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Eduqas GCSE Geology (9-1) > 2.2 Plate Tectonics > Flashcards

2.2 Plate Tectonics Flashcards

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1
Q

What is the lithosphere broken up into?

A

Plates

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2
Q

What are the different types of crust?

A

Oceanic and continental

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3
Q

Where do volcanoes mostly occur?

A

Along plate boundaries

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4
Q

What can the earth being a geological machine also be known as?

A

Plate tectonics

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5
Q

What did the concept of plate tectonics originate with?

A

The idea of continental drift (the continents moving about the planet)

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6
Q

Who first put forward the idea of continental drift?

A

Alfred Wegener in 1915

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7
Q

Who was Alfred Wegener?

A

A meteorologist that came up with continental drift

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8
Q

What evidence shows that continental drift is a correct theory?

A
  • the shapes of continents are fitted
  • ancient rocks and fossils
  • glaciers
  • mountain chains
  • magnetic attractions
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9
Q

How are the gaps between today’s continents when fitted together accounted for?

A

The gaps are due to some pieces of land being submerged due to difference in sea level, as well as erosion and deposition

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10
Q

How can ancient crystalline rocks support continental drift?

A

Different rock types and ancient mountain belts match up

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11
Q

How can fossils support continental drift?

A

Distribution of plant and animal fossils found in S. America, Africa, Antarctica, Australia - showing all southern continents were once joined

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12
Q

How can glaciers support continental drift?

A

Distribution of late palaeozoic glaciations can show movement of glacial ice

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13
Q

How can mountain chains support continental drift?

A

Mapping sea floors - underwater mountain ranges that line up with continental pattern → spreading ridges formed at constructive plate margins

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14
Q

How can magnetic attractions support continental drift?

A

In metals, the tiny compasses point towards where the north pole was when the lava cooled → use this to figure out where continents were at the time

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15
Q

Where is today’s present north magnetic pole?

A

In the south

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16
Q

If the sea floor is spreading, what should be shown on the rock?

A

The rock should show symmetrical magnetic stripes moving away from the ridge

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17
Q

What is a hot spot?

A

An area of very high heat flow in the mantle below the plates - with the heat burning through the plate to create volcanic activity at the surface

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18
Q

What can hot spots also be known as?

A

Mantle plume

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19
Q

Why can hot spots indicate direction of plate movement?

A

Although plates move - hot spot stays in same place e.g. direction that Hawaiian islands get older indicate direction of plate movement

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20
Q

What led geologists to believe that the lithosphere and crust were moving?

A

Patterns of earthquakes and volcanoes

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21
Q

How can plates move?

A

Convection currents in the lower mantle

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22
Q

What is the process of convection currents in the lower mantle?

A
  • hot material rises upwards through the mantle
  • as this nears the lithosphere, it moves sideways and carries a plate with it (this happens as mid-ocean ridges)
  • this material cools and descends at certain points - dragging lithosphere with it at subduction zones
  • lower part of mantle heated and material rises again to complete convection cell
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23
Q

How do mid-ocean ridges form, with relation to convection currents?

A

When hot material in the mantle rises and then move sideways and carries a plate with it

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24
Q

How do subduction zones form, with relation to convection currents?

A

When material at top of mantle cools and descends, dragging lithosphere down with it

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25
Q

Is the mantle a liquid?

A

No

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26
Q

How do convection currents occur in the mantle, if the mantle is a solid?

A

Slow deformation of the solid mantle

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27
Q

What is slab pull?

A

The weight of the crust pull the plate downwards

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28
Q

How is it thought that constructive plate margins begin as?

A

As grabens or rift valleys on land

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29
Q

What are rift valleys?

A

Where the crust is being split under great tension, with sets of normal faults forming opposite one another, and blocks of crust sinking in between

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30
Q

How does an ocean develop as a result of plate tectonics?

A
  • it must start as a rift valley
  • this widens - water floods in and forms a long narrow sea
  • sea widens by sea-floor spreading and opens up into an ocean
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31
Q

Which way do the plates move in constructive boundaries?

A

Move apart - with magma brought up from the upper mantle

32
Q

What happens to magma that is brought up from the mantle at constructive margins?

A

It crystallises on the surface as basalt pillow lavas, and beneath as dolerite dykes or plutons of gabbro

33
Q

What is formed when crust is pushed away in opposite directions at constructive margins?

A

Mid-oceanic ridges - marked by lines of volcanoes

34
Q

What are the fractures in the line of the mid-ocean ridge?

A

Transform faults

35
Q

How are transform faults formed?

A

Formed at the same time as the ridge, and are curved to allow the plates to move at different speeds across the earths spherical surface

36
Q

What happens when one plate moves in the opposite direction to another on either side of a transform fault?

A

Great pressure build up and shallow earthquakes result

37
Q

What do conservative margins result in?

A

Build up of pressure as friction prevents rocks moving along these large transform fault zones

38
Q

How is pressure released at a conservative margin?

