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EAS 201 > Ch 5: Tectonics > Flashcards

Ch 5: Tectonics Flashcards

1
Q

Divisions of the Earth by physical properties

A

Atmosphere, hydrosphere, lithosphere, asthenosphere, mesosphere, outer core, inner core

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2
Q

Divisions of the Earth by chemical compositions

A

Atmosphere, hydrosphere, crust, mantle, core

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3
Q

Continental crust is:

A

less dense rock, more Si and Al

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4
Q

Oceanic crust is:

A

more dense rock, more Fe and Mg

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5
Q

The three lithospheric plate boundary types are:

A

Divergent (spreading centres), Convergent (Subduction zones), Transform fault (transcurrent plate)

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6
Q

Divergent boundaries are:

A

Rifts and ridges

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7
Q

Characteristics of Divergent boundaries

A

marked by a ridge, rises 2-4 km above surrounding ocean floor, submarine volcanoes and earthquake activity, forms new lithosphere

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8
Q

Convergent Boundaries are:

A

convergent boundaries

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9
Q

Characteristics of Convergent boundaries

A

Linear topographic features that parallel boundary: deep ocean trench, volcanic arc (islands), orogens (mountain belts).
Abundant seismicity and magmatic/volcanic activity.(Benioff zone)

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10
Q

Define Orogens

A

belt of Earth’s crust that forms mountains

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11
Q

Define Benioff zone

A

A dipping planar (flat) zone of earthquakes that is produced by the interaction of a downgoing oceanic crustal plate with a continental plate.

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12
Q

Transform fault boundaries are:

A

transcurrent plate boundaries

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13
Q

Characteristics of Transform faults

A

variable length/size. Many smaller transform faults along mid-ocean ridges. Larger ones cut continental crust. Frequent shallow earthquakes. Sheering motion, lateral motion.

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14
Q

Example of transform fault:

A

San Andreas Fault: dextral (right lateral).

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15
Q

Plate movement velocities can be measured by:

A

Magnetic anomalies, GPS, re-occupied sites (via lasers)

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16
Q

Magnetic anomalies & plate movement

A

magnetic anomalies help predict plate movement velocities.

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17
Q

GPS and plate movement

A

network of satellites, provides very accurate locations

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18
Q

Re-occupied sites and plate movement

A

reoccupying sites over a period of years. Measures plate movement directly, usually via laser

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19
Q

Pangaea time

A

palezoic - mesozoic

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20
Q

Rodinia time

A

protozoic

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21
Q

Mechanism of plate movement

A

convection, gravity, wilson cycle, lithosphere drag

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22
Q

Convection & plate movement

A

hot rock rises and cool rock sinks

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23
Q

Lithosphere drag:

A

drives convection, as the plate is forced downwards, the heaviness of the plate helps draw the rest of the plate downwards

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24
Q

Debate:

A

is convection causing drag or is drag causing convection

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25
Q

Gravity

A

another plate movement mechanism, aids lithospheric drag

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26
Q

Paleomagnetism

A

pre-1960s geophysicist argued against continental drift. They validated plate movement using magnetism

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27
Q

Earth’s magnetic field

A

Earth behaves as if there is a bar magnet in the core

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28
Q

Direction of the magnetic field

A

Inclination (steepness), declination (direction).

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29
Q

Inclination indicates

A

indicates distance from pole

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30
Q

Declination indicates

A

indicates direction to pole, orientation

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31
Q

Remanent Magnetism

A

some ancient rocks were magnetized when formed. If age of rocks is known, remanent magnetism indicates the ancient location of the pole.

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32
Q

Silt orient themselves…

A

according to compass direction. Only if not disturbed.

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33
Q

Polar wandering

A

pole appears to have wandered through time.

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34
Q

APWP

A

apparent polar wander path. Samples taken off one lithospheric plate, either the pole moved or the continent moved.

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35
Q

Magnetic reversals:

A

N and S magnetic poles appear to have flipped through time. Reversed polarity in the inner core vs outer core. Outer attempting to invade the inner.

36
Q

Reversal timescale

A

time scale of magnetic reversals, well established on land, relative dating technique

37
Q

Linear magnetic anomalies

A

Field sightly stronger or weaker than normal. What the magnetic was when the rocks were formed

38
Q

Surveys in the oceans show:

A

central positive anomaly, symmetric pattern.

