General 1 Flashcards

Question

cataclasite breccias

Answer 1

These are breccias that are cohesive and strongly indurated because they tend to form at higher pressures with reactive clasts that effectively produce a cement Cataclasites .1mm \< D \< 10mm Ultraclasite D

Answer 2

These are breccias that form from the comminution of material due to frictional sliding and associated cataclasis. They generally have very unsorted, angular clasts within a fine ground matrix. It only occurs within brittle rocks and is usually incohesive.

Answer 3

In the late Creataceous and early Eocene there was active subduction of the Fallaron plate which created Andean style crustal thickening throughout the Western part of the US. It also is what emplaced many of our copper porphyries!

Answer 4

These are folds that are really angular and kinky. They are generally parallel folds with very discrete hinges

Answer 5

This is the fine grained material that forms near the wall of an intrusion. It is usually near contact metamorphosis, auriole, and skarns (reserved for LS)

Answer 6

This is a structure that forms in the lower part of the brittle regime (~10 km) common with passive folding and transposition. It is indicated by a staple symbol when mapping. **Geometry:** They are closely spaced, planar, woody surfaces associated with folds, and may be oblique to bedding. Generally, it has a "domainal" nature where parts are deformed more than others, creating a very finite "banding" of platy minerals like mica. **Stress/Strain:** max shortening perpendicular to sigma 1 and through pressure solution and recrystallization there is a decrease in wavelength and limb thickness Most common is axial planar cleavage which is perpendicular to sigma 1 and parallel to axial planes.

Answer 7

These are closely spaced, regular fractures of distinctly weaker planes.

Answer 8

This is a line given by sigma = C_o + tan(30) sigma n If any stress state is beyond the failure criterion then it fails.

Answer 9

These are folds that show an even thickness across the beds within the fold.

Answer 10

This describes folds that plunge into a flat plane. These are described by the centerline axis (defined as the vector at the tip of the cone) and the opical angle which is the angle between the inflection point and horizontal

Answer 11

These will have a great circle created from planes to poles of the bedding transverse to the hinge and the hinge will plot 90^o off in the "center" of the poles.

Answer 12

These are parallel for thrust and normal faults (like wedges that squeeze the material) and are 60/30 for strike slip.

Answer 13

Metamorphic core complexes tend to be flanked on one side my a low angle detachement fault overlayed by high angle normal faults and interfaced with a mylonitic gneiss (think about this side of the Catalinas). At their center is a granite core related to decrompression melting. The other side is characterized by a listric breakaway fault and a basin with domino style faulting. Across the **whole** complex there is the same sense of shear creating the mylonitic fabric

Answer 14

These are oriented growths of calcite and quartz which originate from saturated fluids causing joints to form. When the pressure of the fluid is relieved the crystals precipitate. The change in direction of the crystals indicates how the principle stresses changed over time aka the dilation history

Answer 15

The footwall and hanging wall cut-off are the points where the marker beds intersect the fault surface and terminate

Answer 16

This is when there is detachment from lower layers and the formation of a cupsate. It is common in concentric folds.

Answer 17

This is the complete **kinematic** evolution of the rock body of interest. It includes: traslation (rigid), rotation (rigid), strain: dilation/change in volume, and distortion

Answer 18

This increases from out to in. Dip is greatest at the north south line

Answer 19

The dip of a plane as a pole on a stereonet is measured from 0 being the inside and 90 being the outside. Alternatively it is 90- angle from outside

Answer 20

This is similar to listric normal faulting but both the footwall and hanging wall rotate so that way the hanging wall dips towards the fault and the footwall rotates so bedding is near perpindicular to the fault surface.

Answer 21

These are folds that occur along the interface of a fault and **appear** to resemble frictional resistance to sliding along the fault. They are actually caused by the propagation of the fault surface from depth. For example, in a normal fault (which represents extension) before the shear plane physically divides strata in a normal fault, the hanging wall will be extended and the materials near the fault "collapse" deforming those on the surface upwards. You are basically removing the support below the layers causing slumpling.

Answer 22

This is the attempt to understand deformation as a function of stress, shear, strain, and rheology...

Answer 23

This is the confining pressure-fluid pressure. Fluid pressure has a very significant impact on the stress state of a rock at depth.

Answer 24

This is where a fringe meets the exposed surface. It is usually at an angle to the main face.

Answer 25

These are opening that form in simple shear zones. They have s shapes and open in the direction of minimum stress.

Answer 26

This is the ratio of the change in length to the original length. e = (L_f - L_o)/L_o and can be expressed as a percent

Answer 27

0-4 km of depth: Breccia/gouge which has angular clasts, can be incohesive, and comminuted material. Gouge is very fine breccia. 4-10 km: cohesive cataclasite (cement) which is angular clasts surrounding by hard muddy material. It is cohesive and usually fluid related. (can become breccia during exhumation) 10+: mylonites This is when quartz begins to ductily deform and you have extremely strained fabrics.

