Unsolved mystery 2 - What causes tectonic plates to move

What is the continental crust made of

Granite

What is oceanic crust made of

Basalt

What is denser oceanic crust or continental crust

Oceanic crust

At the circled boundary, which plate is going down (subducting) beneath the other why 

Oceanic plate (nazca) is being subducted under the south American plate because it is dense

On the cross-section, draw arrows showing where gravity could contribute to plate motion.

What are the forces that move tectonic plates

• Slab pull (main) → The sinking of cold, dense oceanic lithosphere pulls the rest of the plate behind it.

• Ridge push → Gravity acts on the elevated ridge, pushing plates down and outward
  

Earths interior provides energy for plate motion. What powers the movement of Earth’s tectonic plates 

Temperature increases → heat increase is what powers it all

Knowing that heat is the primary energy source, indicate places where hot rocks are rising,
and cool rocks are sinking. Draw arrows in the asthenosphere to indicate the direction of motion.

• Rocks inside the earth are WHAT (mostly from earths internal heat)

• Hot materials becomes less WHAT and WHAT

• As it rises it cools

• Cooler, denser materials WHAT

• This cycle creates a WHAT in the WHAT

• Rocks inside the earth are HEATED (mostly from earths internal heat)

• Hot materials becomes less DENSE and RISES

• As it rises it cools

• Cooler, denser materials SINK BACK DOWN

• This cycle creates a CONVECTION CURRENT in the MANTLE