Plate Tectonics Flashcards
1
Q
What are Tectonic plates?
A
- Plates are rigid, rocky sheets that ‘float’ on the surface of the Earth – process is called ISOSTASY
- They lie on top of underlying ‘plastic’ magma in the Earth’s mantle
2
Q
Where do the most earthquakes occur?
A
- Most earthquakes occur along the edge of the oceanic and continental plates.
3
Q
How many plates are there?
A
- The earth’s crust is made up of several pieces, called plates. The plates under the oceans are called oceanic plates and the rest are continental plates
4
Q
What are the major Tectonic plates?
A
The lithosphere is broken up into seven major plates:
- African plate
- Antarctic plate
- Eurasian plate
- Indo-Australian plate
- North American plate
- Pacific plate
- South American plate
5
Q
Study the diagram of the Earth’s Plates
A
https://docs.google.com/document/d/11SlS_6djE3BGAezT2-FeVRTdxG1P1jVyj-u3X2L5qDo/edit?usp=sharing
6
Q
What is the structure of tectonic plates?
A
- Plates are made of a layer of the Earth called the Lithosphere
- The Lithosphere is a combination of the Crust plus the upper solid mantle
- The Lithosphere ‘floats’ on the underlying Asthenosphere
7
Q
What is the Asthenosphere?
A
- The upper layer of the earth’s mantle, below the lithosphere, in which there is relatively low resistance to plastic flow and convection is thought to occur
8
Q
What are the main components of the lithosphere?
A
- The lithosphere is made up of rocks from two of the Earth’s major layers. It contains all of the outer, thin shell of the planet, called the crust, and the uppermost part of the next-lower layer, the mantle
9
Q
What is the Earth’s mantle and crust mainly composed of?
A
- Earth’s mantle is made up of rock containing silicon, iron, magnesium, aluminium, oxygen and other minerals.
- The crust, is made up of mostly oxygen, silicon, aluminium, iron, calcium, sodium, potassium and magnesium
10
Q
What causes the convection currents of magma?
A
- Earth’s core is very hot
- Earth’s Lithosphere is cold
- We get convection currents as hot magma rises to the Earth’s surface, cools and then sinks back down
- The end result is – plates are not static, they are mobile
11
Q
How do the magma convection currents work?
A
- Molten lava from the mantel rises, heated by the Earth’s core
- Near the surface the rock spreads in two direction and goes sideways.
- As it gets closer to the surface it begins to lose heat and eventually the much cooler rock sinks back down
12
Q
What causes the continents to move?
A
- Through the convection currents the spreading process of the Earth’s crust is very slowly dragged apart and it’s this that ultimately causes the continents to move
13
Q
What do volcanoes release?
A
- Where the plates collide, the rock on the seafloor containing carbon from the dead plankton is carried deep into the Earth
- As it descends, this layer of rock is heated so the rock melts, releasing carbon dioxide and thus, gas is returned back into the atmosphere during an eruption
14
Q
What is Continental Drift?
A
- The continents look like a jig saw puzzle
- This is because plates slip and slide or ‘drift’ past each other and have been moving around very slowly since the Earth differentiated.
15
Q
When was the Continental Drift theory proposed?
A
- The theory of Continental Drift isn’t that old – proposed by Alfred Wegener in 1910’s and only widely accepted in 1960’s
16
Q
List some of the super continents and how long ago they were formed
A
- Vaalbara (3300 MYA)
- Ur (3000 MYA)
- Kenorland (2750 MYA)
- Arctica (2500 MYA)
- Atlantica (2093 MYA)
- Atlantica/Nena (1827 MYA)
- Columbia (1816 MYA)
- Rodinia (1127 MYA)
- Pannotia (745 MYA)
- Gondwana (567 MYA)
- Pangaea (328 MYA)
- Gondwana/Laurasia (151 MYA)
- Laurasia (134 MYA)
17
Q
What is Palaeomagnetism?
A
- Palaeomagnetism is the study of the record of the Earth’s magnetic field in rocks, sediment, or archeological materials. Certain minerals in rocks lock-in a record of the direction and intensity of the magnetic field when they form
18
Q
When was the theory of continental drift accepted?
A
- The theory of Continental Drift was only widely accepted with a type of geophysical evidence called Palaeomagnetism
19
Q
How is Palaeomagnetism used to prove continental drift?
A
- The Earth is a big magnet, hence, North Pole and South Pole
- Every few million years the direction of the poles switches
- Rocks with magnetic minerals (i.e., iron) lock in the prevailing magnetic direction
20
Q
How is Palaeomagnetism evidence for plate movement?
