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Tectonic plates Flashcards

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1
Q

Continetal drift

A

Continents move by sea floor spreading by transform faults

subduction and plate tectonics moving in that direction
Alfred wegener

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2
Q

evidence for continental drift

A

the fit
Places that glaciers are made
Fossil organisms
Rock type + rock structure similarities
Paleoclimates preserved in rocks

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3
Q

Continental fit

A

continental shelf has perfect fit

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4
Q

glacial evidence

A

bottom parts of South America, Africa, India and Australia have Permian glacial till
(Sediment deposit from Permian glaciers)
Once apart of Antarctica

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5
Q

Paleoclimatic evidence

A

Older climate clues show up in Pangea
Pangea over the Permian South Pole (antartica) = tropical coals, reefs
Subtropical deserts, evaporites

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6
Q

Fossil evidence

A

same fossils found on seperated landmasses

Mesosaurus - freshwater reptile (africa and south America )
Glossopteris- subpolar plant with heavy seeds in ALL southern continents

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7
Q

matching geology

A

Across Atlantic
South America and africa- Archean crust, Proterozoic mountain belts
North America and africa- Appalachians, Caledonides

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8
Q

criticisms of drift

A

no mechanism for moving

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9
Q

Earth’s magnetic field

A

N and S ens are tilted 11 degrees from axis of rotation

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10
Q

Rocks in magnetic field

A

some iron minerals align
Preserves magnetic info

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11
Q

magnetic poles

A

magnetic North and south
Move constantly but stay in geographic pole areas (axis)

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12
Q

Declination

A

Horizontal Angle between magnetic north and true north
(180 degrees)
longitude

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13
Q

Inclination

A

Latitude (horizontal) —-
Positive inclination- points into earth
Negative- up to sky
0 at Magnetic equator
90 at magnetic poles

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14
Q

Magnetic overprinting (high temp- 350-550 C)

A

Atoms increase thermal enegry
Dipoles random
No magnetic signature

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15
Q

Magnetic dipoles

A

magnet bar- positive and negative side

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16
Q

magnetic overprinting (Below 350-550 C)

A

atoms slow down thermal enegry
Dipoles align with earth’s field
Permanently magnetizes material

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17
Q

magnetic overprinting (iron minerals)

A

lock in earth’s magnetic signal at the time its formed
Preserves de/inclination
Can be used to determine lat/long

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18
Q

paleomagnetism

A

Fossil magnetism measured
Ancient rocks reveal lat/longitudes

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19
Q

polar wander

A

Magnetic poles wandered in past-> misaligned paleomagnetism in ancient lavas on present field
Each

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20
Q

Continetal polar wander

A

each has seperate polar wander path that aligns when continents are assembled In Pangea
Eurasia and North America paths join together when in Pangea
Continetnest just moved, not the poles themselves

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21
Q

Apparent polar wander

A

Continetnest just moved, not the poles themselves
Evidence of drift

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22
Q

polar wandering curves

A

magnetic pole is fixed at 90 degrees bu when continents moves, the apparent MP becomes displaced at same angle

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23
Q

Ocean floor discoveries

A

Sonar
Deepest parts are near land
A Mountain range in every ocean basin
Submarine volcanos form lines across ocean floors

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24
Q

ocean floor modern views

A

mid-ocean ridges - mountain/ volcano ranges made by divergent plate boundaries, rising magma to make crust
Trenches- very deep gaps form subduction
Fracture zones- mountain lines of cracks

