1. Fold Thrust Belts

2. Fold Thrust Belts
Figure 1. Balanced cross section of the southern Canadian Rocky Mountains (SCRM) at the latitude of Calgary, Alberta (after Price and Fermor, 1985). The southern Canadian Rocky Mountains are considered an archetypal thin-skinned fold-and-thrust belt, and they are used here as a general guide for scaling and interpretation of the numerical models. The positions of two principal detachments are indicated. Postdeformational erosion has removed ∼2–3 km of foreland basin strata at the deformation front, and correspondingly more of the deformed wedge farther to the west (left). S.L.—sea level.
Figure 1. Balanced cross section of the southern Canadian Rocky Mountains (SCRM) at the latitude of Calgary, Alberta (after Price and Fermor, 1985).
Glen S. Stockmal et al. Geological Society of America Special Papers 2007;433:63-98
©2007 by Geological Society of America

4. ANATOMY OF FOLDS
Crest, trough, Limbs, hinge zones, fold axis, axial plane, axial surface, plunge, wavelength, inflection point and vergence.

6. Vergence
Vergence of a fold applies only to folds having one limb that dips more steeply and is shorter than the other-an asymmetric fold. In symmetrical folds vergence is not a property. However, small folds on the limbs of symmetrical fold may exhibit vergence.
Study of vergence may be useful in working out the overall direction of tectonic transport of all structures in an area and help to fix an observer’s location on large fold.

8. Scale types of Folds Folds can present in all scales
microscopic (require magnification)
mesoscopic (specimen and outcrop size)
macroscopic (larger scale)
Pumpelly’s rule: small-scale structures are generally mimic larger-scale.

9. Parasitic Folds

12. Fault Related Folds Fault Bend Folds Fault Propagation Folds
Includes Trishear Folds
Decollement Buckle Folds

13. Fault Bend Folds Fault surface exists across entire cross-section
Flat-ramp-flat geometry for fault surface
Fault surface exists across entire cross-section
Fold develops above ramp where limb angles related to fault dip

17. Classic Fault Bend Fold Example

18. Classic Fault Bend Fold Example
Appalachian Mountains

19. Fault-Propagation Folds
Fault tip propagates thru
cross-section
Fold develops above ramp
with uniform forelimb angles
Original FPP has forelimb with
same dip, trishear dips flatten upwards (trishear = reality)

21. Foreland and Hinterland

22. Additional Complexity