Folds Flashcards
Cylindrical folds:
progressive curvature, hinge zone would wrap around a cylinder
Kink/chevron folds:
sharp hinge zones, localized, planar limbs
Symmetrical folds:
limbs of same length and dip
Asymmetrical folds:
limbs of different lengths and dips
Fold vergence:
Direction fold is leaning, or direction of short, steep limb. Needs to be evaluated in fold profile plane
Parallel folds
folds marked by uniform thickness
Similar folds
thicker near hinge, thinner towards limbs, same geometry between bedding
Synforms:
a fold that is concave up
Antiforms:
a fold that is convex up
Monoclines:
relatively flat lower layer, steep incline over a short distance, into a flat upper layer (2 hinges, 1 anticline and 1 syncline) connected by middle limb, extensive trend (150km+ in length), Colorado Plateau
Hinge lines:
like a crease down the middle, or points on the surface of the fold with maximum curvature, measured by trend and plunge
Hinge zones:
location on a fold with maximum curvature
Limbs:
flanks of a fold
Axial planes:
an axial surface that is planar
Axial surfaces:
passes through all points of maximum curvature in all stacked layers, irregularly curved fold, described in terms of strike and dip
Axial traces:
line that passes through successive hinge points in stacked folded surfaces, OR GENERALLY a line of intersection of the plane with any other surface
Fold profile planes:
plane perpendicular to hinge
Name some types of folds
chevron, circular, cuspate, elliptical, box, teardrop
Inter-limb angle:
describes the fold tightness of a limb (internal angle between limbs)
Gentle inter limb angle
• Gentle 170–90°
open inter limb angle
• Open 90–30°
tight inter limb angle
• Tight 30–10°
isoclinal
• Isoclinal 10–0°
Class 1A
Parallel, inner arc curve > outer arc curve, layer thickness of hinge > layer thickness of limbs
Class 1B
Parallel, inner arc curve > outer arc curve, uniform layer thickness
Class 1C
between parallel and similar folds
Class 2
similar fold, inner arc curve = outer arc curve
Class 3
similar folds, outer arc curve > inner arc curve