A

In the form of an earthquake

39
Q

Which direction are plates at destructive margins moving?

A

Towards each other

40
Q

What does the plate destroyed at destructive plate boundaries compensate for?

A

The new plates forming along spreading ridges

41
Q

What are subduction zones?

A

When one plate is going underneath another

42
Q

What are Benioff zones?

A

Inclined zones of seismicity - when earthquake foci occur in lines at distinct angles leading down from plate margins

43
Q

When do trench systems occur?

A

When an oceanic plate is subducted underneath another oceanic plate

44
Q

What is marked when an oceanic plate subducts another oceanic plate?

A

A deep ocean trench

45
Q

How can earthquakes and volcanoes form from the subduction of oceanic-oceanic plates?

A
  • earthquakes - friction with the other plates (and so a Benioff zone formed)
  • volcanoes - when depth reached where temperature high enough plate will melt, forming magma, which will rise through cracks
46
Q

What type of volcanoes are formed from the subduction of oceanic-oceanic plates?

A

Andesitic

47
Q

What are volcanic arcs?

A

Chain of volcanic islands created in an arc shape, due to the curvature of the earth

48
Q

Where do oceanic-continental mountain belts occur?

A

When an oceanic plate is subducted under a continental plate

49
Q

Why is the oceanic plate subducted under the continental plate?

A

It is denser and thicker than the continental plate

50
Q

What happens to most of the magma when the subducted plate melts in a oceanic-continental subduction zone?

A

Although some reaches the surface to form andesitic volcanoes, most builds up in the continental crust as large granite plutons

51
Q

What will the granite plutons, formed when an oceanic plate is subducted underneath a continental plate, do to the surrounding rock?

A

Produce contact metamorphism of the rocks around them

52
Q

How are fold mountains formed?

A

When sediments that build up along oceanic-continental subduction margins are buckled into great folds and faults

53
Q

How is regional metamorphism related to destructive plate boundaries?

A

The immense pressures and temperatures created by movement along destructive plate margins also produce regional metamorphism on a large scale

54
Q

When do continental mountain belt systems occur?

A

When the subduction of an oceanic plate results in one continent moving towards another - until it eventually collides with it

55
Q

Why are two continental plates squeezed against one another at destructive plate margins?

A

Neither can be subducted

56
Q

What forms when two continental plates are squeezed against one another?

A

The sediments buckle and form fold mountains - also earthquake activity and intrusion of granitic plutons

57
Q

Why is there little volcanic activity at continental-continental destructive plate boundaries?

A

There is so must crust to be penetrated

58
Q

Why is thrust faulting common at continental-continental destructive plate boundaries?

A

Due to the great pressure involved

59
Q

What is the Joides Resolution 360 research cruise?

A

Boat that does ocean drilling of igneous rocks to understand the processes that create mid-ocean ridge basalt

60
Q

What does the mechanical behaviour of the outer earth involve?

A
  • the lithosphere - cold, rigid outer shell

* underlain by the asthenosphere - weaker layer

61
Q

What is the lithosphere composed of?

A

Crust and upper mantle

62
Q

What is the asthenosphere composed of?

A

Upper mantle

63
Q

Are the mechanisms of how tectonic plates move completely understood?

A

No

64
Q

Who discovered evidence for sea floor spreading, and what year?

A
  • Hess - 1960
  • Vine and Matthews - 1963
  • J. Tuzo Wilson - 1965
65
Q

Features at divergent plate boundaries?

A
  • basalt extrusion
  • sea floor spreading
  • ocean ridges
  • melting of upper mantle to form basaltic magma
  • high heat flow
  • rift valleys
  • abyssal plane
66
Q

Example of a divergent plate boundary?

A

Mid-Atlantic Ridge

67
Q

Features at conservative plate boundaries?

A
  • earthquake activity

* transform faults

68
Q

Example of a conservative plate boundary?

A

San Andreas fault zone

69
Q

Features at oceanic-oceanic convergent plate boundaries?

A

Island arc/trench systems

70
Q

Example of a oceanic-oceanic convergent plate boundary?

A

Java-Sumatra/Caribbean

71
Q

Features at oceanic-continental convergent plate boundaries?

A
  • subduction zones
  • Benioff zone
  • partial melting producing andesitic and granitic magmas
72
Q

Example of a oceanic-continental convergent plate boundary?

A

The Andes

73
Q

Features at continental-continental convergent plate boundaries?

A
  • mountain building
  • folding
  • thrust faulting
  • partial melting of crust producing granites
  • associated regional metamorphism
74
Q

Example of a continental-continental convergent plate boundary?

A

The Himalayas

75
Q

What is the only type of material that can be subducted? Why is this?

A

Oceanic plate material - because the granitic crust of the continents is not dense enough to descend into the asthenosphere

Eduqas GCSE Geology (9-1) (13 decks)

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