Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

ES2001 > Geodynamics > Flashcards

Geodynamics Flashcards

1
Q

What is geodynamics?

A

The study of the large scale evolution of the solid earth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is geodynamics?

A

The study of how the Earth operates thermo-mechanically on a large scale

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is Earths first order shape?

A

An oblate spheroid
21.38km thicker at equator than the poles (radius) (equatorial bulge)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is earths second order shape?

A

The geoid - the gravitational equipotential surface relative to mean sea level

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What does gravitational anomalies suggest?

A

That earth is not homogeneous

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are geoid anomalies?

A

Large scale variations in earths structure as reflected in density

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are equipotential surfaces?

A

Surface that is always perpendicular to the gravitational potential direction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What makes a positive and negative geoid anomaly?

A

Density excess= +ve anomaly
Density deficit= -ve anomaly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Why is it useful to look at Geoid anomalies?

A

Tells is about earths deep structure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How do we know that geoid anomalies are caused by deep earth?

A

Lack of correlation between geoid and the continent ocean transitions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is earths third order shape?

A

Topography - land surface above or below the ocean
Bimodal planet - oceans -4km, continents +8km
Largely caused by tectonics

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are the compositional layers of earth?

A

Crust (accessible)
Mantle (sampleable)
Core (inaccessible)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the mechanical layers of earth?

A

Lithosphere - rigid layer, crust and top mantle
Asthenosphere - very ductile layer, mantle
Lower mantle - moderately ductile, mantle
Outer core - liquid
Inner core - solid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What allows the presence of a dynamic earth?

A

Combination of different density and strength is a major control on plate tectonics
(Mechanically layered)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the crust made out of?

A

Oceanic (basalt)
Continent (andesite)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How thick is the crust?

A

30-60km

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How thick is the mantle?

A

2850km

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How thick is the core?

A

3480km

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What does adiabatic mean?

A

A process in which het and mass is conserved.
Temperate increases and decreases as pressure changes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is the density of the crust?

A

2900kg/m3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is the density of the upper mantle?

A

4400kg/m3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is the density of the outer core?

A

9900kg/m3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the density of inner core?

A

12800kg/m3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is the density for the average earth?

A

5500kg/m3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What are primary controls on geodynamic processes?

A

Viscosity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is the viscosity for the outer core?

A

Between water and honey

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What are plates?

A

A discrete segment of lithosphere that behaves as a single unit and has a largely coherent vector
Crust and the upper part of the mantle
Oceanic crust or oceanic and continental crust

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Where does the lithosphere sit?

A

Floats isostatically on the weak low viscosity layer (asthenosphere)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What are the physical attributes of the asthenosphere?

A

Flows as a solid
Low viscosity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What is MOHO?

A

Mohorovicc discontinuity between crust and mantle due to composition and density differences

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

How does the lithosphere transfer heat?

A

Conduction - transferred by direct contact between molecules ie spoon getting hot in tea

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

How does the asthenosphere transfer heat?

A

Convection - transferred by the movement of fluids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

How does the continental crust behave?

A

Thicker
Lower part behaves ductile-y

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What is stronger: oceanic or continental lithosphere?

A

Oceanic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

What are the two theories for isostatic equilibrium?

A

Pratt theory - blocks of same mass, different densities. Explains oceans vs continents
Airy theory- blocks of same density, different masses. Examples continents

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

What makes up a normal isostatic equilibrium?

A

Continents 35km felsic crust, 65km mantle, 700m above sea level
Oceans 7km mafic crust, 93km mantle, 4.5km below sea level

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

What is abnormal isostatic equilibrium?

A

Continents 70-80km felsic crust (Himalayas), 20km felsic crust
Oceans 14km mafic crust

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

How many plates are there today?

A

7-8 major plates
Lots of microplates

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

What are the fastest moving plates?

A

Australian-Indian plate
Pacific plate
Nazca plate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

How has the Indian plate changed from 50Ma to today?

A

Slowed from 200mm/yr to 35mm/yr

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

What are the three types of plate boundaries?

A

Divergent - plates moving apart, new ocean formation
Convergent - plate collision, subduction or orogeny
Transform - lateral, extension or compression

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

What happens at an ocean-ocean divergent boundary?

A

Seafloor spreading

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

What happens at continent-continent divergent boundaries?

A

Rifting

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

What happens at ocean-ocean and ocean-continent convergent boundaries?

A

Subduction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

What happens at continent-continent convergent boundaries?

A

Continental collision

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

What are features at divergent margins?

A

Mid ocean ridges - oceanic divergence, mantle upwelling, decompression causes melting, basaltic ie Atlantic pacific
Continental rifting -continental divergence forms rift valleys, may evolve to new ocean floors, graben structures, high heat flow, volcanic and geothermal activity, mafic igneous rocks ie East African rift

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

What evidence do we have for seafloor spreading?

A

Mapping of seafloor mountain ranges and trenches
Magnetic reversals in seafloor - symmetrical stripes either side of the mid ocean ridge. Basalt cools forming magnetite that locks in the ambient magnetic field at that time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

What is the Curie point?

A

570 degrees c

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

What does the width and height of magnetic stripes tell us?

A

Width = rates of spreading
Height = dependant on age of lithosphere and rate of spreading

50
Q

What are the characteristics of transform boundaries?

A

Associated with ocean spreading
Represent offsets of the mid ocean ridge - can see the offset of magnetic stripes
Have compression or extension on continents

51
Q

Why do MOR transform faults occur?

A

Spherical planet therefore plates are shallow bowl shaped
Plates rotate around a pole of rotation (POR)

52
Q

What does the pole of rotation mean for spreading rates?

A

Further from the pole linear spreading rates must be faster

53
Q

Give an example of a continental transform boundary.

A

San Andreas fault
Alpine Fault, NZ

54
Q

What is transpression?

A

Compressional force makes narrow linear mountain belts
Ie southern alps, NZ

55
Q

What is transtension?

A

Extensional force makes narrow linear basins
Ie Death Valley, CA

56
Q

What happens in ocean-ocean subduction?

A

Older and colder plate subducts under the other
Subducted plate is recycled
Produces deep sea trench’s, adjacent ranges of folded and faulted rock, chains of island arc volcanoes
Ie Indonesian volcanic arc

57
Q

What happens during ocean-continent subduction?

A

Dense oceanic plate under-rides buoyant continental plate
Causes magmatism and creation of new continental crust
Development of mountain chains
Closes ocean basins
Ie Himalayas , alps
Eventually leads to continent-comtinent collision which makes larger continents

58
Q

What is the Wilson cycle?

A

Cycle of creation (ocean spreading) and destruction (subduction)

59
Q

What drives plate tectonics?

A

Slab pull - sinking of old dense ocean lithosphere into the mantle
Ridge push
Plates with largest % of boundary of subduction zones tend to move fastest

60
Q

what are the main consequences of plate tectonics?

A

metamorphism

61
Q

how can you use metamorphism to fingerprint tectonic processes?

A

different plate tectonics settings involve different degrees of burial and heating of rocks

62
Q

what is obduction?

A

where ocean crust is pushed on top of continental crust instead of under it, forming an ophiolite

63
Q

what is hydrothermal metamorphism?

A

interaction of hot basalt magma with cold magma

64
Q

what are spilites

A

hydrated basalt

65
Q

what is metasomatism?

A

metamorphism by fluid changing the rock composition

66
Q

what does hydrated basaltic crust promote?

A

promotes oceanic slab melting in subduction zones with the forms volcanoes

67
Q

what are black smokers?

A

underwater vents that are direct evidence and consequence of hydrothermal metamorphism. gives of Au, Ag, Pb, Zn, Cu
VMS ore deposits

68
Q

what does hydration vary with?

A

depth
can reach all the way through the crust

69
Q

what is earth’s geologic water cycle?

A

water is brought into the crust at MOR’s and via volcanoes
water is returned to mantle at subduction zones
mantle is made of anhydrous minerals, still contain trace of water
more water in mantle than seas

70
Q

what are arcs?

A

way new continental crust is made
driven by magmatism

71
Q

what do ocean-ocean arcs make?

A

makes island arcs

72
Q

what do ocean-continent arcs make?

A

continental volcanic arcs and mountains on the continental margins ie Andes

73
Q

where does subduction metamorphism occur?

A

in the subduction zone and in the arc and back arc environment

74
Q

what causes high pressure-low temperature metamorphism?

A

ocean subduction zones

75
Q

give examples of metamorphism in subduction

A

Glaucophane - blue amphibole mineral found in blueschist metamorphic rocks
Omphacite - green pyroxene found in very high pressure metamorphic rocks

76
Q

why does subduction result in volcanism?

A

water release from metamorphism of oceanic crust
water lowers the melting temperature

77
Q

when is water added to basalts?

A

typically when ocean crust is first formed and hydrated at the mid ocean ridges (hydrothermal metamorphism

78
Q

why are arcs not made of basalt?

A

more granitic or andesitic
fractional crystallisation = more felsic melt
partial melting

79
Q

why is subduction driven by slab pull?

A

formation of eclogite - negatively bouyant

80
Q

where can we see that ocean crust looks like?

