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Geology > •Rock Deformation > Flashcards

•Rock Deformation Flashcards

1
Q

What are the two most important pressures for rock deformation and what causes them?

A

1) Lithostatic pressure caused by the weight of rock pushing down
2) Tectonic pressure/ lateral pressure caused by the movement of tectonic plates

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2
Q

What is the equation for force?

What is it measured in?

A

Mass x Acceleration

Measured in Newtons (N)

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3
Q

What is the equation for stress?

What is it measured in?

A

Force / Area

Measured in Pascals (pa)

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4
Q

What is the definition of strain?

A

The change in shape or volume due to an applied stress

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5
Q

What two stresses at created by force acting on an area?

How do they act?

A

1) normal stress
Acts perpendicular to a surface

2) shear stress
Acts parallel to a surface

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6
Q

What are the the three types of differential stresses?

What creates them?

Where do they exist?

A

1) Tensional stress
Created by divergent forces ⬅️➡️
Constructive plate boundaries

2) Compressional stress
Created by converging forces ➡️⬅️
Destructive plate boundaries

3) Shear stress
Opposing forces sliding past each other ↗️↙️
Conservative plate boundaries

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7
Q

What is the formula for Hooke’s Law?

What does each letter mean?

A

e= (l-lo) / lo

e= strain
lo= original length
l= new length
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8
Q

What is elastic strain?

A

Reversible and non- permanent stress

The removal of this stress creates an immediate return to the original shape

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9
Q

What is brittle failure?

What Rocks does is occur in?

A

Where the rock breaks ( create faults )

Happens in cold and dry rocks that are composed of hard, granular minerals e.g quartz, garnet and olivine

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10
Q

What is ductile deformation?

What rocks will it occur in?

A

Smooth strain which creates colds and shear zones instead of fractures

Occurs in warm and wet rocks or rocks composed of soft minerals e.g gypsum, clay and calcite

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11
Q

What does it mean when a rock behaves plastically?

When does it happen?

A

It will deform continuously in the same manner as moving fluid

It occurs when applied stress is increased until the yield strength of the rock is exceeded

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12
Q

What is a dip?

A

The direction of tilt measured from the horizontal

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13
Q

What is a strike?

A

The direction of a line at a right angle to the dip

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14
Q

What are the two types of fold?

What do they look like?

What are the called if they are the correct way up?

A

1) Antiform
Fold of the crest points up
Anticline

2) Synform
Fold of the crest points down
Syncline

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15
Q

What is the crest?

A

Upper surface at the top of a fold

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16
Q

What is the trough?

A

The upper surface at the bottom of the fold

17
Q

What is the hinge?

A

The area where the rock is most strongly bent

18
Q

What is the hinge line?

A

A line joining the points of maximum bending

19
Q

What is the fold axis?

A

The line of maximum bending along the fold crest

20
Q

What is the axial plane?

A

A line that divides the fold halves and is parallel to the hinge line

21
Q

What is a limb?

A

The area of fold between the hinges

22
Q

What is the plunge?

A

The difference in angle between the fold axis and the horizontal

23
Q

What is happening at a plunging fold?

What shape does it create?

A

The outcrop dips into the ground at angle of plunge

Creates a V-shaped outcrop

24
Q

What is happening at a non-plunging fold?

A

The surface outcrop is always parallel to the edge and the axial plane

25
Q

What is the fault plane?

A

The rock surface along which movement has occurred

26
Q

What is the hanging wall?

A

The rock above the fault plane

27
Q

What is the footwall?

A

The rock below the fault plane

28
Q

What is strike slip?

A

The movement parallel to the strike of the fault plane

29
Q

What is dip slip?

A

Movement parallel to the dip

30
Q

What is the throw?

A

The total vertical displacement

31
Q

A diagram to show the fault terminology

A

➡️heave
⬇️throw

⬆️strike slip
↘️dip slip
➡️ net slip

32
Q

What is a normal fault?

What stress causes it?

A

The hanging wall moved downwards

Caused by tensional stress ⬅️➡️

33
Q

What is a reverse fault?

What stress causes it?

A

Hanging wall moves upwards
(No more than 30 degree dip)

Caused by compressional stress ➡️⬅️

34
Q

What is a thrust fault?

What stress causes it?

A

Reverse fault of less than 15 degrees

Caused by compressional stress ➡️⬅️

35
Q

What is a strike-slip or transcurrent fault?

What are the two types?

A

Movement horizontal to the ground surface

1) Sinistral = block opposite moves to the left
2) Dextral = block opposite moves to the right

36
Q

What is an uncomformity?

A

An erosional boundary

37
Q

What is the differences above and below an unconformity?

A
  • Fossil types will vary
  • Rocks below are more deformed
  • Rock above contains included fragments from below
38
Q

What is a hiatus?

A

A time gap in the geological records where no rock is found/ recorded

39
Q

Where is a hiatus found?

A

At an unconformity

Geology (14 decks)

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