Plate tectonics Flashcards
1
Q
Earth’s structure
A
- Inner core = Solid ball of iron/nickel. Very hot due to pressure and radioactive decay (contains elements that give off heat when they decompose). This heat is responsible for Earth’s internal energy, and it spreads throughout
- Outer core = semi molten, iron/nickel
- Mantle = Mainly solid rock, and the rocks are high in silicon. Very top layer is semi-molten magma, known as the asthenosphere. The lithosphere rests on top.
- Asthenosphere = Semi-molten layer constantly moves due to convection currents. Movements are powered by heat from core.
- Litosphere = Broken up into plates. Majority of the lithosphere is within mantle. The top of the lithosphere is the crust
- The crust = The thin top of the lithosphere
2
Q
Internal energy sources
A
- Earth’s internal heat source provides the energy for plate tectonic motion and consequently earthquakes and volcanic eruptions
- This internal heat energy has accumulated rapidly over the years due to : conversion of gravitational energy and the radioactive decay of unstable isotopes
3
Q
Plate tectonic theory
A
- The lithosphere is broken up into large slabs of rock called tectonic plates.
- These plates move due to the convection currents in the asthenosphere, which push and pull the plates in different directions.
- Convection currents are caused when the less dense magma rises, cools, then sinks. The edges of where plates meet are called plate boundaries (or plate margins).
4
Q
Different plate boundaries
A
- At plate boundaries, different plates can either move towards each other (destructive plate margin), away from each other (constructive plate margin), or parallel to each other (conservative plate margin)
- Different landforms are created in these different interactions.
5
Q
Destructive plate boundaires : Continental and oceanic
A
- Denser oceanic plate subducts below the continental.
- The plate subducting leaves a deep ocean trench.
- Fold mountains occur when sediment is pushed upwards during subduction.
- The oceanic crust is melted as it subducts into the asthenosphere.
- The extra magma created causes pressure to build up.
- Pressurised magma forces through weak areas in the continental plate
- Explosive, high pressure volcanoes erupt through the continental plate, known as composite volcanoes
6
Q
Destructive plate boundaries : Oceanic and oceanic
A
- Heavier plate subducts leaving an ocean trench. Fold mountains will also occur.
- Built up pressure causes underwater volcanoes bursting through oceanic plate.
- Lava cools and creates new land called island arcs
7
Q
Destructive plate boundaries : Continental and continental
A
- Both plates are not as dense as oceanic so lots of pressure builds.
- Ancient oceanic crust is subducted slightly, but there is no subduction of continental crust.
- Pile up of continental crust on top of lithosphere due to pressure between plates.
- Fold mountains formed from piles of continental crust.
8
Q
Constructive plate boundaries : Oceanic and oceanic
A
- Magma rises in between the gap left by the two plates separating, forming new land when it cools.
- Less explosive underwater volcanoes formed as magma rises
. - New land forming on the ocean floor by lava filling the gaps is known as sea floor spreading
9
Q
Constructive plate boundaries : Continental to continental
A
- Any land in the middle of the separation is forced apart, causing a rift valley.
- Volcanoes form where the magma rises.
- Eventually the gap will most likely fill with water and separate completely from the main island.
- The lifted areas of rocks are known as horsts whereas the valley itself is known as a graben.
10
Q
Further forces influencing how convergent boundaries occur :
A
Ridge push: The slope created when plates move apart has gravity acting upon it as it is at a higher elevation. Gravity pushes the plates further away, widening the gap (as this movement is influenced by gravity, it is known as gravitational sliding).
Slap pull: When a plate subducts, the plate sinking into the mantle pulls the rest of the plate (slab) with it, causing further subduction.
11
Q
Conservative plate boundary
A
- Between any crust, the parallel plates move in different directions or at different speeds.
- No plates are destroyed so no landforms are created. When these plates move, a lot of pressure is built up.
- On oceanic crust, this movement can displace a lot of water. On continental crust, fault lines can occur where the ground is cracked by the movement.
12
Q
Magma plumes
A
- Hotspots are areas of volcanic activity that are not related to plate boundaries.
- Hot magma plumes from the mantle rise and burn through weaker parts of the crust. This can create volcanoes and islands .
- The plume stays in the same place but the plates continue to move , which sometimes causes a chain of islands
13
Q
Evidence for tectonic movement
A
- Continental fit
- Mountain ranges
- Fossils
- use of modern technology
14
Q
Continental fit
A
- Wegener used evidence like the coast lines appearing to match as evidence of continental drift
- Disputed by scientists at the time as they mentioned that coastlines were formed through processes of erosion and deposition using modern day technology we are able to see that although the coastlines of the continents might not fit perfectly, the deeper crusts around them that don’t experience erosion and deposition do
15
Q
Mountain ranges (evidence for tectonic movement)
A
- The mountain ranges and rock sequences on opposite sides of the Atlantic also contain a huge number of similarities.
- The Caledonian Mountains can be traced from North America through Greenland, Ireland, Scotland and Scandinavia.
- These mountains are all of the same age, structure and rock type meaning they must have been part of the same mountain range at some point hundreds of millions of years ago.
