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AQA A-Level Physical Geography > 🌋3.1.5.2 - Plate Tectonics > Flashcards

🌋3.1.5.2 - Plate Tectonics Flashcards

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1
Q

How thick is the mantle?

A

2900km

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2
Q

What are intrusive rocks?

A

Rocks formed by the cooling of molten Magma, that crystallises and solidifies slowly below the surface. Forms coarse grained igneous rocks. Vertical dykes and inclined sills may form within.

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3
Q

What are extrusive rocks?

A

Lava that is in contact with the air or sea. It cools, crystallises and solidifies much quicker than Magma that is still underground. Fine grained rocks with small crystals.

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4
Q

What events and landforms occur at Destructive boundaries?

A

Powerful earthquakes
Volcanoes
Fold Mountains
Ocean trenches

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5
Q

What is glacial deposit evidence for tectonic theory?

A

300 million year old deposits found in Africa, Australia, Antarctica, South America and India suggest ancient ice sheet

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6
Q

Where are rift valleys common?

A

Where 3 plates meet at a junction

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7
Q

What happens at destructive boundaries?

A

Dense oceanic plate descends beneath less dense continental plate. Oceanic plate melted due to friction forming magma

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8
Q

What happens at collision boundaries?

A

Two plates of similar densities move together, causing the material between them to buckle and rise up

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9
Q

Where do rift valleys form?

A

On constructive boundaries

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10
Q

How do rift valleys form?

A

Magma rises and plates move apart
Over a magma chamber, crack and faults appear
Blocks of crust descend into mantle, creating steep sided valleys
Central plateaus sink in the middle, forming lakes

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11
Q

What boundaries do ocean trenches form at?

A

Destructive

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12
Q

Crust

A

Earth’s outer shell, between 6-70km thick

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13
Q

Mantle

A

Molten/ semi-molten layer rock layer

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14
Q

Outer Core

A

Molten outer layer of the core, mainly iron

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15
Q

Inner Core

A

Solid centre, made of iron and nickel alloys - up to 5000°c

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16
Q

Asthenosphere

A

Layer beneath the lithosphere that’s semi-molten and the plates float on

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17
Q

Lithosphere

A

Crust and the rigid upper section of the mantle, divided into the tectonic plates

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18
Q

Oceanic Crust- Thickness

A

6-10km

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19
Q

Oceanic Crust- Age

A

> 200million

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20
Q

Which is denser- oceanic or continental crust?

A

Oceanic

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21
Q

Oceanic Crust- Example of rock

A

Basalt

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22
Q

Continental Crust- Thickness

A

30-70km

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23
Q

Continental Crust- Age

A

<1500million

24
Q

Continental Crust- Example of rock

A

Granite

25
Q

What are the 2 internal energy sources?

A

Primordial Heat
Radiogenic Heat

26
Q

What’s primordial heat?

A

Heat left over from Earth’s formation

27
Q

What’s radiogenic heat?

A

Heat produced by the decay of isotopes like Uranium 238
By far the greatest source, but slowly diminishing

28
Q

Explain Alfred Wagner’s theory (1912)

A

Continental Drift- 300 million years ago Pangea existed

29
Q

List 5 pieces of evidences supporting continental drift

A

Fossil Fit
Tectonic Fit
Geological Fit
Jigsaw Fit
Paleomagnetism

30
Q

Fossil Fit Example

A

Mesosaurus found in South Africa and East America

31
Q

What type of fossils are looked at? Why?

A

Land mammals
Don’t swim, don’t lay eggs

32
Q

Tectonic Fit Example

A

Caledonian mountain belt found in Scotland, Canada and Greenland- form a continuous linear pattern when reassembled

33
Q

Why does tectonic fit support Continental Drift?

A

As mountain belts have to be made under the same conditions in the same location

34
Q

Geological Fit Example

A

Mapping South America and West Africa reveals continuous rock outcrops over 2,000 million years old

35
Q

Jigsaw Fit Example

A

Coastlines of South America and West Africa match to a depth of 1,000m below current sea level

36
Q

How can gaps and overlaps in jigsaw fit be explained?

A

Coastal erosion
Coastal deposition
Rises in sea level
Changes in land level

37
Q

How does paleomagnetism explain Continental Drift?

A

. Roughly every 400 million years the Earth’s magnetism changes
. At mid ocean ridges, there are striped symmetrical patterns where the rock has moved apart due to sea floor spreading
. Shows that the plates are moving

38
Q

Sea Floor Spreading

A

Movement of oceanic crust away from constructive plate margins at mid-ocean ridges

39
Q

Slab Pull

A

After subduction, the cooler, heavier edge of the lithosphere sinks into the mantle under its own weight, pulling the plate with in

40
Q

Ridge Push

A

The higher elevation at mid ocean ridges causes gravity to push the lithosphere that’s further from the ridge

41
Q

Gravitational Sliding

A

Movement of tectonic plates as a result of gravity

42
Q

Benioff Zone

A

Where plates melt in the mantle due to increasing heat and friction

43
Q

Constructive Margin

A

Plates move apart
Magma rises from the asthenosphere and cools, filling the gap

44
Q

Constructive Margin Features (and examples)

A

Shield volcanoes- Eyjafjallajokull
Earthquakes
Rift valleys- East African Rift Valley
Mid-Ocean Ridges- Mid-Atlantic Ridge

45
Q

Oceanic- Oceanic Margin

A

2 Oceanic plates move towards eachother
Faster/ denser subducts
Melts in Benioff Zone
Less dense molten material rises

46
Q

Oceanic- Oceanic Margin Features (and examples)

A

Ocean trenches- Mariana Trench
Island Arcs- West Indes
Earthquakes
Composite volcanoes- Montserrat
Tsunamis- Boxing Day

47
Q

Oceanic- Continental Margin

A

Oceanic and continental move towards eachother
Denser oceanic subducts
Melts in Benioff Zone
Less dense molten material rises

48
Q

Oceanic- Continental Margin Features (and examples)

A

Ocean Trenches- Peru-Chile Trench
Composite volcanoes- Cotopaxi
Fold mountains- Himalayas

49
Q

Continental- Continental Margins

A

Continental plates move towards eachother
Both plates have a lower density than asthenosphere
Can’t subduct
Collide and rise upwards

50
Q

Continental- Continental Margin Features (and examples)

A

Earthquakes
Fold Mountains- Himalayas

51
Q

Conservative Margin

A

Plates move past eachother
Friction between plates= stress builds
Suddenly released

52
Q

Conservative Margin Features (and examples)

A

Fault line- San Andreas
Shallow earthquakes

53
Q

Hotspots

A

Small area with unusually high concentration of radioactive elements below the surface
(Magma Plumes)

54
Q

Hotspot Feature (and example)

A

Shield volcanoes- Mauna Loa, Hawaii

55
Q

Magma Plume

A

Rising column of hot rock at a plate margin or through a plate

AQA A-Level Physical Geography (28 decks)

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