Plate Tectonics 1 Flashcards Preview

A level Geography - Physical > Plate Tectonics 1 > Flashcards

Flashcards in Plate Tectonics 1 Deck (41)
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1
Q

Define MOHO (Mohoronicic Discontinuity)

A

Boundary between the crust and the mantle

2
Q

Define Sima

A

Oceanic crust - Silicona nd magnesium

3
Q

Define Sial -

A

Continental crust - Silicon and aluminium

4
Q

Define asthenosphere

A

Highly vicious, mechanically weak region of the upper mantle

5
Q

Define geoid

A

Imperfect sphere. Bulges around the centre and narrows at the poles

6
Q

Give the 4 layers of the Earth

A

Crust
Mantle
Outer core
Inner core

7
Q

Give the key characteristics of the crust

A

Thinnest - between 0-20km on avergae

Composed of continental and oceanic crust

8
Q

Give the key characteristics of the Mantle

A

Thickest section of the Earth at 2900km and makes up 84% of its volume

Made up of iron, silica and magnesium

Over 3000ºC on average

9
Q

Give the key characteristics of the Outer core

A

The inner core is so hot that it causes this lyer to melt and become liquid.

Made up of iron and nickle

Reaches tempatures of 4000-5000ºC

This layer moves around the inner core and creates the Eath’s magnetic field

10
Q

Give the key characteristics of the inner core

A

Tempatures can exceed 6000ºC

Mainly irona nd nickle - silid dense ball of metal

Engine and internal enegy source of the rocks

11
Q

Give the key characteristics of the continental crust

A

Made up of silicon and aluminium

20-30km thick on average

Located on contents and areas close to the shore (continental shelves)

12
Q

Give the key characteristics of the oceanic crust

A

Made up of silicon and magnesium

Thinner than continental (between 5-10km)

Much denser

Under oceans - formed via sea-floor spreading at mid-ocean ridges

13
Q

Why is oceanic crust newer than continental

A

O = constantly being created and destroyed whereas can’t happen so easily with continental

Oceanic can be subducted because its more dense tahn its sorounding area so can be subducted and destryed. Created where sea floor spreads. COntinetal is not dense enough

14
Q

Give 3 reasons why the inner core is so hot

A

Heat from when the planet formed and accreted, which has not yet been lost (Big Bang)

Frictional heating caused by denser core material sinking to the center of the planet

Heat from the decay of radioactive elements

15
Q

Give the 5 pioneers of plate tectoinics

A

Alfred Wenger

Harry Hess

Fredrick Vine and Drummond Mathews

John Tuzo-Wilson

Dan Mckenzie

16
Q

Who was Alfred Wenger

A

German metreologist

Published ‘The Origin of Continents and Oceans’ in 1915, which outlined his theory if cintinental drift

Continental drift theory met by sceptism by lots of scientists

Although he had lots of evidence to support his thoey, he lacked the mechanics on how the plates moved

17
Q

Give the 5 lines of evidence

A

Fossil

Jigsaw

Geological

Glacial

Tectonic

18
Q

Explain fossil evidence

A

Many examples of fossils found on seperate continents suggesting they were once joined together

If continental drift hadn’t occured then it woudl cntradct darwin’s theory of evolution

Fossils of Mesocrus and Lystceterous found on South Africa, India and Antarctica suggesting the continents were joined

19
Q

Explain tectonic evidence

A

Fragments of an old fold mountain belt 450 million yers ago are found on widely seperate continents

When these land masses are re-assembled, the mountain belt forms a continious linear feature

20
Q

Explain jigsaw evidence

A

Any areas where the coast may overlap or leave gaops can be exaplined by costal erosion/deposition and change in sea/land level

21
Q

Explain geological fi evidence

A

When the geology of eastern South America and West AFrica were mapped, it revealled that ancient outcrops over 200m years ago were continious from one continent to the other

22
Q

Explain glacial evidence

A

Today, glaciar deposits from the Permo-Carboniferous period are found in Antarctica, South America, India and Australia

If the continents hadn’t moved then it would suggest an ice sheet extending from the southpole to the equator which is unlikely seeing as the UK was near the equator at that point and showns no evidence of such galiac deposits

23
Q

Who was Harry Hammon Hess

A

Professor of geology at Princeton uni (USA)

Served in the navy in WWII - equiping him with usefull knowlwdge of sonar

24
Q

What book did Hammond Hess publish in 1962

A

The History of Ociean Basins - outlined how continental drift worked

Late rbecame known as “sea floor spreading”

25
Q

Explain the sea floor spreading theory

A

Oceans were shallower in the middle and identified the presence of Mid Ocean Ridges rising as a high as 1.5km

In addition found that the deepest parts of the ocean trenches were found very close to the continental margins in the pacific

Hess believed that oceans grew from their centres from molten material escaping the mantle along the ridges. This created new seafloor which then spread away form the ridge in both directions

The ocean ridge was thermally expanded and consequently higher than the ocean floor further away.
As spreading continued, the older ocean floor cooled, became more dense and eventually subjected at a deep ocean trench

26
Q

Give a limmitation to Hess

A

Hess believed that ocean trenches were the locations where ocean floor was destroyed and recycled - However didn’t have enough evidence to prove it

Couldn’t explain Hawii

27
Q

Describe the work of Vine and Mathews

A

British geologists - their work looked at the patterns of magnetic striopes in the sea floor.

