Structural Exam 2 But Better Flashcards
Hinterland
The direction towards the more deformed
Foreland
Direction towards the undeformed
Allochthonous
The part that is moving
Autochthonous
The part that isn’t moving
Decollement
The stationary, more competent layer under the surface that contributes to the thin-skinned deformation
What is Critical Taper theory
Deformation in the hinterland builds to the critial taper, once reached the thrust sheet moves.
What ways is the critical angle restored?
By forming a thrust fault, eroding the hinterland, and normal faulting caused by gravity
Duplex
Thrust sheet that has a floor thrust and a roof thrust
Free folds
based entirely on physical mechanical properties
forced folds
requires bending and stretching
Fault-bend-fold
The start of a duplex
Forced-propagation-fold
The start of an imbricate fold
Releasing bends
curve in the fold that causes a gap
Restraining bends
curve in the fold that causes bunches
What is the result of releasing bends
extension
normal faults
Grabens/basins
What is the result of Restraining bends
Compression
Reverse faults
uplift/mountains
In a left lateral slip, which direction is the Riedel shear pointed?
Right (opposite)
In a left lateral slip, which direction is the en echelon array pointed?
left
Stratography is known
____cline
Stratography is unknown
____form
Stratography is normal
Young over old
Stratgraphy is not normal and peaks upward
antiformal syncline
Stratography is not normal and peaks downward
synformal anticline
in sequence thrusting
a thrust sequence that has formed progressively and in order in one direction
step over to the left
compression
step over to the right
extension
Transpression
Transform body with compression
Transtension
Transform body with extension
Overturned
At least 1 limb is rotated beyond vertical
Hinge line
line of max curvature on a folded surface
Limb
side of the arch before the crest
axial surface/plane
surface that contains hinge lines from consecutive folded surface
fold axis
in cylindircal fold, it is the part that resembles a fold around a tube. Also known as straight line hinge
Kink fold
Lightning bolt emoji
Chevron fold
sharp angles, cartoon shark teeth
Box fold
boxy or omega shaped
Ptygmatic folds
no consistancy, wiggly worms
Where and why do foreland basins form?
Form at the base of mountains and are result of immense mass on top, resulting in bending to compensate
A flat ramp flat fault formed in a fold and thrust sheet promotes development in which type of fold
fault bend fold
Buckling
Force from either side causing it to eventually buckle/bend
Passive folding
layering with no mechanical significance formed by differential slip/flow along closely spaces planes
fake folding
Bending
rock is stretched, causing forces from above and below to concave the middle
Boudins
Rock anal beads
Laccoliths
Volcano that never breached the surface, depositing igneous rock below the surface causing a bulge above.
Class 1 A folds
Thicker limb, thinner hinge
Class 1B folds
limb = hinge thickness
Class 1C folds
Thinner limbs, thicker hinge
Class 2 fold
curvature of outer arc is same as inner arc
Class 3 folds
curvature of outer arc is tighter than inner
When viewing the cross section of a folding sequence of rocks, an imaginary line that connects the hinges of the fold from each layer defines the:
Axial trace
Folds that have stretched outer arcs and compressed inner arcs are called
neutral surface folds
What causes neutral surface folds
orthogonal flexure
T of F: Another term for buckling is active folding
False, bending
Fold vergance
axial trace is rotated
Instead of arcs, its white caps
What factors effect wavelength
thickness
strength
strength of surrounding rock
The symbol for anticline
Horizontal line with arrows pointed away north and south of it
Symbol for syncline
Horizontal line with arrows pointed in north and south of it
Overturned symbol
Arrows on a curve pointing towards hinge line
Recumbant fold
Fold that is on is side
Two strong buckled sandstone layers produce class 1B folds. A weak shale layer in between the two layers is likely to produce what class of fold?
Class 3 fold
When looking at an image where a quartz vein goes from straight in section a to wiggly in section B, what differences can be said about the surrounding rocks?
A is more resistant aka less viscous
T or F, a non-cylindrical fold does not have a fold axis
True
T or F, a viscosity difference is needed for buckling to occur
True
What does it mean that parasitic folds show vergence?
They are asymmetrical
In a flexural slip/flexural flow, which part will have the most strain?
The limbs
In orthogonal flexure, where is the most strain?
The hinge
