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USGS CMG InfoBank: Types of Folds

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Comment: 08:29 - 09:56 (01:27)
Source: Annenberg/CPB Resources - Earth Revealed - 8. Earth's Structures
Keywords: structure, "fold hinge", "hinge plane", "fold geometry", "Scott Paterson", deformation

Our transcription: The line of greatest curvature along any layer in a fold is called the "fold hinge."
Linked together, the many different hinge lines of a fold make up the fold's hinge plane.
In an outcrop, the position of the hinge plane can be seen at a glance.
The orientation of the hinges and hinge plane of a fold and the amount of folding itself serve as a basis for further classifying the fold.
We can classify folds based on their orientations, whether certain parts of the fold tend to be upright.
Or we can turn the fold over, or turn it on its side, those would all be different types of folds that give us different information.
We can also look at the geometries of the folds; for instance, we can look at how tight the layering is folded.
Here is something where the layering is rather open.
We get these curved hinges in here and very planer limbs.
We could contrast this type of fold with something that looked like this where the folds are much tighter.
You could probably guess from comparing these two rocks that this one has been deformed a lot more or shortened a lot more in this direction than the other fold that I showed you.

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Page Last Modified: Thu Oct 31 04:28:21 PDT 2013  (chd)