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EAS 210 > CHPTR 11/12 Plate Tectonics > Flashcards

CHPTR 11/12 Plate Tectonics Flashcards

1
Q

youngest part of the Earth

A

ocean floors

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2
Q

plumb line

A

rock on string - earliest method to map sea floor

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3
Q

old sonar

A

map time of the sonar wave to reach the bottom and then bounce back

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4
Q

modern sonar

A

multibeam - sonar obtains a profile of a narrow section of seafloor every few seconds

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5
Q

altimeter + how it works

A

measure the variation on sea surface elevation

mountains under sea will have extra gravitational pull and water would mound above it (anomaly)

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6
Q

geoid

A

round shape that models the Earth’s mean sea level and defines zero elevation.

Irregular surface

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7
Q

geoid low

A

mass deficit (valleys)

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8
Q

geoid high

A

excess mass (mountain)

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9
Q

continental margins + types

A

transition from continental crust to oceanic
passive and active

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10
Q

passive margin

A

change from continental crust to oceanic crust on same tectonic plate

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11
Q

active margin

A

plate boundary where one plate subduct below another

(change from continental crust to oceanic crust on different tectonic plates)

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12
Q

deep ocean basin

A
  • trenches: formed by subduction
  • abyssal plains: between trench and mid ocean ridge
  • seamounts: extinct volcanoes
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13
Q

Parts of a passive continental margin - in order of increasing depth

A

continental shelf
continental slope
continental rise

(then the abyssal plane but thats not part of the margin)

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14
Q

continental shelf

A

flooded extension of the continental crust

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15
Q

continental slope

A

boundary between continental and oceanic crust

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16
Q

continental slope angle

A

about 5 degrees

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17
Q

continental rise + formation

A

accumulated sediment at base of continental slope

formed by rifting as continents split apart

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18
Q

continental rise angle

A

about 0.3 degrees

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19
Q

deep sea fan definition and location

A

turbidity current produce turbidite deposits

forms in the continental rise

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20
Q

accretionary wedge

A

wedge formed as the top plate scrapes sediment off of the subducting plate

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21
Q

active continental margin trench

A

trench between the subducting crust and the continental crust

not always present - full of sediment

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22
Q

active continental margin order from greatest depth

A

oceanic crust
accretionary wedge
continental crust

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23
Q

abyssal plain

A

large flat region of the ocean floor

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24
Q

mid-ocean ridge

A

location where the plate moves apart; creates new ocean floor

(divergent plate boundary)

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25
Q

What percentage of the Earth is made up of mid-ocean ridges

A

20%

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26
Q

origin of mid-ocean ridges

A

volcanic

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27
Q

sea-floor spreading

A

the divergent plates move apart
magma rises to meet the water
the magma cools and forms new seafloor

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28
Q

what rocks are formed at mid-ocean ridges

A

intrusive gabbro
extrusive basalt

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29
Q

sheeted dikes location

A

formed at mid ocean ridges

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30
Q

rift zone

A

a deep rift valley where magma from beneath the Earth’s crust wells up, cools, and is pushed away from the ridge’s flanks

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31
Q

unique (dynamic) features of mid-ocean ridges (5)

A
  1. frequent Earthquakes
  2. hydrothermal circulation
  3. formation of mineral deposits
  4. volcanic eruptions
  5. sulpher based ecosystems
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32
Q

what controls the sea water chemistry at mid ocean ridges

A

hydrothermal circulation

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33
Q

ophiolite

A

when ocean basin closes, oceanic crust gets scraped off and placed on land

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34
Q

moho

A

boundary between Earth’s crust and its mantle

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35
Q

Explain the magnetic anomaly present at mid ocean ridges

A
  1. rocks become magnetized when it cools from magma to lava
  2. It is magnetized to the magnetic field that was present at the time
  3. Earth’s magnetic field reverses N/S periodically
  4. You end up with stripes of alternating magnetism at mid ocean ridges
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36
Q

atolls formation

A
  1. volcano sinks as plates moves away from the mid-ocean ridge + loses its source of magma
  2. coral reefs form on the volcano
  3. volcano continues to sink but reef keeps growing; replacing where the volcano initially was
  4. this leaves a lagoon surrounded by coral
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37
Q

Why does the seafloor get deeper as you move away from mid-ocean ridges

A

The plates cool and contract

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38
Q

VMS

A

volcanogenic massive sulphide deposit; important mineral formed at mid-ocean ridges

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39
Q

terrigenous sediments

A

sand sized particles that originated on the continents but are now sea-floor sediments

40
Q

biogenous sediments

A

shells and skeletons of plankton living near the surface of the ocean but are now sea-floor sediments

41
Q

manganese nodules

A

form on abyssal plains; economically valuable

42
Q

Wegener proof the Pangea once existed (4)

A
  1. fit of coastlines
  2. fossil distribution
  3. ancient mountain belt locations
  4. past glaciation pattern
43
Q

Where do coastlines fit best

A

at the continental shelf

44
Q

What did Wegener think of land bridges + other name

A

stupid. Isthmian links where used to explain how similar fossils could be on continents separated by the ocean

45
Q

tillites

A

distinct rock type formed by glacier movement

46
Q

Wegener’s proof from glaciation patterns

A
  1. tillites found in tropical climates
  2. scratches showed glaciers moving away from coastline (impossible)
  3. You could not argue glaciers were flowing from other locations because glaciers do not flow across oceans
47
Q

Polar fleeing

A

Wegener’s original mechanism for the movement of the continents

Centrifugal forces were responsible.

It was wrong and the reason his theory was initially abandoned

48
Q

What years was Wegener’s theory abandoned

A

1930s

49
Q

What years was Wegener’s theory revived and by what

A

1950s
exploration of ocean floor
paleomegnetism

50
Q

paleomagnetism

A

“fossil magnetism”

51
Q

Explain how paleomagnetism supported Wegener’s theory

A

Rocks become magnetized as they solidify.
You get different angles of magnetism at different location.
The angle of magnetism did not match what the expected angle was.

52
Q

Curie Temperature

A

If above; rocks are no longer magnetized
If below; rocks are magnetic

580 degrees C

53
Q

What angle will a compass be at the North Pole

A

vertical

54
Q

what angle will a compass be at the Equator

A

Horizontal

55
Q

changing pole theory

A

the theory that the reason rocks where having magnetism directions that did not match their location was because of a changing magnetic pole

56
Q

polar wandering path support for Wegener

A
  • look at rocks with diff. ages + see they travel along a path
  • path is different at every continent (disproves changing pole theory)
  • if was allow continents to move, the pole does not change (proves moving plates)
57
Q

Seafloor Spreading hypothesis

A

plates move apart at ridges
upwelling mantle creates new seafloor
trenches are where material sank back into the interior

This cycle is mantle convection

58
Q

Harry Hess

A

proposed and found proof for the seafloor spreading hypothesis

found mid-ocean ridges

59
Q

geomagnetic reversal

A

Earth’s magnetic direction changes chaotically

60
Q

How does geomagnetic reversal support Wegener’s theory

A
  • magnetic patterns were measured across sea floor
  • they had a strong/weak pattern
  • both sides of a mid-ocean ridge were a symmetric patter (evidence for sea floor spreading)
61
Q

When was the last geomagnetic reversal

A

780 000 years

62
Q

Why did researches find that the seafloor has a strong/weak magnetic pattern

A

Rocks with normal polarity appeared as strong magnetic intensity

Rocks with reverse polarity appeared as weak magnetic intensity (formed when the Earth’s magnetism was flipped)

63
Q

Expanding Earth Theory

A

Incorrect. Earth is getting bigger which causes continents to crack and get pulled apart

64
Q

Continental Drip Theory

A

Incorrect/Joke: The continents are somewhat upside down water droplet shape. Continents are dripping northwards on the globe

65
Q

are continental plates felsic or mafic

A

felsic

66
Q

are oceanic plates felsic or mafic

A

mafic

67
Q

Plate tectonics theory

A

Lithosphere is strong outer layer
asthenosphere is weak under layer
lithosphere is broken into a set of rigid plates that move
plates contain both oceanic and continental crust

68
Q

mid-ocean ridge speed

A

1-20cm per year

69
Q

continental rift

A

separating continental crust;
will eventually split into two plates
then fill with water and turn into a linear sea

70
Q

What is the oldest seafloor

A

180 million years

71
Q

failed rift

A

a continental rift does not finish separating (we don’t know why)

72
Q

Keweenawan Rift

A

failed rift extending from Lake Superioir to Kansas

73
Q

Examples of oceanic-continent convergent plate boundaries

A

Cascadia, Andes

74
Q

Examples of oceanic-oceanic convergent plate boundaries

A

Western Aleutians (Alaska)

75
Q

Examples of continent-continent convergent plate boundary

A

Tibetan Plateau

76
Q

Depth at which water released from the subducting oceanic plate causes the formation of volcanoes

A

100km

77
Q

How does angle of subduction angle affect how far into the continental crust volcanoes are formed

A

When the subducting oceanic plate reaches 100km, volcanoes form.

If the angle is greater, the volcanoes will form closer to the subduction trench

If the angle is lesser, the volcanoes will form farther from the subduction trench

78
Q

What is the thickness of the crust at continent-continent convergent boundaries

A

> 80km

79
Q

What do continent-continent convergent plates form

A
  • thickened crust and major mountain belt
  • no volcanoes because of no subduction occurring
80
Q

what causes continent-continent convergent boundaries to have partial melt

A
  • higher quantities of radioactive materials that release heat

This partial melt causes flow

81
Q

George Airy

A

If you have much mass above the Earth’s surface, the mantle underneath will have a higher density which counteracts any gravitational effects of the large mass.

82
Q

Examples of transform plate boundaries

A

San Andreas Fault, North Anatolian Fault

83
Q

Relationship between transform faults and mid-ocean ridge

A

transform faults connect mid-ocean ridges.

84
Q

How do Earthquakes support the Plate Tectonic Model

A

Divergent - occur in a narrow and only along the plate boundary area

Convergent - occur in a broad area along the subducting plate

85
Q

How does the age of the seafloor support the plate tectonic model

A

As you move away from the mid-ocean ridge, the seafloor gets older

They used fossils to discover this

86
Q

How do hotspots/mantle plumes support the plate tectonic model

A

as the plume moves, volcanoes are created and alive while the plume is beneath them

when the plate moves, the plume moves with it and the existing volcano loses its magma source

87
Q

How does GPS support the plate tectonic model

A

we can measure the real movement of plates

88
Q

What drives plate motion

A

mantle convection

89
Q

mantle convection

A

magma rises because is it hot then falls when it cools

90
Q

what mechanisms (based on mantle convection) produce forces that move the plates

A

mantle traction/drag
ridge push/sliding
slab pull

91
Q

mantle traction/drag

A

convection current carries plate as it flows

92
Q

ridge push/sliding

A

mid-ocean ridge creates a slight hill that plates fall down

93
Q

slab pull

A

as the plat subducts, it pull the entire plate

94
Q

volcanic arcs are associated with

A

ocean-ocean convergent boundaries

95
Q
A

EAS 210 (20 decks)

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