Theory of the Tectonic Plates

A subduction zone occurs when two plates collide with each other.

Heat causes the mantle to rise towards the surface, causing the crust to move.

Continental crust

Oceanic crust

forms continents

forms the ocean floors

thinker (30-70km)

thinner (5-10 km)

very old (~4 billion years)

younger (<200 million years)

less dense

less dense

made of granitic rocks

made from basaltic rock

CONVERGENT BOUNDARIES:

Subduction:

  • When the oceanic crust is pushed below the continental crust. (oceanic and continental)

  • When the older/heavier oceanic crust is pushed below the younger/lighter oceanic crust. (oceanic and oceanic)

Collision:

  • When two continental crusts collide with each other, they create mountain ranges (continental and continental)

TRANSFORM BOUNDARIES:

  • when tectonic plates slide horizontally past one another. (oceanic and continental) or (oceanic and oceanic) or (continental and continental)

DIVERGENT BOUNDRIES:

  • When two plates are moving apart from each other, a crack forms where the mantle rises to create volcanoes. (oceanic and continental) or (oceanic and oceanic) or (continental and continental)

  • Sea-floor spreading is an example of divergent plates.

  • divergent plate volvanoes have a less viscosity (less thickness)