Chapter 10 PM-1

# 3 d shape cylindrical vs non cylindrical facing

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3-D shape – cylindrical vs. non-cylindrical Facing – whether fold is right-side-up or not. Orientation of axial plane and hinge line. Shape in a profile plane 4. What are the terms describing the interlimb angle? Gentle: 120-180, Open: 60-120, Tight: 10-60, Isoclinal: 0-10 Stereographic projections of bedding normals follow a great circle if fold is cylindrical

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5. What is the difference between parallel (concentric) and similar folds? Class I folds that have constant thickness are called parallel or concentric folds Because concentric fold anticlines have increasing curvature downward, they must die out along a decollement or bedding fault. Class II folds are called similar, because each hinge curvature is the same. They do not have to die out and always have thicker hinges than limbs. 6. What is a dip isogons and how do they relate to layer thickness – Dip isogons are a graphic representation of these curvature relationships. Dip isogons is a line that connects points of equal inclination on the inner and outer surface of a folded layer. Class I folds all have isogons that fan outward in anticlines because inner curvature > outer. Layer thickness does not change Class II folds all have parallel isogons because inner curvature = outer They are also characterized by thinner limbs and thicker hinges Class III folds all have isogons that converge upward in anticlines because inner curvature < outer They also have thinner limbs and thicker hinge zones 7. What class are parallel and similar folds? Parallel are class I and have constant thickness Similar are class II and have thicker hinges than limbs Fold Systems 8. Define the following terms: Enveloping surface – an imaginary surface tangent to hinges in a single folded surface Anticlinorim/synclinorium - large regional folds with associated parasitic folds on a variety of scales.
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• Fall '08
• Staff
• Geology, Thrust fault, Cylindrical fold fold, noncylindrical fold Fold, Noncyldrical fold- folds

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