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Folds analysis techniques

Folds analysis techniques. Goal : To apply some of the basic geometric techniques for analyzing folds and refolded folds. 1. Foliation bedding intersections. Three cases for overturned fold: Bedding upright, dipping more shallowly than foliation

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Folds analysis techniques

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

  2. 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

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

  4. 2. π-axes and β-axes Define fold axis using measurements of bedding from around the fold Plot on stereonet

  5. π-girdle: best-fit girdle to poles to beddingπ-axis: pole to π-girdle

  6. Finding π-axes 1. Plot poles to bedding 2. Find best-fit great circle

  7. β-axis: defined by intersections of bedding planes plotted on net

  8. 050°, 80°-SE 350°, 44°-NE 088°, 72°-NW Use both π-axis and β-axis methods Find a fold axis using these bedding measurements

  9. 3. Refolded folds

  10. Refolded folds recognition • Can often be found in outcrop • Regional patterns in facing direction • Interference patterns

  11. Interpret these maps: Draw in F1 and F2 axes and indicate plunge directions

  12. 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.

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