Module 7 Flashcards
Geological Structures
why do rocks fold and fault
rocks are subject to stress (force per unit area) and undergo strain in response,
compressional stress
forces pushing together
what is an example of compressional stress
C-C, O-C, and O-O convergent plate margins
tensional stress
forces pulling apart
what is an example of tensional stress
divergent plate margins
shear stress
parallel, opposing forces
what is an example of shear stress
transform plate margins
how do rocks respond to stress on a large scale?
in one of three ways: elastic, plastic, or brittle
elastic response
deformed body recovers when stress is removed.
what happens when the stress applied to rock goes beyond its elastic limit
there is permanent deformation, and it can be considered a plastic response
plastic response
rock bends but does not return to its original shape. high temp and pressure lead to plastic behaviour
examples of plastic response rocks
glacial ice and asthenosphere
brittle response
rock breaks or fractures very easily
examples of brittle response
surface rocks, and faults
anticline
upward arching fold
syncline
downward arching fold
what can be said about anticline and syncline folds
often happen together, and the hinge lines are about 90 degrees
hinge line
axis of the fold
axial plane
plane containing all hinge lines of a fold
types of folds
anticline, syncline, monocline, recumbent fold, thrust folds, and overturned folds
overturned folds
anticline axial plane goes over the syncline axial plane
recumbent folds
axial planes of anticline and syncline are orientated parallel to horizon
example of folds
Appalachian valley and ridge
types of fractures in rocks
joints and faults
joints
rock fractures with no displacement, and is usually on a smaller scale
what is a fracture
a break in response to stress
what is a fault
a rock fracture where movement has taken place
active fault
movement within the last 11,000 years
hanging wall block
overlies an inclined fault plane
footwall block
underlies an inclines fault plane
normal fault
hanging wall block moves downward relative to the footwall block. can produce a graben or a horst
example of normal fault
rift valleys
reverse fault
hanging wall block moves upwards relative to the footwall
what stress/boundary causes a reverse fault
compressional stress/convergent boundary
what stress/boundary causes a normal fault
tensional stress/divergent boundary
horst
a block is pushed upwards relative to the blocks on either side by the faulting
graben
a block that has been lowered relative to the blocks on either side due to the faulting
thrust fault
reverse fault with very low angle fault plain (<45 degrees)
strike-slip fault
a fault where the movement is predominantly horizontal and therefore parallel to the strike of the fault
what type of stress/boundary causes a strike-slip fault
shear stress/transform boundaries
what is needed for fossil fuels to form
carbon-based life, heat, and pressure
where may we find water/oil/gas
anticlines and faults
stress
force per unit area
folds
bends in layered rock; plastic strain
strain
a change in size/shape as a response to stress
