STRUCTURAL GEOLOGY HATCHER 14 Flashcards
Wave like structures resulting from deformation of bedding, foliation or other ORIGINALLY planar structure
Folds
In which part of the stress regime does folding occur?
All deformation evnironments in the Crust
Deposits found in the hinges of a fold
Saddle Reef Deposits
Straighter or least curved segmets of a fault
Limbs
Parts of the fold with greatest cruvature
Hinge zones
The line moved parallel to itself to generate folded surface
Fold Axis or Axial Line
the line joining points of greatest curvature
Hinge Line
If the Fold Axis and the hingle line coindicdes the fold is
Cylindrical
The plane compose of several hinge lines on successive folded surfaces of the same fold
Axial Surface or Axial Plane
Fold hinges that is inclined to the horizontal
Plunge
Folds with non horizontal hinges are called
Plunging folds
A line that separates a concave curvature in one direction from concave curvature in the opposite direction
Inflection point
Crest to crest distance
Wavelength
Crest to Inflection oint distance and parallel to axial plane
Amplitude
Degree of leaning or direction of overturning of a fold and is only a property of assymetical fold
Vergence
Produced by relative motion of riginally adjcent reference ponts on either side of a slip surface duriing folding or other deformation
Slip lines
Largest folds in a given area
First order folds
smaller folds on the flanks
Second order folds
A smoothly varying surface tangent to the crest or troughs of a folded surface
Enveloping surface
Folds thata are concave towards older rocks
Anticline
A concave downward fold
Antiform
Folds that are concve towards younger rocks - that is younger strata are in the central part of the structure
Syncline
Concave up fold
Synform
antiform where in layering dips in all directions away from a central point
Dome
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
0
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
