The Solid Earth - Chapter 8: Rock Deformation Flashcards
What are two common ways rocks might deform?
folding
fracturing
When do rocks begin to deform?
When rocks are subjected to stresses greater than their own strength
When stress is applied, rocks respond by deforming ______
elastically
True or false: changes resulting from elastic deformation are reversible
True
When might rocks return to nearly original size and shape?
When stress is removed
What results when the elastic limit surpassed as rocks are deformed?
Plastic deformation or fracture
This results in permanent change, that is, the size and shape of a rock unit are altered through the folding and flowing
Plastic deformation
If stress is applied quickly, rocks tend to ___
fracture
During mountain building, flat lying sedimentary and volcanic rocks are often bent into a series of undulations called -
folds
Two most common forms of folds
anticline
syncline
This type of fold is most commonly formed by the upfolding, or arching, or rock layers. They are sometimes spectacularly displayed where highways have been cut through deformed strata
Anticline
This type of fold is a downfold or trough
syncline
Three adjectives to differentiate anticline and synclines
symmetrical
asymmetrical
overturned
Folds don’t continue forever but die out at the end. The folds are said to be _____ since the axis of the fold is going into the ground
plunging
Most folds are caused by compressional stresses, but are caused by ____ displacement
vertical
When unwarping produces a circular or somewhat elongated structure
Dome
Downwarped structures that have a similar shape to domes
basins
Fractures in the crust along with appreciable displacement has occurred
faults
Faults in which the movement is primarily vertical
dip slip faults
the rock immediately above the fault surface
hanging wall
the rock below the fault surface
foot wall
Dip slip faults are called ____ when the hanging wall moves down relative to the footwall
normal fault
These faults occur when the hanging wall moves up relative to the footwall
reverse
Reverse faults that have a low angle are called -
thrust faults
These faults happen when the dominant displacement is along the trend or strike of the fault
strike slip
When faults have both vertical and horizonal movement
oblique slip faults
Normal faults indicate the existence of _____ stresses that pull the crust apart
tensional
A central block that is bounded by normal faults and drops as the plates separates
graben
These grabens produce an elongated valley bounded by upfaulted structures called…
horsts
Since the blocks involved in reverse and thrust faulting are displaced toward one another, geologists conclude that ____ forces are at work
compressional
Fractures along which no appreciable displacement has occurred
joints
