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Geology > Fold terminology (Geological Maps and Structures) > Flashcards

Fold terminology (Geological Maps and Structures) Flashcards

1
Q

What is the hinge zone?

A

The region of the folded surface with the highest curvature

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2
Q

What are limbs?

A

Two areas of lower curvature along a folded surface, on either side of the hinge zone

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3
Q

What is a hinge / hinge line?

A

The line of maximum curvature along a single folded layer. Hinge lines may be curved or straight

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4
Q

What is a fold axis?

A

A straight hinge line

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5
Q

What is the hinge point?

A

The intersection of a hinge line with another surface (a cross section of the Earth’s surface)

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6
Q

What is the axial surface / plane?

A

The surface connecting the hinge lines of multiple folded layers

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7
Q

What is the axial trace?

A

The intersection of a fold’s axial surface with another surface. The axial trace is a line.

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8
Q

What is the crest line?

A

The line connecting the highest points on an antiform?

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9
Q

What is the trough line?

A

The line connecting the lowest points on a synform

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10
Q

What is a culmination/depression?

A

Highest/lowest points on a crest/trough line.

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11
Q

What is a dome/basin?

A

Area around a culmination on a crest line / depression on a trough line.

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12
Q

What is the inflection line?

A

Points on a single folded layer where the curvature of a limb is minimised / equal to zero

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13
Q

What is the inflection point?

A

The intersection of an inflection line with another surface (a cross section or the Earth’s surface)

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14
Q

What is the inflection surface?

A

The surface connecting the inflection lines of multiple folded layers

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15
Q

What is a cylindrical fold?

A

A fold with a straight hinge line

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16
Q

What is an antiform?

A

A fold which closes upwards

17
Q

What is a synform?

A

A fold which closes downwards

18
Q

What is a neutral fold?

A

A fold which closes sideways (folds without a crest/trough line)

19
Q

What is an anticline?

A

Fold with oldest layers in the core

20
Q

What is a syncline?

A

Fold with youngest layers in the core

21
Q

What is an interlimb angle?

A

The angle between two fold limbs. Used to define the tightness of a fold.

22
Q

What are the ways in which we describe the tightness of an interlimb angle?

A

Gentle
Open
Close
Tight
Isoclinal

23
Q

What is an isoclinal fold?

A

A tight fold with roughly parallel limbs

24
Q

What is roundness in terms of folds?

A

A measure of the curvature of a fold hinge.

25
Q

What are the ways in which we describe the roundness of a fold?

A

Round/blunt
Sub-angular
Sharp

26
Q

What is a horizontal fold?

A

A fold with a horizontal fold axis

27
Q

What is a plunging fold?

A

A fold with a non-horizontal fold axis

28
Q

What is an upright fold?

A

Fold with a vertical axial surface?

29
Q

What is an upright fold?

A

A fold with a vertical axial surface

30
Q

What is an inclined fold?

A

A fold with a non-vertical axial surface

31
Q

What is an overturned fold?

A

An inclined fold in which both limbs dip in the same direction

32
Q

What is a recumbent fold?

A

A fold in which the axial surface is horizontal

33
Q

What is a symmetric fold?

A

Folds where the fold axial plane bisects the limbs. Limbs are equal lengths

34
Q

What is an asymmetric fold?

A

Fold in which one limb is shorter than the other

35
Q

What is the vergence?

A

The direction of apparent shear of the upper, longer limb of an asymmetric fold.

36
Q

What is the wavelength?

A

Distance between two adjacent hinges

37
Q

What is amplitude?

A

The distance between hinge point to inflection point, measured in the plane of the axial surface perpendicular to the hinge line.

38
Q

What is a non-cylindrical fold?

A

A fold with a hinge line that is not straight

Geology (17 decks)

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