Tectonics

Question 0

Asthenosphere

Answer 0

A semi molten zone of rock underlying the lithosphere

Question 1

Lithosphere

Answer 1

The crust of the earth

Question 2

Continental crust

Answer 2

25-100 km thick

Not very dense

Lighter than oceanic crust

Question 3

Oceanic crust

Answer 3

Made of basalt

Between 5-10km thick

So dense that it sinks into the mantle where oceanic and continental crust meet.

Younger than continental crust

Question 4

Why do the plates move?

Answer 4

Convection cells are slow moving currents of mantle material from deep in the mantle, up to the surface, then along the surface then eventually sinking (sub ducting) back into the mantle.

They are powered by the earths internal heat made from radioactive decay and break the crust into pieces (plates)

Question 5

Describe and explain the tectonic processes that occur at constructive plate boundaries

Answer 5

• The plates are sliding apart from each other.
• This is because of diverging convection currents.
• (Explanation of convection currents)
• As the two plates move apart, magma rises to fill the gap creating new ocean ridges and crust.
• Pressure from magma builds up to form domes and ridges.
• Tensional faults are produced into which magma can enter. This cools and solidifies (volcanoes)
• volcanoes produce mainly basalt lava with magma rising from the asthenosphere
• low level explosivity (magma escapes before pressure is built up)
• earthquakes no more than 3 on Richter scale. Friction
• mid Atlantic ridge.
• Surtsey island

Question 6

Describe and explain the tectonic processes that occur at destructive boundaries?

Answer 6

• plates are moving towards each other
• descending limbs of convection currents in the mantle
• two oceanic plates converge
• when oceanic crust meets continental crust
• the denser oceanic crust subducts forming trenches
• where two continental crusts converge (collision margin)