Fault, Fold, Dip, Strike, Joint (Geology)

This presentation slide very helpful for Understanding Geological Feature or Earth Science few impotent topics.

1. WEL COME

2. PRESENTED BY:- JEEVAN CHANDRA PANDEY B. Tech. CIVIL ENGG. DEHRADUN (India) (2019-20)

3. STRUCTURAL GEOLOGY

4. Content Introduction Dip and Strike Folds Faults Joints

5. Understand Geology by Your surrounding Area/ Nature.

6. Introduction STRUCTURAL GEOLOGY Structural geology is the study of the factors such as origin, occurrence, classification, type and effects of various secondary structures like folds, faults, joints, rock cleavage etc. and are different from those primary structures such as bedding and vesicular structure, which develop in rocks at the time of their formation.

7. Dip It means slope or inclination . The angle of inclination of a bedding plane with horizontal plane is called amount of dip . The direction along which the inclination of the bedding plane occurs, is called dip direction . So dip is expressed both as amount and direction . The direction angle is measured with clinometers . The direction is measured with a compass. DIP & STRIKE

8. DIP & STRIKE Strike It’s defined as the direction of a line formed by the intersection of a bedding plane and a horizontal plane . It’s always at right angle with the true dip direction . It is a horizontal line on a surface of rock beds.

9. Dip According to Direction According to Deposition True Dip Apparent Dip Local & Regional Dip Primary Dip Secondary Dip Classification Of Dip

10. According to Direction :- Dip When the dip of layer is measured in a direction that is essentially at right angle (90) to the strike of that particular layer. True Dip When the dip of layer is measured in any other direction, which is not at right angle (90) to its strike direction. Apparent Dip

11. According to Deposition :- Dip When sedimentary rocks are deposited in an originally sloping basin they (SR) are also inclined in the same fashion. Thus, if the original slope of the basin of deposition is anything between 5-10 degrees the sedimentary formations accumulating over there in the period of time, will also have same direction , such dips are called Primary Dip or Depositional Gradient . Primary Dip Local dips are inclinations of the rocks exposed in a limited area of observation. They may primary or secondary or may not show any appreciable variation laterally or with depth. Regional dips is an averaged general inclination of a series of formation exposed over a wide area . These rocks may show varying local dips, both in respect of degree and directions of inclination. Regional dips are prevail over many hundreds km range. Local & Regional Dip Secondary dip is inclination induced in the strata after its deposition due to the Tectonic Force . Secondary dip may range in value up to vertical (90). Most folded mountain ranges of the world strata exhibit Secondary Dip. Secondary Dip

12. FOLDS When a set of horizontal rock layers are subjected to compressive force , undulation or bends curvatures developed in the rock layers. These bends are called folds.

13. FOLD GEOMETRY

14. Parts of Folds Hinge : It is the area of maximum curvature . It is closure of fold sometimes. • Hinge line : It is line of maximum curvature . The hinge line may be horizontal, inclined or vertical . • Limb : These are the areas between the hinges or in other words these are sides of the fold .

15. Parts of Folds Axial plane : The imaginary plane which is equidistant from each limb of a fold. The axial plane actually cuts the hinge zone of the fold along a line, which is termed as fold axis or axis. Plunge : The attitude of the fold axis is measured as the angle between the axis and horizontal. Crest & Trough : The line running through the highest points in an up arched fold defines its Crest . A corresponding line through the lowest p0int in a down arched folds makes its Trough .

16. Classification Of Folds 1 Based on upward and downward bending , It can be classified as:- Anticline 1 Syncline 2 Anticline :- When the beds are bent upwards, the resulting fold is called anticline. This fold is convex upwards. Naturally, in such a fold, the older beds occur towards the concave side , In a simple case, the limbs of anticline slope in opposite directions with reference to its axial plane. Syncline Syncline is just opposite to anticline in its nature, i.e. when the beds are bent downwards the resulting fold is called syncline. This fold is convex downwards . In this the younger beds occur towards the concave side and, in a simple type of syncline, its limbs dip towards each other with reference to the axial plane.