A
- As rocks move away from certain types of plate boundaries, they lock in a magnetic signature which is symmetrical on both sides of the boundary
- Example on the google doc
21
Q
What are plate boundaries called and how many different types are there?
A
Plate boundaries are called ‘margins’ and there are 3 main types:
- Divergent
- Convergent
- Transform
22
Q
What is the Divergent type of plate boundary?
A
- A divergent plate margin is where the two tectonic plates are moving away from each other
23
Q
What is the Convergent type of plate boundary?
A
- A convergent plate margin is where the two tectonic plates are moving toward each other
24
Q
What is Subduction?
A
- When continental and oceanic plates collide, the thinner and more dense oceanic plate is overridden by the thicker and less dense continental plate. The oceanic plate is forced down into the mantle in a process known as “subduction.”
25
What is the Transform type of plate boundary?
- A Transform plate margin is where the two tectonic plates are sliding past each other
26
Study the diagrams of the Layers of the Earth, The Earths Magnetic field and the different types of plate margins
https://docs.google.com/document/d/11SlS_6djE3BGAezT2-FeVRTdxG1P1jVyj-u3X2L5qDo/edit?usp=sharing
27
What are the different types of Lithosphere?
- Continental Crust is thick and light, made of a rock called granite
- Oceanic Crust is thin and dense, made of a rock called basalt
28
What happens at Divergent Margins?
- Sea floor spreading (if it’s under the ocean) or rifting (if it’s on continents)
- New Lithosphere is being formed at divergent margins
29
What are some examples of Divergent Margins?
- The mid Atlantic Ridge, as seen by satellite, is enormous. Africa and America are moving further apart
- Rift Valley – a new ocean will form in the middle of Africa in a few million years
30
What happens at Convergent Margins?
- Volcano making (if ocean crust meets oceanic or continental crust)
- Mountain building (if continental crust meets continental crust)
31
What are the two types of zones created by Convergent Margins?
- Subduction zones
| - Collision Zones
32
Give an example of a subduction zone
- Denser oceanic crust subducting under lighter continental crust – formation of the volcanically active Andes Mountain Ranges in South America
= SUBDUCTION ZONE
33
Give an example of a collision zone
- Light continental crust slams into light continental crust and both push up – formation of the world’s highest mountains, the Himalayas
= COLLISION ZONE
34
What happens at Transform Margins?
- Faults and earthquakes as two plates slide past one another
35
Give two examples of transform margin effects
- The San Andreas Fault in the USA is the boundary between two plates – the Pacific Plate to the west and the North American Plate to the east
- The Alpine Fault in the South Island of New Zealand is also the boundary between two tectonic plates – the Indo Australian Plate to the west and the Pacific Plate to the east
36
What is the consequence for movement of Convergent Oceanic and either another oceanic or a continental plate?
- Volcanoes – as denser crust gets subducted under lighter crust it re-melts in the mantle and the hot material rises to the surface to form volcanoes. However, not all plate margins produce volcanoes, not all volcanoes are near plate margins
37
What is the consequence for movement of two Convergent, continental plates?
- Mountains – the product of collisions between massive plates
38
What is the consequence for movement of two Transform plates?
- Earthquakes – the friction as plates slide past, above and underneath each other means that earthquakes are always going to happen
39
What is another consequence of plate tectonics other than mountains, volcanoes and earthquakes?
- Biodiversity – it may have taken a long time, but different animals and plants moved along on the different plates creating geographical differences in species composition
40
How do we get earthquakes in the middle of a plate, like Australia?
- These are rare but they can be powerful
- Result from the accumulation of stresses at the nearest convergent plate boundary
- E.g. In the Newcastle Earthquake in 1989, the collision zone between the Australian Plate and the Pacific Plate
41
Study the diagrams for the types of Lithosphere, Divergent boundaries, Convergent boundaries and Transform boundaries
https://docs.google.com/document/d/11SlS_6djE3BGAezT2-FeVRTdxG1P1jVyj-u3X2L5qDo/edit?usp=sharing
42
What are Hot Spot Volcanoes
- Activity away from plate margins
- Hawaii is nowhere near a plate boundary but you’ve probably seen footage of volcanic eruptions there
- The mechanism for its activity is called a ‘hot spot’ = a thin layer in the Lithosphere where magma from the mantle presses up against the crust
- Yellowstone is another example of a Hot Spot volcano
