Tectonic Plates
Geography: Edexcel A Level, topic 1.1.1
Types of Plate Margins
When tectonic plates meet, we call it a plate margin (or plate boundary). The three main types of plate margin are destructive, constructive and conservative margins.
Convergent plate margins
- Convergent (or destructive) margins happen when the oceanic plate slides beneath the continental plate.
- The crust is destroyed as one plate dives under another at the subduction zone.
- The rocks catch against each other as the plates are not smooth.
- The pressure between plates builds until the plates can't take the stress.
- The plates slip past each other, which can cause both plates to move resulting in the ground shaking.
Divergent plate margins
- At divergent (or constructive) plate margins, the plates move apart (diverge).
- The convection currents diverge (push apart) and cause a gap between the plates.
- Magma rises up to fill the gap that is created.
- New crust is generated as the plates pull away from each other.
Conservative plate margins
- At conservative (or transform) plate margins, plates are sliding past each other horizontally.
- The crust is neither produced nor destroyed.
- The plates are made of rock that has jagged edges so they catch and snag against one another.
- Friction and pressure between the plates builds until the plates can't take the stress.
- The plates slip past each other, which can cause both plates to move resulting in the ground shaking.
Types of Tectonic Plates
The Earth's crust is broken into large pieces called tectonic plates. Tectonic plates move according to the movements below in the mantle. There are two kinds of tectonic plates:
Oceanic plates
- Oceanic plates make up the ocean floor. This type of plate has the following features:
- High-density materials.
- Made of basaltic rock.
- Only 7-10 km thick.
- Oceanic plates can sink (subduct) under other plates.
Continental plates
- Continental plates make up the Earth’s land masses. This type of plate has the following features:
- Thicker (25-75 km) than oceanic plates.
- Less dense than oceanic plates.
- Made of granitic rock.
- Continental plates do NOT sink (subduct).
Test yourself on Tectonic Plates
What type of plate margin is shown in this diagram?
What are oceanic tectonic plates made of?
Which of the following is true of continental plates?