Presentation is loading. Please wait.

Presentation is loading. Please wait.

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

Similar presentations


Presentation on theme: "Folds analysis techniques Goal: To apply some of the basic geometric techniques for analyzing folds and refolded folds."— 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: a)Bedding upright, dipping more shallowly than foliation b)Bedding overturned dipping more steeply than foliation c)Bedding 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-axes Define fold axis using measurements of bedding from around the fold Plot on stereonet

5 π-girdle: best-fit girdle to poles to bedding π-axis: pole to π-girdle

6 Finding π-axes 1. Plot poles to bedding2. Find best-fit great circle

7

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

9 Find a fold axis using these bedding measurements 050°, 80°-SE 350°, 44°-NE 088°, 72°-NW Use both π-axis and β-axis methods

10 Interpreting π-axis diagrams

11

12 Concentric fold Fold with narrow hinge

13

14 Chevron fold Asymmetric fold Use caution!!

15 3. Refolded folds

16 Refolded folds recognition 1.Can often be found in outcrop 2.Regional patterns in facing direction 3.Interference patterns

17

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

19 Interpret these maps: Draw in F 1 and F 2 axes and indicate plunge directions

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.

21 Sketch where these fold axes would plot on a stereo net

22 Type-2Type-3

23 Type-0Type-1 Type-2Type-3


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

Similar presentations


Ads by Google