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Earth structure and tectonics - 33740 > Important for test info on tectonics > Flashcards

Important for test info on tectonics Flashcards

1
Q

What are the 7 major plates from largest to smallest?

A
  1. Pacific
  2. Eurasia
  3. North America
  4. South America
  5. Africa
  6. Antarctica
  7. Australian
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2
Q

How large is the pacific plate?

A

~14000km

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3
Q

What type of crust is the pacific plate made of?

A

Oceanic

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4
Q

What is the difference between plate and lithosphere?

A

A plate is a piece of lithosphere, which can have either continental or oceanic crust (or both) at its top. Continent is the emerged part of a plate

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5
Q

What is the position of the mid-Atlantic ridge between south America and Africa?

A

Symmetrically in the middle

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6
Q

What distance is the Mid-Atlantic ridge from South America and Africa?

A

Both ~2500km

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7
Q

Is the Mid-Atlantic ridge segmented or a straight boundary?

A

Segmented (by strike slip)

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8
Q

How long is the longest and shortest ridge segments of the Mid-Atlantic ridge?

A

Long =~1000km
Short =~50km

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9
Q

What is the maximum lateral offset of the Mid-Atlantic ridge?

A

870km

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10
Q

What is an example of where a spreading ridge occurs above sea level?

A

Iceland

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11
Q

What is the bathymetric profile along the south mid-Atlantic ridge?

A

Ridge is large elevated areas in centre of the ocean.

Coast to coast, the depth increases up to a maximum of -5500km and decreases again where the ridge starts

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12
Q

Where is the highest elevation along the Mid-Atlantic ridge?

A

In the centre at the divergent margin

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13
Q

What is the total height of the Mid-Atlantic ridge?

A

Around 3000m

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14
Q

How wide is the Mid-Atlantic ridge?

A

~2900km

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15
Q

Why is the Mid-Atlantic ridge so wide/ what controls this?

A

elevated area (ridge) is hotter than other oceanic rocks and therefore more buoyant. Temperature decreases from the ridge towards the ocean-continent boundary and so does the elevation (colder = less buoyant = deeper)

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16
Q

What is the age distribution of oceanic crust in the Atlantic ocean like?

A

Symmetric

17
Q

What was the initial opening age of the mid-Atlantic ridge between NW Africa and the USA?

A

175-180 Ma

18
Q

What is the spreading rate of the Mid-Atlantic ridge between NW Africa and USA?

A

3.2cm/year

19
Q

What is the sequence of opening and age of the North, central and south Mid-Atlantic ridge?

A

North Atlantic = 130 Ma (southern part); Central Atlantic = 180 Ma;
South Atlantic = 130 Ma.

20
Q

How old is the oldest oceanic crust?

A

~280 Ma

21
Q

What has the spreading rate been like in the Central Atlantic?

A

Relatively constant

22
Q

What does the difference between the age of oceanic and continental crust?

A

Oceans are continuously recycled during the various Wilson cycles, while continents are not

23
Q

How many types of convergent plate boundary are there?

A

Ocean-ocean,
ocean-continent,
continent-continent.

24
Q

What is the main large scale product of intra-continental and ocean-continent subductions?

A

orogenesys

25
Q

What is the main large scale product of intra-oceanic convergent boundaries?

A

Island arc

26
Q

Is the convergence of the Juan de Fuca plate perpendicular to the trench direction?

A

Subduction can be oblique to the trench, as for the Nazca plate.

27
Q

What is the overall shape of the down-going plate?

A

From the abyssal plain, depths increase towards the trench, reaching a maximum depth at the trench where lithosphere inflects downward into the subduction zone

28
Q

What is the overall depth of the overriding plate compared with the down-going plate?

A

Always higher

29
Q

Along which type of plate margin do volcanoes occur more often?

A

Convergent margins

30
Q

Where can a large number of volcanoes that are not associated with a plate boundary?

A

East African rift valley (a new plate margin is developing there as this is a rift)

31
Q

What is the topographic profile and alignment of volcanoes in the East African rift valley?

A

Are aligned within the rift valley, which is a topographic depression

32
Q

What is the process responsible for the topographic profile and volcano alignment in the east African rift valley?

A

Continental rifting

33
Q

What is the distance between some volcanoes and trenchs?

A

South America: 320 km
North America: 290 km
Japan: 300 km

34
Q

What type of margin do large volcanoes occur?

A

Convergent

35
Q

Is there a link between depth of
the earthquake and distance from the trench?

A

Yes - depth increases away from the trench
reflecting the shape of the subduction zone.

36
Q

What is the distribution of earthquakes on the plate called?

A

Benioff zone

Earth structure and tectonics - 33740 (7 decks)

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