CHPTR 9 Deformation Flashcards
deformation
changes in the shape, volume, position or orientation of rock layers
folds
wavy deformation - anticline
fault
straight deformation
primary structures
occur when rock formed
primary structures example
strata
cross-bedding
ripple marks
mud-cracks
graded belts
secondary structures
occurs after rock forms
secondary structure examples
folds
faults
stress
force per unit area :)
differential stress
the force is not being applied evenly - the element will be deformed
strain
change in shape of a rock when stress is applied
elastic limit for rocks
0.001
plastic behaviour + example
material behaves as a very viscous liquid - does not return to original shape when stress is removed
ex. glacial ice
fracture
breaks, with formation of cracks
area under the curve of a stress-strain graph
toughness (absorbed energy before fracture)
where does compressional stress occur and what does it cause
convergent plate boundaries - faulting and folding
where does tensional stress occur and what does it cause
divergent plate boundaries - faults
where does shear stress occur
transform plate boundaries
what encourages brittle deformation
- low temp./pressures (near surface)
- crystalline igneous rocks
- fast deformation
what does brittle deformation form
joints and faults
what encourages ductile deformation
- high temp.//pressures (deep/close to magma body)
- sedimentary + metamorphic rocks
- slow deformation
what does ductile deformation form
folds
strike direction
intersection of a horizontal plane with an inclined plane (compass direction)
dip angle
max angle of inclined plane
anticline
concave down (Arch)
syncline
concave up (like a sink)
axial plane
axis of symmetry with limb on each side
axis
intersection of axial plane and a particular rock layer
plunge
difference in angle between horizontal and axis. (if you go along the axial plane, does the ground change elevation)
upright fold
- symmetric
- axial plane vertical
- limbs dip at same angle in opposite directions
inclined fold
- asymmetric
- axis plane not vertical
- limbs dip at different angles (from horizontal)
overturned fold
- asymmetric
- axis plane not vertical
- different angles in same direction (from horizontal)
ways to see folds
outcrops, geophysics
outcrops
visible exposure of underground rocks
- dig it up
- beach cliffs
geophysics (seismic reflection)
map rock layers with reflected sound waves
when doing seismis reflection, which rock type has worse quality lines
igneous
monocline
single change in direction:
- fault moves
- as sedimentary rocks settle on top, they drape over the fault, creating a gradual incline
dome
concave down warping of crustal rocks - anticline in all directions
basin
down-warping of crustal rocks - syncline in all directions
dome ages of layers
centre strata is oldest
outer strata is youngest
(highest is oldest)
basin ages of layers
centre strata is youngest
outre strata is oldest
(highest is oldest)
joint
fractures with no appreciable displacement has occurred
(cracks in rocks but no movement like a fault would have)
what kind of rocks can have joints
igneous and sedimentary
fault
fractures along which appreciable displacement has occurred
fault trace
the fault line
fault scarp
cliff or steep incline along the faultline
hanging wall
the side of the fault that you could hang off of
foot wall
the side of the fault that you could stand on
dip slip faults + types
the slip is parallel to the dip
reverse
normal
thrust
normal fault
hanging wall moves down relative to footwall
reverse fault
hanging wall moves up compared to footwall
thrust fault
reverse fault with a dip less than 45 degrees
megathrust fault
occurs in subduction zones
responsible for the largest earthquakes
klippe
remnant portion of a nappe after erosion has removed connecting portions
nappe
sheetlike body of rock that has been moved above a thrust fault
strike slip fault
strike and slip are parallel
right lateral fault
when looking at the fault, the other side appears to have moved right
left lateral fault
when looking at the fault, the other side appears to have moved left
true or false: faults can have a mix of dip-slip and strike slip motion
True
strike slip faults result in:
- sag ponds
- offset drainage
- linear valley
sag ponds
body of water collected in a depression formed by strike slip movement
it is disconnected from any source of water
offset drainage
one side of a river is moved; the path of the flow of water changes
linear valley
along the fault line creates a linear valley
blind thrust fault
fault does not rupture to the surface - no scarp but there is deformation
Economic importance of faults
- water flows through faults
- reliable source of oil and gas resources
Economic importance of faults - water flows through faults
heavy and valuable minerals are deposited in faults - particularly at the intersections of major faults
Economic importance of faults - source of oil and gas
- organic materials experience high temp and pressure when buried
- oil and gas form and move upwards
- impermeable layer overlies a porous layer and resevoirs form
Structural traps by faults/folds; list types
- antiklinale trap
- fault trap
- salt trap
stratigraphic trap by deposition explain
formed by the sequence of deposition
- places an impermeable cap rock above a porous reservoir layer
antiklinale trap
anticline structure creates an oil/gas reservoir
fault trap
a fault structure creates an oil/gas reservoir
salt trap
the oil/gas reservoir is trapped between the salt dome and an impermeable cap rock
