3. Crustal Movement Evalution of Land forms - Distrophism Folds and Faults

1. 3. Crustal Movement Evalution of Land forms -DistrophismFolds and Faults Dr. Salve P.N. M.J.S. College Shrigonda, Dist- Ahmednagar

2. Deformation • The process by which the shape of a rock changes because of stress. • There are two types of stress that occur in rocks: Compression Tension

3. Compression • Compression occurs when rock is squeezed. • Compression happens when two plates collide at a convergent boundary. • Compression occurs and forms large mountain ranges.

4. Evidence • Folds – occur when rocks are deformed slowly due to pressure.

5. Evidence • Faults – happen when rocks are deformed quickly due to pressure of tension.

6. Folding & Faulting Folding • When Earth’s crust bends, folds occur • Folding occurs under compression when forces act towards each other, such as when plates collide. Definitions • Compression • Is a process of forcing something into smaller compass, reducing it in volume by pressing it together • Tension • Is a pulling force, tending to stretch, to cause an extension of a body or to restore the shape of an extended elastic object

7. Compression/ Mountain Building The Himalayas, for example, were raised by the compression that accompanied collision of the Indian plate with the Eurasian plate. Another example is Europe's Alps and Jura mountains which were also formed by horizontal compression, generated in their case by collision with the African plate and the Eurasian plate.

8. Tension • Tension occurs when an object is stretched. • Tension occurs when plates move away fromeach other at plate boundaries. • At the Mid-Atlantic ridge the seafloor is spreading at a rate of about 3cm per year. The frequency of earthquakes at a mid-ocean ridge will depend on how much tension is happening at that point. The more tension means the more seafloor spreading, resulting in a higher frequency of earthquakes at a particular mid-ocean ridge.

9. Folding • Folding is the bending of rock layers due tostress in the Earth’s crust. • Depending on how rock layers deform, different types of folds occur: • Anticline • Syncline • Monocline

14. Anticline • An anticline is an upward-arching fold. • An anticline is formed when there is horizontal stress on rock layers. Horizontal stress

16. Syncline • Synclines are downward folds. • They are also caused by horizontal stress. Horizontal Stress

17. Anticline • An anticline occurs when a tectonic plate is compressed by movement of other plates. This causes the center of the compressed plate to bend in an upwards motion. • Fold mountains are formed when the crust is pushed up as tectonic plates collide. When formed, these mountains are usually enormous like the newly formed Rocky Mountains in Western Canada and the United States • To the top right is a picture of an anticline. Beneath is a picture of the Rocky Mountains.

18. Syncline • A syncline is similar to an anticline, in that it is formed by the compression of a tectonic plate. However, a syncline occurs when the plate bends in a downward motion. • The lowest part of the syncline is known as the trough. • To the top right is a diagram of a syncline fold (The bottom of the fold center is the trough). Beneath, is an example of a syncline in California. Can you distinguish the trough in this picture?

19. Tight Fold • A tight fold is a sharp peaked anticline or syncline. • It is just a regular anticline or syncline, but was compressed with a greater force causing the angle to be much smaller. • Folds such as these occur to form steep mountain slopes like those in Whistler, British Columbia. • To the left is a photo of a tight fold formed by extreme pressure on these rocks.

20. Overfold • An overfold takes place when folding rock becomes bent or warped. • Sometimes the folds can become so disfigured that they may even overlap each other. • An example of overfolding is shown in the diagram below.

21. Recumbent Fold • This type of fold is compressed so much that it is no longer vertical. • There is a large extent of overlapping and it can take the form of an “s”. • To the right is a diagram that shows the process of recumbent folding.

22. Nappe Folding • This fold is similar to a recumbent fold because of the extent of folding and overlapping. However, nappe folding becomes so overturned that rock layers become fractured. • To the right is a picture of someone standing under a fractured fold.

23. Faults • A fault is when tension and compression associated with plate movement is so great that blocks of rock fracture or break apart. This process can occur very rapidly, in the form of earthquakes. The damage caused by this event can be very destructive and cause severe changes to the earths surface. There are five types of faults that can occur: • Normal Fault • Reverse Fault • Tear Fault • Rift Valley • Horst Fault

24. Normal Fault • This occurs when rocks move away from each other due to the land moving apart. • When the rocks move apart, the side with the less stable tectonic plate drops below the side with the more stable plate. • On the top right is the movement of a normal fault. A picture is also shown below. Notice the displacement of the different types of rock on each side of the fault.

25. Reverse Fault • Reverse faults are the opposite of normal faults. Rocks are compressed such that one plate moves up while the other descends below it. • When plates compress and crack, usually the more dense one is forced under the less dense one. This is similar to the action of the continental crust colliding with the oceanic crust. Here the more dense crust, being the oceanic crust is forced under the continental crust. • To the right is an animation of a reverse fault. Below that is a real picture of what a reverse fault looks like.

26. Tear Fault • A tear fault, also known as a transform fault, occurs when two tectonic plates slide in a lateral motion past each other. • This type of fault causes the most severe earthquakes because they grind against each other. These earthquakes can either be shallow or deep and cause tremors over a short or long period of time. • Tear faults can occur frequently, especially along the coast of California.

27. Rift Valley • A rift valley is when two normal faults occur parallel to each other and the land sinks between the faults. • There are two major examples of this. One being the Great Rift Valley in North Africa and the other, the San Andreas Fault in California. • The top right picture is San Andreas Fault and on the bottom right is a diagram of what a rift valley looks like.

28. Horst Fault • A Horst is the opposite of a rift valley. The land between the parallel faults is forced upward because the two faults are being pushed together. • This process can take a long time to occur because the average plate movement is one inch per year. • There are examples of horst faults on the left.

29. Summary • Folding and faulting has a major influence on the way the earth looks. Mountains form and disappear over time, as well as large rift valleys and other features. This has an impact on where and how we live.

31. Isoclinal-Recumbant Folds in Amphibollite and Granitic Gneiss near Clemson South Carolina

32. Isoclinal-Recumbant Folds near Walhalla South Carolina with subsequent open folding

35. Monocline • Monoclines are rock layers that are folded so that both ends of the fold are horizontal.

39. Faults • Some rock layers break when stress is applied to them. • The surface along which rocks break is called a fault. • The blocks of crust on each side of the fault are called fault blocks. • A fault has a foot wall and a hanging wall.

40. Fold Definition • Folds are wave-like structures that result from deformation of bedding, foliation, or other originally planar surfaces in rocks. • Fold can be very broad to tightly compressed. • They may occur as isolated folds or extensive fold trains of different sizes.

42. Footwall Footwall You could walk up this face of the fault, on foot, hence the name footwall.

43. Hanging Wall • You could hang from this wall. Hanging Wall This is a normal fault. Notice how the rock layers are the same at the red lines.

44. Hanging wall and Footwall

45. 3 Types of Faults • Normal Fault • Reverse Fault • Slip-Strike Fault

46. Normal Fault • Rocks are pulled apart because of tension. Hanging wall Footwall In a normal Fault, the hanging wall slides down the footwall.

49. Reverse Fault In a reverse fault the hanging wall is pushed upward due to compression.