Folding and Faulting Flashcards

1
Q

Fault

A

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

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2
Q

Throw

A

is the amount of vertical displacement measured vertically between the top of the same bed seen on both sides of the fault

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3
Q

Hanging wall

A

is the side that lies above the fault plane

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4
Q

Footwall

A

is the side that lies below the fault plane

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5
Q

Downthrow

A

is the side of the fault that has moved down

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6
Q

Upthrow

A

is the side of the fault that has moved up

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7
Q

Fault types

A

Dip-slip, strike-slip

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8
Q

Dip-slip fault

A

Where the movement along the fault plane is parallel to the dip of the fault plane

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9
Q

Normal

A

Hanging wall on the downthrow side
Dip-slip movement

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10
Q

Reverse

A

Hanging wall on the upthrow side
Dip-slip movement

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11
Q

Strike-slip fault

A

Where the fault plane is vertical and the movement along the fault is horizontal - parallel to the strike of the fault plane

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12
Q

Sinistral

A

Left handed movement

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13
Q

Dextral

A

Right handed movement

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14
Q

Features formed by faults

A

Graben and horsts, Slickensides, Fault breccia

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15
Q

Slickensides

A

is the polishing and striations found on a fault plane indicating the direction of relative movement

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16
Q

Fold

A

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

17
Q

Axial plane

A

is a plane that joins the hinges of all the beds. It bisects the fold

18
Q

Plunge

A

is the angle of dip of the fold axis from the horizontal

19
Q

Antiform

A

is a upward closing fold

20
Q

Synform

A

is a downward closing fold

21
Q

Symmetrical folds

A

Formed by equal pressure from both sides
The length of fold limbs is the same

22
Q

Asymmetrical folds

A

Formed by more pressure on one limb than the other limb
Limb length will be different on either side of the axial plane

23
Q

Overfolds

A

Formed by a lot more pressure one one side than the other side
Both limbs dip in the same direction but at different angles
The axial plane is inclined from the vertical
One limb of the fold is inverted

24
Q

Recumbent folds

A

Formed by very high pressures from one side
The axial plane must be sub horizontal less than 30 degrees
Both the limbs and the axial plane will be at very low angles
One limb of the recumbent fold is inverted
The rocks are usually incompetent or plastic

25
Isoclinal
Formed by large amounts of pressure equally from both sides They can be recognised by parallel limbs at angles of over 70 degrees forming closed and tight folds Axial plane traces are usually vertical They can be recognised on maps by outcrops of repeated and parallel beds
26
Monoclines
Formed by pressure from only one side They are folds with only one limb so they are step shaped folds They have two areas of nearly horizontal strata separating an area of very steeply dipping strata
27
Nappes
These are huge recumbent folds that have broken along thrust planes Movement is horizontal along thrust planes which are the lines along which a recumbent fold breaks
28
Domes
A dome is an anticlinal fold shaped like an upturned bowl The beds dip outwards all directions The oldest rocks are found in the centre Domes have roughly circular outcrop patterns
29
Basins
A basin is a synclinal fold shaped like a saucer The beds dip inwards in all directions The youngest rocks are found in the centre Basins have roughly circular outcrop patterns
30
Plunging
Where the axes of the folds are tilted so they dip away from the horizontal or plunge The angle of plunge is the angle between the axis and the horizontal plane A plunging fold will have a V shaped outcrop pattern It will have three angles of dip