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43 Cards in this Set

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Anticline

Fold that is convex up, in the direction of the youngest beds. Old in center.

Syncline

Fold that is convex down, in the direction of the oldest beds. Young in center.

Antiform & Synform

Convex up




Convex down

Facing direction

Direction of the younging of the beds.

Synformal Anticline

Fold that is convex down but oldest layer in middle, youngest on bottom.

Antiformal Syncline

Fold that is convex up but oldest layer is on top and youngest in middle.

Hinge point/line

Point of max curvature, all points on a folded surface form a line

Axial surface

Imaginary surface formed by connecting hinge lines of all folded surfaces.


Interlimb angle

Measure of angle between limbs of fold.

Concentric folds

Thickness doesn't change throughout folds.

Ptygmatic folds

Common in very ductile materials.

Symmetrical fold




Asymmetrical fold

Median surface & axial surface are perpendicular. Asymmetric if not.

Overturned folds

Have a limb that has rotated beyond vertical - a limb dipping past 90 degrees.

Gentle Fold




Open Fold




Tight Fold




Isoclinal Fold

170-179 degrees




90 - 170 degrees




10 - 90 degrees




0 - 10 degrees

Upright Folds




Recumbent Folds




Inclined Folds

Axial surface vertical




Axial surface horizontal




Axial surface inclined

Classifications of folds based on thickness (2):

1) Parallel/concentric folds: Layer thickness does not change (low T)




2) Similar folds: Layer thickness changes; thickening in hinge and thinning in limbs (higher T)

Cylindrical fold




Non- cylindrical

A well-defined linear fold axis (straight hinge line)


Too complex to have a single well-defined axial surface

Monocline

Step-like fold, only one limb

Anticlinorium




Synclinorium

An anticline that has limbs folded by smaller folds




A syncline that has limbs folded by smaller folds.

Dip Isogon classfication




Class 1




Class 2




Class 3

1) Isogons converge




2) Isogons parallel to the axial trace




3) Isogons diverge

Flexural Slip Folding

Folding is accommodated by slip along layer/bedding interfaces.

Flexural Fold Folding

Folding is accommodated by the plastic migration of material out of the high shear zones of the limbs into the low shear hinges.

Active folding

Fold profiles are based entirely on physical-mechanical properties of the layers

Passive folding

Generated by simple shearing are perfectly similar folds

Forced folds
Folds required to form geometrically as a result of another process.

What are Fault Bend Folds?




What is amplitude determined by?




What happens once the fold has achieved max amplitude?

Folds forced to form as a result of motion upon faults. Through going faults - slip is conserved.




Fold amplitude is determined by the thickness above the lower hanging wall flat.




Once the fold has achieved max amplitude, it only grows in width.

Fault Propagation Folds

Fault slip is not conserved. Fault displacement is taken up by folding.




Fault tip is marked by a ductile 'process zone'.




Ideally these evolve into fault bend folds.

Fabric

Built of minerals and mineral aggregates (fabric elements) with a preferred orientation that penetrate the rock .

Fabric elements

May include non-isotropic minerals, fossils, and clasts/lithics of any composition.

S - Tectonite




L - Tectonite




L-S Tectonite

Have a dominant planar fabric.




Have a dominant linear fabric, elongate in one direction.




Has elements of both.

So Bedding

Primary fabric.




S(1+n): Subsequent foliations found in rock.

Tectonic foliation

A planar structure formed by tectonic processes.

Cleavage

A secondary fabric element, formed under low T, that gives a rock the tendency to split along planar surfaces.

Continuous cleavage




Spaced cleavage

No uncleaved portion down to the grain scale.




Regions of uncleared rock separated by discreet cleavage planes.

Microlithons

Uncleaved rock

Types of continuous cleavage: Purely based on grain size

1) Compaction


2) Pencil (intersecting)


3) Slaty (fine-grained)


4) Phyllitic (med. grained, shiny)


5) Schistosity (coarse grained, can see micas)

Crenulation Cleavage

Two distinct foliations, older layer being cut by the younger.

Which would have a steeper angle of cleavage - sandstone, or shale?

Shale would have a lower angle than sandstone.

Axial planar cleavage

Cleavage parallels the axial plane.

Fanning Cleavage

Fans out, cleavage happened before folding.

Transecting Cleavage

Runs oblique.

Three ways cleavage can form:

1) Mechanical rotation of minerals (contributes a bit)




2) Directional Recrystallization (contributes a bit)




3) Pressure solution (dominant)

What is lineation?




What are the 2 Types:

Penetrative linear fabric.




1) Intersection: Intersection of two planar features.


2) Mineral and Stretching: Preferred alignment of minerals or elongate clasts due to deformation and/or recrystallization during deformation.