Fold & its classification

A presentation on
Fold & its classification

1. DR. HARISINGH GOUR VISHWAVIDYALAYA, SAGAR (M.P) ( A CENTRAL UNIVERSITY) A presentation on Fold & its Classification Submitted to- Prof. A. K. Shandilya Dept. of Applied Geology Dr. Harisingh Gour Vishwavidyalaya , Sagar Submitted by- Praphulla Sonowal M. Tech 1 st Semester Reg. No. Y17251016

2. CONTENTS Introduction  Elements of fold Classification of fold Conclusion Bibliography

3. Introduction The word fold was used by Hall ( 1815 ) for the first time to explain the rock structures. Van Hise ( 1894 ) contributed on the geometry of folds, while Willis ( 1891 ) worked out their mechanics. Fold is a wave like structure which is formed by bending or flexuring of any type of planes or layers in igneous, sedimentary and metamorphic rocks due to compressional force. Folds are best displayed by stratified formations.

4. Elements of folds

5. Classification of fold Basis of classification: 1. Fold Closure 2. Symmetry 3. Plunge of fold axis 4. Orientation of axial plane 5. Direction of younging relative to fold closure 6. Nature of hinge line 7. Interlimb angle 8. Shape of hinge 9. No of hinges 10. Geometrical elements (Dip isogons, axial plane thickness & Orthogonal thickness) 11. Superposition of fold

6. 1. Classification of fold on the basis of fold closure Antiform Synform Neutral fold Vertical fold

7. 2. Classification of fold on the basis of symmetry Symmetrical fold Asymmetrical fold

8. Photo: Asymmetrical fold from Mawkajem village, Meghalaya

9. 3. Classification of fold on the basis of plunge of fold axis Horizontal fold Plunging fold Vertical fold

10. 4. Classification of fold on the basis of orientation of axial plane Upright fold Recumbent fold Inclined fold Reclined fold Overturned fold

11. Fluety’s Classification based on amount of plunge of fold & dip of axial plane Amount of plunge of fold: Sub-horizontal Gently plunging Moderately plunging Steeply plunging Sub-vertical Amount of dip of axial plane: Upright Steeply inclined fold Moderately inclined Gently inclined Recumbent Given by – Fluety (1964)

12. Fluety’s Classification based on Amount of Plunge of Fold & Dip of Axial Plane

13. 5. Classification on the basis of direction of younging relative to fold closure Anticline Syncline Anticlinorium Synclinorium Synformal anticline Antiformal syncline

14. 6. Classification on the basis of nature of hinge line Cylindrical – generated by moving a line parallel to itself Non-cylindrical – cannot generated by moving a line parallel to itself Conical – a non cylindrical fold whose shape is approximately a part of a cone.

15. 7. Fluety’s classification on the basis of interlimb angle Given by Fluety ( 1964 ) Gentle fold - interlimb angle between 180-120 o Open fold - interlimb angle between 120-70 o Close fold - interlimb angle between 70-30 o Tight fold - interlimb angle < 30 o but > 0 o Isoclinal fold – with subparallel limb. Fan Fold – with negative interlimb angle.

16. 8. Classification on the basis of shape of hinges Round-hinged or broad hinge fold – broad hinge zone compared to limb. Chevron fold – straight limbs and sharp hinge. Arrow-head fold – sharp hinge and curved limbs. Cuspate fold – 1 set of closure with sharp hinge other with round.

17. 9. Classification on the basis of number of hinges Single hinged fold – single hinge Conjugate fold – double hinged fold with sharp hinge Box fold – double hinged with rounded hinges.

18. 10. Geometrical classification of fold Given by John G. Ramsay in 1967 based on dip isogons, axial plane thickness and orthogonal thickness. Class 1 Class 1A Class 1B Class 1C Class 2 Class 3

19. 10. Geometrical classification of fold Parameter Type of folds Class 1 A Class 1 B Class 1C Class 2 Class 3 Dip isogons Strongly Convergent Convergent Weakly Converget Parallel Divergent t α ’ > 1 = 1 Cos α < t α ’ < 1 Cos α Cos α < t α ’ < 0 T α ’ > Sec α Sec α Sec α > T α ’ > 1 1 < 1 Comparison of curvature of inner and outer arcs i > o i > o i > o i = o i < o

20. 11. Classification of fold based on superposition of folds Ramsay (1967) and Hubber (1987) classified interference pattern of superposed folds on the basis of attitude of two folds axes and attitude of axial planes and flow direction of the second deformation Classification: Type 1 superimposed folds Type 2 superimposed folds Type 3 superimposed folds

21. 11.1 Type 1 superimposed fold (Dome & basin) Upright F 1 folds with fold axes and axial planes oriented at large angle to the F 2 fold. Angle between dip of axial plane of F 1 and flow direction of F 2 is low. Dome & Basin produced.

22. 11.2 Type 2 superimposed fold (Crescent & mushroom pattern) Hinges of F 2 fold oriented at high angle to axial planes of F 1 fold. Fold hinges of both fold oriented at high angles. After superposition it takes crescent and mushroom geometry.

23. 11.3 Type 3 superimposed fold (Doubled zigzag or hook shaped) Flow direction of F 2 fold lies at higher angle to axial planes of F 1 . Hinge line of F 2 fold lies very close to hinge lines of F 1 fold. After superposition hinges of both the fold become parallel & show Hook shape

24. Conclusion Folding bring minerals like copper & lead closer to the surface making their extraction easy. Fold mountain receives heavy rainfall giving rise to rivers which are use for hydroelectric power generation. During folding faults develops leading to earthquakes. Lee ward sides of fold mountains receives low rainfall which discourage agriculture and settlement.

25. Bibliography Ramsay J. G. and Huber, M.I . : The techniques of modern structural geology – Volume 2 : Folds and Fractures. Ghosh , S. K. : Structural Geology - Fundamentals and Modern Developments. Jain, A. K. : An Introduction to Structural Geology, Geological society of India. Billings, M. P. : Structural Geology, 3/E. Fossen , H. : Structural Geology.

26. Thank You