Tectonics (Chapter 1)

Question 1

Think in terms of mantle material and convection currents

How do convection currents lead to tectonic plate movement?

Answer 1

1. Heat from eaths core causes mantle material to be less dense
2. Mantle material rises towards surface
3. Rising convection currents spread beneath the plates and drag them apart, causing divergent plate movement
4. Mantle material loses heat and sinks towards core
5. Convergent plate movements occurs when convection currents collide
6. Rising and sinking of mantle material forms convection currents

Question 2

How does slab-pull force contribute to tectonic plate movement?

Answer 2

1. When 2 plates converge, the denser oceanic crust is pulled down by gravity as it subducts beneath the less dense oceanic crust
2. The dense roceanic crust sinks deeper into the mantle under its own right, pulling the rest of the plate with it, contributing to further convergence

Question 3

Evidence of seafloor spreading

Answer 3

1. Where two plates move away from each other at divergent plate boundaries, seafloor spreading occurs
2. Magma from deep within the earth rises though the mid-oceanic ridge, new oceanic crust is formed

Question 4

How does the evidence of seafloor spreading support plate tectonic theory?

Answer 4

1. Rocks nearer to the crest/centre of the mid oceanic ridge are youngest, rocks further away are progressively older.
2. Shows how new oceanic crust is created at divergent plate boundaries and moves laterally on both sides of the mid-oceanic ridge as seafloor spreading continues
3. Little sediment accumulation is found at oceanic trenches, as older oceanic crust is being destroyed at oceanic trenches
4. Oceanic crusts are usually younger than continental crusts
5. Proves new crust keeps forming at divergent boundaries and the mid ocean ridges, and as the plates move, older crust is destroyed further away at oceanic trenches

Question 5

Define magnetic striping

Answer 5

Earth has geographical and magnetic north and south poles. Geographical doesn’t change but magnetic can (reverse polarity vs. normal polarity)
1. Magnetic striping is the zebra-like pattern where there are strips of normal polarity rocks alternating strips on reverse polarity rocks on the seafloor. Its symmetrical on both sides of the mid-oceanic ridge
2. Magnetic striping occurs as:
- Basaltic rocks from the oceanic crust are volcanic rocks from iron-rich lava
- Contain magnetic materials
- When iron-rich lava erupts, it cools and solidifies, its magnetic materials point towards earths magnetic north, recording evidence of earth polarity at that time

Question 6

How does evidence of magnetic striping support PTT?

Answer 6

Zebra-like Pattern is symmetrical on both sides of the mid-oceanic -ridge showing that it’s not a random or isolated occurrence
Provides evidence that plates mode, supporting PTT as:
- Oceanic plates move away from each other
- Iron-rich lava erupts from the center of the ride.
- Lava cools, solidifies and forms a new oceanic crust
- The crust is pushed in both directions away from the ridge when new lava erupts and solidifies and plates move apart
- When earths polarity reverses, the rocks record the reversals
- Over time, as more lava moves away from the ridge due to plate divergence, a symmetrical zebra-like pattern forms.

Question 7

What happens are divergent plate boundaries?

Answer 7

1. Tectonic plates are moving away from each other, resulting in mid-oceanic ridges, volcanoes including submarine ones and volcanic islands, rift systems and earthquakes

Question 8

Describe Oceanic-Oceanic divergent plate boundaries

Answer 8

1. 2 oceanic plates begin to move apart
2. Decrease in overlying pressure causes parts of underlying mantle to melt, forming magma
3. Magma rises through the weak areas in the crust to the earths surface, and fills gaps caused by the spreading plates
4. Lava cools and solidifies to form basaltic rocks
5. Rocks make up a new oceanic crust
6. An extensive underwater chain - the mid oceanic ridge -forms
7. At the centre of this ridge is a deep rift valley with steep sides
8. Magma rises through the weak areas in the crust to the eaths surface forming submarine volcanoes
9. After many eruptions the volcanoes may break the surface of the ocean to form volcanic islands
10. Earthquakes also occur here due to the stress and tension released when plates move

Question 9

Describe continental-continental divergent plate boundaries

Answer 9

1. 2 continental plates begin to move apart
2. Rocks eventually fracture to form parallel faults
3. The rocks between these faults collapse to form a deep rift valley with steep sides
4. Decrease in overlying pressure causes parts of underlying mantle to melt, forming magma. Magma rises through weak areas in the crust to the Earth’s surgave, forming volcanoes
   - Earthquakes occur as stress and tension are released when the plates move.

Question 10

What happens at convergent plate boundaries?

Answer 10

Tectonic plates are moving towards each other, resulting in fold mountains, volcanoes (including submarine ones), oceanic trenches and earthquakes

Question 11

Describe Oceanic-Oceanic Convergent plate boundaries

Answer 11

1. 2 oceanic plates collide
2. The denser plate subducts beneath the other plate
3. This forms a deep depression knows as oceanic trench
4. As the subducting plate sinks into the mantle, the high pressure forces water out of its oceanic crust. Water lowers the melting point of the overlying mantle, causing it to melt, forming magma.
5. Magma rises through weak areas in the crust to the earth;s surface
6. This forms a chain of volcanoes know as volcanic island

Friction along the subducting oceanic plate also causes earthquakes to occur

Question 12

Describe Continental-Continental Convergent plate boundaries

Answer 12

1. 2 continental plates collide
2. No subduction because the continetal plates to too buoyant to subduct
3. Enormous pressure causes the rocks to be uplifted and buckles to form fold mountains
   - Friction along the convergent plate boundaries also causes earthquakes to occur
   - Magma does not rise to the surface, hence no volcanoes are formed

Question 13

Describe Oceanic-Continental convergent plate boundaries

Answer 13

1. An oceanic plate collides with a continental plate
2. The denser oceanic plate subdicts beneath the continental plate
3. This forms an oceanic trench in the subduction zone
4. As the subducting plate sinks into the mantle, the high pressure forces water out of its oceanic crust. Water lowers the melting point of the overlying mantle, causing it to melt, forming magma.
5. Magma rises through weak areas in the crust to the Earth’s surface, forming volcanoes on the continental plate.
   - Friction along the subducting oceanic plate causes earthquakes to occur.
6. Enormous pressure at this plate boundary causes rocks on the continental plate to be uplifted and buckled, forming fold mountains.

Question 14

What happens at transform plate boundaries?

Answer 14

• Tectonic plates slide past each other
• No crust is created or destroyed
• Stress caused by the plate movement produces a fault (deep fracture), which is a zone of fractures
• Magma does not rise to Earth’s surface, hence there are no volcanoes

Question 15

Summary for 1.4

Answer 15

Divergent
- Oceanic Oceanic
- Mid-oceanic ridge (Landforms)
- Volcanoes (LF)
- Rift valleys (LF)
- Earthquakes (LF)
- Continental Continental
- Volcanoes (LF)
- Rift valleys (LF)
- Earthquakes (LF)

Convergent
- Oceanic Oceanic
- Oceanic trench
- Volcanoes
- Earthquakes
- Continental Continental
- Fold mountains
- Earthquakes
- Oceanic Continental
- Oceanic trench
- Volcanoes
- Fold mountains
- Earthquakes

Transform
- Faults
- Earthquakes