Presentation on theme: "Folds analysis techniques"— Presentation transcript:
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 foliationBedding overturned dipping more steeply than foliationBedding 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-axesDefine fold axis using measurements of bedding from around the foldPlot on stereonet
5 π-girdle: best-fit girdle to poles to bedding π-axis: pole to π-girdle
6 Finding π-axes1. Plot poles to bedding2. Find best-fit great circle
18 Interference patterns: Four end-member classes Type-0: Tightening of pervious foldsType-1: Dome and basin (Bullseye shapes) — upright folds at a right angle to each otherType-2: BoomerangType-3: Hook folds
19 Interpret these maps: Draw in F1 and F2 axes and indicate plunge directions
20 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 outsideIs the hook/boomerang shape a syncline or anticline?What decide what kind of fold refolded the first fold.
21 Sketch where these fold axes would plot on a stereo net