Chapter 11, test 2: crustal deformation adn mountain building Flashcards
deformation
a general term that refers to all changes in the original form and/or size of a rock body.
stress
the forces that deform rock
compressional stress, and tensional stress
compressional stress
stress that squeezes and shortens rock mass
tensional stress
stress that pulls apart or elongates a rock mass
elastic deformation
like a rubber band the rock will return to nearly its original size and shape when stress is removed
brittle deformation
when the limit of rock strength is surpassed the rock fractures
low temp
ductile deformation
solid state flow (like water or taffy) that produces a change in shape without fracturing.
high temp
factors that influence the strength of a rock
temperature
confining pressure
rock type
time
temperature
high temp causes ductile deformation
low temp causes brittle deformation
confining pressure
greater pressure causes ductile deformation
rock type
sedimentary rocks and foliated metamorphic rocks deform by ductile deformation.
igneous tend to deform by brittle deformation
time
when techtonic forces are applied slowly over a long time, rocks display ductile deformation
folds
rocks bent in a series of waves
most folds result form compressional forces that shorten and thicken crust
types: anticline, syncline
anticline
up folded or arched rock layers
syncline
down folded rock layers
symmetrical
limbs mirror images
asymmetrical
limbs are not mirror images
overturned
one limb is tilted beyond the vertical
faults
fractures or breaks in rocks along which appreciable displacement has taken place
dip slip fault
movement along the inclination (dip) of fault plane
2 types: normal and reverse/thrust
hanging wall
the rock above the fault surface
footwall
the rock below the fault surface
normal dip slip fault
hanging wall moves down
associated with fault block mountains
caused by tensional forces <>
reverse dip slip fault
hanging wall moves up
caused by compressional stress ><
dips greater than 45 degrees
thrust dip slip fault
hanging wall moves up
caused by compressional stress ><
dips less than 45 degrees
megathrust earthquakes
due to shallow dip of the plate boundary large sections tend to get stuck
these are most powerful earthquakes, a lot of tension builds up
strike slip fault
slide past each other
dominant displacement in horizon
often associated with plate boundaries
joints
fractures along with no appreciable displacement has occurred (no movement)
example is arches national park
orogenesis
refers to processes that collectively produce mountain belts
example: laramide orogeny produced the rocky mountains
continental volcanic arc
oceanic-continental crust convergence
volcanic island arcs
oceanic-oceanic crust convergence
continental collisions
continental-continental crust convergence