17. 2 Based On Position of the axial plane , It can be classified as: Classification Of Folds Symmetrical Folds :- When the axial plane divides a fold into two equal halves (half) in such a way that one half is the mirror image , then the fold is called as symmetrical fold. 1 Symmetrical 2 Asymmetrical 4 Fan folds 3 Overturned 5 Recumbent 6 Isoclinals folds 8 Box folds 7 Conjugate folds

18. Asymmetrical Folds :- If the compressive forces responsible for folding are not of the same magnitude , asymmetrical folds are formed. Classification Of Folds 2 Based On Position of the axial plane, It can be classified as: Overturned Fold An overturned fold is an inclined (asymmetric) fold in which both limbs dip in the same direction but with different angles .

19. Classification Of Folds 2 Based On Position of the axial plane, It can be classified as: Isoclinal Folds Usually the folds have inclined limbs, i.e. the limbs will be mutually diverging or converging with reference to axial planes . But in some folds, the limbs will be mutually parallel to a great extent. Such folds are called isoclinals folds. These folds may be vertical inclined or horizontal. Box Fold Box fold are special type of fold with exceptionally flattened top and steeply inclined limbs almost forming 3 sides of a rectangle.

20. Classification Of Folds 2 Based On Position of the axial plane, It can be classified as: Fan Folds In Fan folds the anticline tops are said to have opened up unto a broad, fan-shaped outline due to intense compression in the lower region. Conjugate Folds Conjugate folds are a pair of folds that are apparently related to each other may have mutually inclined axial planes . Recumbent Folds Recumbent folds are extreme types of overturned folds in which the axial plane acquires on almost horizontal attitude and limbs comes to lie exactly under the other limb.

21. 3 Based On Degree of Compression, It can be classified as: Classification Of Folds Open folds 1 Closed folds 2 closed Folds The folds in which thickened crests or trough s and thinner limbs are found. Open Fold The folds in which the thickness of the rocks is not affected during the process.

22. 4 Based On Mode Of Occurrence, It can be classified as: Classification Of Folds Anticlinorium & synclinorium 1 Dome and basin 2 Synclinorium Synclinorium is the reverse of anticlinorium & may defined as an extensive system of folds having clearly down-arched folding trend. Anticlinorium Anticlinorium is a system of exceptionally large sized folds running often for several hundred km in length & several km in width and having up-arched folding trend.

23. 4 Based On Mode Of Occurrence, It can be classified as: Classification Of Folds Dome and basin 2 Dome Domes are a group of strata central uplifted in such a way that they seen from the top these dip away in all direction Basin Basin are the reverse of the domes & may be defined as a group of strata that are centrally depressed in such a way that the involved layer dip towards a common central point from all the sides.

24. 5 Based On Plunge Of the Folds, It can be classified as: Classification Of Folds Plunging folds 1 Non-Plunging folds 2 Plunging folds Any fold in which fold axis is not horizontal . Non-Plunging folds Any fold in which fold axis is essentially horizontal .

25. 6 Based On outer surface profile, It can be classified as : Classification Of Folds Cheveron folds 1 Cuspate folds 3 Conjugate folds Conjugate folds are composite folds characterised with 2-hinges & 3 planner limbs in which the central limb is exceptionally flattened. Cheveron folds These are characterized with well-defined, sharp hinge points & straight planner limbs. Cylindrical folds 4 Conjugate folds 2

26. 6 Based On outer surface profile, It can be classified as : Classification Of Folds Cylindrical folds The cylindrical folds resemble sections of pipes and have very well defined axes of folds repeated parallel to each other. In Non-Cylindrical folds repetition of axes parallel to themselves is not possible. Cuspate folds The limbs of the folds are not planner they are quite clearly curved becoming concave upward in the case of Anticlines & concave downward in the case of Synclines.

