Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Geology > Geological Structures > Flashcards

Geological Structures Flashcards

1
Q

Define a fault

A

A fracture in a rock along which there has been an observable amount of displacement

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What events occur when stored stres is released?

A

Earthquakes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How are faults formed and how long can they be?

A

Tension, compression or shear forces
Few cm to hundreds of km

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What types of shattering may occur along the fault plane? What other process occurs?

A

Brecciation or fault gouge (finely ground). The movement of mineralising fluids/water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How is the downthrow side marked on a geological map?

A

A tick

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is throw?

A

The vertical displacement of rocks along the fault plane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Footwall, hanging wall, downthrown wall, upthrown wall

A

Below fault, above fault, moves down, moves up

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Two main types of fault?

A

Dip slip and strike slip

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Types of dip slip faults

A

Normal
Graben and Horst
Reverse
Thrust

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is a dip slip fault

A

Movement along the fault plane is parallel to the dip

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What type of fault does tension cause?

A

Normal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What type of fault does compression cause?

A

Reverse

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Describe a normal fault

A

Principally vertical stress direction due to lithostatic pressure, minimally horizontal
Occur close to surface where crust is stretched and fractured.
Hanging wall = downthrown (gravity).
Tension causes crustal extension
Breaks previously continuous beds of rock

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Describe graben

A

When two normal faults dip towards each other a graben (rift valley) is formed. Graben forms the downthrow between two faults. Occur at the centre of mid ocean ridge and E-African Rift Valley System

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Describe Horst

A

Two normal faults dip away from one another and form Horst - the elevated block as areas either side have dropped down

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Describe a reverse fault

A

Formed by principally horizontal compressional forces - shortening of the Earth’s crust close to the surface. Hanging wall = upthrown. Overlap in the strata causes repetition of formerly continuous bed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Describe a thrust fault

A

Type of reverse where fault dip is less than 45 degrees (usually between 10-40°). Associated w major fold mountain systems, w displacements measured in km. Can result in inverted strata

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Define a strike slip fault

A

Where the fault plane is (near) vertical and the movement along the fault is horizontal, parallel to the strike

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Two main types of strike slip faults

A

Tear and transform

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Describe tear fault

A

Result of shearing forces applied. Typically large scale with large displacements. e.g. Great Glen Fault

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Describe a transform fault

A

Associated w plate margins (conservative plate margins/transform plate boundaries). common at right angles to MOR. Result from different rates of movement within a plate and allow rigid plates to adjust for difference in rates

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Earthquake frequency at transform vs tear fails.

A

Few to none at tear faults as there is little to no relative movement

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What do dextral and sinistral mean

A

Right handed and left handed. If the block of rock on the opposite side of the fault has moved it the right it is dextral. If it has moved to the left it is sinistral

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Define slickensides

A

The linear striations (grooves and ridges) and polishing found in a fault plane indicating the direction of relative movement (parallel to the orientation of striations) caused by pieces of grinding rock between the walls.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Define fault breccia

A

The broken fragments from the rocks on either side of the fault plane. They are large and angular and made of hard competent rock, that may be cemented by minerals precipitated in the fault zone at a later stage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Define fault gouge

A

The very fine particles of rock formed when the grinding of rock along the fault plane occurs at very high pressure and frictional heating.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is mylonite?

A

A rock produced by dynamic recrystallisation of minerals on a fault plane (particularly of fault gouge)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Define a fold

A

A fold is a flexure in rocks where there is a change in the amount of dip in a bed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What causes folds

A

Horizontal compressive forces, usually at destructive plate margins

30
Q

Define antiform. What is an anticlinal fold

A

Upward closing fold with dips pointing inwards. Anticlinal when the age of the rocks is known, antiform describes only the shape

31
Q

Define synform. What is synclinal?

A

Downwards closing fold with dips pointing outwards. Synclinal when the age of the rocks is known, synform describes only the shape

32
Q

In regards to inter-limb angle:
1) Gentle
2) Open
3) Closed
4) Tight
5) Symmetrical/Upright
6) Asymmetrical/Inclined

A

1) 180-120°
2) 120-70°
3)70-30°
4) <30°
5) AP is vertical
6) AP dips, limbs have different dips

33
Q

Where are the oldest rocks in an anticline fold?