39
Q

Sea-spreading hypothesis:

A

magnetic anomalies result from remanent magnetism acquired during spreading of ocean-floor while magnetic reversals occured

40
Q

Vine-Matthews hypothesis

A

magma would come to the surface and solidify with the current magnetic form

41
Q

Useful for mapping ocean:

A

match magnetic anomalies with reversal history, measure growth rates, new ocean floor is found along mid-ocean ridges

42
Q

Define Focus

A

(hypocentre) point of rupture on the fault. Energy can be spread in all directions, 360

43
Q

Define Epicentre

A

point on the surface directly above the focus. Energy moves only sideways in all directions

44
Q

majority of Earthquakes happen

A

majority of earthquakes happen within 70 km of the surface, more within 12 km.

45
Q

Most earthquakes are on the _____ instead of the _____

A

subduction zone instead of the divergent zone

46
Q

Measuring ground shaking

A

Ancient seismic detector, traditional seismograph, seismometer.

47
Q

Magnitude:

A

amount of total energy released by an event.

48
Q

Richter:

A

first values after an earthquake, at the epicentre.

49
Q

Moment:

A

more accurate, later will be the official measurement, measures energy at the focus

50
Q

Intensity

A

qualitative description, strength of ground shaking at a point. Depends on many factors

51
Q

Seismic waves

A

Body waves or surface waves

52
Q

Body waves: P-waves

A

From focus, primary waves, similar to sound wavs,
compression and expansion (dilation). Vibration direction parallel to propagation. Pass through solid, liquid or gas.
3-7 km/s in the crust

53
Q

Body waves: S-waves

A

From focus, secondary waves. Shear waves, vibration direction perpendicular to propagation, solids only. 1.5-5 km/s in the crust

54
Q

Surface Waves:

A

surface waves on land, form when body waves reach the surface, slower but larger than body waves, cause most damage

55
Q

Further away from the source of the energy, the further…

A

the S-waves from the P-waves

56
Q

Tsunami waves

A

Surface waves on the ocean, due to water displacement. Not tidal waves

57
Q

Tsunami wave heights

A

low on open ocean, in shallow water, slow down and get higher

58
Q

Origin of earthquakes

A

results from elastic strain followed by brittle fracture/failure.

59
Q

Where do earthquakes occur

A

in cold rocks, typically less 70 km deep, most are within 12-15 km. Lithosphere

60
Q

More strain =

A

more probability of having an earthquake

61
Q

Finding the distance from an earthquake

A

distance of focus is found from interval between P and S arrival

62
Q

Earthquake and the interior of the Earth

A

P waves from major earthquakes, redirect by something dense in the core, can determine the boundaries of the core.

63
Q

Evidence from P-waves

A

evidence from core, P-waves are refracted by something dense in the core, acts as lens. Can determine the boundaries of the core

64
Q

Interior: evidence from S-waves

A

S waves from major earthquake

65
Q

S-waves and the core

A

S-waves are blocked by liquid core, evidence for core. S-wave shadow zones.

66
Q

Distortion of plates

A

Large scale movement stresses material. This results in folds and breaks and extension and compression of crust.

67
Q

Define isostasy

A

buoyancy of the lithosphere

68
Q

Define orogenesis

A

mountain building process

69
Q

Geophysics used what to map large scale changes

A

distortion of plates

70
Q

Gravity _____ slightly from place to place on the Earth

A

varies

71
Q

Gravity measurements are made with a

A

gravimeter

72
Q

Gravity is affected by

A

density, composition, altitude, thickness

73
Q

Gravity is slightly stronger over

A

dense rocks

74
Q

Gravity is weaker over

A

thicker units of less dense rocks

75
Q

Gravity and crustal thickness

A

many negative gravity anomalies are due to thick, low-density crust

76
Q

Plate reconstructions

A

Rifting and spreading

77
Q

Rifting

A

may eventually lead to opening of a new ocean

78
Q

Ancient rift

A

rifting of an ancient continent led to opening of Atlantic ocean

79
Q

Mountain Belts (orogens)

A

Plates are not perfectly rigid, large zones of distortion where continental crust is involved in subduction.l

80
Q

Mountain belts typically

A

form high mountain ranges (orogens) –> crustal thickening

81
Q

Rocks within orogens are…

A

crumpled (deformed)

82
Q

Cordilleran orogens

A

Continental and oceanic crust above a subduction zone

83
Q

Collision orogens

A

collision orogens form when two continents collide, isostasy prevents subduction of lower density crust

84
Q

Subduction zone: oceanic and oceanic merging

A

volcanic islands

85
Q

Subduction zone: oceanic and continental

A

cordilleran orogens, classic

86
Q

Subduction zone: continental and continental

A

collision orogens

EAS 201 (11 decks)

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