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Geology, LEC 172 > Deformation, lectures 9 & 10 > Flashcards

Deformation, lectures 9 & 10 Flashcards

1
Q

Deformation takes place on a range of spatial scales…

2 examples

A
  1. atomic level in single crystals

2. regional scale within mountain belts

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2
Q

Deformation takes place on a range of temporal scales

2 examples

A
  1. seconds-minutes during seismic activity

2. Ma for mountain building (logarithmic scale used)

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3
Q

Equation for stress

A

force/area

same as pressure

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4
Q

Compression stress

A

acts to shorten an object

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5
Q

Tension stress

A

acts to lengthen an object

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6
Q

Normal stress

A

acts perpendicular to a surface (compression or tension)

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7
Q

Shear stress

A

acts parallel to a surface

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8
Q

The Earth is…

A

dynamic

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9
Q

The Earth is dynamic which means that

A

deformation occurred in the past and the present

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10
Q

Two types of compression stress

A

hydrostatic/uniform

directed/differential

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11
Q

Hydrostatic/uniform stress

type of compression stress

A

Uniform in all directions

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12
Q

Directed/differential stress

type of compression stress

A

isn’t uniform in all directions

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13
Q

Strain

A

A measure of the extent of deformation, eg: a measure of the change in shape or volume due to stress.

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14
Q

Strain

change in dimension…

A

change in dimension relative to the original dimension

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15
Q

Two types of deformation

A

plastic

brittle

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16
Q

Plastic deformation

A

results in folding

eg: folded dyke

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17
Q

Brittle deformation

A

results in fracturing

eg: fault in sedimentary rock

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18
Q

Faults and folds

A

Geologic features resulting from deformation, provide a record of the forces which operated in the past

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19
Q

Benefits of interpretation of geologic structures

3

A
  1. helps to understand the history of the Earth
  2. aids exploration of natural resources
  3. helps to select appropriate sites for infrastructure
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20
Q

Sources of information on deformation processes

4

A
  1. field observations
  2. lab experiments
  3. computer simulations
  4. theoretical calculations
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21
Q

Three factors which affect how minerals and rocks respond to stress

A
  1. temp. and pressure
  2. minerals/rock type
  3. strain rate (rate of deformation)
22
Q

Temperature and pressure

factors which affect how minerals and rocks respond to stress

A

more likely to deform under high temps.

23
Q

Mineral/rock type

factors which affect how minerals and rocks respond to stress

A
  • hard igneous/metamorphic rocks tend to behave as brittle material (faults)
  • softer sedimentary rocks tends to deform in a ductile manner (folds)
24
Q 
Strain rate (rate of deformation)
(factors which affect how minerals and rocks respond to stress)
A
  • rapid deformation may result in brittle failure/faulting

- slow deformation in plastic deformation/folding

25
Q

Dip and strike of strata

A

used to describe the orientation of deformed strata

26
Q

Strike

A

The direction of a line formed by the intersection of a horizontal plane with an inclined plane, such as a rock layer.

27
Q

What is strike direction relative to?

A

North,

compass used

28
Q

Dip

A

A measure of the maximum angular deviation of an inclined plane from the horizontal

29
Q

What is dip measured as relative to?

A

perpendicular to the strike direction

30
Q

Classification of folds

A

based on geomtery and symmetry, and orientation of fold axis

31
Q

Monocline

A

A step-like fold in strata with a zone of steeper dip in approximately horizontal sequence

32
Q

Mechanism of formation of monocline

2 steps

A
  • Differential compaction over underlying structure at edge of basin and greater compatibility of the basin fill
  • Reactivation if underlying fault coupled with uplift/ subsidence
33
Q

Non-plunging fold

A

fold axis is horizontal

34
Q

Plunging fold

A

fold axis is inclined

35
Q

Features of a plunging fold

A
  • plunging anticline or plunging syncline
  • all rocks dip away from the axis
  • oldest rocks are exposed in the centre
36
Q

Dome and basin

A

circular or oval equivalents of antiform and synform respectively

37
Q

Dome

A

beds dip away from a central point

38
Q

Basin

A

beds dip in towards a central point

39
Q

Classification of joints

A

based on geometry or process of formation

40
Q

Classification of faults

A

based on orientation of fault plane …

41
Q

Joints

A

Fractures along which little or no movement has occurred or movement is perpendicular to the surface.

42
Q

Faults

A

Fractures along which blocks on opposite sides of the fracture plane have moved.

43
Q

GPS & LPS

faults

A

greatest principle stress axis

least principle stress axis

44
Q

Two types of joints

A

tensional

cooling

45
Q

Cooling joints

A

commonly occur in basaltic lavas

46
Q

Antiform/anticline

A

an ‘n-shaped/up-arched’ fold

47
Q

Synform/syncline

A

A ‘u-shaped/down-arched’ fold

48
Q

Symmetrical/upright fold

A

Axial plane is vertical and each limb dips at the same angle

49
Q

Asymmetrical fold

A

Axial plane is inclined and limbs dips at different angles

50
Q

Overturned fold

A

one limb has been rotated so much that it is now upside down, common in mountain ranges

51
Q

Recumbent fold

A

Axial plane is horizontal, common in…

Geology, LEC 172 (6 decks)

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