final

Question 1

Dynamic recrystallization:

Answer 1

A process by which mineral grains in shear zones
accumulate crystal lattice defects to a point at which the crystals become unstable
and recrystallize as new, smaller crystal. This is a grain-size reduction process
associated with extensive or severe plastic shear deformation at elevated
temperatures (i.e., below the brittle-ductile transition)

Question 2

Fabrics:

Answer 2

Some shear zones display what is called C-S type foliation, in which more
intensely sheared zones (C-planes) alternate with less intensely sheared zones of
schistose (S-type) foliation.

Question 3

Mineral fish:

Answer 3

Porphyroclasts that do not show wing structures, but are roughly
rhombohedral (monoclinic) in shape, usually due to microfaulting. Porphyroclasts
that are approximately equidimensional but have no wings are called naked clasts

Question 4

Mylonitic gneiss: Rocks/minerals that have been subject to grain-size reduction via
dynamic recrystallization (mylonitization), but for which the characteristic grain-size
(the fine-grained matrix) is greater than 50μm in diameter

Question 5

Mylonite:

Answer 5

Rocks/minerals that have been subject to grain-size reduction via dynamic recrystallization (mylonitization), with the fine-grained matrix consisting of grains
< 50μm and containing less that 50% porphyroclasts. Mylonites are further
subdivided into protomylonites, which have matrix grains < 50μm and >50%
porphyroclasts; (regular) mylonite (matrix grains < 50μm and porphyroclasts
comprising 10–50% of the rock), and ultramylonites, which have matrix grain diameters < 10μm and porphyroclasts making up < 10% of the rock mass.

Question 6

Mylonitization:

Answer 6

The process of grain-size reduction through dynamic (solid-state)
recrystallization of minerals in a shear zone

Question 7

Pophyroclasts:

Answer 7

Coarse mineral grains in a zone of mylonitization that are relict of the
country rock, surrounded by a fine-grained matrix of dynamically recrystallized
minerals. Not to be confused with porphyroblasts, which are large grains of
metamorphic minerals that have grown in-place within a fine-grained matrix.

Question 8

Shear bands:

Answer 8

Shear bands may develop late in the mylonitization process of shear zone
development, when C-S foliations are offset by late-developing shearing, usually at an
angle (≈ 45◦) to C-S foliations. Shear bands are typically observed as small offsets at
centimeter spacings

Question 9

Shear bands:

Answer 9

Shear bands may develop late in the mylonitization process of shear zone
development, when C-S foliations are offset by late-developing shearing, usually at an
angle (≈ 45◦) to C-S foliations. Shear bands are typically observed as small offsets at
centimeter spacings

Question 10

Winged pophyroclasts:

Answer 10

Coarse mineral grains (porphyroclasts) in a zone of
mylonitization surrounded by a mantle of fine-grained, recrystallized minerals having
characteristic “tail” shapes. Winged porphyroclasts are classically of the sigma (σ)
or delta (δ) type, although other types (e.g., φ-type) are possible.

Question 11

Antitaxial:

Answer 11

A mode of mineral deposition associated with the process of crack-seal, in
which repeated cracking and healing takes place at one or both walls of the fracture
(not along the centerline of the fracture, as in syntaxial mineralization). Antitaxial
vein fill lacks a centerline separation, and is usually distinguished by the presence of
thin, often discontinuous inclusions of wall rock running parallel to the wall boundary.

Question 12

Vein (or vein fill):

Answer 12

When minerals precipitate in the open space of Mode I (opening-mode) fractures, they result is the formation of a vein. The precipitated
minerals are called vein fill or fracture fill.

Question 13

Syntaxial:

Answer 13

A mode of mineral deposition associated with the process of crack-seal, in
which repeated cracking and healing (precipitation) occurs in the center of the
fracture. Syntaxial veins are usually distinguished by a centerline separation in the
vein

Question 14

Plumose texture:

Answer 14

A wavy or “feather-like” texture found on the walls of many joints.
Plumose textures (or plume strucure) develop during fracture propagation, and
generally consist of feather-like striations radiating from a central point and diverging
in the direction of fracture propagation, called hackles, and broad, concentric bands
superposed over, and at right angles to, the hackles, known as ribs, that mark
successive episodes of fracture growth (i.e., fracture tip migration).

