Deformation of the Crust

1. Deformation of the Crust By: Mrs. Severe Earth Science

2. Section 1 – How the Crust is Deformed Objectives: • Predict isostatic adjustments that will result from changes in the thickness of the earth’s crust. • Identify sources of stress in crustal rock.

3. Deformation • Bending, tilting, and breaking of the earth's crust • Plate tectonics is the major cause of crustal deformation, but is not the only force that shapes the earth’s crust.

4. Other Forces • Changes in the weight of some parts of the crust • Thicker and heavier = sink more deeply into the mantle • Thinner and lighter = rise higher on the mantle

5. Isostatic Adjustment • Up-and-down movements of the crust occur because of two opposing forces. • Crust presses down on the mantle • Mantle presses up on the crust • When the two forces balance, the crust moves neither up nor down

6. Isostatic Adjustment Continued… • When weight is added to the crust, it sinks until a balance of the forces is reached again • Balancing of the two forces is called: • ISOSTASY

7. Isostatic Adjustment Continued… • Up-and-down movements of the crust to reach isostasy is called • ISOSTATIC ADJUSTMENTS • As the adjustments occur, areas of the crust are bent up and down • Pressure from this causes rocks in that area of the crust to deform

8. Isostatic Adjustment Still Continued… • Isostatic adjustments occur constantly: • Mountain ranges • *As the crust becomes lighter, the region may rise • Rivers flow into large bodies of water carrying large amounts of mud, sand, and gravel • *Added weight cause the floor to sink

9. Isostatic Adjustment STILL Continued… • Isostatic adjustments occur constantly: • Glaciers once covered the land • *Weight of the ice caused the crust underneath it to sink • Glacial ice retreats • Land slowly begins rising again in response to its reduced weight

10. Isostatic Adjustment FINAL!

11. Stress (Not the kind you cause your teacher to have) • Isostatic adjustment and plate movement cause stress in rocks that make up the earth’s crust • Amount of force per unit area that is placed on any given material

12. Strain • Crustal stress occurs when lithospheric plates collide, separate, or rub together • A change in the shape or volume of rocks that results from the stress of being squeezed, twisted, or pulled apart

13. Types of Stress • Compression - occurs when crustal rocks are squeezed together • often reduces the volume of the rocks • Tension - the force that pulls rocks apart • rocks tend to become thinner • Shearing - sliding rocks past each other in opposite horizontal directions

14. Types of Stress

15. Review • Explain isostatic adjustment… • Define Stress and Strain… • Draw a diagram of each of the following: • Compression • Tension • Shearing

16. Section 2 – The Results of Stress Objectives: • Compare folding and faulting as responses to stress • Describe four types of faults

17. The Results of Stress Introduction • High pressure and temperatures caused by stress deform rocks • Stress applied slowly = rock may return to its original shape as the force is removed • If the force exceeds an acceptable amount, the shape of the rock changes permanently • Rock may also break because of extreme stress

18. Folding • Rock responding to stress by becoming permanently deformed without breaking • Usually occurs deep in the crust where overlying rocks create great pressure so behavior is more plastic

19. 3 Types of Folds • Anticline • Syncline • Monoclin

20. Anticline • Up-curved fold in which the oldest layer is in the center of the fold • Generally forms a ridge • Can you think of examples…

21. Syncline • Down-curved fold in which the youngest layer is in the center • Generally forms a valley • Can you think of examples…

22. Monocline • Fold in which both limbs remain horizontal • Gently dipping one way or the other • Can you think of examples…

23. Faulting • Breaks in rocks when the rocks on either side of the break move is faulting • Breaks in rocks when the rocks on either side of the break do not move is fracture • Near the crust’s surface rocks are more brittle and tend to break, not bend

24. Fault Vocabulary • Fault plane - surface of a fault along which any motion occurs • Hanging wall - in a non-vertical fault, the rock above the fault plane • Footwall - rock below the fault plane

25. 4 Types of Faulting • Normal Fault • Reverse Fault • Thrust Fault • Strike-slip Fault

26. Normal Faulting • Hanging wall moves down relative to the footwall • Form along divergent boundaries • Usually occurs in a series of parallel fault lines

27. Reverse and Thrust Fault • Reverse - Forms when compression causes the hanging wall to move up relative to the footwall • Thrust - Fault plane is at a low angle or nearly horizontal. • Common in steep mountains such as the Rockies and Alps

28. Strike-slip Fault • Rock on either side of the fault plane slides horizontally • Often occur in transform boundaries • Example: San Andreas Fault

29. Review • What results when rock responds to stress by permanently deforming without breaking? • Explain why faulting is more likely to occur near the surface than deep within the earth… • Draw and describe four types of faults

30. Section 3 – Mountain Formation Objectives: • Identify the types of plate collisions that build mountains. • Identify four types of mountains and discuss the forces that shaped them.

31. Mountain Formation Introduction • A mountain range is a group of adjacent mountains with the same general shape and structure • A group of adjacent mountain ranges make up a mountain system • Largest mountain systems are part of still larger systems called mountain belts • Circum-Pacific Belt • Eurasian-Melanesian Belt

32. Plate Tectonics and Mountains • Circum-Pacific and Eurasian-Melanesian mountain belts are located along convergent plate boundaries • Scientists think this is evidence that most mountains were formed when lithospheric plates collided

33. How Plate Collisions Form Mountains • Collisions between Continental and Oceanic Crust = Subduction zones form coastal volcanoes • Collisions between Oceanic Crust and Oceanic Crust = Volcanic island arcs form on ocean floor • Collisions between Continents = Crust crumples and rises (Example are the Himalayas)

34. Types of Mountains • Mountains are complicated structures with rock formations that yield evidence of the forces that created them. • Classified by: deformation and shape • 4 Types

35. Folded Mountains and Plateaus • Continental Crust is pushed together and up • Highest mountain ranges in the world • Plateaus are large uplifted flats are also formed near folded mountains

36. Fault-Block Mountains • Range fronts rise along normal faults as a result of crustal stretching • Examples: Lost River Range, most of Nevada

37. Volcanic Mountains • Mountains that form when molten rock erupts onto the earth’s surface • Hot Spots – formed on the ocean floor

38. Dome Mountains • Formed when molten rock rises through the crust and pushes up the rock layers above it • When pushed up, rock layers are worn away exposing hardened rock • Where the rock wears away and leaves separate high peaks is dome mountains

39. Review • Describe the types of lithospheric plate collisions that build mountains. • Name the four types of mountains and explain how each is formed. • How do volcanic mountains grow?