Earth Systems 3209

1. Earth Systems 3209 Reference: Chapters 4, 15, 16, 19; Appendix A & B Unit: 4The Forces Within Earth

2. Unit 4: Topic 3.1 Forces and Factors that affect Deformation Focus on . . . • defining crustal deformation, force, and stress. • outlining and describing three types of deformation. • identifying and describing the forces that cause deformation. • identifying and describing the factors that affect deformation.

3. Terminology associated with Crustal Deformation: • Crustal Deformation is associated with Internal Forces within Earth! • Crustal Deformation • General term that refers to all changes that occur tothe original form and/or size of a rock body. • It may also produce changes in the location and orientation of rocks. • Most crustal deformation occurs along plate tectonic margins. • Plate motions and the interactions along plate boundaries generate tectonic forces that cause rock units to deform.

4. Terminology associated with Crustal Deformation: • Force • anything that tends to put stationary objects in motion or change the motion of moving bodies. • Stress • is defined as the amount of force applied to a given area. • Two types of stress;1) Uniform – equal stress in all directions.2) Differential – varying stress in different directions. • Strain • causes an irreversible change in the shape and size of a rock body. Original configuration is not retained during deformation.

5. Types of Crustal Deformation: Differential Stresses:

6. Types of Crustal Deformation: • When rocks are subjected to stresses greater than their own strength, they begin to deform, usually by folding, flowing, or fracturing. • 3 types of deformation: • Elastic Deformation - recoverable • Brittle Deformation - permanent • Ductile Deformation - permanent

7. Types of Crustal Deformation: • 3 types of deformation: • Elastic Deformation • stress is applied gradually and when the stress is removed the rock will return to nearly its original size and shape. • elastic deformation is recoverable after stressing. • earthquakes result from stored elastic energy. • once the elastic limit is reached it either flows (ductile) or fractures (brittle).

8. Types of Crustal Deformation: • 3 types of deformation: • Brittle Deformation • stress is applied gradually and when the rocks strength is exceeded the rock will behave like a brittle solid where it will fracture and the rock will not return to its original size and shape. • occurs near the surface where temperature and confining pressures are lower. • brittle deformation is permanent.

9. Types of Crustal Deformation: • 3 types of deformation: • Ductile Deformation • stress is applied gradually and when the rocks strength is exceeded the rock will flow in solid state and produce a change in the original size and shape without fracturing. • occurs at great depths beneath Earth’s surface where temperature and confining pressures are higher. • ductile deformation is permanent. • An example would be similar to a penny placed on a railway track and flattened by a passing train. Metal is permanently changed.

10. Factors that Affect Crustal Deformation: • The factors that influence the strength of a rock and thus how it will deform include; • Temperature • Confining Pressure • Rock Type • Time

11. Factors that Affect Crustal Deformation: • The factors that influence the strength of a rock and thus how it will deform include; • Temperature • the colder the Earth materials, the more brittle the deformation will be. • the warmer the Earth materials, the more elastic or ductile the deformation will be.

12. Factors that Affect Crustal Deformation: • The factors that influence the strength of a rock and thus how it will deform include; • Confining Pressure • confining pressure will only result in elastic or ductile deformation at varied depths beneath Earth’s surface. • brittle deformation typically occurs on the surface when there is no confining pressure from above.

13. Factors that Affect Crustal Deformation: • The factors that influence the strength of a rock and thus how it will deform include; • Rock Type • all rock types can be deformed. • however, sedimentary rocks could be more easily deformed since they are softer.

14. Factors that Affect Crustal Deformation: • The factors that influence the strength of a rock and thus how it will deform include; • Time • rapid deformation tends to result in brittledeformation. • slower deformation over longer periods of time tends to result in elastic or ductile deformation.

15. Example 1: Which factors would cause a rock to deform by brittle deformation ?

16. Example 2: Which type of stress and faulting occurs at divergent plate boundaries?

17. Your Turn . . . Take the time and complete the following questions . . .(Solutions to follow) Question: Which rock type is most easily deformed by stresses in Earth’s crust? (A) igneous plutonic (B) igneous volcanic (C) metamorphic (D) sedimentary

18. Solutions . . . Question: Which rock type is most easily deformed by stresses in Earth’s crust? (A) igneous plutonic (B) igneous volcanic (C) metamorphic (D) sedimentary

19. Summary . . . Overview of Points covered: • Crustal deformation is a direct result of stresses put on rocks. • 3 types of stress include;1) Tensional, 2) Compressional, 3) Shear • 3 types of crustal deformation include;1) Elastic, 2) Brittle, 3) Ductile • Factors affecting crustal deformation include;1) Temperature, 2) Confining Pressure, 3) Rock Type, 4) Time