Question 15

Joint:

Answer 15

Fractures in a rock mass for which there is no discernable displacement across the fracture aperture. Joints are Mode I (opening mode) fractures, and are sometimes called extension fractures. Joints typically form in sub-parallel sets, or groups of joints that share approximately the same orientation and formed at the same time. Often multiple joint sets will be collocated; together, these sets comprise a joint
system.

Question 16

Fault:

Answer 16

A type of failure for which the rock mass on opposite sides of the discontinuity (fracture) are displaced relative to each other. Faults are the result of shear stress (Mode II or Mode III fracture

Question 17

Euhedral (crystal):

Answer 17

A precipitated mineral that shows clear crystal surfaces. The presence of euhedral crystals indicate formation (precipitation) without external controls (i.e., growth into an open space or cativity) on its growth

Question 18

Crack-seal:

Answer 18

A process of vein formation in which mineral precipitation effectively
proceeds at the same rate as fracture aperature increases (i.e., the open space is filled with mineral precipitates as fast as it appears). Minerals precipitated as crack-seal are typically fibrous, and may be either syntaxial or antitaxial

Question 19

En echelon fractures:

Answer 19

Sets of fractures that are arranged at an angle (usually around
45◦) to the average trend of the fractures. En echelon fractures are typically rotated
counterclockwise in a right-lateral shear environment and clockwise in a left-lateral
shear environment

Question 20

Brittle/ductile transition:

Answer 20

The zone in the earth’s lithosphere at which depth the brittle strength of rocks equals their ductile strength. The transition zone is not a point depth, but a zone, because the exact depth depends on the strain rate, local pressure, temperature (heat flow), and material properties of the rocks. In general, however, the brittle/ductile transition is the strongest part of the crust, and it is the depth at which most shallow earthquakes occur. In warm, young crust, the brittle/ductile transition is roughly 10–20 km in depth; for old, cold crust, it is usually deeper (on the order of 20–30 km). For continental (felsic) crust (quartz and feldspar rocks) at temperatures around 250–400 C◦, the brittle/ductile transition is at a depth of approximately 20 km

Question 21

Aperture:

Answer 21

The space between the two bounding walls of a fracture. If there is any open
space between the two walls, it is reported as a distance (e.g., the fracture has a 1
mm aperture”)

Question 22

Cooling fractures:

Answer 22

Extension fractures that form due to stresses in either intrusive or
extrusive igneous rocks that accumulate during cooling and subsequent decrease in
specific volume of the rock. An especially familar example is furnished by columnar
basalt, although cooling fractures are not restricted to basalts.

Question 23

Exfoliation joints:

Answer 23

Also called sheeting joints. Surface-parallel joint sets that develop
on the exposed outer surfaces of felsic intrusions exhumed by rapid erosion

Question 24

Joints:

Answer 24

Synonomous with extension fractures, joints are tensile fractures (Mode I) that
open in the plane perpendicular to the direction of minimum compressive stress (σ3)

Question 25

Profile joints:

Answer 25

Joints (or veins, called profile veins) that form perpendicular to the fold
axis, in cases where there is significant extension in the direction of the fold axis.
Sometimes called ac veins.

Question 26

Radial joints:

Answer 26

In this class, we discussed two situations that may result in the formation
of radial joints: 1) during the intrusion of magma; for example, joints may form
radially around an intruded volcanic neck; and 2) in response to orthogonal flexure,
joints may form radially on the convex side of competent units (i.e., on the tensile
side of the neutral stress plane

Question 27

Saddle reef:

Answer 27

Saddle reefs, or saddle reef veins, form on the inside of competent layers
in Class 1B folds, at the contact with weaker layers when the weaker units cannot
deform sufficiently to accommodate the accumulated strain.