Answer 28

This is a stair-step like surface which coincides with fault zones where the total displacement is given by the summation of the step heights

Answer 29

These are discrete (usually elliptical) surfaces where slip occurs due to faulting. The maximum displacement occurs at the center (r=0) and decreases outward reaching 0 at the **tip line loop**

Answer 30

These are always with thick lines Normal faults = line with a dot and dip Thrust fault = line with teeth and dip Strike slip = arrows approximate location = dashes concealed = vertical dashes uncertain = dashes with question marks

Answer 31

Discrete fracture surfaces/zones where slip has occurred and is recorded. These are the result of compressional stress compensation and are formed from the preferred alignment of microcracks forming a shear fracture. These occur at phi of ~30^ofrom the principal stress (sigma 1)

Answer 32

If it is strike slip then it is double arrows If it is not vertical then there is an arrow pointing in the dip direction with the dip. If it is normal then sticks with dots are normal an on the hanging wall. If it is thrust then there are teeth on the HW. Generally we map the **fault trace** which is the planar feature interfacing the topographic surface.

Answer 33

1. plot poles to the bedding planes on both sides of fold 2. Align the dots so they lie along a great circle. Draw the great circle. 3. ) Count 90 along the horizontal and plot a point. This is beta 4. The plunge of beta is found by rotating beta to north and counting from the inside out 5. ) Align beta so that it aligns to the great circle representing the plunge. Draw 6. Connect the outer edges of the plane. This represents the plane of the axial surface and beta is the trend and plunge of the fold axis.

Answer 34

1. plot the dip/dip direction as points 2. rotate the stereonet so that the dots align to a great circle. 3. This is the true plane

Answer 35

To find the true strike and dip of a plane that intersects two surfaces first find the strike and dip of each of the faces. Then find the rake from the plane to the intersection of the bed of interest. Make sure to note the rake and direction. Plot the surfaces as planes with lines at the rake. Align to be on a great circle and plot. This plane is your true plane.

Answer 36

This is the idea of folds where less competent layers assume the bulk of strain/deformation. This means that during folding there is shear along the boundaries of layers and that the more competent layers are more likely to maintain their original mid-point length. Flexural slip is when weaker beds (shales, mudstones...) accommodate the slip of harder, less elastic rocks nearby This creates shear through folding. The individual displacements are small but rapidly accumulate.

Answer 37

P_f/P_r = ρ_f g h_f/ρ_r g h_r This represents the fluid pressure from a column divided by the lithostatic pressure

Answer 38

Wavelength, width, height, interlimb angle, symmetry, and vergence is common

Answer 39

Find the strike and dip of the axial surface and the trend/plunge of the hinge line.

Answer 40

If folds are assymetric terms like "top-to-east" or "top-to-right" to give a sense of shear. This would correlate to an east-vergent fold.

Answer 41

This is given by the interlimb angle which can be found via direct measurement or by taking strike/dip of the inflection points of the limbs. Plotting these as poles and align them to a great circle to find the angle between them.

Answer 42

These describe regional periodicity in waveforms of folding.

Answer 43

These are when the rock behaves like a ductile material when compensating for stress/strain which results in curved, bent, or crumpled strata.

Answer 44

1. map marker beds and define hinge zones 2. connect the hinge zones and draw an axial trace 3. define anticline vs syncline and use an arrow to show plunge direction. Synclines will have arrows pointing inwards and dips pointing inwards (oldest beds at center) anticlines will have dips and lines pointing outwards (oldest beds out) Overturned beds will be in the same direction but use the original dip direction to ID.

Answer 45

This is penetrative planar fabric that forms because of mineral recrystallization and **plastic deformation** at temperatures exceeding 300 celsius

Answer 46

**Any** penetrative planar elements Within metamorphic rocks foliation is a f(plasticity) and a secondary structure Within igneous rocks foliation is a f(primary structure) It includes layering produced by **ductile** deformation

Answer 47

This is the bottom rock. It has the resting surface for the rock above.

Answer 48

This is something that changes the motion of a body via acceleration F = ma in Newtons

Answer 49

These are folds that are related to faulting and the fault geometry

Answer 50

This is defined as the median spacing/bed thickness. Usually it increases with bed thickness

Answer 51

Any mix of pure and simple shearing. It is also in plane. This will result in a mixture of smooshing and translation.

Answer 52

Penetrative plane layering with compositional banding, mineral laminae, and quartz eigens

Answer 53

This is a form of kinematic analysis that says that cracks that are perpendicular to σ₃ form joints to relieve tension. It also speculates that the largest microcrack perpendicular to tension will be the origin for a joint and other joints that are not orthogonal close when the joint forms.

