STRUCTURAL GEOLOGY HATCHER 14 Flashcards by Sean Levi Abiera

Wave like structures resulting from deformation of bedding, foliation or other ORIGINALLY planar structure

Folds

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In which part of the stress regime does folding occur?

All deformation evnironments in the Crust

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Deposits found in the hinges of a fold

Saddle Reef Deposits

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Straighter or least curved segmets of a fault

Limbs

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Parts of the fold with greatest cruvature

Hinge zones

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The line moved parallel to itself to generate folded surface

Fold Axis or Axial Line

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the line joining points of greatest curvature

Hinge Line

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If the Fold Axis and the hingle line coindicdes the fold is

Cylindrical

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The plane compose of several hinge lines on successive folded surfaces of the same fold

Axial Surface or Axial Plane

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Fold hinges that is inclined to the horizontal

Plunge

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Folds with non horizontal hinges are called

Plunging folds

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A line that separates a concave curvature in one direction from concave curvature in the opposite direction

Inflection point

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Crest to crest distance

Wavelength

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Crest to Inflection oint distance and parallel to axial plane

Amplitude

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Degree of leaning or direction of overturning of a fold and is only a property of assymetical fold

Vergence

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Produced by relative motion of riginally adjcent reference ponts on either side of a slip surface duriing folding or other deformation

Slip lines

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Largest folds in a given area

First order folds

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smaller folds on the flanks

Second order folds

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A smoothly varying surface tangent to the crest or troughs of a folded surface

Enveloping surface

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Folds thata are concave towards older rocks

Anticline

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A concave downward fold

Antiform

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Folds that are concve towards younger rocks - that is younger strata are in the central part of the structure

Syncline

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Concave up fold

Synform

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antiform where in layering dips in all directions away from a central point

Dome

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synnform in which layering dips inward to a central point

Basin

An downward facing syncline

Antiformal Synclines

Upward Facing Anticline

Synformal Anticlines

Rocks that dip uniformly in one direction

Homocline

A step like fold produced by local steepening of an otherwise uniform regional dip

Monocline

A step like fold produced by local flattening of an otherwise uniform regional dip

Structural Terrace

How would you know if a fold is cylindrical?

If a fold axis can be traced or moved parallel to itself

Folds that deviate slightly from the ideal cylindricity

Aberrant Fold

Folds that contains hinges that are not parallel on successive folds

Non Cyndrical Fold

Folds that are non cylindrical and are generated by moving one end of a line in a cricular arc whie the other end stays stationary

Conical Fold

Strongly non cylindrical folds thata re closed at one end and fold hinges curve within tha axial surface

Sheath Fold

Folds with vertical axials surface

Upright Fold

one inverted limb

Overturned Fold

Axes plunge at nearly the same angle as the axial surface or when the axis plunge normal to the strike of the axial surface

Reclined Fold

Horizontal axes and axial surface

Recumbent Fold

Limbs are VERY GENTLY AWAY from or toward one another

Open Folds

Fold that have limbs are STEEPLY DIPPING away or toward one anotehr

Closed Folds

Tight Folds that have axial Surface and limbs parallel

Isoclinal fold

Flds with constant layer thickness

Parallel Folds

Parallel folds in which folded surfaces define cicular arcs and maintain same center of curvature

Concentric Folds

Folds that have lobate and nearly concentric shape and attentuate limbs (Isaw-Like)

Ptygmatic Folds

Folds that maintain their shape throughout a section and do not die out upward or downard but has varying thickness in the axial zones which is thicker and thinner in the limbs

Similar folds

Folds with straight limbs and sharp angular hinges

Chevron (Large Scale) and Kink Folds (mas sharp si kink)

Folds in which shape or wavelength changes from one layer to another

Disharmonic Folds

Folds in which Anticlines are are thinned while synclines are thickened

Suprataneous Folds

Angle between the limbs of a fold and is the measure of the tightness of a fold

Interlimb Angle

180-120

Gentle

120-70

Open

70-30

Closed

30-0

Tight

Isoclincal

negative angle

Elastica

Classifacation of angles based on Dip isogons which are lines connecting points of equal slope or dip

Rasmsay Classification

Isogons change direction faster than the bedding surface

Class 1

Isogons change direction in the same rate as bedding surface

Class 1B Parallel

Isogons change direction slower than the bedding surface

Class 1C

Isogons are parallel

Class 2 similar

Isogons change direction in the opposite sense to the surface they connect

Class 3

Classification based on mean ductility and dusctility contrast within the fold sequence (Generic mechanical Scheme)

Donath and Parker

Folds in which the shape are controlled by layering in the rocks

Flexural Folds

Folds in which layering serves only as displacement marker

Passive Folds

Formed from displacement or slip along beding surfaces that is analogous to holding an open or bending of a telephone book. (Within Layers) Maintaining Constant thickness

Flexural Slip

Involves applicaton of force transverse to the layer and form folds that are very gentle with large interlimb layers. May involve passive flow in response to such transverse forces that may be caused by Differential Compaction, Forceful intrusion

Bending

Occurs when force is applied parallel to the bedding or layering of rocks and the easiest way of relief is normal to the applied force. Often accompanied by Flexural slip in low T and P

Buckling

Slip at an angle to the layering that result in new cleavage or schistosity that accommodate movement parallel to the new surface and in which bedding and layering only serves as strain markers

Passive Slip

How do kink/ chevron forms?

Parallel compression og thinly layered rocks with an intial flexural slip

formed when there is moderate to high ductility contrast between layers of rocks and when deformation occurs highly ductile rocks undergo thinning while brittle rocks may not undergo appreciable thickness change

Flexural Flow

A uniform ductile flow due to lack of contrast in ductility between layers which in this case only serve as strain markers only

Passive Flow

examples of flexural flow folds

Simlar type folds (Class 1C and 3)

Examples of Passive Flow Folds

Ideal Similar type folds Class 2

Results where one set of folds overprints another

Superpose or Interference Folds

STRUCTURAL GEOLOGY HATCHER 14 Flashcards

(75 cards)