folds analysis techniques

13
Folds analysis techniques Goal : To apply some of the basic geometric techniques for analyzing folds and refolded folds.

Upload: khristos-kellis

Post on 30-Dec-2015

58 views

Category:

Documents


2 download

DESCRIPTION

Folds 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

TRANSCRIPT

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

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

Note that for cylindrical folds, bedding-foliation intersection lineation lies close to fold hinge.

2. π-axes and β-axesDefine fold axis using measurements of

bedding from around the fold

Plot on stereonet

π-girdle: best-fit girdle to poles to bedding

π-axis: pole to π-girdle

Finding π-axes

1. Plot poles to bedding 2. Find best-fit great circle

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

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

3. Refolded folds

Refolded folds recognition1. Can often be found in outcrop

2. Regional patterns in facing direction

3. Interference patterns

Interpret these

maps: Draw in F1

and F2 axes and

indicate plunge

directions

Steps to interpret maps1. 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. Decide what kind of fold refolded the first fold.