Question 28

Mohr’s

Answer 28

• Fails @ 60, theta of 30, 2theta of 90, diameter is differenctial stress and center is lithostatic load. Determining amount of shear and normal stress a rock can undergo before failure. Shear = cohesion of rock (S0) + coeff of internal friction (mu) * normal stress (sigma)

Question 29

Antithetic fault:

Answer 29

Term describing a minor fault that dips in the opposite direction as the
associated master fault

Question 30

Cutoff point/line:

Answer 30

The contact between some older geologic feature (bedding,
unconformity, intrusion, etc.) and a fault plane, indicating the pre-existing feature
was truncated by displacement on the fault. In 2D, the point of truncation is called
the cutoff point, in 3D, the trace of the intersection is called the cutoff line

Question 31

Dextral:

Answer 31

Synonym for right-lateral. Used to describe the relative displacement of strike
separation.

Question 32

Fault:

Answer 32

A fracture (failure surface) across which there is non-negligible displacement of the
walls, relative to each other

Question 33

Fault scarp:

Answer 33

A “small” cliff or rapid change in surface elevation across the plane of a fault

Question 34

Fault strands:

Answer 34

Smaller segments of the main fault that may be physically connected or
somewhat disconnected, but which are tectonically linked, and cumulatively represent
the total deformation of the master fault

Question 35

Graben:

Answer 35

A downthrown block between two normal faults

Question 36

Half-Graben:

Answer 36

A downthrown block, bounded by a normal fault on one side, that has
been rotated or flexed to form a basin structure.

Question 37

Knickpoint:

Answer 37

A sharp change in slope; commonly used for changes in the slope of a stream
channel, it is also applied to fault scarps, where knickpoints are an indication of
episodic displacement

Question 38

Master fault:

Answer 38

A major fault (i.e., the largest fault in a local region) that is often
associated with a number of smaller, subsidiary faults called minor faults.

Question 39

Offset:

Answer 39

A generic term used to indicate that features on opposite walls of a fault plane
have experienced relative movement (displacement).

Question 40

Separation:

Answer 40

The distance between cutoff lines on opposite walls of a fault. The
component of separation distance measured parallel to the strike of the fault (i.e., in
plan view), is called strike separation; if measured in the plane of, and parallel to
the dip of, the fault (i.e., in cross-section) it is known as dip separation

Question 41

Sinistral:

Answer 41

Synonym for left-lateral. Used to describe the relative displacement of strike
separation

Question 42

Slickenlines:

Answer 42

Scratches or fibers on a fault plane that are generated by movement on the
fault. Slickenlines are indications of the direction (but not magnitude) of slip.

Question 43

Slip:

Answer 43

A vector of fault motion, comprising both the direction and magnitude of
displacement of wall rocks across the fault plane.

Question 44

Horst:

Answer 44

An upthrown block between two normal faults

Question 45

Synthetic fault:

Answer 45

Term describing a minor fault that dips in the same direction as the
associated master fault

Question 46

Fault architecture:

Answer 46

The organization of structural elements found associated with faults
and faulting. The basic structural elements used to describe fault architecture are the
fault core, the damage zones, and the protolith

Question 47

Piercing point(s):

Answer 47

A cutoff point of a linear feature on the wall rock of a fault that can
be traced across the fault plane to the same linear feature on the opposite wall of the
fault. If two such piercing points can be identified on opposite sides of the fault
plane, they define a unique slip vector for the fault

Question 48

Slickensides:

Answer 48

A surface of rock on a fault plane that has been polished by friction during
differential movement (displacement) of the wall rocks. Slickensides typically display
grooves or scratches called striae (plural; singular is striation); these striae are
called slickenlines, and they are oriented parallel to the direction of displacement.

