Rock Deformation Flashcards
How are rocks distorted?
By tectonic rocks
What are the types of tectonic forces?
Compressive, tensional, and shearing
What are compressive forces?
squeeze and shorten a body
What are tensional forces?
Stretch a body and tend to pull it apart
What are shearing forces?
push two sides of a body in opposite directions
What is stress?
The push, pull, or shear that a material feels when subjected to a force
force applied per unit area
FORCE/AREA
How easy or hard it is to crush
What are the different kinds of stress that occur in rock bodies
Tensional stress, compressional stress, and shear stress
What is strain?
Change in shape of a rock in response to deformation
What’re the different types of strain
stretching, shortening, and shear strain
What is stretching?
if a layer of rock becomes longer
What is shortening?
if a layer of rock becomes shorter
What is shear strain?
if a change in shape involves the movement of one part of a rock body past another
In what direction are rocks formed?
Every rock is formed horizontally
What does stress cause?
Stress causes strain
What does tensional stress cause?
Stretching
What does compression stress cause?
Shortening
What does shear stress cause?
Shear strain
What is pressure? (Stress)
Objects feel the same stress on all sides
Undeformed
What is extension?
Pull apart
Greater stress in one direction
Thins material
Makes it longer
What is compression?
Squeezing
Greater stress in 1 direction
Thickens material
Makes it shorter
What is shear?
Blocks of rock sliding past one another
What are the measurements to describe the orientation of a layer of rock at a given location
Dip and Strike
What is dip?
The amount of tilting
The angle where the bed inclines from the horizontal
Walk up or down
What is strike?
The direction of the intersection of a rock layer with a horizontal surface
Perpendicular to the direction of the dip
Walk along the strike
What determines whether a rock bends or breaks?
Their strength
How some resist deformation more than others in response to the forces to which they are subjected
How do some rocks deform?
Ductile and brittle
some can do both
What is ductile?
Capable of being easily shaped or molded
Flexible
Smooth and continuous plastic deformation
What is brittle?
Likely to break
Rigid
Undergoes little change until it breaks suddenly
What qualities determine whether the rock is ductile or brittle?
Kind of rock
TEMPERATURE
PRESSURE
Magnitude of the force
Speed with which the force is applied
What does ductile behavior in rocks cause?
Folds
What does brittle behavior in rocks cause?
joints and faults
What does folds imply
the structure was originally planar, such as a sedimentary bed, has been bent
COMPRESSIVE FORCES WERE AT WORK
What’re some types of folds
Anticlines Synclines Limbs Axial plane Fold axis Plunging fold Asymmetrical fold Overturned fold Dome Basin
Anticlines
Upfolds or arches of layered rocks
Synclines
Downfolds or troughs of layered rocks
Limbs
The two sides of the fold
Axial plane
an imaginary surface that divides a fold as symmetrically as possible
One limb on either side
SYMMETRICAL FOLDS
Fold axis
the line made by the lengthwise intersection of the axial plane with the beds
Plunging fold
If the axis is not horizontal
Asymmetrical fold
one limb is dipping more steeply than the other
Overturned fold
One limb is tilted beyond the vertical
Both limbs dip in same direction, but one limb has tilted beyond vertical
Dome
ANTICLINAL structure
a broad circular or oval upward bulge of rock layers
encirlce a central point and did rapidly away from it
Oldest sedimentary rock is on the bottom (CORE)
Youngest sedimentary rock in on the top (EXPOSED)
Basin
SYNICAL structure
bowl shaped depression
beds dip rapidly towards a central point
Oldest sedimentary rock is on the top (EXPOSED)
Youngest sedimentary rock in on the bottom (CORE)
Plunging anticline
direction of plunge towards V
Plunging syncline
direction of plunge away from V
What are eroded remnants of a folded mountain belt?
The Valley and Ridge province of the Appalachian Mountains
In Pennsylvania
What are joints?
Fractures in rock caused by regional stress or by the cooling and contraction of the rock
Lacks any visible or measurable displacement
Most frequently occur as joint sets and systems
How can joints be caused?
Can be caused by all three forces: compressive, tensional, and shearing
How can faults be caused?
Can be caused by all three forces: compressive, tensional, and shearing
What is Dip-slip fault (normal)?
relative movement down the fault plane
Tension
Normal
block slide down in relation to other
Extension of the section
happening along dip
ex. Wasatch fault-Utah
60 degree angle
What is Strike-slip fault?
Movement is horizontal, parallel to the strike of the fault plane
sideaways
Shearing forces
SAN ANDRES FAULT (still active)
What is transform fault?
A strike slip fault that forms a plate boundry
What is oblique-slip fault
Movement along strike and simultaneously up or down dip
Combination of forces
Shear and Tension
What is Dip-slip fault (reverse)?
relative movement up the fault plane
block goes up in relation to the other
Compression
Shortening
happening along dip
Hanging wall moves up the footwall
Fault dip is steeper than 35 degrees
What are caused by Dip-slip faults (normal)
Rift valley
East African rift valleys, mid-ocean ridges
Rhine river valley
Red Sea rift
Right-lateral (dextral) strike-slip fault
the block on the other side is displaced to the right
San Andreas
Left-lateral (sinistral) fault strike-fault
the block on the other side is displaced to the left
What s a thrust fault?
a low angle reverse fault
a reverse fault where the dip of the fault plane is small, so that overlying block is pushed horizontally
Hanging wall moves up the footwall
Fault dip is less than 35 degrees
transport thrust sheets 100s of kilometers
common in the ocean floor
East-central neveda
What is shortening?
breaking and one sheet overrides the other
caused by compression
Overthrusts belt (Western USA)
What’re blocks classified as on a dipping fault
Hanging wall block
Footwall block
What is a hanging wall block?
Above the fault
Your head is near the hanging wall block
the one that moves
What is a footwall block?
below the fault
standing on the foot wall block
What is a rift?
a linear zone where the Earth’s crust and lithosphere are being pulled apart (Tensional forces)
Extensional tectonics
What’re typical rift features?
Central linear downfaulted depression (graben)
normal faulting
What are examples of rifts?
The East African Rift (best one)
The Red Sea Rift
Throughout the Basin and Range Province in North America
The Rio Grande Rift in southwestern US
What is the denali fault
a major intracontinental right lateral strike-slip fault in western North America, extending from northwestern British Columbia, Canada, to the central region of the U.S state of Alaska
Dead Sea Transform
Left lateral strike slip fault
moved 100km over the last 10 million years
What are the Columbia Plateau made of?
flood basalts
What are horst
is the raised fault block bounded by normal faults or graben.
by ranges
Teton range
flat land followed by a high mountain
Grand Teton
A teton fault caused it
