folds analysis techniques
Post on 30-Dec-2015
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DESCRIPTIONFolds 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
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.