Topic – Fold Presented - PowerPoint Presentation

1. Topic –FoldPresented byDr. R. R. GawandeAssociate ProfessorDepartment of GeologyDeogiri College, Aurangabad

2. ContentsIntroductionDescriptions of fold Elements of foldTypes of foldCausesThank you

3. Fold may be definde as a curved or zig zag structure shown by the rock bed. In other words wavy undulations in the rock beds are called as folds. They consist of crest & trough in alternate manner. They are best displayed in the sedimentary rocks. The sizes of folds vary greatly.When the compressional stress act on body that time made a fold.Fold

4. undulations in the rock beds Horizontal deposited rock beds

5. Fold Terminology

6. Hinge: It is the area of maximum curvature. It is closure of fold sometimes. Limb: these are the areas between the hinges or in other words these are sides of the fold. Hinge line: it is possible to define a hinge line as line of maximum curvature. The hinge line may be horizontal, inclined or vertical. A single fold is comprised of a hinge and 2-limbs.Axis : The line or plane which divides the fold into two equal halvesAxial Plane : The axial plane is the surface connecting all hingesCrest and troughPlunge : Folds having inclined axis are called “plunging fold". it's angle of inclination of fold axis with the horizontal, is called the “angle of plunge”Fold Terminology or parts of fold

7. limbsGenerally planar region of a fold which lies between two adjacent hinge lines and is confined between the zones of maximum curvature

8. Types of folds Based on Interlimb angleInterlimb angleFold>0-30 °Tight30-70 °Close70-120 °Open 120-180°Gentle

9. Hinge

10. Axial planeThe axial plane of a fold is the plane or surface that divides the fold as symmetrically as possible. The axial plane may be vertical, horizontal, or inclined at any intermediate angle. An axis of a fold is the intersection of the axial plane with one of the strata of which the fold is composed

11. Attitude of Axial Surface

12. Crest and trough: In inclined fold the highest and lowest points on the fold, generally known as undulationsCrest and trough

13. Amplitude and wavelength: These two elements are helpful in measuring the size of the fold. If the hinges are not visible. λ/2 may be measured, instead by taking the distance between the two inflection points on the either sides of the fold hinge. ‘inflection point are points where, the sense of curvature changes from one fold to other. The amplitude or height of a fold may be measured by taking half of the perpendicular distance from the hinge to the line between the two adjacent hinges, or the perpendicular distance from the hinge to the line between two inflection points.’

14. Amplitude and wavelength

15. Nomenclatures of fold/Classification of foldsBased on Symmetry of the foldBased on Axial SurfaceBased on dip of Isogons

16. Anticline & SynclineAnticline- convex upwardSyncline- convex downwardYounger at centreOlder at centrecc

17. Based on Symmetry of the foldSymmetric fold- M & WAsymmetric- Z & S

18. Asymmetrical fold- An Asymmetrical fold is one of the where the limbs dip at unequal angles in opp. Direction. In this case the axial plane is inclined and it not necessary passes through the crest line.symmetrical fold It is one where the two limbs dip at the same angle but in opp. Direction. In this case the axial plane is vertical and it passes through the crest & trough.

19. Overturned fold – it is an asymmetrical fold whose one limbs is turned past a vertical. In this case the axial plane is inclined and both the limbs is turned upside down.Recumbent fold- in this case the limb becomes almost horizontal. And axial plane also become nearly horizontal and lower limb get overturned. in this fold fractures usually developed across bends to produce over thrust.Axis of foldSurface line

20. Isoclinal fold- folds that have parallel limbs are called “isoclinal fold” .in this case limbs dip at the same direction. it is are of three types a)inclined isoclinal fold. b)vertical isoclinal fold. C)recumbent isoclinal folds Chevron fold -Angular fold with straight limbs and small hinges.

21. In the “open fold “ the folding is mild & there fore the limbs meet at an obtuse angle. In this case the thickness of the constitute beds remains unchanged everywhere .In the “close fold” the folding is so tight that the incompetent strata flow towards the crests & trough. This is fold developed under great stresses.Open fold & close folds Axis Of Fold

22. Drag FoldA minor geological fold produced in soft or thinly laminated beds lying between harder or more massive beds in the limbs of a major fold.Competant

23. Fold HarmonicsA fold which maintains its geometric form, integral wavelength, and symmetry throughout a sequence of layers. Such folds form where the competent layers comprising the sequence are of similar thickness and evenly spaced, and the contrast in competence is constant between each layer and the next.

24. Ramsay classification of fold

25. On the basis of curvature changes on adjacent surfaces in the folded layer:Class 1: Folds with convergent dip isogons towards the axis of fold. Curvature of the inner fold arc always exceeds that of the outer arc. Subclass 1A: Folds with strongly convergent dip isogons. Subclass 1B: Parallel isogons towards the folds and fold axis. Subclass 1C: Folds with weakly convergent isogons.Three types of fold as an fundamental clases.

26. Fold classCurvature (C)CommentClass-1Cinner > CouterDip isogons converge1A Orthogonal thickness on  limbs exceeds thickness at  hinge; uncommon1B Parallel folds1C     Orthogonal thickness onlimbs is less than thickness at hingeClass-2Cinner = CouterDip isogons are parallel  Class 2 = similar folds)Class-3Cinner < CouterDip isogons are diverge

27. Sub-class 1ASub-class 1BSub-class 1C

28. Class 2Folds with parallel isogons. Curvature of the inner and outer arcs are equal.

29. Class 3 Folds with divergent isogons. Curvature of the inner fold arc is always less than that of the outer arc

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31. Causes1.Orogenic Activity2.Igneos intrusive body etc

32. THANK YOU