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43 Cards in this Set
- Front
- Back
Anticline |
Fold that is convex up, in the direction of the youngest beds. Old in center. |
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Syncline |
Fold that is convex down, in the direction of the oldest beds. Young in center. |
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Antiform & Synform |
Convex up Convex down |
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Facing direction |
Direction of the younging of the beds. |
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Synformal Anticline |
Fold that is convex down but oldest layer in middle, youngest on bottom. |
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Antiformal Syncline |
Fold that is convex up but oldest layer is on top and youngest in middle. |
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Hinge point/line |
Point of max curvature, all points on a folded surface form a line |
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Axial surface |
Imaginary surface formed by connecting hinge lines of all folded surfaces.
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Interlimb angle |
Measure of angle between limbs of fold. |
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Concentric folds |
Thickness doesn't change throughout folds. |
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Ptygmatic folds |
Common in very ductile materials. |
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Symmetrical fold Asymmetrical fold |
Median surface & axial surface are perpendicular. Asymmetric if not. |
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Overturned folds |
Have a limb that has rotated beyond vertical - a limb dipping past 90 degrees. |
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Gentle Fold Open Fold Tight Fold Isoclinal Fold |
170-179 degrees 90 - 170 degrees 10 - 90 degrees 0 - 10 degrees |
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Upright Folds Recumbent Folds Inclined Folds |
Axial surface vertical Axial surface horizontal Axial surface inclined |
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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) |
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Cylindrical fold Non- cylindrical |
A well-defined linear fold axis (straight hinge line)
Too complex to have a single well-defined axial surface |
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Monocline |
Step-like fold, only one limb |
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Anticlinorium Synclinorium |
An anticline that has limbs folded by smaller folds A syncline that has limbs folded by smaller folds. |
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Dip Isogon classfication Class 1 Class 2 Class 3 |
1) Isogons converge 2) Isogons parallel to the axial trace 3) Isogons diverge |
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Flexural Slip Folding |
Folding is accommodated by slip along layer/bedding interfaces. |
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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. |
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Active folding |
Fold profiles are based entirely on physical-mechanical properties of the layers |
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Passive folding |
Generated by simple shearing are perfectly similar folds |
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Forced folds
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Folds required to form geometrically as a result of another process.
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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. |
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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. |
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Fabric |
Built of minerals and mineral aggregates (fabric elements) with a preferred orientation that penetrate the rock . |
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Fabric elements |
May include non-isotropic minerals, fossils, and clasts/lithics of any composition. |
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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. |
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So Bedding |
Primary fabric. S(1+n): Subsequent foliations found in rock. |
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Tectonic foliation |
A planar structure formed by tectonic processes. |
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Cleavage |
A secondary fabric element, formed under low T, that gives a rock the tendency to split along planar surfaces. |
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Continuous cleavage Spaced cleavage |
No uncleaved portion down to the grain scale. Regions of uncleared rock separated by discreet cleavage planes. |
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Microlithons |
Uncleaved rock |
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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) |
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Crenulation Cleavage |
Two distinct foliations, older layer being cut by the younger.
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Which would have a steeper angle of cleavage - sandstone, or shale? |
Shale would have a lower angle than sandstone. |
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Axial planar cleavage |
Cleavage parallels the axial plane. |
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Fanning Cleavage |
Fans out, cleavage happened before folding. |
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Transecting Cleavage |
Runs oblique.
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Three ways cleavage can form: |
1) Mechanical rotation of minerals (contributes a bit) 2) Directional Recrystallization (contributes a bit) 3) Pressure solution (dominant) |
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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. |