Lecture 1- deformation, stress and strain

Question 1

What is structural geology?

Answer 1

the study of deformation of rock by looking at their geometrical structures

Question 2

What do you need to get the big picture of an areas geology?

Answer 2

due to the geological record being so discontinuous must look at very small samples

Question 3

Why is structural geology imporant?

Answer 3

Mapping and exploitation of resources (oil, gas, ores, groundwater) (seismic survey)
Geological reconstruction of areas (alps)

Question 4

What is the method of structural geology?

Answer 4

Observe and measure which allows for restoration of original environment allowing possibility to know cause, mechanism and timing of deformation

Question 5

What can be seen from the 3D imaging of the Mid-Atlantic ridge?

Answer 5

Parallel striations on a fault plane

Question 6

What are corrugations?

Answer 6

the shaping of parallel ridges or grooves

Question 7

What are oceanic detachment faults?

Answer 7

faults found on the sea floor that allow for spreading of the lithosphere allowing more plate divergence

Question 8

Why wouldnt you expect to find a fault on the sea floor?

Answer 8

due to the magmatic processes which enact here

Question 9

What do detachment faults provide a new mechanism for the formation of?

Answer 9

ocean basins

Question 10

What is tectonics?

Answer 10

Set of processes that operate at a large scale (e.g., mountain building, plate motion) and generate a characteristic set of structures

Question 11

What is scale invariance/ fractalation?

Answer 11

an element in microscopic scale will be reflected exactly identical at the macroscopic scale

Question 12

What is an example location where foliation of gabbro linked to mountain building?

Answer 12

Tibet-Himalaya

Question 13

What are the 4 types of deformation?

Answer 13

Dilation (volume change)
Translation (change in position)
Rotation (orientation change)
Distortion/ strain (shape change)

Question 14

Is dilation an increase or decrease in volume?

Answer 14

both

Question 15

What is translation?

Answer 15

change in position of a rigid body

Question 16

What is rotation?

Answer 16

change in orientation

Question 17

Does rotation deformation have to occur at a central point in the object?

Answer 17

no it can occur elsewhere which leads to translation also the occurring

Question 18

What will the displacement field look like under strain?

Answer 18

longer arrows (faster movement) and shorter arrows leading to a skew in the rock

Question 19

What simple shear do with proportions?

Answer 19

shortening in one direction and extension in the perpendicular direction

Question 20

With simple shear what happens to the lines not parallel to shear direction?

Answer 20

they rotate

Question 21

What happens to orthogonal lines after deformation by simple shear?

Answer 21

no longer perpendicular

Question 22

How is deformation produced with pure shear?

Answer 22

contractional or extensional forces

Question 23

Do lines rotate in deformation by pure shear?

Answer 23

No they do not

Question 24

What happens to the orthogonal lines during pure shear?

Answer 24

they remain perpendicular

Question 25

What is strain like when thought of as a number?

Answer 25

dimensionless

Question 26

What is stress?

Answer 26

a force (F) applied over a unit area (A) producing deformation

Question 27

What is the measure of stress?

Answer 27

the same as a pressure (force/area) unit is N/m*2 or pascal (pa)

Question 28

Is stress visible?

Answer 28

No (i.e. you cant see gravity)

Question 29

What plate motion is affecting the Anatolian plate?

Answer 29

The northwards movement of the African and Arabian plates which push the Anatolian plate in to the stable (large) Eurasian plate

Question 30

What faults are created in Anatolian plate due to squeezing?

Answer 30

North Anatolian fault and the Eastern Anatolian fault

Question 31

What deformation is Anatolian plate experiencing?

Answer 31

Rotation

Question 32

What is compaction?

Answer 32

A reduction in the pore spaces between sedimentary rocks due to lithostatic pressure

Question 33

How much can sediments be compacted from their original volume?

Answer 33

50%

Question 34

What type of deformation does compaction induce?

Answer 34

Strain and dilation

Question 35

What is the Bolivian orocline?

Answer 35

a section of the Andean cordillera that has been bent into present arcuate shape

Question 36

What deformation occurred at the Bolivian orocline?

Answer 36

rotation and translation

Question 37

How did the Himalayan belt form?

Answer 37

When the Indian plate moved northwards ~8000km and collided with Asia

Question 38

What deformation did India undergo?

Answer 38

Translation and rotation

Question 39

What is serpentinisation?

Answer 39

the hydration of mantle rocks (peridotites)

Question 40

How does serpentinisation affect rock volume?

Answer 40

causes up to a 40% volume increase

Question 41

What rocks are involved in serpentinisation?

Answer 41

olivine breaks down into serpentine

Question 42

What type of deformation is serpentinisation?

Answer 42

dilation