A

obduction zones ie spreading above a subduction zone, sole formation above old crust, final emplacement onto continent

81
Q

what do mountains represent?

A

where crust/lithosphere has been thickened, sometimes to more than double its normal

82
Q

what are mountains controlled by?

A

isostacy (iceberg effect)
ie higher the mountain=thicker the crust

83
Q

what happens to the crust when it forms mountains?

A

interally deforms during continent-continent collision

84
Q

why does the continental crust deform?

A

weaker than oceanic crust

85
Q

what are orogens?

A

mountain ranges caused by accretion/collision

86
Q

how do continents grow?

A

by having arcs added to its exterior

87
Q

name two orogens in todays earth

A

cordilleran orogen (west coast of americas)(rocky mountains)
alpine-himalayan orogeny (asia mid east europe

88
Q

what formed the cordilleran orogeny?

A

accretionary orogeny
continent built up by accreting arcs and sediments
mountains at the edge of the continental plate

89
Q

what is the tasmanides?

A

an ancient accretionary system ~550Ma
australia, new zealand, antarctica

90
Q

what is zealandia?

A

a lost continent
accreted continent that is now underwater, sank with australia and NZ separated

91
Q

where do we find mountain belts?

A

in the middle of new combined continents ie Himalayas
linear belts

92
Q

why does the eurasian plate take up most of the deformation caused by the continent-continent collision with india?

A

more buoyant and weaker

93
Q

why is mountain building asymmetric?

A

subduction is one sided
different continental plates have different structure and strength
mountains are typically eroded on one side

94
Q

what happens during slab breakoff?

A

section of slab breaks off, remaining slab becomes more buoyant and is exhumed and thus rises
ie rocks in the alps that have been down to 100km

95
Q

what does blueschist-eclogite record?

A

the transition from subduction to collision
expected in high dP/dT

96
Q

what does greenschist-amphibolite-granulite record?

A

main crustal thickening during ongoing collision ie barrow sequence

97
Q

why is there a clockwise P-T path?

A

fast burial -> burial slowing down ->retrograde -> fast burial

98
Q

what controls the height of mountain belts?

A

orogenic collapse
erosion

99
Q

what happens in orogenic collapse?

A

mountains rapidly thickening but eventually become too big to support themselves.
mountain weight overcomes rock strength = normal faulting
deep hot rocks flow out from beneath the mountain = no support

100
Q

why does earth have an imperfect record?

A

only have a fragmentary history
further from today = less certainty in predictions

101
Q

what are continents defined by?.

A

defined by todays plate boundaries but were created by ancient plate boundaries

102
Q

what are continents composed of?

A

big blobs of archean crust (cratons) glued together by narrow belts of younger Proterozoic rocks (old orogens or mobile belts, forming shields

103
Q

what are narrow younger belts dominated by?

A

deeply eroded metamorphic rocks (old mountain chains/orogens therefore old accretionary/collisional boundaries)

104
Q

what is a suture?

A

where two continents/arcs are collided/accreted form a larger continent

105
Q

what are models of continental age based on?

A

dateable rock units i.e. shales, zircons

106
Q

what percentage of exposed crust is archean?

A

5%

107
Q

what are complexities in dating the crust?

A

old crust buried by thick sedimentary packages
making vs reworking of rock

108
Q

how do we know when there was continental collision?

A

metamorphism = collision
zircons = magmatism and metamorphism
not continuous growth = sampling bias

109
Q

what are supercontinents?

A

discrepancy
involves all or nearly all of the continental masses
making up a significant part of the continental mass

110
Q

give examples of supercontinents

A

gondwana
pangea
rodina

111
Q

what do we rely on to reconstruct continents?

A

rock distributions and geomagnetics

112
Q

when was gondwana?

A

750-550Ma

113
Q

when was pangea?

A

450-320Ma

114
Q

what do we expect future continents to look like?

A

atlantic ocean to keep opening, closing of the mediterranean, suturing of asia, africa and america

115
Q

The Tasmanides is an ancient ________ system that formed on the coast of the ancient supercontinent _________.

A

Accretionary system
Supercontinent Gondwana

116
Q

The Himalayan mountain chain is a ______ tectonic setting that formed when the ______ plate collided with the ________ plate. The oceanic crust of the _______ plate was subducted under the ________ plate prior to collision.

A

Colllisonal
Australian-Indian
Eurasian
Australian-Indian
Eurasian

117
Q

What is the main force driving subduction?

A

Slab pull

118
Q

Give examples of island arcs

A

Indonesia
Japan

119
Q

What layers of the earth are liquid?

A

Outer core

120
Q

True or false:
The Eurasian plate is entirely composed of continental crust

A

False

ES2001 (9 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions