Lecture 4: Solid Earth Dynmics

Question 1

What mechanism did Alfred Wegner not have that would have been crucial to the continental drift theory?

Answer 1

That oceanic crusts are denser than continental which allows the latte to glide over the former

Question 2

What evidence did Alfred Wegner use for his theory?

Answer 2

South America and West Africa appeared to fit together like a jigsaw which was supported by the geological patterns on both continents

Question 3

What were the two geological patterns which matched up between South America and Africa?

Answer 3

Cratons: an ancient deep part of the crust

Orogenic Uplift: Essentially a mountain range

Question 4

What evidence do we have for the explanation of the matching up between South America and Africa?

Answer 4

The fossil record - some animals must have been able to migrate between the continents and so they must have been able to swim (?) or walk between them

Question 5

When could the sea floor start to be mapped and using what technology?

Answer 5

In the 1960s sonar pulses could be send through the ocean

Question 6

What was found out about the ocean bathymetry in the early 1960s using the sonar technology?

Answer 6

there was the existence of of ridges/mountain ranges in which the sea floor’s elevation was higher

Question 7

What is the name give today to the mountain ridge in the Atlantic that was found in the 1960s?

Answer 7

Mid-Atlantic ridge

Question 8

What research helped to improve the understanding of the mid-atlantic ridge and its geological significance?

Answer 8

Palaeomagnetism studies

Question 9

Give the brief explanation of sea floor spreading?

Answer 9

Known changing polarity of earth - studies found alternating metal orientation - Iron deposits orientated themselves with the earth’s polarity and this was then preserved in record - pattern back to ridge paired with the other side which suggested there was rock and metal emerging from ridge

Question 10

What other evidence was found on the Atlantic sea floor which also supported sea floor spreading?

Answer 10

Accumulated sediment depth increased with distance from ridge - those places further from ridge will have had more time to accumulate sediment compared to those at the ridge edges

Question 11

What subsequent problem was identified after the source of crust production was found (MAR)?

Answer 11

There must be somewhere else where the crust is being destroyed because the earth is not getting bigger

Question 12

If these huge crusts are being destroyed at some point then what must the destruction process be like? What would you consequently expect to find somewhere else?

Answer 12

Turbulent and not smooth - there must be earthquakes/seismic activity somewhere

Question 13

What evidence was there to support the idea of seismicity and plate destruction?

Answer 13

Seismic activity appeared to organise itself along certain lines that suggested they were the boundaries where plates were being destroyed.

Question 14

What did the presence of sites of destruction and construction suggest?

Answer 14

That there are plates that make up the earth’s surface

Question 15

What was a divergent plate boundary?

Answer 15

Crust being torn apart from eachother

Question 16

What is an example of an oceanic/oceanic divergent boundary?

Answer 16

MAR

Question 17

What is an example of a continental/continental boundary?

Answer 17

East African Rift Valley

Question 18

What Islands has the MAR created?

Answer 18

Iceland and Surtsey

Question 19

What is a convergent plate boundary?

Answer 19

Crust being forced together

Question 20

What is an example of an oceanic/continental convergent boundary?

Answer 20

San Andreas Fault

Question 21

What is an oceanic/oceanic convergent boundary example?

Answer 21

Caribbean

Question 22

What is an example of a continental/continental boundary?

Answer 22

Himalayan Mountain Range

Question 23

How are different volcanoes created on an convergent boundary that involves an oceanic plate?

Answer 23

The oceanic plate contains a lot of organic matter, sediments and other volatile materials that is less dense to the surrounding mantle when it gets sub ducted. It wants to escape so rises up through the crust.

Question 24

What sort of volcanoes can be created on an O/O convergent boundary?

Answer 24

Island Arc

Question 25

Where will the volcano form on an O/C convergent boundary?

Answer 25

It will probably form underneath and then above the continental crust

Question 26

What happens when there is a C/C convergent boundary?

Answer 26

It will force the land to squeeze thereby forcing it down and up. 80-85% of this squeeze will be forced down and around 15-20% will be forced up.

Question 27

How do you define a young mountain range?

Answer 27

<200mya

Question 28

Where are young mountain ranges located?

Answer 28

At convergent plate boundaries

Question 29

What is the name given to a plate boundary that has become relatively inactive?

Answer 29

Passive margins

Question 30

What are cratons?

Answer 30

These are particularly old parts of the continental crust that are places of early life

Question 31

What is an example of a craton and how old is it?

Answer 31

In Northwestern Australia, that is around 3Ga

Question 32

What does mantle flow like?

Answer 32

A glacier that does not simplistically flow up as a single plume and then down via two “cells” - it is more random and sporadic

Question 33

What is a Rayleigh cell?

Answer 33

A convection cell which better illustrates how the mantel cells operate

Question 34

What direction does the pacific plate move in?

Answer 34

NW

Question 35

What islands are created via different hot spots under the pacific plate?

Answer 35

Hawaii
Cobb Seamount
Austral Seamount Chain

Question 36

What happens when hot spots are located underneath continental crust?

Answer 36

It ruptures the crust creating a volcano that are much bigger in size and geographical coverage compared to those under oceanic crust.

Question 37

What is the name given to the volcanoes that form under continental crust?

Answer 37

Large Igneous Provinces

Question 38

How can we tell areas which are subducting?

Answer 38

By looking at areas with faster flow velocities to the areas surrounding them

Question 39

What is the Wilson Cycle?

Answer 39

This represents how the continent may change over time from separation to reattachment across the surface of the earth

Question 40

Outline the stages of the Wilson cycle

Answer 40

All united - divergence between continents - continents reunite on other side of earth

Question 41

What is the estimate time it takes for the Wilson Cycle to complete?

Answer 41

500mya

Question 42

How many possible supercontinents might there have been in the earth’s history?

Answer 42

~8-10?

Question 43

What are two other supercontinents other than Pangea?

Answer 43

Nuna and Rodina

Question 44

When is the next supercontinent expected to form from now?

Answer 44

250mya