Elements of fold

ELEMENTS OF FOLD

1. ELEMENTS OF FOLD Guided By Presented By Dr. Poonam Bhatnagar Jaya Pandey Class-M.Sc.(I Sem.) Govt. Holkar Science College, Indore(M.P.) 1

2. CONTENT Introduction Historical Development Elements of Fold C o n c l u sion Reference 2

3. INTRODUCTION The bending of rock-strata due to compressional forces acting tangentially towards a common point or plane from opposite directions is known as folding. It results in the crumbling of strata, forming wavy undulations on the surface of the earth, which are known as folds. Folds are best displayed by stratified formations. 3

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5. HISTORICAL DEVELOPMENT The word fold was used by HALL(1815) for the first time to explain the rock structure. VAN HISE(1894) contributed on the geometry of folds. WILLIS(18910) worked out their mechanics. 5

6. ELEMENTS OF FOLD Hinge point:- Point located at the maximum curvature. Hinge line:- A line joining hinge point. Hinge zone:- Region on the folded surface near hinge line. 6

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8. Enveloping surface:- The enveloping surface is the surface tangent to individual hings along a folded layer. 8

9. Crest point:- Point located at maximum height of the folded layer with reference to a horizontal reference plane. Crest line:- A line joining successive crest point. Crestal plane:- P There is a separate crest for each bed. The plane or surface formed by all the crests is called the crestal plane. 9

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11. Trough:- A point located at minimum height with reference to horizontal reference plane. Trough line:- A line joining point of minimum height. Trough plane:- The trough is the line occupying the lowest part of the fold. The plane containing such lines may be called the trough plane. 11

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13. Culmination point:- The culmination also refers to the highest point along any geologic structure. Depression point:- Point where the trough line reaches its minimum elevation. 13

14. C o r e : - T h e i n n e r p a r t o f t h e fold . E n v e l o p : - O u t e r p a r t o f t h e f o l d . 14

15. Wavelength of fold:- Distance between two continuous anticline or syncline. Amplitude of fold:- Distance between maximum or minimum height to median surface. 15

16. Inflexion point :- The inflexion point of a fold is the point on a limb at which the concavity reverses; on regular folds, this is the midpoint of the limb. Inflexion line :- A line joining such points on a folded surface is called inflexion line. Inflexion surface:- A surface joining succession inflexion lines in different layer within a single fold and defines the limit of a fold in 3-dimensions. 16

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18. Limbs :- Limbs are the sides of a fold. An individual fold will have two limbs ; whereas, in a series of folds, the central limb is common to any two adjacent folds. 18

19. Interlimb angle :- The smaller angle made by the limbs of fold is known as the interlimb angle. 19

20. Fold axis :- An imaginary line in space along which the fold is generated. It does not have a fixed position on the folded surface unlike the hinge. 20

21. Axial plane :- Axial plane is the imaginary plane bisecting between the two limbs of a fold, thus dividing the fold into two parts, as symmetrically as possible. Axial plane may be vertical, inclined, or even horizontal. 21

22. Axial surface :- The surface containing the hinge lines from consecutive folded surfaces. 22

23. Plunge of the fold :- When the fold axis is inclined, the angle which it makes with the horizontal, as measured in a vertical plane is called the angle of plunge or plunge of the fold. 23

24. Anticline :- When the beds are up-folded into an arch-like structure, it is called anticline or an anticline fold. Syncline :- When the beds are down-folded into a trough like form, the structure is called a syncline, because in this case the beds on either side “inclined together’’ towards the keel. 24

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26. C O N C L USION F o l d i s v e r y important s t r u cture . F o l d i n g b r i n g m i n e r als l i k e c o p p er & l e a d c l o s e r t o t h e s u r f a c e m a k i n g t h e i r e x t r a c t i o n e a s y . F o l d m o u n t a i n r e c e i v e s h e a v y r a i n fall g i v i n g r i s e t o r i v e r s w h i c h a r e u s e f o r h y d r o e l ectric p o w e r g e n eration . D u r i n g f o l d i n g f a u l t s d e v e l o p s l e a d i n g t o e a r t h q u ake . 26

27. REFERENCE 27 1. G ARG SANTOSH KUMAR “PHYSICAL AND ENGINEERING GEOLOGY” Published By Khanna Publishers New Delhi. (Page no. 368-370). 2. J AIN A. K. “An Introduction to Structural Geology” Published By the Geological Society of India. (2014 Edition) (page no. 115-166). 3. MAHAPATRA GIRIJA BHUSHAN “ A TEXT BOOK OF GEOLOGY ” Published By CBS Publishers & Distributers Pvt. Ltd. (2017 Edition) (Page No. 80-88).

28. THANK YOU 28