Deformation (Structural Geology)

Question 1

What are the two general types of deformation processes, with examples?

Answer 1

brittle (faults, joints…);

ductile (folds)

Question 2

What is stress?

Answer 2

force applied

Question 3

What is strain?

Answer 3

deformation - size and shape change as a result of applied stress/force

Question 4

What are the controlling factors of deformation, and how do they relate to those of metamorphism?

Answer 4

tempreature, confining pressure, directed pressure, time, fluids, original character of the rock;
exact same!

Question 5

What is often the only evidence of stress?

Answer 5

strain

Question 6

How does temperautre affect deformation?

Answer 6

rock is more ductile as temperature increases;

recrystallization (whose rates change with temp) changes rock behaviour

Question 7

How does recrystallization change rock behaviour?

Answer 7

makes rock behave more ductile and in a more homogeneous fashion

Question 8

How does tempearature change with depth, and how does this relate to deformation processes?

Answer 8

increases with increasing depth;

brittle deformation more likely to happen near surface of crust

Question 9

How does confining pressure affect deformation?

Answer 9

rock is more ductile as pressure increases

Question 10

How does confining pressure change with depth?

Answer 10

increases with depth

Question 11

How does directed/tectonic pressure affect deformation?

Answer 11

determines the orientation of deformation

Question 12

What are the 3 types of tectonic pressure?

Answer 12

compressive (squeezing);
tension (pulling apart);
shear (tearing)

Question 13

What is used to deduce stress?

Answer 13

strain - its geometry

Question 14

What limits the possible orientations of deformation?

Answer 14

free surface of lithosphere/atmosphere

Question 15

What is the major controlling stress in the crust, and what is its orientation?

Answer 15

gravity; vertical

Question 16

What orientations can plate tectonic forces be in?

Answer 16

vertical or horizontal

Question 17

How does time affect deformation and why?

Answer 17

fast deformation more likely to be brittle;
slow deformation more likely to be ductile;
since silicate minerals take time to change

Question 18

How do solutions affect deformation?

Answer 18

affect friction

Question 19

What does pressure solution do to deformation? (?)

Answer 19

slow ductile failure (?)

Question 20

How does rock type affect deformation?

Answer 20

minerals have different physical properties - strength, inhomogenetities…

Question 21

What is needed for the brittle/ductile transition in the crust?

Answer 21

10-15 km depth, 350-450 deg C

Question 22

What happens to a rock when it the stress on it is below the elastic limit?

Answer 22

rebounds from deformation

Question 23

What happens to a rock when the stress is in its ductile behaviour range?

Answer 23

when stress is released, rock stays bent; bending takes very little stress to increase

Question 24

What happens when a rock reaches its rupture strength?

Answer 24

breaks

Question 25

What is the strike line?

Answer 25

line representing the intersection of a geological feature (a plane) with the horizontal

Question 26

WHat is the dip?

Answer 26

inclination of a plane (of a geological feature) to the horizontal

Question 27

What is the relationship between the strike and dip?

Answer 27

dip is always at 90 degrees to the strike

Question 28

What types of brittle deformation exist?

Answer 28

joints and faults

Question 29

What are joints?

Answer 29

fractures with no displacement

Question 30

What are faults?

Answer 30

fractures along which movement has occurred

Question 31

What tyeps of faults are there?

Answer 31

dip-slip (normal, reverse, thrust), strike-slip, oblique-slip

Question 32

What are strike-slip faults?

Answer 32

shear horizontal movement - one block slides horizontallly past another (parallel to strike line), so there is no relative vertical motion

Question 33

What are dip-slip faults?

Answer 33

sldiding occurs up or down the slope (dip) of the fault

Question 34

What are oblique-slip faults?

Answer 34

anything not strike-slip or dip-slip - sliding occurs diagonally along fault plane

Question 35

What are normal dip-slip faults?

Answer 35

hanging rock slides down relative to other rock due to pulling tensile forces (must dig down to seam of coal)

Question 36

What are reverse dip-slip faults?

Answer 36

hanging rock slides up relative to other rock due to compressive forces (must dig up to seam of coal)

Question 37

What are thrust faults?

Answer 37

reverse fault with low angle

Question 38

How does the abundancy of joints relate to that of faults?

Answer 38

more abundant to faults

Question 39

When do joints form?

Answer 39

as soon as a rock can deform brittly

Question 40

In what type of rock are joints most regular?

Answer 40

homogeneous rock

Question 41

What is a normal result of uplift - rasing a rock to the surface?

Answer 41

decrease in pressure causes expansion and brittle deformation, creating joints

Question 42

What can joints vary in?

Answer 42

orientation, spacing, length

Question 43

What is a slickenside and how is it formed?

Answer 43

polished surface of fault (lineated ones have groooves indicating direction of fault movement); caused by slip on fault

Question 44

What is a fault gauge?

Answer 44

ground up rock of a fault zone; can be impermeable

Question 45

What is fault scarp?

Answer 45

small step on the ground surface where one side of a fault has moved vertically wrt the other

Question 46

What are vein?

Answer 46

mineral-filled fractures

Question 47

HOw are veins formed?

Answer 47

water gets into fracture (joint, etc.) and precipitates minerals from walls

Question 48

What two types of folds can be made?

Answer 48

anticlines and synclines

Question 49

Whate are folds cuased by?

Answer 49

compression (stress)

Question 50

What are anticlines?

Answer 50

up-fold - has arch-like shape; limbs dip away from the hinge

Question 51

What are synclines?

Answer 51

down-fold - trough-like shape; limbs dip toward the hinge

Question 52

What is the usual symmetry of folds?

Answer 52

symmetrical

Question 53

What does an asymmetrical fold look like?

Answer 53

one side is shorter than the other - wave is dipping to one side

Question 54

What does an overturened fold look like?

Answer 54

peak of fault bent so much it overshoots one of the "limbs"

Question 55

What do recumbant folds look like?

Answer 55

sideways

Question 56

What do isoclinal folds look like?

Answer 56

perfect "u" - limbs don't dip toward or away from hinge - perfectly straight

Question 57

Why is erosion required to bring folds to the surface?

Answer 57

folds form at depth

Question 58

What is a plunging fold?

Answer 58

dips below axis

Question 59

On what scales can deformations be found?

Answer 59

microscopic, mesoscopic (cm - 100 m), regional (km), tectonic (1000s km)

Question 60

What is the scale of amountain belt?

Answer 60

1000s of kms