FOLDS

Chapter 11: Description of Folds

Chapter 12: Kinematic Models of Folding

Most of the week’s lectures were based on slides. Some topics/terms covered:

Mechanisms of Folding

1 lateral forces (most common)

2 vertical forces (eg. diapirs, isostatic uplift)

3 folding related to faulting

4 ductile, differential flow

5 flow on unconsolidated sediments

6 drag (lateral shear stress)

 

 

Geometric features-

hinge point- the point of highest curvature along a fold

closure- the central line on fold (may or may correspond to hinge point)

inflection line- line where curvature changes from convex to concave

crest line- point of highest elevation on fold

trough line- point of lowest elevation

axial surface- plane of surface that connects adjacent hinge lines

fold axis- approximates the central hinge line of structure over large area

Classification-

By attitude of the fold axial plane (p 225)- upright, horizontal, moderately inclined

horizontal, recumbent, upright moderately plunging, vertical, reclined

 

Style of fold (p 228-231)

Bluntness- sharp, angular, subangular, subrounded, rounded, blunt

Tightness- acute (gentle, open, close, tight), isoclinal, obtuse (fan, involute)

Aspect Ratio P- ratio of amplitude to distance between adjacent inflection points of

fold- wide, broad, equant, short, tall

Other slides:

fault bend fold, disharmonic folds, basin and dome (interference in deformation to form intersecting waves), box fold.