•Rock Deformation Flashcards
What are the two most important pressures for rock deformation and what causes them?
1) Lithostatic pressure caused by the weight of rock pushing down
2) Tectonic pressure/ lateral pressure caused by the movement of tectonic plates
What is the equation for force?
What is it measured in?
Mass x Acceleration
Measured in Newtons (N)
What is the equation for stress?
What is it measured in?
Force / Area
Measured in Pascals (pa)
What is the definition of strain?
The change in shape or volume due to an applied stress
What two stresses at created by force acting on an area?
How do they act?
1) normal stress
Acts perpendicular to a surface
2) shear stress
Acts parallel to a surface
What are the the three types of differential stresses?
What creates them?
Where do they exist?
1) Tensional stress
Created by divergent forces ⬅️➡️
Constructive plate boundaries
2) Compressional stress
Created by converging forces ➡️⬅️
Destructive plate boundaries
3) Shear stress
Opposing forces sliding past each other ↗️↙️
Conservative plate boundaries
What is the formula for Hooke’s Law?
What does each letter mean?
e= (l-lo) / lo
e= strain lo= original length l= new length
What is elastic strain?
Reversible and non- permanent stress
The removal of this stress creates an immediate return to the original shape
What is brittle failure?
What Rocks does is occur in?
Where the rock breaks ( create faults )
Happens in cold and dry rocks that are composed of hard, granular minerals e.g quartz, garnet and olivine
What is ductile deformation?
What rocks will it occur in?
Smooth strain which creates colds and shear zones instead of fractures
Occurs in warm and wet rocks or rocks composed of soft minerals e.g gypsum, clay and calcite
What does it mean when a rock behaves plastically?
When does it happen?
It will deform continuously in the same manner as moving fluid
It occurs when applied stress is increased until the yield strength of the rock is exceeded
What is a dip?
The direction of tilt measured from the horizontal
What is a strike?
The direction of a line at a right angle to the dip
What are the two types of fold?
What do they look like?
What are the called if they are the correct way up?
1) Antiform
Fold of the crest points up
Anticline
2) Synform
Fold of the crest points down
Syncline
What is the crest?
Upper surface at the top of a fold
What is the trough?
The upper surface at the bottom of the fold
What is the hinge?
The area where the rock is most strongly bent
What is the hinge line?
A line joining the points of maximum bending
What is the fold axis?
The line of maximum bending along the fold crest
What is the axial plane?
A line that divides the fold halves and is parallel to the hinge line
What is a limb?
The area of fold between the hinges
What is the plunge?
The difference in angle between the fold axis and the horizontal
What is happening at a plunging fold?
What shape does it create?
The outcrop dips into the ground at angle of plunge
Creates a V-shaped outcrop
What is happening at a non-plunging fold?
The surface outcrop is always parallel to the edge and the axial plane
What is the fault plane?
The rock surface along which movement has occurred
What is the hanging wall?
The rock above the fault plane
What is the footwall?
The rock below the fault plane
What is strike slip?
The movement parallel to the strike of the fault plane
What is dip slip?
Movement parallel to the dip
What is the throw?
The total vertical displacement
A diagram to show the fault terminology
➡️heave
⬇️throw
⬆️strike slip
↘️dip slip
➡️ net slip
What is a normal fault?
What stress causes it?
The hanging wall moved downwards
Caused by tensional stress ⬅️➡️
What is a reverse fault?
What stress causes it?
Hanging wall moves upwards
(No more than 30 degree dip)
Caused by compressional stress ➡️⬅️
What is a thrust fault?
What stress causes it?
Reverse fault of less than 15 degrees
Caused by compressional stress ➡️⬅️
What is a strike-slip or transcurrent fault?
What are the two types?
Movement horizontal to the ground surface
1) Sinistral = block opposite moves to the left
2) Dextral = block opposite moves to the right
What is an uncomformity?
An erosional boundary
What is the differences above and below an unconformity?
- Fossil types will vary
- Rocks below are more deformed
- Rock above contains included fragments from below
What is a hiatus?
A time gap in the geological records where no rock is found/ recorded
Where is a hiatus found?
At an unconformity
