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

Post on 16-Dec-2015

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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

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