Plate Tectonics

Question 1

What evidence supports the theory of continental drift?

Answer 1

the breakup of the supercontinent Pangea
- the fit of continents
- location of glaciations
- fossils
- rock types and structural similarities
- paleoclimates preserved in rocks

Question 2

What is paleomagnetism?

Answer 2

study of the record of the Earth’s magnetic field in rocks, sediment, or archeological materials

Question 3

Why can’t you use the polarity of the Earth to determine where the continents have drifted from?

Answer 3

Earth’s polarity is not set, it “wanders” and “true north” changes

Question 4

What is bathymetry? And when was it used in the oceans?

Answer 4

the measurement of depth of water in oceans, seas, or lakes

Mapping during ww2 for submarines to be able to navigate

Question 5

How are the continents moving?

Answer 5

The oceanic crust is being pushed below continental crust because it is more dense

Question 6

What is the deepest part of the ocean?

Answer 6

Mariana trench

Question 7

What are mid ocean ridges?

Answer 7

Area where new sea floor is being created by the splitting of two plates moving apart
linear mountain ranges in the ocean basins

Question 8

Where are deep ocean trenches found?

Answer 8

border of volcanic arcs

Question 9

Where is heat flow greatest?

Answer 9

mid-ocean ridge axis (where the sea floor is spreading and making new material)

Question 10

How/where are volcanos formed?

Answer 10

at the meeting of the two plates under extreme pressure the volcano forms. molten lava is created from the pressure and immense heat

Question 11

What are seamount chains?

Answer 11

Underwater mountains (usually dormant volcanos) that might have land above them from when they were active

Question 12

What are guyots?

Answer 12

an underwater mountain with a flat top (used to be above the water level but worn down by waves over time to form the flat top)

Question 13

What are volcanic arc islands?

Answer 13

long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries

ring of fire

Question 14

What is the difference between seamount chains and volcanic arc islands?

Answer 14

both are in chains but only one island (at the end of the chain) remains capable of
erupting

Question 15

How are islands formed (such as hawaii)

Answer 15

A seamount volcano erupts and the stuff settles on top of the volcano/mountain on the water. Then over time the tectonic plates shift and the volcano is exposed over water again

Question 16

What is the oceanic crust made of?

Answer 16

Basalt

Question 17

What is sediment?

Answer 17

a layer of sediment on the ocean floor
overlying crustal rock thickens away from mid-ocean ridges

weathering, erosion

Question 18

Where do earthquakes most commonly occur?

Answer 18

oceanic earthquakes occur along belts
belts coincide with trenches, ridges and
fracture zones

Question 19

What are bathymetric features?

Answer 19

places where the crust is moving

Question 20

What are two things that support sea floor spreading?

Answer 20

1. magnetic anomaly
2. sediment thickness

Question 21

What is magnetic anomaly equation?

Answer 21

(expected strength of Earth’s main dipole at a certain location) - (actual measured strength of magnetic field at that location)

Question 22

Why is the sea floor striped with magnetic anomalies (section pointing to true north, the next to south)?

Answer 22

“True north” wanders and even switches to point “north” to south. The stripes show the direction change
(magnetic reversal)

Question 23

What is the difference between positive and negative anomolies?

Answer 23

Positive anomalies show normal polarity crust, negative anomalies are reversed and point south

Question 24

What two theories make up the plate tectonic theory?

Answer 24

Wegener (continental drift) + Hess (sea-floor spreading) = Plate Tectonic Theory

Question 25

What is the lithosphere?

Answer 25

“Crust” that the 20 plates make up
Bends into the asthenosphere when loaded

Question 26

What is the asthenosphere?

Answer 26

Layer underneath the lithosphere

Question 27

What are the two types of lithosphere?

Answer 27

Continental
Oceanic

Question 28

What is the difference between active and passive margins?

Answer 28

• margins near plate boundaries are “active”
• margins far from a plate boundary are “passive”

Question 29

What are the three types of plate boundaries?

Answer 29

Divergent
Convergent
Transform

Question 30

What is a divergent plate boundary?

Answer 30

tectonic plates move apart and material is created
mid atlantic ridge

Question 31

What is a convergent plate boundary?

Answer 31

tectonic plates move together and one is consumed by the other (subduction)
ring of fire

Question 32

What is a transform plate (transform fault) boundary?

Answer 32

tectonic plates slide past one another
plate material is neither created nor destroyed
san andreas fault

Question 33

what is low basalt?

Answer 33

magma quenched at sea floor

Question 34

what are dikes?

Answer 34

preserved magma channels

Question 35

what is gabbro?

Answer 35

deeper magma

Question 36

What are black smokers and how do they work?

Answer 36

vents in the ocean with black “smoke”
water entering fractured rock is heated my magma
- hot water dissolves minerals and cycles back out
of the rock
- when water reaches the sea, minerals precipitate
quickly

Question 37

How does Earth maintain a constant circumference?

Answer 37

subduction of ocean basalt crust balances out the creation of new crust at mid ocean ridges

Question 38

What happens to subducted plates?

Answer 38

Once they start going down, it goes down like an anchor on a rope (steeper over time) (slab pull)
The plates go deeper into the asthenosphere until it melts

Question 39

What are accretionary prisms?

Answer 39

sediments are scraped off of subducting plates and thrusts sediment onto overriding plate
contorted prism can be pushed above sea-level
Taiwan

Question 40

What are back arc basins?

Answer 40

a marginal sea between an accretionary prism or island arc and a continent

Question 41

What are triple junctions?

Answer 41

places where 3 plate boundaries coincide

Question 42

What are hot spots?

Answer 42

Area perforated in the plate where magma can bubble up, usually volcanic
forms chains of volcanos and islands as plates move
hawaii

Question 43

What are continental rifts?

Answer 43

spreading on continents that eventually forms oceans between them
great rift valley in east africa