folds analysis techniques goal: to apply some of the basic geometric techniques for analyzing folds...

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

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  • Slide 1
  • Folds analysis techniques Goal: To apply some of the basic geometric techniques for analyzing folds and refolded folds.
  • Slide 2
  • 1. Foliation bedding intersections Three cases for overturned fold: a)Bedding upright, dipping more shallowly than foliation b)Bedding overturned dipping more steeply than foliation c)Bedding highly oblique to foliation
  • Slide 3
  • Note that for cylindrical folds, bedding- foliation intersection lineation lies close to fold hinge.
  • Slide 4
  • 2. -axes and -axes Define fold axis using measurements of bedding from around the fold Plot on stereonet
  • Slide 5
  • -girdle: best-fit girdle to poles to bedding -axis: pole to -girdle
  • Slide 6
  • Finding -axes 1. Plot poles to bedding2. Find best-fit great circle
  • Slide 7
  • Slide 8
  • -axis: defined by intersections of bedding planes plotted on net
  • Slide 9
  • Find a fold axis using these bedding measurements 050, 80-SE 350, 44-NE 088, 72-NW Use both -axis and -axis methods
  • Slide 10
  • Interpreting -axis diagrams
  • Slide 11
  • Slide 12
  • Concentric fold Fold with narrow hinge
  • Slide 13
  • Slide 14
  • Chevron fold Asymmetric fold Use caution!!
  • Slide 15
  • 3. Refolded folds
  • Slide 16
  • Refolded folds recognition 1.Can often be found in outcrop 2.Regional patterns in facing direction 3.Interference patterns
  • Slide 17
  • Slide 18
  • Interference patterns: Four end-member classes Type-0: Tightening of pervious folds Type-1: Dome and basin (Bullseye shapes) upright folds at a right angle to each other Type-2: Boomerang Type-3: Hook folds
  • Slide 19
  • Interpret these maps: Draw in F 1 and F 2 axes and indicate plunge directions
  • Slide 20
  • Steps to interpret maps 1.Draw two lines representing fold axes. Which one is refolded? 2.Identify pattern of younger and older rocks. e.g. youngest on outside 3.Is the hook/boomerang shape a syncline or anticline? 4.What decide what kind of fold refolded the first fold.
  • Slide 21
  • Sketch where these fold axes would plot on a stereo net
  • Slide 22
  • Type-2Type-3
  • Slide 23
  • Type-0Type-1 Type-2Type-3