PLATE TECTONICS

• Continental drift : PANGAEA ; Gondwanaland and Laurasia

• EVIDENCE

• Plate boundaries

• Plate movements• Destructive margin

• Constructive margin

• Collision margin

• Conservative margin

The Theory of Continental Drift

• A theory put forward by Alfred Wegener in 1912.

• The continents were once joined together in a single landmass.

• It split up to form separate continents.

Pangaea

Original Continent : Pangaea

Tectonic Plates and Continental Drift

Pangea

Proof that Pangaea existed

Movement of the continents .

• Heat inside the earth is the driving force .

• Heat rises from the mantle.

• It deforms the earth’s crust and breaks it into large pieces .

• Tectonic plates carry both continents and oceans.

Convection Currents .

• Heat in the mantle causes convection currents which cause the plates to move.

• The plates move a few centimetres every year.

• The edges of the plates are called plate boundaries.

• The mantle has a plastic consistency and can therefore move or flow. ( slush )

• Associated with earthquakes and volcanoes.

Plate boundaries• Constructive/ diverging plate boundaries

• New seafloor is being formed and plate move apart• Mid oceanic ridges – seafloor moving apart

• Rift valleys – continental plate move apart

• Destructive/ converging plate boundaries• Seafloor pushed back into mantle

• trenches – seafloor collides

• Peripheral fold mountains – seafloor and continent collides

• Inter-cratonic fold mountains – 2 continents collide

• Transform boundary• Plate boundaries that move parallel to each other in

opposite directions

Seafloor spread lead to plate tectonics

Constructive plate boundary

Destructive plate boundary

The theory of continental drift is now based on seafloor spreading. There seems to be hotspots in the mantle that cause convection currents that drags the solid crustal plates along. Plate tectonics refer to the study of landforms formed due to these movements.

Destructive

plate

boundaries:

Trenches

Peripheral

fold

mountains

Intercratonic

fold

mountains

Activity 7: Identify Plate types and movementsPlate Margin Two types of crust involved Direction of plate

movement

Conservative Continental Crust Slide sideways past each other. Eg: San Andreas Fault

Destructive Oceanic and Continental crust

Move towards each other. Eg: Nazca and South American Plate

Collision Two Continental crusts Towards each other. Eg: Indo-Australian and Eurasian plate

Constructive Oceanic and Continental crust

Moves away from each other, Eg: Mid-Atlantic ridge