27. 7 Based On Behaviour with depth, It can be classified as : Classification Of Folds Concentric folds 1 Similar folds 3 Supertanuous folds These showing differences in thickness at crest and the trough regions , not induced by folding process but essentially being due to erosional & depositional processes operating in the folding regions. Concentric folds The strata in concentric or parallel folds has reacted to the effecting tangential compression in such a way that the thickness of the involved layer remained uniform and constant even after folding. Supertanuous folds 2 Similar folds Those folds in which the degree of folding is observed to be similar for indefinite depths are grouped as similar folds .

28. 8 Based On Relative curvature of outer & inner arcs , It can be classified as : Classification Of Folds Class 1 folds 1 Class 3 folds 3 Class 2 folds All those folds in which the degree of curvature in the outer arc ( o ) of the fold is equal to that of the inner arc ( i ). { o = i } Class 1 folds All those folds in which the degree of curvature in the outer arc ( o ) of the fold is less than that of the inner arc ( i ). { o < i } Class 2 folds 2 Class 3 folds All those folds in which the degree of curvature in the outer arc ( o ) of the fold is greater than that of the inner arc ( i ). { o > i }

29. Classification Of Folds 9 Miscellaneous :- Monocline folds Monocline described as essentially a localized warping in which case otherwise horizontal strata show a single bend for a limited length & again the horizontal attitude once again . Homocline folds Homocline described as a Sequence of strata , dipping in the same general direction at a uniform angle. Drag folds Drag may be defined as minor folds developed within the body of weaker rocks surrounded on both the sides by layer of stronger rocks .

30. Cause of Folding Due to Intrusions Due to Differential Compression Due to Tangential Compression Shear folding Flexural folding Flowage folding Most of the important folds, as already pointed out, are due to tectonic causes. But a few folds of a minor type are due to non-tectonic causes . Non-tectonic causes like landslides, creeping , differential compaction, and glaciations too are responsible for some folds. These are minor in terms of frequency of occurrence and magnitude.

31. Faults A fault may be defined as a fracture surface along which relative movement of adjacent blocks has taken place . Faulting is entire process of development of fracture & displacement of the blocks against each other.

32. Faults occur when brittle rocks fracture and there is an offset along the fracture. When the offset is small , the displacement can be easily measured , but sometimes the displacement is so large that it is difficult to measure. Faults

33. Parts of Faults Fault plane :- It is the planar surface of fracture along which relative displacement of the blocks takes place during the process of faulting. When it is not planar, the same surface is simply described as Fault Surface. Fault line:- It is the line of intersection between the fault plane. Walls:- 1- Hanging Walls 2- Foot Walls Hanging Walls:- Fault blocks above the fault place . Foot Walls:- Fault block below the fault plane. Fault line

34. Types of Faults Apparent movement of fault blocks 1 Attitude of fault plane 2 Slip 4 Mode of occurrence 3 Faults are classified on the basis of :-

35. Normal faults 1 Strike slip faults 3 1- Normal Faults:- In normal faults hanging wall has apparently moved down with respect to foot wall. Reverse faults 2 Types of Faults 1 Based On Apparent movement of fault blocks , It can be classified as:- Horst Vertical Fault Garben Hinge faults 4 Normal Faults

36. 1 Based On Apparent movement of fault blocks , It can be classified as:- Types of Faults 3- Strike-slip Faults:- In this faulted blocks have been moved against each other in an essentially horizontal direction. I is found in large scale like in oceanic ridge. 2- Reverse Faults:- In this hanging wall appears to have moved up with respect to the foot wall. 4- Hinge Faults:- Hinge faults are characterised by a movement of the disrupted faults along a medial point . The movement is therefore rotational .

