STRUCTURAL GEOLOGY

FOLDS, FAULTS AND JOINTS

1. GOVERNMENT POLYTECHNIC PEN STRUCTURAL GEOLOGY- FOLDS, FAULTS & JOINTS CIVIL ENGINEERING DEPARTMENT GUIDED BY: PRESENTED BY: S.N. CHOURE PREETI SANTOSH PATIL

2. CONTENTS INTRODUCTION IMPORTANCE OF STRUCTURAL GEOLOGY TYPES OF GEOLOGIC STRUCTURES FACTORS AFFECTING HOW A ROCK DEFORM OUTCROP DIP & STRIKE FOLDS - DESCRIPTION OF FOLD - TYPES OF FOLDS FAULT - COMPONENTS OF FAULT - TYPES OF FAULTS JOINTS - TYPES OF JOINTS CONCLUSION

3. INTRODUCTION Structural geology is the study of the three dimensional distribution of rock units with respect to their deformational histories. The primary goal of structural geology is to use measurements of present day rock geometries to uncover information about the history of deformation in the rock. Structural geology , scientific discipline that is concerned with rock deformation on both a large and a small scale. Its scope of study is vast, ranging from submicroscopic lattice defects in crystals to fault structures and fold system of the earth’s crust.

4. IMPORTANCE OF STRUCTURAL GEOLOGY The study of structural geology has a primary importance in economic geology, both petroleum geology and mining geology. An essential importance of structural geology is know areas that contain folds and faults because they can form traps in which the accumulation and concentration of fluids such as oil and natural gas occur. Environmental geologist and hydrologists need to understand structural geology because structures are sites of groundwater flow and penetration which may have an effect an leakage of toxic materials from waste dumps or leakage of salty water into aquifers.

5. TYPES OF GEOLOGICS STRUCTURES

6. FACTORS AFFECTING HOW A ROCK DEFORM DEPTH TIME FLUIDS

7. OUTCROP Outcrop is simply defined as an exposure of a solid rock on the surface of the earth. solid rocks are not exposed everywhere on the surface of the earth, these are mostly covered with a thick or a thin layer of loose deposits called as alluvium or in most common language called as soil.

8. DIP & STRIKE Strike is the direction of the line produced by the intersection of the inclined plane with the horizontal plane. It is expressed as the angle of the line from the north. Dip is the angle between the inclined plane and the horizontal plane. Strike and dip directions are always mutually perpendicular.

9. FOLDS Folds are bends or flexures in the earth’s crust, and can therefore be identified by a change in the amount and /or direction of dip of rock units. Most folds resulted from the ductile deformation of the rocks when subjected to compressional or shear stress.

10. DESCRIPTION OF FOLD

11. DESCRIPTIONS OF TERMS OF FOLD Hinge line is the line of maximum curvature on a folded surface. The axial plane is an imaginary plane dividing the fold into two equal parts known as limbs. Limb is the sloping side of the fold. The crest is the highest point of the folded surface. Trough is the lowest point of the folded surface. The Inter-limb angle is the angle between two limbs of same fold. The median surface is the surface that passes through the points where the fold limb changes its curvature from concave to convex. The amplitude is the vertical distance between the meridian surface and the fold hinge, both taken on the same surface of the same folded unit. T he angle of plunge is the angle between the fold axis and the horizontal plane measured in vertical plane. The wavelength is the distance between two consecutive crests or trough taken on the same folded surface.

12. TYPES OF FOLDS anticline : upfolds or arches of rock layers syncline : downfolds or troughs of rock layers. monocline : only one direction of dip prevails in a fold system. symmetrical fold : the axial plane is vertical with the limbs dipping symmetrically from the axis asymmetrical fold : the axial plane is inclined from the vertical with one limb dipping more steeply than the other. overturned fold : one limb is inclined beyond the vertical recumbent fold : this is an overturned fold "lying on its side" so that the axial plane is nearly horizontal.

13. TYPES OF FOLDS Recumbent fold

14. FAULT A fault is a fracture in the earth’s rock unit along which there has been an observable amount of movement and displacement. Unlike folds which are formed predominantly by compressive stress, faults are formed from either tension, compression or shear.

15. The names of hanging wall and footwall came from miners mining along fault zones, who hung their lanterns on the hanging wall and walked on the footwall. ( Tarbuck and Lutgents )

16. COMPONENTS OF FAULT Hanging wall : if the fault plane is not vertical, then the block lying on the top of the fault plane is known as hanging wall. Footwal l: whereas the block lying below the fault plane is known as footwall. Fault plane : is the plane of fracture along which displacement occurs. The down-thrown and up-thrown block : the block that has moved down is down-thrown whereas the block that has moved up is up-thrown block. The dip of the fault plane is the angle of inclination of fault plane measured from horizontal plane perpendicular to its strike. Fault throw : is the vertical displacement of a fault. Dip slip and Strike slip : the amount of displacement measured on the fault plane in the direction of its dip is known as dip slip whereas in the direction of its strike is known as strike slip.

17. TYPES OF FAULTS Normal fault Reversed fault Thrust fault (Dip slip fault: normal fault, reversed fault, thrust fault) Strike slip fault: left lateral, right lateral Oblique slip fault: has both strike-slip and dip-slip component. Note: The textbook calls it "translation fault", which is rarely used.

18. Normal fault is the fault in which hanging wall has moved downward relative to the footwall. Reversed fault is the fault in which hanging wall has moved upward relative to the footwall. Thrust fault is a reversed fault in which the fault plane is dipping at low angles (<45’).

19. Strike slip fault is the fault in which the movement is horizontal along the strike of the fault plane. Oblique slip fault is the fault in which displacement was both in the strike and dip directions.

20. JOINTS Joints are the fractures in the rocks characterized by no movement along their surfaces. Although most joints are secondary structures , some are primary forming at the time of formation of rocks.

21. TYPES OF JOINTS Columnar joints : These joints are formed in the basalt rock, when the basaltic lava cools, it contracts giving rise to hexagonal shaped column. Mud cracks: These are the joints formed in mud. As the mud loses its water, it contracts and cracks. COLUMNAR JOINT MUD CRACKS

22. Secondary joint : these joints are formed in the rocks as a result of their subjection to any form of stress . Sheet joint : these joints are formed in granitic rocks in the deserts causing them to break into thin parallel sheets. S econdary joint Sheet joint

23. CONCLUSION Structural geology is obviously one of the most important subjects for geoscientists working in petroleum as they can identify the locations that may have traps such as folds, faults and joints which are good for the accumulation of oil and natural gas. T he study of structural geology is important for the geologists to acquire knowledge and data about the deformation caused in rock such as folds, faults and joints due to subjected tension, compression or shear stresses. The folds are the bends or flexure on the earth’s surface. A fault is a fracture in the earth’s rock unit. Joints are the fractures in the rocks characterized by no movement along their surfaces.

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