Question 49

Breccia:

Answer 49

Rock consisting of angular fragments of wall rock that have been crushed,
broken, and rotated out of their original orientation in the core of a fault. Fault
breccias contain less than 70% matrix, and individual clasts are generally ≥ 2 mm in
diameter. Breccias with large (> 5 mm) clasts and less than 10% matrix that are
cemented into a solid mass are called crush breccia. Breccias with clasts in the
range 2 ≤ d ≤ 4 mm are often referred to as microbreccia

Question 50

Cataclasite:

Answer 50

A material found in fault cores consisting of fragments of wall rock smaller
than 2 mm in diameter. Note that cataclasite is a noun; the physical process of
grinding and crushing rock to a powder is called cataclasis (a verb). Technically,
cataclasite is differentiated from gouge by an absence of foliation.

Question 51

Damage zone(s):

Answer 51

Zones of deformation, usually flanking both sides of the fault core,
associated with fault displacement. Damage zones are differentiated from the fault
core by the fact that strain is insufficient to destroy (overwrite) the character of the
original protolith; however, material close to the fault core can be subject to
extensive strain in the form of fractures, folds, deformation bands, etc.

Question 52

Deformation bands:

Answer 52

Damage zone structures that develop in faulted porous rocks
(especially sandstone). Each deformation band is a thin (< 1 cm) zone of grain
comminution (crushing) that accommodates about the same amount of slip as the
width of the band. Greater amounts of offset result in the formation of more
deformation bands, which tend to organize into groups called deformation band
zones (DBZs)

Question 53

Drag folds:

Answer 53

Small folds that develop in wall rocks adjacent to the fault core or
slip-surface. Drag folds form due to temporary “locking” of the fault during
displacement; locking transfers strain to the wall rocks, which may deform plastically
in response

Question 54

Fault core:

Answer 54

The portion of a fault that accommodates the majority of deformation (slip)

Question 55

Fault gouge:

Answer 55

Cataclasite formed in rocks containing significant fractions of clays
(phyllosilicate minerals) can deform in a ductile fashion and develop weak fabric
(foliation) called gouge. Gouge is typically very soft in outcrop and impermeable to
fluids. In casual usage the terms “gouge” and “cataclasite” are often used
interchangably

Question 56

Fault-bend folds:

Answer 56

Small folds that form at locations where the fault plane is curved or
bent, in response to kinematic (strain) incompatibility.

Question 57

Fault-propagation folds:

Answer 57

Small folds that form at the tip of a fault in response to
accumulated strain during fault growth, but before the fault tip progresses.
Fault-propagation folds may be preserved in the wall rocks of faults, where they may
later be mistakenly identified as drag folds.

Question 58

Pseudotachylite:

Answer 58

Thin veins or stringers of glassy, dark-colored rock that are the result
of melting and quenching of protolith from frictional heating during rapid
displacement. Pseudotachylite is thought to be relatively common in large faults, but
is often poorly-preserved, because the fine-grained, glassy features are quick to
devitrify in the presence of water (especially at elevated temperatures

Question 59

Riedel shears:

Answer 59

Secondary shear fractures that form in association with larger faults, in
response to stesses in the wall rock during fault propagation and displacement.
Synthetic Riedel shears (also called R-shears) have the same sense of slip as the
main fault, and tend to form at an angle of about 15◦ to the main fault plane.
Antithetic Riedel shears form at an angle of about 75◦ to the main fault and have
an opposite sense of shear

Question 60

Slip-surface:

Answer 60

A narrow portion of a fault, characterized by a shear plane bounded by thin
zones of often glassy wall rock that accommodates the majority of deformation (slip).
True slip-surfaces are primarily found in porous rocks (especially sandstones), where
they play the part of the fault core. In crystalline rocks, the slip-surface is usually
replaced by a core of breccia or cataclasite with greater thickness.

