Lesson 10: Rock Deformation Flashcards
What is stress?
the amount of force applied per unit area of a rock
What types of stresses work in convergent plate boundaries?
Compressive - rocks are being squeezed; causes shortening
What types of stresses work in divergent plate boundaries?
extensive (tensional) stress - rocks being pulled apart; causing lengthening
What types of stresses work in transforming plate boundaries?
shear stress - there are forces in opposite directions parallel to a plane; causes tearing/bending
What causes folding to occur?
compressional stresses
What are the different types of folds?
1 Anticline
2. Syncline
3. Symettrical Folds
4. Isoclinal Folds
5. Asymetrical Folds
6. Overturned Folds
7. Recumbent Folds
8. Chevron (Zig-Zag) Folds
9. Plunging Folds
10. Domes
11. Basins
12.Monoclines
What is the characterization of Anticlines? (F1)
- up folded/arched rock layers;
- oldest strata are in the center
What is the characterization of Syncilines? (F1)
(Hint: a syn makes you grin)
- downfolded/troughs of rock layers
- youngest strata are in the center
How can anticlines and synclines be described depending on their orientation?
- Symmetrical
- Asymmetrical
- Overturned - axial plane is inclined/tilted
- Recumbent - axial plane is horizontal
- Plunging - plunging (inclined/tilted) hinge line (non-plunging if the horizontal hinge line are non-plunging folds)
How are symmetrical folds characterized? (F2)
Limbs are mirror images of each other
How are Isoclinal folds characterized? (F3)
- have the same angle
- limbs are parallel
How are asymmetrical folds characterized? (F4)
Limbs are not mirror images of each other
How are overturned folds characterized? (F5)
- axial plane inclined/tilted
- beds on one limb are upside down
How are recumbent folds characterized? (F6)
horizontal axial plane
How are chevron folds characterized? (zig zag) (F7)
- straight limbs and sharp hinges
- v-shaped beds
How are plunging folds characterized? (F8)
folds have an inclined/tilted hinge line (NOT horizontal)
How are domes characterized?
- upwarped circular features
- oldest rocks are in the center
How are basins characterized?
- downwarped circular features
- Youngest rocks are in the center
How are monoclines characterized?
- large, steplike folds, in an otherwise horizontal sedimentary strata
- Brittle basement rocks displaced upward with overlying ductile sedimentary strata draped over them.
What are the types of faults
- Dip-slip faults
- Strike-slip faults
- Oblique-slip faults
How are Dip-Slip faults characterized?
- inclined fault plane
- relative displacement along dip direction; parallel to fault’s slope
- vertical displacement along fault produces long, low cliffs called fault scarps.
- has a hanging wall and a footwall
What part of a dip-slip fault is the hanging wall? (F9)
the block of rock above a non-vertical fault
What part of a dip-slip fault is the footwall? (F9)
the block of rock below a non-vertical fault
What are the 3 types of Dip-Slip faults?
- Normal fault - tensional stress
- Reverse fault - compressional stress
- Thrust fault - compressional stress
How are normal dip-slip faults characterized?
(Hint: Geology is FUN) (F10)
- result from horizontal tensional stresses; accommodates crustal stretching
- Foot wall is up relative to strata in hanging wall
How are reverse dip-slip faults characterized?
(Hint: FDR) (F11)
- result from horizontal compressional stresses in brittle rocks
- Footwall is down relative to strata in hanging wall
How are thrust dip-slip faults characterized?
- dip is less than 40 degrees so the overlying plate moves almost horizontally
- considerable displacement that can result in older strata overlaying younger strata
- the result of compressional stress
How are strike-slip faults characterized?
- caused by shear stresses
- motion on fault has taken place along a horizontal direction (no up and down motion)
How are right-lateral strike-slip faults characterized?
The block moved to the right during faulting
How are left-lateral strike-slip faults characterized?
The block across the fault moved to the left during faulting
How are oblique-slip faults characterized?
- exhibit both strike and dip-slip motion
_______ refers to the amount of force applied per unit area of a rock.
Stress
Stress applied unequally in different directions is called _____ stress.
differential
What is the definition of strain?
a change in a rock’s:
size
shape
volume
as a result of differential stress.
At low temperatures (shallow depths), rocks tend to behave in a ____ manner and fracture.
brittle
____ materials have a small region of ductile behavior before fracture.
Brittle
At high temperatures, materials will behave in a more ____ manner.
ductile (plastic)
Rocks are subject to stress; the main cause of this stress is _______.
plate tectonics
Folds are the result of _____ deformation.
ductile
Most rocks exhibit ______ deformation at shallow crustal depths.
brittle
Joints result from _____ stresses acting on brittle rock.
tensional
Reverse faults result from horizontal ____ stresses in brittle rocks.
compressional
Most folds result from _____ stresses that result in a shortening and thickening of the crust
compressional
