Fold Mechanics

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Fold Mechanics
Goal To understand some basic mechanisms that
operate during fold formation
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Active vs. Passive folding

• Passive folding Layers play no mechanical role
  in developing folds.
• Active folding Layer thickness and viscosity
  determine fold shape
• Active folding involves buckling or bending of
  stiff (more viscous) layers

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Layer thickness, viscosity, and fold shape

• Thicker layer greater arc length
• Greater viscosity contrast greater arc length

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(No Transcript)
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Finite element numerical model
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Data from rocks
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High or low viscosity ratio?
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High or low viscosity ratio?
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Some folding mechanisms

• Flexural slip folding
• Neutral surface folding
• Shear folding

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• Flexural slip folding Layers slip past one
  another during folding. Active folding.
• Generally forms parallel folds or chevron folds
• Still requires deformation in the hinge zones of
  individual layers

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• Neutral surface folding Folded layer contains
  only one plane with no internal deformation, the
  neutral surface. Active folding.

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• Shear folding Rocks are sheared unevenly like a
  deck of cards.

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Make a shear fold then find a way to prove that
it is a similar fold