A

In the core

34
Q

Where are the oldest rocks in a syncline fold

A

The outside

35
Q

Define hinge

A

The line along which there is a change in the amount and or direction of dip forming the most sharply curved part of the fold

36
Q

Define axial plane trace

A

The outcrop of the axial plane at the earth’s surface

37
Q

Define plunge

A

The angle of dip of the axial plane from the horizontal

38
Q

Symmetrical vs Asymmetrical

A

S) angle of dip the same
A) angle of dip different
S) limbs same length
A) limbs diff lengths and limb w low angle of dip has wider outcrop than limb with higher angle
S) AP vertical
A) AP inclined

39
Q

Define dome

A

An anticline that dips away from the centre in all directions

40
Q

Define basin

A

A syncline that dips towards the centre from all directions

41
Q

Define oversold

A

Folds which have both fold limbs dipping in the same direction but by different amounts

42
Q

Define recumbent

A

Folds w axial planes and fold limbs close to horizontal, less than 30°

43
Q

Define nappe

A

Recumbent fold broken along thrust plane

44
Q

Isoclinal fold

A

Fold w parallel limbs nearly vertical in very tight folds

45
Q

Cross symbol on map?

A

Horizontal

46
Q

How are dykes drawn ?

A

Perpendicular to base of cross section

47
Q

Define stress

A

The force applied to rocks

48
Q

Define strain

A

The change in the shape or volume of a body as a result of applied stress (deformation)

49
Q

What is the equation linking the original length of the line, the strain and the change of length of the line in regards to how vertical stress affects perfectly elastic material

A

Strain=change of length/original length

50
Q

Define competent

A

Rocks that are strong and brittle that tend to joint and fault, staying the same thickness when they are deformed

51
Q

Three examples of competent rocks

A

Sandstones, limestones and most igneous rocks

52
Q

Define joint

A

A fracture in competent rocks along which no observable movement has occurred

53
Q

Define incompetent rocks

A

Rocks that vary in thickness when they are deformed as they behave in a plastic way. They are weak and plastic and tend to fold and develop cleavage

54
Q

Two examples of incompetent rocks

A

Mudstones and shales

55
Q

Define shear forces

A

Forces which act along a plane in the rock and promote sliding along that plane

56
Q

Go look at those sad little graphs sigh (p174)

A
57
Q

What three factors affect the stresses applied to a rock and the resulting strains

A

1) higher temp = more plastic, cold rocks = brittle
2) strength of rocks increases w confining pressure, determined by the weight of overlying rocks
3) time is crucial in determining the type of deformation - pressure applied short period of time rocks may behave brittle manner pressure applied over an extended time can result in plastic deformation

58
Q

What do tensional forces cause

A

Fracturing of rocks and crustal extension

59
Q

What do compressional forces result in

A

Fracturing or folding of rocks

60
Q

What do shear forces result in

A

The deformation of rocks in one plane usually horizontally. May result in faults or folds

61
Q

How can fossils be used to measure deformation?

A

Deformation of bilaterally symmetrical fossils or ooliths

62
Q

What forces may result in joints?

A

Folding, cooling or unloading of rocks

63
Q

Where do joints form

A

Competent rocks - they are brittle and break when put under tension. Joints in sedimentary rocks are usually found perpendicular to the beds

64
Q

What causes tectonic joints and what are their characteristics

A

Folding - tension joints parallel to the axial plane and cross joints on the limbs

65
Q

What causes cooling joints

A

Perpendicular to cooling surfaces of igneous bodies so oft vertical - Form as a result of contraction on cooling igneous rocks. The rock cools and crystallises, contracting into a series of columnar polygonal structures

66
Q

What causes Unloading joints

A

Lower pressure near the surface - often horizontal as well as vertical - load pressure declines as a result of uplift and erosion

67
Q

Why do rocks fracture under compressive forces

A

The outward surface, containing the competent rock of the bed is stretched more than the inner forces

68
Q

What are the two common forms of tectonic joints?

A

Tension joints (parallel to axial plane trace of the fold)
Cross joints (at angle to APT of the fold)

69
Q

Describe the cleavage/beddings in a rock in the normal and inverted limb

A

In both, platy minerals align perpendicular to the principal stress direction. On the normal limb, the bedding dips at a lower angle than the cleavage. On the inverse, the bedding dips at a higher angle than the dip of the cleavage

70
Q

How can you recognise bedding from photographs and diagrams?

A

Diff in colour or comp
Diff in grain size
Structures within beds and along planes

71
Q

How to recognise jointing

A

Fractures along which there is no displacement
Often perpendicular to bedding
Possible mineralisation along the joints
Only develops in competent rocks such as sandstones and limestones

72
Q

How to recognise cleavage from diagram or pictur

A

Rocks splits easily along parallel planes making slates
Often parallel to the axial plane of folds
Planes very close (few mm) together
Only in incompetent rocks like shales

Geology (8 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions