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. 1. Foliation bedding intersections. Three cases for overturned fold: Bedding upright, dipping more shallowly than foliation - PowerPoint PPT Presentation

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

  • 1. Foliation bedding intersectionsThree cases for overturned fold:Bedding upright, dipping more shallowly than foliationBedding overturned dipping more steeply than foliationBedding highly oblique to foliation

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

  • 2. -axes and -axesDefine fold axis using measurements of bedding from around the foldPlot on stereonet

  • -girdle: best-fit girdle to poles to bedding -axis: pole to -girdle

  • Finding -axes1. Plot poles to bedding2. Find best-fit great circle

  • -axis: defined by intersections of bedding planes plotted on net

  • Find a fold axis using these bedding measurements 050, 80-SE350, 44-NE088, 72-NW Use both -axis and -axis methods

  • 3. Refolded folds

  • Refolded folds recognitionCan often be found in outcropRegional patterns in facing directionInterference patterns

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

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