Description of folds

1. Description of folds Matlab project Ana Isabel Martínez Poza

2. The classification of the folds is important because the structure produced by experimental models on deformed layered can be compared with the theoretical models of rock deformation and hence with the results on the geological processes. The following classification (Ramsay, 1967) offers a very sensitive method for determining slight changes in the fold geometry from layer to layer in a fold structure.

3. The geometrical classification of folds • This classification depends on the shape of the profile section of the folded layers. • The form of any one layer in the structure depends on the relationship of the bounding surfaces of the layer, and in particular, the relative rates of change of the inclination of these bounding surfaces. • There are several ways in which we can measure these relatives rates of change and hence describe the shape of the folded layer. • The successive positions of the fold hinges form an important curved or plane surface known as the axial surface.

4. Orthogonal thickness. In a cross section of any fold we can determine the thickness t∞ of the material between two folded surfaces by constructing tangents to each surface making an angle of 900-α with tha axial trace of the fold. t0= hinge zone of the fold. Thickness parallel to the axial surfaces, T. Describes the variation in thickness of the folded layers records the distance between the bounding the bounding surfaces measured in a direction parallel to the axial surface of the fold. In each fold we can determinate various parameters of amplitude, wavelength, rates of curvature and the size and curvature of the hinge zone for each surface. So we could make a complete and systematic description of the fold. Lines of equal dip, or dip isogons. On the profile section of the fold it is possible to determine points on the folded surface which have the same slope. By joining points of the same slope on adjacent surfaces, we obtain lines of equal slope known as dip isogons.

5. There are three types of fold which we can consider fundamental classes. • Their definition is based on the comparison of curvature changes on adjacent surfaces in the folded layer: Class 1: Folds with convergent dip isogons. Curvature of the inner fold arc always exceeds that of the outer arc. Subclass 1A: Folds with strongly convergent dip isogons. Subclass 1B: Parallel folds. Subclass 1C: Folds with weakly convergent isogons.

6. Class 2: Folds with parallel isogons. Curvature of the inner and outer arcs are equal. Class 3: Folds with divergent isogons. Curvature of the inner fold arc is always less than that of the outer arc

7. t’= tα / to T’= Tα/To Tα= thickness of the fold in the parallel direction if the axis of the fold. T0= thickness of the hinge of the fold α= angle of inclination tα= proportional thickness to= thickness of the hinge of the fold

8. Objetive: Anaylize this image and specially the folds marked in green. -- 

9. Matlab approach • Using the edge-based approach and the morphological approach to decide which develop the best structure of the folds. Edge-based Morphological

10. Different filters to enhance the folds edges. Best result: Bottom hat Skeleton Image after several filters Inverted image

11. Further coding • Get the axial plane of the fold. • Get the tangent lines of the fold. • Get the thickness of the fold, tα, to, Tα and T0. • Get the inclination α. In order to define the fold type.

12. Bibliography • Folding and fracturing of rocks. John G. Ramsay (1967). • Matlab image tool box guide.