Tectonics Topic 1.1 (Plate Tectonic Theory)

plate tectonic theory

explains that :

• earth has a 3 layered structure

• earth’s lithosphere is broken up into huge pieces called tectonic plates

• tectonic plates are constantly moving

• plate movement results in formation of landform and phenomena

internal structure of the earth

Core

• innermost position

• highest temperature (4400-6000°C)

• thickest (3300km)

Mantle

• in between core and crust

• temperature (1000-3700°C)

• thickness (2900km)

Crust

• outermost position

• lowest temperature

• thinnest (6-70km)

convection current

1. Heat from the earth’s core causes the mantle material to become less dense.

2. Mantle material rises towards the surface

3. The rising mantle material then spread beneath the plates and drag them apart, causing divergent plate movement

4. The mantle material then loses heat and sinks towards the core

5. Convergent plate movement occurs where the convection currents collide

6. The materials then get heated up again and the process repeats. The rising and sinking of mantle material is known as convection currents.

slab-pull force

1. When two plates converge, the denser oceanic crust is pulled down by gravity and subducts under the less dense crust.

2. The denser oceanic crust sinks deeper into the mantle under its own weight, pulling the rest of the plate with it, contributing to further convergence.