Confirmed Hess’ theory

28
Q

How does magnetic stripes work

A

When the material from the mantle rises up through mid-ocean ridges and cools, it preserves a record of the Earth’s magnetic field.

This is because the magnetite in the basalts is strongly magnetic, and aligns with the field when it cools

29
Q

What was Frederick Vine’s and Drummond Mathew’s theory

A

Hess lacked the evidence to assert that oceanic plates were created at Mid Ocean Ridges

When basaltic lava cools on the sea floor, individual minerals separate - especially iron - and these minerals then align themselves on the sea floor in the direction of the magnetic pole

Earth’s magnetic field swaps direction at points throughout time

Noticed there was a symmetrical pattern of magnetic stripes on either side of the mid ocean ridges. In addition when the basalts of the sea floor were dated, they were found to be the same age at similar distances away from the ridge on each side.

This suggested that the ocean floor was created at the mid ocean ridges, then was split in half by later activity and pushed sideways.

30
Q

How did Vine and Mathews publish their theory

A

1963, in a paper called ‘magnetic anomomlies over oceanic ridges’.

Became the first scientiic test for sea floor spreading

But still didn’t explain Hawii

31
Q

Why is Hawii an anomolie

A

Most volcanic activity is found at locations of sea floor spreading (Hess) or subduction zones.

Some volcanic locations such as Hawaii are far away from any known sea floor spreading location or subduction zone.

32
Q

Who is John Tuzo-Wilson

A

Continental drift theories were accumulating without any explanation for land masses such as Hawii

In 1963, Tuzo-Wilson proposed that plates may move over fixed hotspots in the mantle to create a string of volcanic islands

Hawaii is composed of 19 volcanic islands.

33
Q

What are hotspots

A

Radioactive decay in the Earth’s core generates hot temperatures.
If the decay is concentrated, hotspots will form around the core

Heat the lower mantle creating localised thermal currents where magma plumes rise vertically

Burn through the lithosphere to create volcanic activity on the surface

Hotspot remains staionary, the movement of the overlying plate reults in formation of a chain of active volcanoes. Hawii

As oceanic lithosphere oves away, volcanic activity ceases, cools and becomes an island

34
Q

Other than hotspots, what did Wilson also discover

A

Conservative plate boundries

Plates move transversely – causes earthquakes but no volcanoes, without destroying or creating any oceanic crust

35
Q

Who was Dan Mckenzie

A

There was lots of evidence about continental drift but now evidence to prove why it was happening

Heard Fredrick Vine speak about sea florr spreading and magnetic anomolies

36
Q

What was Mckenzie’s theory - Mantle Convection Hypothesis

A

He suggested there are two layers in the mantle, each of which are in motion, controlling the movement and behaviour of the tectonic plates above.

Convection currents in the mantle occur when the hot + less dense magma in mantle rises, cools and sinks becuase it is more dense. This repeast in a cyclical motion forming convection currents

Destructive - convection currents force the continental and oceanic plate together. Oeceanic more dense so subducts

Constructive - two plates are forced apart by convection currents forning a gap between the plates

37
Q

Give a limmitation to Mckenzie’s theory

A

Mantle convection being resposnible for the movent of tectonic olates is now largely out of favour, with modern imagaing techniques unable to identify convection cells in the mantle sufficientley large to drive plate movement

38
Q

What is the most recent theory on plate movements

A

Gravitational sliding

39
Q

What is gravitational sliding

A

Combination of ridge push and slab pull

40
Q

What is ridge push (Gravitational sliding)

A

Takes place with plate movement driven because of the higher elevation of plates at ocean ridges.

As fresh magma wells up at mid-ocean ridges to form new young, oceanic lithosphere, a higher elevation is formed at spreading ridges.

The new oceanic crust gradually cools, gets denser and thickens with age and is pushed ‘downhill’ by gravity as new magma emerges from the active zone of divergence behind it (and thus adds distance from the ridge).

41
Q

What is slab pull

A

More significant gravitational force acting on the plates

Occurs at destructive plate margins where an oceanic plate subducts under a continental plate, working in tandem with convection currents and gravity

Due to the extreme density and mass, the subducting plate pulls with it the rock behind and forces it to move along as it subducts