glacial dating- visualizing in 3D Flashcards
Why do rocks fold and fault?
- when rocks are subjected to stress and undergo strain they fold and fault
- there are different kinds oof stress including compressional, tensoinal, and shear
How do rocks respond to stress?
- rocks respond in two ways:
- Elastic strain: deformed body recovers when stress is removed. Think elastic band. When the stress is beyond the elastic limit, permanent deformation is caused
- Plastic strain: bends but does not return to original shape. Rocks under increased temperature/pressure. For example, rocks in the mantle. Ex. glacial ice, asthenosphere
- brittle
*How do rocks fold?
- folds or bends in layered rocks. caused by plastic strain
- depending on the stress, strain behaviour on the rock changes. Folds can become permanent after strain is removed: this can casued a fault
- types of folds: anticline, syncline, overturned, recumbent
What are fractures and faults?
joints- rocks fractures, no displacement (not a fault)
faults- fractures along which movements has taken place. An active fault is classified as having movement within 11000 years
- Types of faults: normal, reverse, thrust, strike slip
How does fault formation reflect the type of stress to which rocks are subjected?*****
- different types of faults are caused by different types of stress
anticline
- upward arching fold
- synclines and anticlines often occur together
syncline
- downward arching fold
- synclines and anticlines often occur together
overturned fold
anticline goes over syncline due to lots of folding
recumbent fold
- axial plane is at the axsis of orientation. straight lines in the horizion
- axial plane is essentially horizontal,
compressional stress
- forces pushing together
- convergent boundaries have compressional stress
- ex. convergent plate margins
tensional stress
- forces pulling apart
- ex. divergent plant margins
shear stress
- parallel; opposing forces
- ex. transform plate margins
normal fault
- hanging wall block moves downward relative to footwall block
- caused by tensional stress
- can produce a graben or horst
- ex. East african rift valley, or just a rift valley in general
reverse fault
- hanging wall block moves upwards relative to footwall block
- causes by compressional stress
- often caused by compressional stress
thrust fault
- reverse fault with very low angle fault (less than 45 degrees)
- causes by compressional stress
strike slip fault
- a fault where the movement is predominantly horizontal and therefore parallel to the strike of the fault
- causes by shear stress
- found in transform boundaries
hanging wall block
- overlies an inclined fault plane
footwall block
- underlies an incline fault plane
strain
change in size/shape in response to stress
folds
- bends in layered rock due to plastic strain
hinge line
axis of the fold
axial plane
plane contaiing all hinge lines of a fold
where do we find water/gas/oil?
- we can map out where faults may be
- most fossil fuels are found in sedimentary rock
- reasources can be found in a resivor over an anticline trap, oil and gas rise to the crest(top) of the fold
- also found in fault traps which is where oil and gas collect in tilted strata adjacent to the fault
- also salt dome traps and stratigraphic trap
- it takes millions of years for reasoureces to replenish
- it is important because we are buring fossil fuels so quickly that they will not be replenished in our lifetime
horst
a block pushed upward relative to the blocks on either side b the faulting
graben
a block that has been lowered relative to the blocks on either side due to the faulting
brittle
- breaks or fractures, ex. faults
- surface rocks
appalacian valley and ridge
- folding at appalacians tells us that appalacians are no longer growing
- it is an old mountain range
- folds are only found at active tctonic plate boundaries
- at the appalacians, it is no lonher active and is eroding away
