Chapter 2 - Plate Tectonics

Question 1

Francis bacon

Answer 1

Noticed that Africa fits with South America

Question 2

Give evidence for theory of continental drift

Answer 2

1) fossils of Mesasorus found coming to South Africa and Brazil
2) Geological evidence (rocks of similar age, type and structure)
3) coal deposits found under Antarctic ice caps and glaciations scars in warm areas
4) mid Atlantic Ridge
- 1000km wide
- 2.5km high
- young volcanic rocks
5) earth’s magnetic pole has had 171 reversals over the last 76 million years
6) seafloor spreading

Question 3

Earths layers

Answer 3

Oceanic crust

• consists of mainly basalt
• Average 6 to 10 km thick

Continental crust
-70 km thick

Mantle

• 2900 km deep
• temperature reaches 5000°C
  1) upper mantle : composed of silicate rocks rich in iron and magnesium, and is rigid layer
  2) asthenosphere - semi molten state

Core
-Consist of iron and nickel, and is the size of Mars
-Centre is 6371 km below earths surface
-temperature is 6200°C
Outer core is in a semi molten state and the inner core is solid

Question 4

What moves tectonic plate

Answer 4

Convection cell currents

Question 5

Magnetic declination

Answer 5

The Earth’s magnetic field tilt 11° to the planets rotational axis therefore the geographical poles of the Earth do not coincide exactly with the magnetic poles and this difference is called the magnetic declination

Question 6

Palaeomagnetism

Answer 6

The record of ancient strength and orientation of the Earth’s magnetic field preserved in a rock

Question 7

Polar wander path

Answer 7

A curved line traced out by success of positions of date at Paleopoles

Question 8

What is a Paleopole

Answer 8

Refers to the supposed position of the Earth’s magnetic North Pole in the past

Question 9

Mid ocean ridges

Answer 9

Elongated submarine mountain ranges who’s peaks lie only 2 to 2.5 km below sea level

Question 10

Deep ocean trenches

Answer 10

When the ocean floor reaches depths of 8 to 12 km which define elongated gated trenches

Question 11

Seamount chains

Answer 11

Chain of isolated submarine mountains which were once active volcanoes

Question 12

Fractured zones

Answer 12

Narrow band of vertical fractures at roughly right angles to mid ocean ridges

Question 13

Describe the nature of the oceanic crust

Answer 13

Much of the ocean floor is covered by a layer of sediment composed of Clay and the tiny shells of dead plankton but ocean ridges have no sediment on.
Contains no Grannite and no metamorphic rock
Common rock types on continents but only contains basalt and gabbro

Question 14

Active and passive plate boundaries

Answer 14

Active plate boundaries coincide with tectonic plate boundaries
Passive plate boundaries do not coincide with tectonic plate boundaries and characteristic of such plate boundaries is the development of a continental shelf

Question 15

Continental shelf

Answer 15

Abroad, shallow region on the surface of a thick accumulation of sediment cover that were deposited along a massive margin with a continental crust is thinner the norm

Question 16

Divergent plate boundary

Answer 16

A plate Boundary at which two plates move apart from each other

Question 17

Convergent plate boundary

Answer 17

A plate Boundry at which two plates move towards each other so that one plate sinks beneath the other

Question 18

Transform plate Boundary

Answer 18

A boundary at which one plate slips along the side of another plate

Question 19

Explain plate tectonics

Answer 19

The lithosphere of the Earth is divided into plates that move relative to one another and to the underlying asthenosphere
During plate movements the internal area of the plates remains largely rigid and intact but rock along the plate Boundry undergoes D formation

Question 20

Sea floor spreading

Answer 20

As to oceanic plates move apart, new oceanic lithosphere forms along the divergent boundary.
Process takes place at mid ocean ridges

Question 21

Pillow lava

Answer 21

Lava that spills from mid ocean ride axis and cools instantly to form a layer of basalt blobs on the sea floor

Question 22

Black smoker

Answer 22

Chimneys that spew hot mineralised water that rose through cracks in the sea floor, after being heated by magma below the surface

Question 23

Subduction

Answer 23

As two plates move towards each other, the oceanic plate may collide, or one plate Bends and sinks down into the asthenosphere beneath the other plate

Question 24

Downgoing and overriding plate in convergent boundaries

Answer 24

The plate that sinks in the process of subduction must be composed of oceanic lithosphere
The plate that does not sink in the subduction process can consist of either oceanic or continental lithosphere

Question 25

Wadati Benioff zone

Answer 25

A belt of earthquakes in the down going plate to a depth of 660km

Question 26

accretionary prism

Answer 26

a wedge shaped mass that includes sediment that had settled on the surface of the downgoing plate that gets scraped up during the subduction process

Question 27

volcanic arc

Answer 27

magma formed above the downgoing plate rises into the overriding crust and finally to the surface to form a chain of active volcanoes that parallels with the ocean trench

Question 28

forearc and back-arc region

Answer 28

forearc region is the area between the trench and the arc

the back-arc region is on the side away from the trench

Question 29

triple junctions

Answer 29

places where three plate boundaries intersect at a point

Question 30

hot spots

Answer 30

places where a plume of hot mantle rock rises from just above the the core-mantle boundary and causes abnormal volcanism at an isolated volcano