Test 1 Flashcards

1
Q

Primary Structures

A

Develop during formation of the rock body

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2
Q

example of primary structures

A

cross bedding, ripples, mud cracks

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3
Q

Secondary Structures

A

Form as a result of deformation after rocks formed

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4
Q

What are joints?

A

Tensile fractures with little displacement

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5
Q

How do joints form?

A

Joints arise from brittle fracture of a rock or layer due to tensile stress.

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6
Q

trend?

A

the orientation of a linear feature

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7
Q

plunge?

A

the angle from horizontal of a linear feature

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8
Q

rake?

A

the angle to a linear featured measured from the strike line of a plane

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9
Q

vein?

A

fractures filled with minerals that crystallized/precipitated from fluids flowing through rock

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10
Q

fault?

A

shear fractures that have accommodated notable displacement

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11
Q

folds?

A

systematically curved layers

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12
Q

Cleavage?

A

closely spaced surfaces that give

a ‘woody’ appearance

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13
Q

foliation?

A

Layering produced by ductile deformation

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14
Q

lineations

A

elongate linear features

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15
Q

shear zones

A

deformation distributed over a thickness of

rock (meters to kilometers)

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16
Q

most common joint arrays/sets

A

orthogonal (90 degree angles)

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17
Q

plumose structure?

A

similar to a feather, shows joint propagation direction

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18
Q

hackle lines?

A

accentuate plumose structure, like individual fibers of feather

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19
Q

arrest lines?

A

look like ovals in plumose structure

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20
Q

griffith crack theory

A

pre-existing microcracks in a rock act as stress “concentrators”, largest properly oriented Griffith Cracks
(i.e., perpendicular to tensile direction)
propagate to form a through-going crack

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21
Q

what can produce cracks?

A

thermal contraction, outer arc extension, removal of overburden (unloading), exfoliation joints (pluton)

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22
Q

why are joints in uppermost crust (few km)?

A

Stresses become more compressive with depth to the

point where rocks can’t “pull-apart”

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23
Q

rock strength, depth and temp relationship

A

strength increases with depth until temps raise to the point where strength begins to decrease.

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24
Q

shear fracture?

A

Fractures with a component of “sliding” motion

due to compression, most common

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25
shear fracture angle
roughly 30 from sigma 1
26
normal fault dip angle
around 60
27
thrust fault dip angle
around 30
28
Anderson Classification of Tectonic Stress Regimes?
On average, shear fractures form 30° | from s1 and often form as conjugate sets
29
hanging wall
the block above the fault | hang your lantern on it
30
foot wall
the block below the fault | stand on it
31
stratigraphy?
the age of the rocks
32
The Keys to Describing Slip Along a Fault
direction, sense, magnitude
33
Slickenlines/Striations:
scratches (lineations) on a surface (slicken surface
34
Mullions?
Linear deformation structures formed in the interface between a competent and an incompetent rock (significant viscosity contrast)
35
Chatter Marks?
Step-like features oriented perpendicular to striations; | give information about the sense of shear
36
drag folds?
can be used to determine sense of a fault
37
normal/extensional faults
Dip slip fault on which the hanging-wall has moved down relative to the footwall. younger on older
38
scarps?
triangular faceted spurs due to valleys cutting through a fault scarp. wasatch front
39
horst
high section of normal fault
40
graben
low section of normal fault
41
listric normal fault
bowl looking
42
domino normal fault
domino sections tilt as extension increases
43
graben vs half graben
graben surrounded by 2 horsts, half is on one side (listric)
44
sedimentary growth strata
if it can be dated, great for getting at timing & rates of extension. thickens towards fault. drag folds
45
rift
forms where the crust is pulled apart by tectonic forces.
46
3 rift phases
Early extension, Stretching phase, Post rift subsidence and | sedimentation
47
reverse faults accommodate what?
shortening
48
what are orogenic systems/wedges like?
snow plow
49
Two types of structural styles in thrust belts
thin skinned and thick skinned
50
flat
fault remains parallel to bedding
51
ramp
fault crosses bedding at an angle
52
imbricate fans
blind thrust faults, new faults rotate old ones in the snowplow like effect
53
duplexes
blind thrust faults, includes horses, 3 types.
54
2 types of strike slip step overs
bends and oversteps
55
2 directions of strike slip
right and left lateral
56
what do strike slip fans and duplexes resemble in map view?
horse tails
57
2 types of duplexes
extensional (neg flower) and contractional (pos flower)
58
shear fracture
sigma one is at an angle to the fault
59
echelon veins
tip points away from movement direction
60
riedel shears
sigma one at an angle to fault, end up with extension in sigma 3