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DISP Earth Science > Deformation (Structural Geology) > Flashcards

Deformation (Structural Geology) Flashcards

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1
Q

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

A

brittle (faults, joints…);

ductile (folds)

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2
Q

What is stress?

A

force applied

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3
Q

What is strain?

A

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

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4
Q

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

A

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

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5
Q

What is often the only evidence of stress?

A

strain

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6
Q

How does temperautre affect deformation?

A

rock is more ductile as temperature increases;

recrystallization (whose rates change with temp) changes rock behaviour

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7
Q

How does recrystallization change rock behaviour?

A

makes rock behave more ductile and in a more homogeneous fashion

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8
Q

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

A

increases with increasing depth;

brittle deformation more likely to happen near surface of crust

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9
Q

How does confining pressure affect deformation?

A

rock is more ductile as pressure increases

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10
Q

How does confining pressure change with depth?

A

increases with depth

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11
Q

How does directed/tectonic pressure affect deformation?

A

determines the orientation of deformation

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12
Q

What are the 3 types of tectonic pressure?

A

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

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13
Q

What is used to deduce stress?

A

strain - its geometry

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14
Q

What limits the possible orientations of deformation?

A

free surface of lithosphere/atmosphere

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15
Q

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

A

gravity; vertical

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16
Q

What orientations can plate tectonic forces be in?

A

vertical or horizontal

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17
Q

How does time affect deformation and why?

A

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

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18
Q

How do solutions affect deformation?

A

affect friction

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19
Q

What does pressure solution do to deformation? (?)

A

slow ductile failure (?)

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20
Q

How does rock type affect deformation?

A

minerals have different physical properties - strength, inhomogenetities…

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21
Q

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

A

10-15 km depth, 350-450 deg C

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22
Q

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

A

rebounds from deformation

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23
Q

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

A

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

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24
Q

What happens when a rock reaches its rupture strength?

A

breaks

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25
Q

What is the strike line?

A

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

26
Q

WHat is the dip?

A

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

27
Q

What is the relationship between the strike and dip?

A

dip is always at 90 degrees to the strike

28
Q

What types of brittle deformation exist?

A

joints and faults

29
Q

What are joints?

A

fractures with no displacement

30
Q

What are faults?

A

fractures along which movement has occurred

31
Q

What tyeps of faults are there?

A

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

32
Q

What are strike-slip faults?

A

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

33
Q

What are dip-slip faults?

A

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

34
Q

What are oblique-slip faults?

A

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

35
Q

What are normal dip-slip faults?

A

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

36
Q

What are reverse dip-slip faults?

A

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

37
Q

What are thrust faults?

A

reverse fault with low angle

38
Q

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

A

more abundant to faults

39
Q

When do joints form?

A

as soon as a rock can deform brittly

40
Q

In what type of rock are joints most regular?

A

homogeneous rock

41
Q

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

A

decrease in pressure causes expansion and brittle deformation, creating joints

42
Q

What can joints vary in?

A

orientation, spacing, length

43
Q

What is a slickenside and how is it formed?

A

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

44
Q

What is a fault gauge?

A

ground up rock of a fault zone; can be impermeable

45
Q

What is fault scarp?

A

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

46
Q

What are vein?

A

mineral-filled fractures

47
Q

HOw are veins formed?

A

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

48
Q

What two types of folds can be made?

A

anticlines and synclines

49
Q

Whate are folds cuased by?

A

compression (stress)

50
Q

What are anticlines?

A

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

51
Q

What are synclines?

A

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

52
Q

What is the usual symmetry of folds?

A

symmetrical

53
Q

What does an asymmetrical fold look like?

A

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

54
Q

What does an overturened fold look like?

A

peak of fault bent so much it overshoots one of the “limbs”

55
Q

What do recumbant folds look like?

A

sideways

56
Q

What do isoclinal folds look like?

A

perfect “u” - limbs don’t dip toward or away from hinge - perfectly straight

57
Q

Why is erosion required to bring folds to the surface?

A

folds form at depth

58
Q

What is a plunging fold?

A

dips below axis

59
Q

On what scales can deformations be found?

A

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

60
Q

What is the scale of amountain belt?

A

1000s of kms

DISP Earth Science (7 decks)

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