Key Terms - Plate Tectonics

Question 1

Core (4)

Answer 1

Densest, hottest part of the planet
Made of rocks rich in iron and nickel
Temps can exceed 5000°C
Heat is from primordial and radiogenic heat

Question 2

Primordial heat

Answer 2

Heat left from the earths formation

Question 3

Radiogenic heat

Answer 3

Heat produced by the radioactive decay of isotopes

Question 4

Mantle (3)

Answer 4

Surrounds the core
Thickest layer made of silica rocks rich in iron and magnesium
Upper mantles is semi molten and is known as aesthenosphere

Question 5

Crust (2)

Answer 5

Thinnest outer solid layer
Tow types of crust = oceanic and continental

Question 6

Oceanic crust (3)

Answer 6

Found beneath the world oceans
Composed of relatively dense basalt
Between 6-10km thick
Formed at spreading mid oceans ridges at constructive margins

Question 7

Continental crust (5)

Answer 7

Forms the continents
Thicker and older
Can be up to 70km thick
Composed of granite
Formed at subduction zones

Question 8

Lithosphere

Answer 8

The crust and rigid upper mantle

Question 9

Aesthenosphere (2)

Answer 9

The semi-molten upper mantle
Below the lithosphere

Question 10

Plate tectonic theory (2/5)

Answer 10

Suggests the crust is divided into tectonic plates that move due to convection in the aesthenosphere
Movement = mid-ocean ridges, ocean trenches, fold mountains and causes earthquakes and volcanoes

Question 11

Alfred Wegener (3)

Answer 11

Published a theory in 1912 suggesting there was once a super continent caused Pangea and that overtime the landmasses drifted apart
Theory based on evidence = geological, climatological, biological
He counsels exp,Ian how the continent ps moved though

Question 12

Mid - Atlantic ridge (3)

Answer 12

Continuous uplift feature that runs down the centre of the Atlantic Ocean
The central part of the ridge is marked by a Central Valley
First seen in 1940s when the ocean floor was first mapped

Question 13

Sea floor spreading (5)

Answer 13

Surveys of the ocean floor established
Rocks found closest to mid oceanic ridges = youngest
Rocks nearest the Continental landmasses were the oldest
Supports idea that sea floors are spreading out from mid oceanic ridges where new crust was being formed
Magma reached the surface as two oceanic plates moved apart at a constructive margin

Question 14

Palaeomagnetism (5)

Answer 14

Rocks that form the ocean floor show stripes of alternating polarity
Lavas that erupt at mid-oceanic ridges contain iron which aligns to the Earth’s polarity = fixed when the lava solidifies.
Earth’s magnetic field reverses 4 to 5 times per million years.
These switches are recorded in the rocks of the ocean floor as a series of ‘magnetic stripes’ with rocks aligned alternatively towards north and south poles.
The pattern suggests that ocean crust is spreading out from the mid- ocean boundary

Question 15

Convection currents (3)

Answer 15

High temps at Earth’s core help create continuous convection currents in the aesthenosphere that transfer heat from the core to the Earth’s surface.
As the heated magma spreads out underneath the crustal plates it causes them to move due to traction.
The magma then cools, becomes denser and sinks downwards again.

Question 16

Ridge push (3)

Answer 16

Occurs at mid-oceanic ridges where hot magma rises to the surface and forces up the crust at constructive margin to form a slope on either side.
As the new rock cools, it becomes denser and the weight causes it to ‘slide’ downwards away from the ridge, due to gravity.
This results in a pushing force and in seafloor spreading

Question 17

Slab pull (2)

Answer 17

At a subduction plate margin the heavier plate sinks down into the mantle.
As the edge of the plate sinks it pulls the rest of the plate with it

Question 18

Destructive plate margin (4)

Answer 18

These occur where two plates move together and one is destroyed as it subducts beneath the other.
Oceanic + Continental = denser oceanic plate subducts and is destroyed.
Two oceanic plates converge the denser of the two subducts.
Earthquakes, volcanoes, ocean trenches and fold mountains are associated with these margins.

Question 19

Constructive plate margin (4)

Answer 19

These occur where two plates move apart and new crust is created.
In the oceans this produces mid-ocean ridges.
Shallow focused earthquakes and submarine (underwater) earthquakes can occur at these margins.
Divergence can also occur within a continent = rift valleys and volcanic activity.

Question 20

Conservative plate margin (2)

Answer 20

These occur where two plates rub past each other
Earthquakes are a feature of these margins

Question 21

Ocean ridges (4)

Answer 21

The longest continuous uplift feature on the surface of the planet
Two plates pull apart = a weaker zone in the crust and an increase in heat near the surface
The hotter expanded crust forms a ridge
The central part of the ridge may feature a Central Valley

Question 22

Transform faults (2)

Answer 22

Cracks in the Earth’s crust that form at right angles to constructive plate margins
As the plates pull apart the parts of the crust on either side of the fault move at different rates = friction and earthquakes

Question 23

Young fold mountains (3)

Answer 23

Fold mountains are formed at destructive plate margins
Young fold mountains are 10 to 25 million years old and include the Rockies, Andes and Himalayas.
They form from sedimentary rocks which crumple and fold as plates push together, causing uplift

Question 24

Rift valleys (2)

Answer 24

At constructive margins in continental areas the brittle crust fractures as sections of it move apart.
Areas of crust drop down between parallel faults to form rift valleys.

Question 25

Deep sea trenches (3)

Answer 25

Found along the seaward edge of destructive margins.
They are long, narrow, steep-sided depressions in the ocean floor.
They mark where one plate begins to subduct beneath another.

Question 26

Island arcs (3)

Answer 26

A slightly curving line of volcanic islands
Formed at a subduction destructive margin off the coast of a continental plate
Or in the ocean where two oceanic plates converge.

Question 27

Benioff zone

Answer 27

The area where friction is created between two plates as a result of subduction at a destructive plate margin.

Question 28

San Andreas fault (4)

Answer 28

Visible line in the Earth’s crust
In California
Marks an active conservative plate margin
Earthquakes occur here

Question 29

Magma plumes (4)

Answer 29

A huge upwelling of super-heated magma
In the mantle
Rises from a ‘hot spot’
Melts through the crust causing lava to erupt at the surface

Question 30

Island chains (3)

Answer 30

A line of volcanic islands
Form in the middle of an ocean plate
From lava erupted when the plate moves over a mantle plume