Folds analysis techniques

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Folds analysis techniques
Goal To apply some of the basic geometric
techniques for analyzing folds and refolded folds.
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1. Foliation bedding intersections

• Three cases for overturned fold
• Bedding upright, dipping more shallowly than
  foliation
• Bedding overturned dipping more steeply than
  foliation
• Bedding highly oblique to foliation

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• Note that for cylindrical folds,
  bedding-foliation intersection lineation lies
  close to fold hinge.

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2. p-axes and ß-axes

• Define fold axis using measurements of bedding
  from around the fold
• Plot on stereonet

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p-girdle best-fit girdle to poles to
beddingp-axis pole to p-girdle
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Finding p-axes
1. Plot poles to bedding
2. Find best-fit great circle
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(No Transcript)
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ß-axis defined by intersections of bedding
planes plotted on net
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Find a fold axis using these bedding measurements

• 050, 80-SE
• 350, 44-NE
• 088, 72-NW

• Use both p-axis and ß-axis methods

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3. Refolded folds
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Refolded folds recognition

• Can often be found in outcrop
• Regional patterns in facing direction
• Interference patterns

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Interpret these maps Draw in F1 and F2 axes and
indicate plunge directions
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Steps to interpret maps

• Draw two lines representing fold axes. Which one
  is refolded?
• Identify pattern of younger and older rocks. e.g.
  youngest on outside
• Is the hook/boomerang shape a syncline or
  anticline?
• Decide what kind of fold refolded the first fold.