deformation
all changes in the shape or position of a rock body in response to stress
rock or geologic structures
the features that result from forces generated by the interactions of tectonic plates (includes folds, faults, and joints)
stress
the force that deforms rocks
confining pressure
stress applied uniformly in all directions
differential stress
stress applied unequally in different directions
compressional stress
squeezes a rock and shortens a rock body
tensional stress
pulls apart a rock unit and lengthens it
shear stress
produces a motion similar to slippage that occurs between individual playing cards when the top of the stack is moved relative to the bottom
strain
the change in shape of a rock caused by differential stress
elastic deformation
the rock returns to nearly its original size and shape when the stress is removed (recoverable)
ductile deformation
when a rock reaches its elastic limit and bends;
(high temp., high pressure, slow strain rate);
Sedimentary Rock - weak
brittle deformation
when a rock reaches its elastic limit and breaks;
(high temp., low pressure, fast strain rate);
Igneous Rock - strong
temperature (affecting rock strength)
higher temperature rocks deform by ductile deformation wheras cooler rocks deform by brittle deformation
confining pressure (affecting rock strength)
squeezes rocks, making them stronger and harder to break
rock type (affecting rock strength)
crystalline igneous rocks generally experience brittle deformation, wheras sedimentary and metamorphic rocks with zones of weakness generally experience ductile deformation
time (affecting rock strength)
forces applied over a long period of time generally result in ductile deformation
Most rocks exhibit ________ behavior in the upper 10 kilometers of the crust.
brittle
joints
cracks in the rocks resulting from the rock being stretched and pulled apart
faults
fractures in the rocks where rocks on one side of the fault are displaced relative to the rocks on the other side of the fault
Most folds result from ____________ that result in a shortening and thickening of the crust.
compressional stresses
anticlines
upfolded or arched sedimentary layers (oldest strata are in the center)
synclines
downfolded or troughs of rock layers (youngest strata are in the center)
domes
upwarped circular features (oldest rocks are in the center)
[ex] the Black Hills
basins
downwarped circular features (youngest rocks are in the center)
[ex] basin structure in Michgan
monoclines
large, steplike folds in otherwise horizontal sedimentary strata
[ex] around Rocky Mountains
Sudden movements along ___________ are the cause of most earthquakes.
faults
dip-slip faults
occur when movement is parallel to the inclination
hanging wall
a rock surface above the fault
footwall
the rock surface below the fault
normal faults
characterized by the hanging wall moving down relative to the footwall (associated with tensional stress as the rocks pull apart)
Larger scale normal faults are associated with ___________.
fault-block mountains
horsts
uplifted blocks
grabens
down-dropped blocks
half-grabens
tilted fault blocks
detachment faults
represent the boundary between ductile and brittle rock units
reverse faults
characterized by the hanging wall moving up relative to the footwall
thrust faults
have an angle less than 45 degrees, so the overlying plate moves almost horizontally
strike-slip faults
characterized by placement that is horizontal and parallel to the strike of the fault
right-lateral (strike-slip fault)
as you face the fault, the opposite side of the fault moves to the right
left-lateral (strike-slip fault)
as you face the fault, the opposite side of the fault moves to the left
transform faults
large strike-slip faults that cut through the crust to accommodate plate motion
[ex] San Andreas Fault
oblique-slip faults
exhibit both a strike-slip and a dip-slip movement (diagonal movement)
strike
the compass direction of the line produced by the intersection of an inclined rock layer or fault with a horizontal plane
dip
the angle of inclination of the surface of a rock unit or fault measured from a horizontal plane
plate boundaries
Most crustal deformation occurs along _______________.
Types of Deformation
These 3 things are ____________________?
-Translation (change in location)
-Rotation (change in orientation)
-Distortion (change in shape & causes strain)
Types of Stress
These things are __________________?
-compression
-tension
-shear stress
-pressure
Stress; strain
___________ causes _____________?
(stress, strain) (stress, strain)
Ductile Deformation
Fold is an example of which type of deformation?
[happens deeper in earth]
Brittle deformation
Fault is an example of which type of deformation?
[happens near earth's surface]
folds
Himmalayas are made by crustal deformation of ______?
Limbs
the two sides of the fold are called _______?
Hinge (line)
drawn down the points of max. curvature of each layer
Axial Plane
imaginary surface that divides fold symmetrically
right lateral
San Andreas fault is moving NW of Pacific Plate which is ________?
(left lateral, right lateral)
Joints (brittle deformation)
Influences stream courses.
San Andres Fault
Fault that is between North American & Pacific Plate.
Normal Faults
Continental rift valley of East American has what type of faults?