Crustal Deformation Flashcards
Where does most deformation occur?
Along Plate Boundaries
What type of stress is most often associated with convergent plate boundaries?
Compressional
What type of fault is present when dominant displacement is horizontal and parallel to the trend
(direction) of the fault surface?
Strike-slip
Which occurs when stress exceeds rock strength?
Deformation
In what type of fault does the hanging wall moves up relative to the foot wall?
Reverse fault
Which of the following correctly describes a fault?
It is a crack or fracture on the Earth’s crust (not sure)
Which of the following are the factors that affect rock strength?
Rock type, temperature, time, and confining pressure
What type of deformation results when the rock surpassed its elastic limit and breaks?
Brittle deformation
Which feature is the characteristic of synclines?
It is a fold where the rock layers are warped downward that resulted from compressional stress.
Which is the force that deforms rocks?
Stress
Which type of deformation exhibits recoverable changes, where the rock will snap back to nearly
original size and shape when the stress is removed?
Elastic deformation
Which type of differential stress pulls the rocks apart?
Tensional
What refers to the factor that increases with depth and squeezes the materials in Earth’s crust that makes rock more stronger?
Confining pressure
Refers to the changes in the shape or position of a rock body in response to differential stress?
Deformation
Explain Compressional Stress
Differential stress that squeezes a rock mass as if placed in a vise is known as compressional stress.
Explain Tensional Stress
Differential stress that pulls apart or elongates rock bodies is known as tensional stress.
What type of stress is most often associated with divergent plate boundaries?
Tensional Stress
Explain Sheer Stress
Differential stress can also cause rock to shear, which involves the movement of one part of a rock body past another. Shear is similar to the slippage that occurs between individual playing cards when the top of the deck is moved relative to the bottom.
What type of stress is most often associated with Transform plate boundaries?
Sheer Stress
Difference between Stress and Strain
- Stress is the force that acts to deform rock bodies.
* Strain is the resulting deformation (distortion).
Explain the Elastic Deformation.
- When stress is applied gradually, rocks initially respond by deforming elastically.
- It acts like a rubber band,
- When the stress is removed, the bonds snap back to their original length.
Explain Brittle Deformation.
• When the elastic limit (strength) of a rock is surpassed, the rock either bends or breaks.
Explain Ductile Deformation
- Ductile deformation is a type of solid-state flow that produces a change in the shape of an object without fracturing.
- eg. a coin placed on a railroad track will be flattened but not destroyed.
Explain the 4 factors that affects rock strength.
- Temperature
- Higher temperature means higher malleability ( they deform by folding (ductile deformation))
- Lower temperature means that rocks behave like brittle solids and fracture.
- Confining Pressure
- Higher pressure means harder to break. Imagine a stack of bond paper being stacked together, it’s difficult to break.
- Rock Types
- Igneous rocks and some metamorphic rocks have strong internal chemical bonds.
- Sedimentary rock are weakly cemented and metamorphic rocks that contain zone of weakness behave in a ductile manner (eg. rock salt).
- Time
- Rocks that are applied with stress over time tend to behave in a ductile manner (eg. books in a wood bookshelf).
- Rocks that applied with stress suddenly will break.
What are the common types of folds and the difference between them?
- Synclines are the downfolds
* Anticlines are the ones who arise by folding.
What are folds?
Folds are geologic structures consisting of stacks of originally horizontal surfaces, such as sedimentary strata, that have been bent as a result of permanent deformation.
What are he difference between symmetrical, asymmetrical, and overturned?
- Symmetrical limbs are mirror images
- Asymmetrical limbs are not mirror images
- Overturned (if one or both limbs are tilted beyond the vertical. Basically more than asymmetrical.
How do faults form?
Faults form where brittle deformation leads to fracturing and displacement of Earth’s crust.
Explain Dip-Slip Fault
Faults in which movement is primarily parallel to the inclination (also called dip) of the fault surface are called dip-slip faults. Geologists identify the rock surface immediately above the fault as the hanging wall block and the rock surface below as the footwall block.
What are the types of Dip-Slip Faults?
Normal and Reverse
Explain Normal Fault
- Dip-slip faults are classified as normal faults when the hanging wall block moves down relative to the footwall block.
- Normal faults are associated with tensional stresses that pull rock units apart, thereby lengthening the crust. This “pulling apart” can be accomplished either by uplifting that causes the surface to stretch and break or by horizontal forces that have opposing orientations.
Explain Reverse Fault
- ip-slip faults in which the hanging wall block moves up relative to the footwall block are called reverse faults.
- Thrust faulting is most pronounced along convergent plate boundaries. Compressional forces associated with colliding plates generally create folds as well as thrust faults that thicken and shorten the crust to produce mountainous topography.
Explain Strike-Slip Fault
- A fault in which the dominant displacement is horizontal and parallel to the trend (direction) of the fault surface is called a strike-slip fault.
- I think this is associated with shear stress.
