanic
The denser plate is subducted forming a deep sea trench.
Island arcs form when the subducted plate begings to melt; hot magma leaks out of the cracks in the crust as a series of volcanoes.
Island arcs are clusters of islands that sit in a curved line e.g. the Japanese islands.
Destructive margins: Continental-continental
aka collision
Pressure builds up between the two plates, causing earthquakes.
Fold mountains also form here, e.g. the Himalayas where the Eurasian and Indian plates meet.
Destructive margins: Oceanic-continental
Deep sea trench
Fold mountains
Earthquakes
Volcanoes
Deep sea trench at an OC boundary
They form when the denser oceanic plate is subducted.
e.g. the Atacama trench formed when the Nazca plate was subducted by the South American plate. A 8065m deep V-shaped trench was formed 160km off the coast of Peru.
Fold mountains at OC boundaries
Sediments that have accumulated on the continental crust are folded upwards along with the edge of it.
Volcanoes at OC boundaries
The subducted oceanic crust melts to magma when it is heated by friction and contact with the upper mantle.
Magma is less dense so it rises to the surface to form volcanoes.
Earthquakes at OC boundaries.
Caused when the two plates get stuck as one is subducted. Pressure builds up and is eventually released in the form of an earthquake.
