Lesson 10: Rock Deformation

Question 1

What is stress?

Answer 1

the amount of force applied per unit area of a rock

Question 2

What types of stresses work in convergent plate boundaries?

Answer 2

Compressive - rocks are being squeezed; causes shortening

Question 3

What types of stresses work in divergent plate boundaries?

Answer 3

extensive (tensional) stress - rocks being pulled apart; causing lengthening

Question 4

What types of stresses work in transforming plate boundaries?

Answer 4

shear stress - there are forces in opposite directions parallel to a plane; causes tearing/bending

Question 5

What causes folding to occur?

Answer 5

compressional stresses

Question 6

What are the different types of folds?

Answer 6

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

Question 7

What is the characterization of Anticlines? (F1)

Answer 7

1. up folded/arched rock layers;
2. oldest strata are in the center

Question 8

What is the characterization of Syncilines? (F1)
(Hint: a syn makes you grin)

Answer 8

1. downfolded/troughs of rock layers
2. youngest strata are in the center

Question 9

How can anticlines and synclines be described depending on their orientation?

Answer 9

1. Symmetrical
2. Asymmetrical
3. Overturned - axial plane is inclined/tilted
4. Recumbent - axial plane is horizontal
5. Plunging - plunging (inclined/tilted) hinge line (non-plunging if the horizontal hinge line are non-plunging folds)

Question 10

How are symmetrical folds characterized? (F2)

Answer 10

Limbs are mirror images of each other

Question 11

How are Isoclinal folds characterized? (F3)

Answer 11

1. have the same angle
2. limbs are parallel

Question 12

How are asymmetrical folds characterized? (F4)

Answer 12

Limbs are not mirror images of each other

Question 13

How are overturned folds characterized? (F5)

Answer 13

1. axial plane inclined/tilted
2. beds on one limb are upside down

Question 14

How are recumbent folds characterized? (F6)

Answer 14

horizontal axial plane

Question 15

How are chevron folds characterized? (zig zag) (F7)

Answer 15

1. straight limbs and sharp hinges
2. v-shaped beds

Question 16

How are plunging folds characterized? (F8)

Answer 16

folds have an inclined/tilted hinge line (NOT horizontal)

Question 17

How are domes characterized?

Answer 17

1. upwarped circular features
2. oldest rocks are in the center

Question 18

How are basins characterized?

Answer 18

1. downwarped circular features
2. Youngest rocks are in the center

Question 19

How are monoclines characterized?

Answer 19

1. large, steplike folds, in an otherwise horizontal sedimentary strata
2. Brittle basement rocks displaced upward with overlying ductile sedimentary strata draped over them.

Question 20

What are the types of faults

Answer 20

1. Dip-slip faults
2. Strike-slip faults
3. Oblique-slip faults

Question 21

How are Dip-Slip faults characterized?

Answer 21

1. inclined fault plane
2. relative displacement along dip direction; parallel to fault’s slope
3. vertical displacement along fault produces long, low cliffs called fault scarps.
4. has a hanging wall and a footwall

Question 22

What part of a dip-slip fault is the hanging wall? (F9)

Answer 22

the block of rock above a non-vertical fault

Question 23

What part of a dip-slip fault is the footwall? (F9)

Answer 23

the block of rock below a non-vertical fault

Question 24

What are the 3 types of Dip-Slip faults?

Answer 24

1. Normal fault - tensional stress
2. Reverse fault - compressional stress
3. Thrust fault - compressional stress

Question 25

How are normal dip-slip faults characterized? (Hint: Geology is FUN) (F10)

Answer 25

1. result from horizontal tensional stresses; accommodates crustal stretching 2. Foot wall is up relative to strata in hanging wall

Question 26

How are reverse dip-slip faults characterized? (Hint: FDR) (F11)

Answer 26

1. result from horizontal compressional stresses in brittle rocks 2. Footwall is down relative to strata in hanging wall

Question 27

How are thrust dip-slip faults characterized?

Answer 27

1. dip is less than 40 degrees so the overlying plate moves almost horizontally 2. considerable displacement that can result in older strata overlaying younger strata 3. the result of compressional stress

Question 28

How are strike-slip faults characterized?

Answer 28

1. caused by shear stresses 2. motion on fault has taken place along a horizontal direction (no up and down motion)

Question 29

How are right-lateral strike-slip faults characterized?

Answer 29

The block moved to the right during faulting

Question 30

How are left-lateral strike-slip faults characterized?

Answer 30

The block across the fault moved to the left during faulting

Question 31

How are oblique-slip faults characterized?

Answer 31

1. exhibit both strike and dip-slip motion

Question 32

_______ refers to the amount of force applied per unit area of a rock.

Answer 32

Stress

Question 33

Stress applied unequally in different directions is called _____ stress.

Answer 33

differential

Question 34

What is the definition of strain?

Answer 34

a change in a rock's: size shape volume as a result of differential stress.

Question 35

At low temperatures (shallow depths), rocks tend to behave in a ____ manner and fracture.

Answer 35

brittle

Question 36

____ materials have a small region of ductile behavior before fracture.

Answer 36

Brittle

Question 37

At high temperatures, materials will behave in a more ____ manner.

Answer 37

ductile (plastic)

Question 38

Rocks are subject to stress; the main cause of this stress is _______.

Answer 38

plate tectonics

Question 39

Folds are the result of _____ deformation.

Answer 39

ductile

Question 40

Most rocks exhibit ______ deformation at shallow crustal depths.

Answer 40

brittle

Question 41

Joints result from _____ stresses acting on brittle rock.

Answer 41

tensional

Question 42

Reverse faults result from horizontal ____ stresses in brittle rocks.

Answer 42

compressional

Question 43

Most folds result from _____ stresses that result in a shortening and thickening of the crust

Answer 43

compressional