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25
subduction
2 plates converge and one overtakes the other
26
transform fault (crack)
Plates grind horizontlally against each other at the crack= earthquakes
27
New observations on oceanic crust
sediment covered Thickest near continents Thinnest at mid-ocean ridge Crust- mafic (basalt + gabbro) No granite or metamorphic rocks High heat flow at mid ocean ridges Belts of earthquakes
28
Sea earthquakes
ocean fracture zones Mid ocean ridge axes Deep ocean trenches
29
Sea floor spreading
harry hess- theory Rising mantle erupts at mid ocean ridges New crust moves away from here, gathering sediment Trenches= sea floor goes back into mantle Continental drift mechanism
30
magnetic anomalies in ocean crust
magnetism = varies perpendicular to MOR variations are + and - anomalies Anomalies= align as linear belts to MOR
31
magnetic reversal
Polarity reverses from N magnetic to S geographic pole Lava flow layers show this, and mark time (rapid) Explains Anomalies
32
magnetic reversals cont
radioactivity allows age of rock absolute to be dated Resversals occur every 500-700 chrons Subchrons= shorter durations (200)
33
sea. Floor spreading proof
anomalies are symmetric across MOR Positives- normal polarity - crus Negatives- reversed polarity crust - Anomalies mimic lava flows In dried stripes at MOR - Ocean crust spreads away from MOR
34
cooled basaltic lava
reversals are recorded here (striped lava layers)
35
ages of crust samples (60s)
they increase away from MOR Are mirror images across MOR
36
Plate. Tectonics
outer shell of earth Hess/ dietz (60s) sea floor spreading
37
Tectonic mechanism
All rock types Distribution of earthquakes and volcanoes Origins of continent and basins Distribution of fossil plants + animals Genesis and destruction of mountain chains Continetal drift
38
Lithosphere
crust adn upper mantle Moves over asthenosphere Bends elastically, then asthenosphere flows plastically underneath
39
oceanic lithosphere
basaltic crust 7- 10 km thick Heavier (more dense) Less buoyant - sinks lower
40
continental lithosphere
Granitic crust 35-40 km thick Lighter (less dense) More buoyant - floats higher
41
plate movmenet
continuously at rate of 1 to 15 cm/yr Rapid geologically Interact along their boundaries
42
plate boundaries
20 tectonic plates Where they meet - earthquake concentrations - interiors have no earthquakes
43
continental margins
land meets ocean Margins near plate boundaries= active Far away = passive
44
Active margins
Where land meets ocean being near plate boundaries
45
passive margin
where land meets ocean far away from plate boundaries - gets thin towards sea - becomes oceanic crust - traps eroded sediment - becomes continental shelf
46
Divergent boundaries
moving apart Lithosphere thickens away from MOR axis Sea floor spreads-> plates spread
47
convergent
move towards each other Become subdued (subduction)
48
Transform boundary
slide sideways against each other Transform fault Nothing created or destroyed
49
divergent boundaries creation
sea floor spreads-> plates spread Magma fills up gap Magma cools and adds to each plate
50
sea floor spreading progression stage 1
stage 1- MOR forms - ocean not wide enough yet - long thin ocean basin of young ocean crust Red Sea
51
sea floor spreading stage 2
ocean begins to wide New sea floor added at MOR Continents spread more Greenland and North Atlantic
52
sea floor spreading stage 3
mature, wide ocean basin of young Farther from central ridge= linear age increase Edge of basin= oldest Close to ridge= youngest Atlantic Ocean
53
MOR
linear mountain ranges in ocean basins
54
Mid-atlantic ridge
snakes N-S through entire Atlantic Ocean Above abyssal plains Axial rift valley = 500 m deep 10 km wide Symmetric Site of eruptions
55
MOR
sea floor spreads opens axial rift valley Rising asthenosphere melts into mafic magma Which turns to oceanic crustal rock - - pillow basalt - dikes - gabbros
56
pillow basalt
magma quenched at sea floor
57
dikes
preserved magma conduits
58
Gabbro
deeper magma
59
Black smokers in MOR
water entering fractured rocks get heated by magma -> dissolves minerals and come out, reaching sea and precipitating quickly
60
Ocean crustal age
Newest= closest to ridge axis Oldest= far edge of basin
61
ocean lithosphere
hot asthenosphere at base of MOR Old ocean crust moves away from its heat source-> cools, becomes denser, and slowly sinks as thick sediment
62
convergent boundaries - subduction
recycles oceanic lithosphere Balanced by sea floor spreading Maintains constant circumference
63
subduction
old oceanic lithosphere is more dense than mantle Flat oceanic plate doesnt subduct easily Once bent downward, leading edge sinks like anchor
64
convergent boundaries
subducting plate sinks at 45 degrees Plate descent -> Wadati-Benioff earthquakes Mineral transformations Far from trench = deeper earthquake (660 KM)
65
Subducted plate
goes past earthquake limit Lower mantle= plate graveyard
66
Accretionary prisms (subduction)
Deformed sedimentary wedge during convergence Scraped onto overriding plate Above sea leve= Olympic peninsula, Taiwan
67
volcanic arc (subduction)
Magma burns through overriding plate , creating chain of volcanoes Falling plate partially melts at 150 km deep Arc type= continental crust= continental arc Oceanic crust = island arc
68
Back-arc basin (subduction)
Marginal sea behind arc forms between island arc and continent Offshore subduction traps piece of crust or stretches to make new spreading ridge
69
transform boundaries
continetal transforms- chop continental crust. San Andreas fault
70
triple junctions
places where 3 plat boundaries coincide Rift and 2 spreading ridges Multiple boundary combinations Change overtime
71
Hot spots
volcanic plumes with no tectonic plates Far from plate boundaries Mafic magmas from lower mantle Tattoo overriding plates with volcanoes
72
Hot spots + sea floor
pokes through overriding plate Builds above sea level Plate motion pulls volcano off plume -> goes extinct and erodes, creates guyot Makes sea floor spread
73
hot spots age
Seamounts age away from original hot spot rate of plate motioN marked by age change Line of seamounts = direction of plate motion
74
Tectonic boundaries evolve
Change overtime geologic time Oceanic —- Made at MOR centers Destroyed at subduction zones Continetal —— Torn apart at rifts Joined during collision
75
Continetal rifting
Lithosphere- stretches and thins Upper crust flats Lower crust flows Asthenosphere melts Melt erupts All leads to full sea floor spreading
76
Continental rifting examples
East africa-Arabian plate rifts from African plate Rift-> sea floor spreading in: Red Sea Aden gulf East African rift- thinned crust, elongated trough Volcanoes
77
Plate collision
subduction consumes ocean basins Can occur with island arc Causes ocean to close Buoyant (float) cont crust does not subduct Mountains uplift after subduction finishes
78
Moving mechanisms
convection in asthenosphere adds or subtracts Ridge-push- elevated MOR pushes lithosphere away Slab-pull- gravity pulls subducting plate downward
79
plate velocities
Mapped by using fixed mantle spot to plot motion Measure ig volcano age/ distance along a hot-spot track GPS using satellites
80
earth movmenet
mantle transfers to surface and back down again
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