structural geology (week 2)

Question 1

what is deformation

Answer 1

• causes rocks to change shape, size, location or orientation

Question 2

what analysis can be performed on deformed rocks

Answer 2

• descriptive
• kinematic, where changes in position or shape of the rock
• dynamic, where forces/stress acting on rock *rheology

Question 3

how are things kinematically analysed

Answer 3

• motion of objects
• interpret deformational movements
• translation, distortion, rotation, dilation and dilation

Question 4

what is stress

Answer 4

• is the force applied to a given area and is defined per unit area
• stress= force/area

Question 5

what is differential stress

Question 6

what is stress ellipsoid

Answer 6

• maximum extension occurs when stress=3

Question 7

what is strain ellipsoid

Answer 7

• when maximum compression occurs towards stress=1

Question 8

what are the two types of strain and how is it formed

Answer 8

• product of stress
• brittle- cracking/fracturing
  -ductile- bending and flowing

Question 9

co axial vs non co axial

Answer 9

-CO AXIAL
-horizontal stretching/ shortening

NON CO AXIAL
- shear strain

Question 10

is a pure shear co axial or non-coaxial

Answer 10

co-axial

Question 11

is a simple shear co axial or non-coaxial

Answer 11

• non co axial

Question 12

under what conditions does brittle and ductile deformation occur

Answer 12

low temperature= brittle
high temperature= ductile

Question 13

deformation style is dependant of rheology, what factors come into play

Answer 13

• temperature
• minerology
• grain size
• rock fabric
• fluids

Question 14

how can strength be quantified in rocks

Answer 14

• a compression rig can be used to yield the strength of rocks and soils
• 3 principal axis of strength

Question 15

how can the failure envelope be calculated

Answer 15

• based on representative rig compression results
• ## represents the force needed to cause a specific material to fail (fracture)

Question 16

a very important example of modelled stress in rocks

Answer 16

• the shakespeare cliff

Question 17

what is a fault

Answer 17

-ma structural break in a rock across which there is notable dispacement

Question 18

what is a joint

Answer 18

• fractures which have no notable displacement
  important in engineering geology

Question 19

two examples of faults

Answer 19

• highland boundary fault
• moine thrust

Question 20

fault rock to describe the moine thrust

Answer 20

mylonites

Question 21

what are the 3 main types of fault movements

Answer 21

• dip slip
• oblique- slip fault
• strike- slip

Question 22

what are the types of dip slip faults

Answer 22

• normal fault
• reverse fault

Question 23

what is a normal fault

Answer 23

• hanging wall block moves down relative to the footwall
• extension of the earths crust thins the crust

Question 24

what are reverse dip-slip and thrust faults

Answer 24

• hanging wall block moves up relative to the footwall
• results in compression of the earths crust= thickens the crust
• ## reverse faults are steeper than thrust faults

Question 25

how do faults work as mineralisation zones

Answer 25

- precipitation of ore minerals can occur within the fault and surrounding fractures

Question 26

how do faults operate as conduits

Answer 26

- formation of hydrothermal ore deposits on the seafloor from fluid transport along faults

Question 27

what are horst and graben structures

Answer 27

- normal fault bounded valleys= grabens -normal fault bounded ridges=horsts for example, the basin and range province, in western USA

Question 28

how are mountain belts formed

Answer 28

- compression- thrust faults- mountain belts

Question 29

what is the process in which mountain belts build

Answer 29

orogenesis

Question 30

how do sinistral strike slip faults

Answer 30

- sinistral - (left lateral) strata on the opposite side of the fault plane is displaced on the left - dextral- (right lateral) - strata on the opposite side of the fault plane is displaced to the right

Question 31

how do faults operate as conduits

Answer 31

provide natural resources as hydrothermal ore deposits on the seafloor due to fluid transport along faults

Question 32

how do ores operate as mineralisation zones

Answer 32

- precipitation of ore minerals can occur within the fault and the surrounding fractures

Question 33

what deposit provides gold to the scotgold resource Limited

Answer 33

cononish

Question 34

what is strike

Answer 34

- orientation of a horizontal line on a planar structure

Question 35

what is dip

Answer 35

-angle of inclination on a planar structure

Question 36

what is dip direction

Answer 36

- the compass direction in which the planar structure is dipping

Question 37

how do folds form

Answer 37

- caused by compression stress parallel to the bedding planes in a rock body - ductile deformation process-very slow process (avg= 100,000 years to several mill)

Question 38

ANATOMY OF A FOLD

Answer 38

- hinge- zone of max curvature - hinge line- line of maximum curvature

Question 39

what can be used to quantify tightness

Answer 39

- interlimb angle - shows how much distrotion a rock has experienced

Question 40

what is the axial trace

Answer 40

- where the axial plane intersects the earths surface

Question 41

whats an antiform

Answer 41

- fold closes upwards (angry)

Question 42

whats a synform

Answer 42

- fold closes downwards (smiley!)

Question 43

old rocks in the fold core

Answer 43

synformal anticline

Question 44

young rocks in the core of the fold

Answer 44

antiformal syncline