Question 61

Fault segments:

Answer 61

Smaller faults that have grown to the point at which their stress fields
interact are considered to be segments of the larger fault, which consists of all
segments so-related. Fault segments may be either soft linked (interacting stress
fields, but without a connecting plane of failure) or hard linked (a through-going
fracture joins the segments)

Question 62

Horst:

Answer 62

A block of rock bounded by the footwalls of normal faults, where the bounding
normal faults are dipping away from each other (and the horst block). Horst blocks
are sometimes said to be upthrust relative to the down-dropped (hanging wall) blocks
on either side

Question 63

Graben:

Answer 63

A block of rock bounded by the footwalls of normal faults, where the bounding
normal faults are dipping towards each other, and the graben (hanging wall block) is
down-dropped relative to the horsts on either side. In situations involving listric faulting or a subhorizontal fault base below the brittle crust, formation of a half-graben is also common (see rollover anticline

Question 64

Listric fault:

Answer 64

A fault in which the dip of the fault plane shallows with depth, i.e., the
plane of the fault flattens, and ultimately may become horizontal in the deep crust

Question 64

Left-step:

Answer 64

When standing on the rear segment of a fault, if the front segment is to the
observer’s left when looking parallel to strike in the direction of the next segment, the
fault is left-stepping

Question 65

Overlap:

Answer 65

The distance, measured parallel to strike, between the tips of two fault
segments. If the tips do not overlap, they are said to underlap

Question 66

Ramp structure:

Answer 66

Connecting zone between two fault segments. Two fault segments are
said to be soft-linked if there is no through-going fracture between the two segments
(i.e., they are only linked by sharing a stress-field). If the segments are connected by
a fracture, they are hard-linked

Question 67

Ramp breach:

Answer 67

Location of a through-going fracture between two hard-linked fault
segments. The breach is an upper ramp breach if the inactive termination is in the
front segment, and a lower ramp breach if the inactive termination is on the rear
segment

Question 68

Right-step:

Answer 68

When standing on the rear segment of a fault, if the front segment is to the
observer’s right when looking parallel to strike in the direction of the next segment,
the fault is right-stepping.

Question 69

Rollover anticline:

Answer 69

When a large normal fault forms in an extensional tectonic setting,
kinematic incompatibility between the hanging wall and footwall results from the
tendency of the hanging wall to move away from the footwall. To accommodate this
incompatibility, the hanging wall rocks will bend down, increasing dip with increasing
proximity to the fault plane. The resulting bending fold is called a rollover
anticline

Question 70

Segment:

Answer 70

A smaller fault that is part of a larger group of related (hard- or soft-linked),
usually en echelon, fault segments. When an observer is standing on the ramp
between two segments looking down-dip, the segment in front is called the front
segment and that behind is the rear segment.

Question 71

Spacing:

Answer 71

The distance between two fault segments, measured parallel to dip

Question 72

Allochthonous:

Answer 72

A displaced assemblage of rocks. Rocks that are not in their original
stratigraphic position

Question 73

Autochthonous:

Answer 73

An assemblage of rocks that are in their original stratigraphic position

Question 74

Duplex:

Answer 74

A geometry often observed in fold and thrust belts in which multiple listric
thrust/reverse faults with the same branch off from a lower thrust fault flat (called
the floor thrust), then rejoin in an upper thrust-fault flat called the roof thrust

Question 75

Fenster:

Answer 75

An exposed area of footwall rocks, completely surrounded by rocks from the
hanging wall. Fensters are sometimes called tectonic windows.

Question 76

Foreland:

Answer 76

The area beyond a thrust fault or fold and thrust belt towards which the rocks
verge.

Question 77

Hinterland:

Answer 77

The area behind a thrust fault or fold and thrust belt; that is, the direction
from which the rocks verge

Question 78

Hanging wall anticline

Answer 78

An anticlinal fold that sometimes forms in the ramp area of the
overthrust (hanging wall) sheet of a thrust fault

Question 79

Imbricate fan:

Answer 79

A geometry common in fold and thrust belts in which multiple listric
thrust/reverse faults with the same vergence branch off from the flat (horizontal)
floor thrust.

