Module 6: Plate Tectonics

What evidence did Wegener offer for Continental Drift?

• And what was the name of the supercontinent that explained this evidence? (4)

• Pangaea → continents formed this supercontinent

• Geologic evidence

• Glacial evidence

• Fossil evidence

Why was Continental Drift rejected? (2)

• Wegener proposed the continents moved due to tide-like forces of the sun & moon → was inaccurate

• Wegener proposed the continents moved tens of meters per year → was inaccurate

What process occurs at mid-ocean ridges

• How did the discoveries of magnetic anomalies and the age of the seafloor support this idea?

• Rifting

• Magnetic particles alternate between facing north & south; patterns of this show that the seafloor is moving in a ←→ direction

What are the lithosphere and the asthenosphere? (6)

• What properties distinguish these two layers?

• What causes the lithosphere to move?

• Lithosphere includes crust & uppermost mantle

  • Is brittle → breaks apart

• Asthenosphere includes the 2nd part of mantle

  • Ductile/plastic → can be shaped and not broken

    • Still solid, though

  • Convection cells cause the asthenosphere to move

What are convection cells? (2)

• The cycle of cool rock sinking and hot rock rising

• Causes the plates to move

How did Pangaea break up? Where can we see that happening today?

• Pangaea broke up due to convection under the mantle splitting the plates apart

• We can see this happen at divergent boundaries

What features and events would you find at a divergent boundary and why? (4)

• Mid-ocean ridges

• Rifting (rift valleys)

• General earthquakes & general volcanoes

• Magnetic anomalies

What features and events would you find at a convergent boundary and why? (4)

• Ring of Fire

• Deep sea trenches

• Deep earthquakes & deep volcanoes

• B/c the subducting plate travels deep

How do we detect subduction?

Deep earthquakes & deep volcanoes @ convergent boundaries

What are the three types of convergent boundaries?

1. Ocean-ocean: ocean plate subducts under ocean plate

   1. Island arc volcanoes

2. Ocean-continent: ocean plate subducts under continent plate

   1. Continental arc volcanoes

3. Continent-continent: plates collide, not subduct

   1. Mountain chains — no volcanic activity

   2. Yes, earthquakes

What features and events would you find at a transform boundary and why (3)

• Cracks, faults

• Earthquakes

• No volcanoes, tsunami, or rifting

What are hot spots?

Sources of magma originating deep in the mantle

What are mantle plumes?

Places where magma from hot spots shoot up through the crust and fuel volcanoes

How do hot spots provide evidence for plate tectonics?

• Which way does a plate move relative to a chain of hot spot volcanoes?

• Mantle plumes stay stationary; the plates move

• Movement creates new hot spot volcanoes

  • Plate moves away from the new hot spot volcano