## Interlimb angle fold stereonets

The amount of spread is also a function of how well behaved the populations is the natural variation, or dispersion and the amount of measurement error. Field Exercises. The red box and great circle are the programs statistical best-fit pole girdle and the pole to that girdle, which is the best estimate of the fold axis. It greatly aids in the visual interpretation of data clouds. The purple line and rectangle is a hand-picked estimate of the equivalent girdle and fold axis. If measurements of the strikes and dips are representative of the fold surface as a whole then distinct clusters likely represent fold limbs longer portions that should be representatively sampled more. A key and important finding here is that different fracture sets are vound in different rocks. The data was acquired by students during a field trip inand are from the west end of the Arbuckle mountains near Turner Falls and along thruway Objectives: To learn to plot linear and planar elements distributed in a 3D space. On the other hand biased sampling may produce clusters or patterns that do not reflect reality, especially if your sample size is small less than 30 readings.

29/10/ 6. FOLD SHAPE.

• How rounded or pointy is the hinge zone? FOLD SHAPE. • Interlimb angle: the angle between the limbs!. Pi-plots and folds on stereonets. 5.

Video: Interlimb angle fold stereonets Stereonets 2: Plotting fold data - with Carl Stevenson

some of the more common uses of stereonets in structural geology. . the best fit girdle relates to the interlimb angles. axis of a cylindrical fold is to construct a beta diagram (or. B-diagram). Any two. axial plane, interlimb angle, symmetry, and fold class. Simple equal-area.

Both limbs would be shallowly dipping remember that the poles are at 90 degrees and so the poles plunge steeply, and here the NE dipping limb readings are more prevalent. Download the exercise sheet clicking here Back to Top Exercise 3: Migmatites, Folds, Facing, Tillites Objectives: To improve participants outcrop analysis skills, deciphering cross-cutting relationship, rock and mineral identification, Structural analysis of fold.

Equal angle stereonets have distorted areas and so a symmetrical, bullseye data population will appear distorted. One could speculate that two limbs are evident in the two bullseye, and that the one limb is better represented and thus the folds may be asymmetric.

Video: Interlimb angle fold stereonets Stereonet 7 part1

It greatly aids in the visual interpretation of data clouds. This is so that when you are counting on the stereonet's margin and part of the counting circle is outside of the stereonet you can count the 'missing' portion which actually lies diametrically opposed on the other side of the stereonet.

Two major 'cloud' patterns often found are: a a bullseye distributionand b a girdle distribution.

### Field Exercises

Ice pops dc |
Some fractures are much more planar, others anastomose. You will need to decide on a contour interval. Contouring data is basically a way of mapping the density distribution of data.
Look at your percentage values and their pattern and decide which interval will serve the best. If you are dealing with planar data, plot it as poles since you can not contour great circles. |

The first exercise involves structural analysis in folded and metamorphosed data onto a stereonet, classify the fold, interpret the interlimb angle of the fold, and. Trough points (Mark with a T) Exercise 2: For the folded surfaces below measure the interlimb angles of: 1.

Antiform in the right of the photograph 30°. 2.

It is assumed that you will know how to plot structural data on a stereonet. The black lines are the great circle plots of the bedding.

You also have the strikes and dips of fault planes in the area. A key and important finding here is that different fracture sets are vound in different rocks. You can download the exercise sheet here: Exercise 1 Here is the fold we will visit: Below is a detail of the above aerial photograph

You will plot these data onto a stereonet, classify the fold, interpret the interlimb angle of the fold, and calculate the pi-axis.

Here, the structure is more complex with evidence for multiple phases of deformation that you will make measurements of and interpret using a stereonet.

## Stereonet analysis of data from Arbuckle mountains near Turner Falls Oklahoma

Repeat for every intersection until the all the grid intersections within the stereonet have been 'counted'. Back to Top Exercise 2: Folds Objectives: To improve participants outcrop analysis skills, deciphering cross-cutting relationship, rock and mineral identification, Structural analysis of fold.

Sometimes small-circle girdle distributions can also be found, indicating conical fold forms.

Kamb plots are where the departure from a random distribution of points is mapped. Bedding for Pennsylvanian conglomerates and sandstones, Turner Falls, Oklahoma.