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Tectonics (1) > Plate boundaries > Flashcards

Plate boundaries Flashcards

1
Q

Describe the global distribution of volcanoes

A

Ring of fire which a great density in Iceland

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2
Q

Describe the global distribution of earthquakes

A

Greatest distribution in East Asia and West coast of America

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3
Q

Describe intraplate earthquakes

A

Within tectonic plates there are fault zones where relatively few earthquakes occur because most occur near plate margins. They occur along faults in the interior of normally stable plates formed by stresses from zones of weaknesses due to the spherical surface of the earth along ancient fault or rift zones.

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4
Q

Why are intraplate earthquakes more dangerous?

A

because they’re so rare as old structures may cause the crust to slip to accommodate regional tectonic strain

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5
Q

What are hotspot volcanoes?

A

A hotspot develops above the plume where magma rises through the rigid plates of the lithosphere which produces active volcanoes

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6
Q

What happens when hotspot volcanoes move?

A

As they move from the hot spot they cool and subside to produce islands, if they are continental then they become extinct

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7
Q

What is a hotspot?

A

Places within a mantle where rocks melt to form magma

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8
Q

How can a hotspot be detected?

A

Volcanoes not at a plate boundary e.g. Hawaii

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9
Q

What is divergent plate movement?

A

When plates move away from each other. Constructive plate margins are mainly found at mid-ocean ridges, earthquakes originating from here are f a shallow focus and have three main causes

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10
Q

What are the three causes of constructive plate earthquakes?

A
  • Harmonic tremors associated with rising magma from the asthenosphere
  • Earthquakes are located along faults associated with fracturing of the lithosphere as it moves away from the ridge
  • Earthquakes occur along transform faults at the ridge
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11
Q

What are conservative plate margins?

A

E.g. San Andreas Fault where plates slide past each other, earthquakes that occur here are of a shallow focus

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12
Q

What is the cause of earthquakes at conservative plate margins?

A

Sections of the fault seem to lock and then tension is suddenly released

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13
Q

Describe a convergent plate margin

A

Subduction generally denser oceanic under lithospheric beneath continental crust

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14
Q

What is the Benioff zone?

A

The area in which shallow, intermediate and deep earthquakes are recorded in the subduction zone

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15
Q

What are the three causes of convergent/ destructive earthquakes?

A
  • Shallow earthquakes in the descending slab from fracturing in the outward part of the downward bending cold oceanic lithosphere
  • Shallow earthquakes in the overlying slab of the continental lithosphere from bulk uplift and subsidence as the continental slab is disturbed
  • Intermediate and deep earthquakes in the descending slab related to compression/ extension
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16
Q

What are rocks made from? Give the example of granite

A

Minerals, granite = quartz (white), feldspar (yellow) and biotite (black)

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17
Q

Give the two types of igneous rocks

A

Intrusive from cooling magma (large crystals from slow cooling) and extrusive from lava (small crystals from quick cooling)

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18
Q

How are metamorphic rocks formed?

A

When rocks are changed by heat and pressure e.g. granite becomes gneiss

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19
Q

How are sedimentary rocks formed?

A

Eroded material is laid down in layers and form rock under heat and pressure

20
Q

Give an example of extrusive igneous rock

A

Basalt

21
Q

Give an example of intrusive igneous rock

A

Granite

22
Q

Give an example of metamorphic rock

A

Gneiss

23
Q

Give an example of sedimentary rock

A

Sandstone/ Limestone

24
Q

Describe volcanic and seismic activity at constructive/ divergent plate boundaries

A

Magnitude 5-6

Effusive eruptions

25
Q

Describe volcanic and seismic activity at destructive/ convergent oceanic and continental plate boundaries

A

Shallow to 700km along Benioff zone, magnitude 8-9

Explosive eruptions

26
Q

Describe volcanic and seismic activity at destructive/ convergent oceanic and oceanic plate boundaries

A

Shallow to 700km along Benioff zone, magnitude 7-9

Explosive eruptions

27
Q

Describe volcanic and seismic activity at destructive/ convergent continental and continental plate boundaries

A

Shallow to intermediate plate boundaries, magnitude 6-8

Usually no volcanic activity

28
Q

Describe volcanic and seismic activity at transform/ conservative plate boundaries

A

Shallow focus, magnitude 6-8

Usually no volcanic activity

29
Q

What theory did Alfred Wegner propose?

A

Theory of Continental drift but this was largely disproved until recently

30
Q

How did the theory of continental drift start in the 17th century?

A

South America and Africa looked like they could fit together

31
Q

What development happened in 1912 of the continental drift theory?

A

Alfred Wegner proposed the theory of continental drift (Pangea) using geology and fossils

32
Q

What development of the continental drift theory happened in 1940?

A

Harry Hess reveals the shape of the ocean floors using sonar and radar

33
Q

What development of the continental drift theory happened in 1960?

A

A drill ship collected samples and dated them

34
Q

What development of the continental drift theory happened in 1963?

A

J. Tuzo Wilson proposes theory of sea spreading

35
Q

What development of the continental drift theory happened in 1965?

A

J Tuzo Wilson and Harry Hess proposed the theory of plate tectonics

36
Q

What evidence was used to support the Pangea?

A

Caledonian mountains found on both sides of the Atlantic ocean

37
Q

What evidence was used to support Wilson’s theory of sea spreading?

A

Carboniferous glaciated areas subsequently moved including glacial deposits created close to the South Pole

38
Q

Define ‘paleomagnetism’

A

The study of the history of the earth’s magnetic field

39
Q

What happens every 200k-400k years according to paleomagnetism?

A

The magnetic field reverses polarity

40
Q

How does the Earth have a magnetic field?

A
  • Magma erupts from mid-ocean ridges
  • Magnetic minerals in molten rock aligns themselves with the earth’s magnetic field
  • As the new crust solidifies the rock alignment fixes
  • This creates alternating magnetic strips along the sea floor when the minerals align in the opposite direction
41
Q

How can the age of the sea floor be determined?

A

The magnetic stripes along the sea floor, the further they are from the mid-ocean ridge, the older the floor is when the plates are moving apart

42
Q

Which of the earth’s layers holds the tectonic plates?

A

Plates float in the lithosphere above the asthenosphere

43
Q

Describe the composition of the asthenosphere

A

Semi-fluid layer of partly molten rock that resembles a very thick and slow-moving warm tar

44
Q

What tectonic activity occurs at transform/ conservative plate margins? (When the plates slide past each other)

A

Often cause earthquakes but don’t tend to have volcanoes or mountain ranges

45
Q

What happens when two oceanic plates converge?

A

An ‘island arc’ forms as usually the older rock sinks under the younger rock which forms volcanic islands and active earthquakes

46
Q

Give an example of continental collision

A

India collided into the Himalayas

47
Q

What tectonic activity occurs at divergent boundaries? (Plates move away from each other)

A

On land, a rift zone is created where crust moves away from each other usually causing volcanic activity and minor earthquakes usually in the ocean to form a mid-ocean ridge.

Tectonics (1) (7 decks)

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