Structural Exam 2 Flashcards
Vergence
Direction relating to the sense of asymmetry folds
Antiform
Rainbow shaped, age is unknown
Fold axis
Straight hinge on a cylindrical fold
Concoical fold
Doesn’t have a fold axis, but has a hinge line
Hinge
Top of a fold where the direction changes
Axial Plane
Successive hinge line lie on the same plane
Axial Trace
The intersection of the axial surface with any other plane
S-Fold
The right side of a parasitic fold
Z-fold
The left side of a parasitic fold
How is the attitude of a fold defined and described?
Hinge and axial surface orientation
Requirements of Buckling
- Active folding
- Layer has mechanical significance
- layer is shortened parallel to layering
- layer must be more competent than the surrounding material
Parasitic folds
Small folds related to larger folds
M-Folds
Top of the parasitic fold
Anticline
Rainbow shaped, age is known
Synform
Smile shaped, age is unknown
Syncline
Smile shaped, age is known
Synformal Anticline
Upside down anticline
Antiformal syncline
Upside down syncline
Cylindrical fold
Straight hinge line
Limb
Area between hinge areas
Axial surface
The surface containing hinge lines fro consecutive folded surfaces
Passive folding
Layer with no mechanical significance
Bending
Forces acting across layers causing folding, active folding mechanism
What effects the wavelength of a fold?
Thickness of the bed, strength of the bed, strength of the surrounding material
What mechanisms affect folding?
Orthogonal flexure, flexure shear (slip or flow buckling)
Where is strain concentrated in folding?
The Crux
What is the anticline symbol?
Line with perpendicular arrows that point outwards
What is the syncline symbol?
Line with perpendicular arrows that point inwards
Aysmmetric fold symbol
line with perpendicular arrows on each side pointing outwards
What is the overturned fold symbol?
Line with a U-shaped double arrow
Fabric
Geometric arrangement of penetrative and distributive components
Foliation
FAbric elements that is planar and parallel
Cleavage
Fabric elements that impacts a splitting property
How can cleavage be used to interpret folding patterns and younging directions?
the acute angle closes and whatever direction it closes in points to the hinge
Small crinkly lineation
Crenulation lineation
Large uniform scratches from glaciers
Glacial Striations
Grooves from the movement of a fault
fault slickenlines
intersection of 2 planar features
intersection lineation
layers show causing lineation
Bedding/cleavage lineation
The result of 2 equally developed tectonic cleavages
Mullion structures
layer sets compressed in some spots, beaded necklace like
Boudinage
Fabric element, slightly metamorphosed
stretch pebble conglomerate
Class 1a fold
Limbs are thicker than the hinge
Class 1b fold
Limb thickness is constant
Class 1c fold
Hinge is thicker than limbs
Class 2 fold
Inner and outer arcs have identical curvature
Class 3 fold
Curvature of outer arc is greater than the inner arc
Chevron folds
sharp hinges, straight limbs
Box fold
Two planes fold inwards, making omega sign
Ptygmatic Folds
irregular, chaotic, no constant thickness; usually
found in metamorphic rocks. Looks like a wiggle worm
Order of major foliation types based on temp and depth
Compaction –>Cleavage –>Pencil –>Slaty –>Phylittic –>Schistosity –>Gneissic
What leads to the presences of more cleavage
High clay content
Primary Fabric
Original to when the rock formed
Tectonic Fabric
results from stress/deformation/metamorphism
