THE FOLDING AND FAULTING OF ROCKS-ELS.pptx

science module 10

1. THE FOLDING AND FAULTING OF ROCKS

2. FOLDS AND FAULTS What do you think will happen if the rocks were exposed to stress or strain?

3. Stress is defined as the force applied to an object. In geology, it is the force per unit area that is placed on a rock. There are four types of stresses act on materials:

4. Confining stress The force acts equally in all directions. When a deeply buried rock is pushed down by the weight of all the material above it. Since the rock cannot move, it cannot deform.

5. Compression is force acting perpendicular to and towards a surface. It happens when rocks squeezes together, causing rocks to fold or fracture or break. Compression is the most common stress at convergent plate boundaries

6. Tension is a force acting perpendicular to and away from a surface. When rocks that are pulled apart, they are under tension. Rocks under tension lengthen or break apart. Tension is the major type of stress at divergent plate boundaries.

7. Shear is a force acting parallel to a surface happens. When forces are parallel but moving in opposite directions. Shear stress is the most common stress at transform plate boundaries.

8. When stress causes a material to change shape, it has undergone strain or deformation. Deformed rocks are common in geologically active areas

9. Strain is the change in a solid's shape caused by the application of a stress. Depending on the solid, a given stress might cause a great or small strain. Rocks only strain when placed under stress.

10. Kinds of Deformation Elastic deformation the rock returns to its original shape when the stress is removed

11. Plastic deformation takes place when the rock does not return to its original shape when the stress is removed.

12. WHAT ARE FOLDS AND FAULTS? Fracture happens when the rock breaks

13. WHAT ARE FOLDS AND FAULTS?

14. FOLD A fold is defined as a bend in rock that is the response to compressional forces. Folds are most visible in rocks that contain layering. Rocks deforming plastically under compressive stresses crumple into folds depending on the rock materials. They do not return to their original shape. Deformation happened slowly. If the rocks experience more stress, they may undergo more folding or even breakage.

15. Types of Folds

16. Mononcline is a simple bend in the rock layers so that they are no longer horizontal.

17. Anticline is a fold that arches upward. The rocks dip away from the center of the fold. The oldest rocks are at the center of an anticline and the youngest are draped over them

18. Syncline is a fold that bends downward.

19. FAULT Fault is a fracture or zone of fractures between two blocks of rock. Faults allow the blocks to move relative to each other. This movement may occur quickly, in the form of an earthquake – or may occur slowly, in the form of creep.

20. Types of Faults 1. Normal Faulting occurs when the crust is being pulled apart in which the overlying (hanging-wall) block moves down with respect to the lower (foot wall) block.

21. 2. Reverse Faulting occurs when the crust is being compressed in which the hangingwall block moves up and over the footwall block – reverse slip on a gently inclined plane is referred to as thrust faulting.

22. 3. Strike-Slip Fault is a dip-slip fault in which the dip of the fault plane is vertical. Strikeslip faults result from shear stresses