CHPTR 11/12 Plate Tectonics Flashcards
1
Q
youngest part of the Earth
A
ocean floors
2
Q
plumb line
A
rock on string - earliest method to map sea floor
3
Q
old sonar
A
map time of the sonar wave to reach the bottom and then bounce back
4
Q
modern sonar
A
multibeam - sonar obtains a profile of a narrow section of seafloor every few seconds
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)
6
Q
geoid
A
round shape that models the Earth’s mean sea level and defines zero elevation.
Irregular surface
7
Q
geoid low
A
mass deficit (valleys)
8
Q
geoid high
A
excess mass (mountain)
9
Q
continental margins + types
A
transition from continental crust to oceanic
passive and active
10
Q
passive margin
A
change from continental crust to oceanic crust on same tectonic plate
11
Q
active margin
A
plate boundary where one plate subduct below another
(change from continental crust to oceanic crust on different tectonic plates)
12
Q
deep ocean basin
A
- trenches: formed by subduction
- abyssal plains: between trench and mid ocean ridge
- seamounts: extinct volcanoes
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)
14
Q
continental shelf
A
flooded extension of the continental crust
15
Q
continental slope
A
boundary between continental and oceanic crust
16
Q
continental slope angle
A
about 5 degrees
17
Q
continental rise + formation
A
accumulated sediment at base of continental slope
formed by rifting as continents split apart
18
Q
continental rise angle
A
about 0.3 degrees
19
Q
deep sea fan definition and location
A
turbidity current produce turbidite deposits
forms in the continental rise
20
Q
accretionary wedge
A
wedge formed as the top plate scrapes sediment off of the subducting plate
21
Q
active continental margin trench
A
trench between the subducting crust and the continental crust
not always present - full of sediment
22
Q
active continental margin order from greatest depth
A
oceanic crust
accretionary wedge
continental crust
23
Q
abyssal plain
A
large flat region of the ocean floor
24
Q
mid-ocean ridge
A
location where the plate moves apart; creates new ocean floor
(divergent plate boundary)
25
What percentage of the Earth is made up of mid-ocean ridges
20%
26
origin of mid-ocean ridges
volcanic
27
sea-floor spreading
the divergent plates move apart
magma rises to meet the water
the magma cools and forms new seafloor
28
what rocks are formed at mid-ocean ridges
intrusive gabbro
extrusive basalt
29
sheeted dikes location
formed at mid ocean ridges
30
rift zone
a deep rift valley where magma from beneath the Earth's crust wells up, cools, and is pushed away from the ridge's flanks
31
unique (dynamic) features of mid-ocean ridges (5)
1. frequent Earthquakes
2. hydrothermal circulation
3. formation of mineral deposits
4. volcanic eruptions
5. sulpher based ecosystems
32
what controls the sea water chemistry at mid ocean ridges
hydrothermal circulation
33
ophiolite
when ocean basin closes, **oceanic crust gets scraped off and placed on land**
34
moho
boundary between Earth's crust and its mantle
35
Explain the magnetic anomaly present at mid ocean ridges
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
36
atolls formation
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
37
Why does the seafloor get deeper as you move away from mid-ocean ridges
The plates cool and contract
38
VMS
volcanogenic massive sulphide deposit; important mineral formed at mid-ocean ridges
39
terrigenous sediments
sand sized particles that originated on the continents but are now sea-floor sediments
40
biogenous sediments
shells and skeletons of plankton living near the surface of the ocean but are now sea-floor sediments
41
manganese nodules
form on abyssal plains; economically valuable
42
Wegener proof the Pangea once existed (4)
1. fit of coastlines
2. fossil distribution
3. ancient mountain belt locations
4. past glaciation pattern
43
Where do coastlines fit best
at the continental shelf
44
What did Wegener think of land bridges + other name
stupid. Isthmian links where used to explain how similar fossils could be on continents separated by the ocean
45
tillites
distinct rock type formed by glacier movement
46
Wegener's proof from glaciation patterns
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
Polar fleeing
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
What years was Wegener's theory abandoned
1930s
49
What years was Wegener's theory revived and by what
1950s
exploration of ocean floor
paleomegnetism
50
paleomagnetism
"fossil magnetism"
51
Explain how paleomagnetism supported Wegener's theory
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
Curie Temperature
If above; rocks are no longer magnetized
If below; rocks are magnetic
580 degrees C
53
What angle will a compass be at the North Pole
vertical
54
what angle will a compass be at the Equator
Horizontal
55
changing pole theory
the theory that the reason rocks where having magnetism directions that did not match their location was because of a changing magnetic pole
56
polar wandering path support for Wegener
- 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
Seafloor Spreading hypothesis
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
Harry Hess
proposed and found proof for the seafloor spreading hypothesis
found mid-ocean ridges
59
geomagnetic reversal
Earth's magnetic direction changes chaotically
60
How does geomagnetic reversal support Wegener's theory
- 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
When was the last geomagnetic reversal
780 000 years
62
Why did researches find that the seafloor has a strong/weak magnetic pattern
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
Expanding Earth Theory
Incorrect. Earth is getting bigger which causes continents to crack and get pulled apart
64
Continental Drip Theory
Incorrect/Joke: The continents are somewhat upside down water droplet shape. Continents are dripping northwards on the globe
65
are continental plates felsic or mafic
felsic
66
are oceanic plates felsic or mafic
mafic
67
Plate tectonics theory
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
mid-ocean ridge speed
1-20cm per year
69
continental rift
separating continental crust;
will eventually split into two plates
then fill with water and turn into a linear sea
70
What is the oldest seafloor
180 million years
71
failed rift
a continental rift does not finish separating (we don't know why)
72
Keweenawan Rift
failed rift extending from Lake Superioir to Kansas
73
Examples of oceanic-continent convergent plate boundaries
Cascadia, Andes
74
Examples of oceanic-oceanic convergent plate boundaries
Western Aleutians (Alaska)
75
Examples of continent-continent convergent plate boundary
Tibetan Plateau
76
Depth at which water released from the subducting oceanic plate causes the formation of volcanoes
100km
77
How does angle of subduction angle affect how far into the continental crust volcanoes are formed
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
What is the thickness of the crust at continent-continent convergent boundaries
>80km
79
What do continent-continent convergent plates form
- thickened crust and major mountain belt
- no volcanoes because of no subduction occurring
80
what causes continent-continent convergent boundaries to have partial melt
- higher quantities of radioactive materials that release heat
This partial melt causes flow
81
George Airy
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
Examples of transform plate boundaries
San Andreas Fault, North Anatolian Fault
83
Relationship between transform faults and mid-ocean ridge
transform faults connect mid-ocean ridges.
84
How do Earthquakes support the Plate Tectonic Model
Divergent - occur in a narrow and only along the plate boundary area
Convergent - occur in a broad area along the subducting plate
85
How does the age of the seafloor support the plate tectonic model
As you move away from the mid-ocean ridge, the seafloor gets older
They used fossils to discover this
86
How do hotspots/mantle plumes support the plate tectonic model
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
How does GPS support the plate tectonic model
we can measure the real movement of plates
88
What drives plate motion
mantle convection
89
mantle convection
magma rises because is it hot then falls when it cools
90
what mechanisms (based on mantle convection) produce forces that move the plates
mantle traction/drag
ridge push/sliding
slab pull
91
mantle traction/drag
convection current carries plate as it flows
92
ridge push/sliding
mid-ocean ridge creates a slight hill that plates fall down
93
slab pull
as the plat subducts, it pull the entire plate
94
volcanic arcs are associated with
ocean-ocean convergent boundaries
95