Question 80

Klippe:

Answer 80

An area of hanging wall that is completely surrounded by footwall

Question 81

Ramp-flat geometry:

Answer 81

A term used to describe aspects of a low-angle thrust fault, in
which flats are areas in which rock unit bordering the fault are parallel to the fault
plane (i.e., the slip-surface), while ramps are areas in which the fault plane truncates
(cross-cuts) units. Areas in which hanging wall units truncate against the fault
surface are called hanging wall ramps; conversely, footwall ramps are areas
where the footwall units are truncated against the fault plane

Question 82

Thrust fault:

Answer 82

A reverse fault (i.e., hanging wall moves up relative to the footwall) with
a characteristically low-angle of dip. Technically, any reverse fault with a dip < 45◦ is
classified as a thrust fault, but the term is usually applied to reverse faults with dips
< 30◦ and large amounts of separation

Question 83

Vergence:

Answer 83

The direction towards which the hanging walls of thrust faults in a fold and
thrust belt tend to move, relative to the footwalls.

Question 83

Flower structure:

Answer 83

A feature that develops within a fault duplex of a fault bend, in which
extensional (in transtension) or compressional (in transpression) strain is
accommodated by normal or reverse faulting, respectively. The traces of faults
accommodating strain tend to steepen and merge with the plane of the main fault at
depth. When viewed in cross-section, the down-dropped fault block structure formed
by normal faulting is called a normal, negative, or tulip structure, while the
upthrust fault blocks of reverse faults in a restraining step are called reverse,
positive, or palm tree structures

Question 84

Fault bend:

Answer 84

Also called a stepover, fault bends are similar to the stepover/ramp
structure familiar from segmented normal faults. Fault bends are commonly occuring
areas of local transpression (restraining bends) or transtension (releasing bends) in
large strike-slip faults

Question 85

Restraining/releasing bend:

Answer 85

Non-ideal tectonic stress that occurs within a fault bend
area of a large strike-slip fault gives rise locally to either transtension or
transpression. A left-step in a fault with left-lateral (sinistral) offset, or a right-step
on a right-lateral (dextral) fault result in a releasing step or releasing bend
(transtension). Left-stepping right-lateral faults and right-stepping left-lateral faults,
on the other hand, result in restraining bends (transpression)

Question 85

Pull-apart basin:

Answer 85

A topographically low area associated with a transtensional (releasing)
bend or jog in a strike-slip fault. Pull-apart basins tend to fill with erosion-derived
sediments from the surrounding, topographically higher, areas. When a pull-apart
basin is filled with water, it is called a sag pond

Question 86

Scissors faulting:

Answer 86

In many real-life transfer zones (stepovers) in large strike-slip faults,
one edge of a fault duplex will be in transpression, while the other edge is in
transtension. This results in the faults of the duplex having a reverse sense of slip on
one half, and a normal displacement on the other half, known as scissors faulting.

Question 87

Tail cracks:

Answer 87

Stresses near the tip of an active fault with some strike-slip component
impart a rotational component that may be resolved by the development of small
fault propagation folds; alternatively, the orientation of shear stress on one side of
the fault tip causes opening mode (Mode I) fractures that propagate away from the
fault tip at a predictable angle; these tail cracks will either dissipate the stress or
merge with another fault segment to which they transfer stress.

Question 88

Transpression:

Answer 88

A non-ideal strike-slip tectonic regime that combines regional
compression (crustal thickening) with lateral offset.
- restraining bend
- reverse fault

Question 89

Transtension:

Answer 89

A non-ideal strike-slip tectonic regime that combines regional extension
(crustal thinning) with lateral offset.
- normal fault
- releasing bend

Question 90

En Echelon

Answer 90

strikes off trend that merge into 1. overlapping parallel minor structural features like faults or tension fractures.

Question 91

extensional bend

Answer 91

when a right lateral strike slip right steps or left lateral strike slip left steps (draw diagram)

Question 92

listric faulting

Answer 92

flattens with depth