Lecture 4: Plate tectonics

Question 1

How do Seismic waves reveal Earth’s interior?

Answer 1

• P waves are refracted by changes in density = p wave “shadow zone”
• S waves cannot travel through liquids = s wave “shadow zone”

Thus earth has liquid outer core

Question 2

Describe continental crust:

Answer 2

Granite (average composition)
35-40 km thick
Density ~2.8 g/cm3

Question 3

Describe Oceanic crust:

Answer 3

Basalt (average composition)
7-10 km thick
Density ~3 g/cm3

Question 4

Describe the mantle:

Answer 4

Peridotite (solid rock)
Density ~3.3 g/cm3

Question 5

Describe Earth’s core:

Answer 5

Fe-Ni alloy
Liquid outer core
Solid inner core

Question 6

Describe the Lithosphere:

Answer 6

0 – 100 km deep
Strong, cool, rigid
- crust + upper mantle

Question 7

Describe the Asthenosphere:

Answer 7

100 – 350 km deep
High temperature
Weak, easily deformed, solid
- mantle

Question 8

Describe the Mesosphere:

Answer 8

350 – 2883 km deep
High temperature & pressure
Strong, solid
- mantle

Question 9

Is the mantle molten?

Answer 9

NO

The mantle is solid rock that deforms in a ductile (plastic) way when at high pressures and temperatures (>1300°C)

Question 10

How many major Lithospheric plates are there?

Answer 10

9 major and many minor plates

Question 11

What are the three margins where plates interact?

Answer 11

1. Divergent margins where plates pull apart - creates continental and oceanic rifts
2. Convergent margins where plates are driven together - you can have Ocean to Ocean plates or Ocean to Continental plates coming together and subducting (ocean under continent) or Continent to Continent which causes a collision zone.
3. Transform margins where plates move along side each other is opposite directions,