Fold Thrust Belts Fold Thrust Belts Figure 1
Fold Thrust Belts
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). Glen S. Stockmal et al. Geological Society of America Special Papers 2007; 433: 63 -98 © 2007 by Geological Society of America
ANATOMY OF FOLDS • Crest, trough, Limbs, hinge zones, fold axis, axial plane, axial surface, plunge, wavelength, inflection point and vergence.
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.
Scale types of 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.
Parasitic Folds
Fault Related Folds Fault Bend Folds Fault Propagation Folds Includes Trishear Folds Decollement Buckle Folds
§ Flat-ramp-flat geometry for fault surface Fault Bend Folds § Fault surface exists across entire cross-section § Fold develops above ramp where limb angles related to fault dip
Classic Fault Bend Fold Example
Classic Fault Bend Fold Example Appalachian Mountains
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)
Foreland Hinterland
Additional Complexity
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