37. Strike faults 1 Oblique faults 3 Dip faults 2 Types of Faults 2 Based On Attitude of fault plane , It can be classified as:- 2- Dip Faults:- Dip faults develop parallel to the dip of the strata . 1- Strike Faults:- These are the faults that develop parallel to the strike of the strata. 3- Oblique Faults:- Oblique faults strike make an oblique angle with the strike of the rocks in which it has it has caused the displacement.

38. Parallel faults 1 Peripheral faults 3 1- Parallel Faults:- A group of faults occurring in close proximity, having their faults planes striking essentially in the same direction & having parallel & equal dips from what are commonly called parallel faults. Enechelon faults 2 Types of Faults 3 Based On Mode of occurrence, It can be classified as:- Radial faults 4 2- Enechelon Faults:- A group of small sized faults that overlap each other in the region of their occurrence.

39. 3 Based On Mode of occurrence, It can be classified as:- Types of Faults 4- Radial Faults:- A group of faults appear emerging outward from a common central region are classed as radial faults. 3- Peripheral Faults:- When in any given region the majority of faults are concentrated along the border or margin of the area.

40. Strike-slip faults 1 Oblique-slip faults 3 Dip-slip faults 2 Types of Faults 4 Based On slip , It can be classified as:- 2- Dip-slip Faults:- All those faults in which the net slip has taken place parallel to the dip of the faults , also called Normal-dip-faults. 1- Strike –slip Faults:- In which net slip is essentially parallel to the strike of the faults , the slip along the dip being almost absent . 3- Oblique –slip Faults:- In which the direction of net slip is neither parallel to the dip of the faults nor to the strike of the fault but is inclined to both these direction.

41. Effects of Faults Faulting change in the elevation of the ground. Omission of some strata where they are normally expected . Repetition of some strata in a given direction against the normal order of super-position. Displacement & shifts in the continuity of the same rocks in the certain regions. Kashmir Himalayas Garhwal Himalayas Shimla Thrust Example of faults-

42. Joints Joints are defined as divisional planes or fractures along which there has been no relative displacement. Or Any fracture, without any movement is called as joint. Nature of Joints:- Open joints Close joints Smooth joints Rough joints Small joints Master joints

43. Classification of Joints Spatial Relationship 1 Attitude of fault plane 2 Slip 4 Mode of occurrence 3 Joints are classified on the basis of :-

44. Types of Joints Joints are classified on the basis of :- Spatial Relationship 1 Geometry 2 Origin 3 Regular or Systematic Joints Irregular or Non-Systematic Joints Tension Joints Shear Joints Compression Joints Strike Joint Dip Joint Oblique Joint Bedding Joint

45. Types of Joints 1. On the basis of Spatial Relationship:- Regular or Systematic Joints Irregular or Non-Systematic Joints These shows a distinct regularity in their occurrence , which Can be measured & mapped easily . Such joints occur in parallel or sub-parallel joints sets that are repeated in the rocks of regular intervals. As the name implies, these joints do not possess any regularity in their occurrence & distribution . They appear at random in the rocks & may have incompletely defined surfaces.

46. Types of Joints 2. On the basis of Ge0metry:- Strike Joint When joints sets strike, parallel to the strike of the rocks, they are called Strike Joints. Dip Joint When joints sets strike, parallel to the dip direction of the rocks, they are called Strike Joints. Bedding Joint When in stratified rocks, joints are develo p essentially parallel to the bedding planes , these joints are called Bedding joints. Oblique Joint When strike of the joints is at any angle between the dip & strike of the layers , these are also called Diagonal Joints

47. Types of Joints 3. On the basis of Origin:- Tension Joint Those are develop due to the tensile forces acting on the rocks, called Tension Joints. These found in folded sequence is on the outer margin of crests & trough. Shear Joint Joints those are commonly observed in the near of faults planes & shear zones where the relationship with shearing forces is clearly established. Compression Joint Those are develop due to the compressive forces acting on the rocks, called compression Joints. These are found in core regions of folds or opposite of Tension Joint.

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