Answer 54

This is the wall of a fault that lies on the top. The fault undercuts the rocks. ALL map symbols go onto the hanging wall

Answer 55

Heave is the horizontal component of the displacement along a fault. Throw is the vertical component.

Answer 56

This is irregular and non-uniform deformation which is best broken into vectors of homogenous deformation.

Answer 57

This is the 1d vector that describes the trend and plunge of the hinge line. ## Footnote It is also called the fold axis.

Answer 58

This is the systematic and uniform deformation of a body. In this form of deformation straight lines stay straight (although rotated and changed) and circles become ellipses.

Answer 59

These are characterized by high areas flanked by normal faulting on both sides. They are consistent with andersons theory of faulting (highs have normal lows have thrust) often underlined by a **detachment fault** defined as a low-angle normal fault most commonly found at depth. This fault determines if individual structures are synthetic (dip in the same direction) or antithetic (dip in the opposite direction)

Answer 60

It is similar to a bending moment in a beam where at the uppermost crest sigma 1 is vertical (normal faulting) and at lower areas it is horizontal (thrust faulting)

Answer 61

Because the middle of the basalt is usually the hottest part, the joints start at both the top and the bottom to propagate and meet in the center

Answer 62

Real rocks have an initial elastic deformation which is followed by strain hardening (an increase in E) or strain softening (a decrease in E)

Answer 63

1. The rotation of minerals (small contribution): grains orient perpendicular to sigma 1 so that their smallest width orientation creates maximum compaction 2. Directional recrystallization. This is when things like mica recrystalize due to high pressures and form "sheets" or laths of crystals perpindicular to sigma 1. 3. pressure solution (primary factor): Quartz dissolves, micas do not. In addition, pressure solution is going to be greatest in the direction perpinduicular to the greatest principle stress which means that grains will "elongate" perpindicular to that direction.

Answer 64

Below 12 km mylonites form from 12-10 km is the crystal plastic regime where breccias become quasi mylonites because T=250-350 C Above 10 km is the frictional regime where rocks are rather brittle. This is the region that produces breccias

Answer 65

IF there is a large difference in elasticity between a stronger layer in a weaker host the folds will become ptygmatic whereas is there contrast is small then buckling occurs and it creates cupsate lobate folds/

Answer 66

Fluid pressure lowers both principal stresses moving Mohr's circle to the left **without** changing the differential stress. This occurs until it intersects tensile failure or coloumb failure.

Answer 67

In the brittle regime strength is depth dependent. In the ductile regime strength decreases exponentially with temperature and then in the viscous regime it is strain rate dependent.

Answer 68

With strain rate strength **increases** With temperature strength **decreases** With depth strength **increases**

Answer 69

Rocks that are weak on the surface (mafic rocks) are strong at depth and rocks that are strong in the brittle regime (quartzite) are weak at depth. The rheology of quartzite controls rock deformation.

Answer 70

As temperature increases strain rate increases exponentially and strength decreases exponentially.

Answer 71

Connect the topo lines of equal elevation where the upper/lower bound of the structure intersects said topo line. This is because strike is defined as the direction where elevation does not change.

Answer 72

1 mark the strike on the circumference of the plot and rotate it to north 2 count from the center out to the dip circle and draw

Answer 73

1. plot the great circle representing the plane 2. rotate the great circle to N-S and count 90 degrees along the horizontal line 3. plot the pole

Answer 74

1. ) using strike and dip of the plane find the great circle (rotate CC to strike and count out from center to dip 2. ) With the great circle oriented N-S count along the circle to the rake angle. Plot a dot. 3. ) Find apparent dip by rotating the plot until the dot is on the N-S line and count in. 4. ) find trend by returning the great circle to N-S and drawing a line from the center of the plot to the radius. Where this intersects the circumference of the circle is the trend.

Answer 75

The C-surfaces are the linear planes where the mica exists, S surfaces are elongation surfaces that are 45 degrees off. The sense of shear is top to the right as noted by how the S surfaces merge into the C surfaces by curving right.

Answer 76

These are effectively rock bursts that form from holes in the fault. They are usually cemented by hydrothermal cements and clays.

Answer 77

This only refers to brittle fault rocks with angular clasts in a fine matrix and represents positive dilation. **megabreccias** D\> .5m **breccias** 1mm **microbreccias**.1mm **gouge** D

Answer 78

These are where the second derivative of the line that describes the strike of the fold switches sign. It is where convexity switches sign.

Answer 79

A circle with an x is into the page and a circle with a dot is coming out of the page. It is like an arrow from a bow.

Answer 80

This is the contact of igneous rock and country rock

Answer 81

Joint intersections help to indicate the pathway of formation. Y-interceptions are characteristic of thermal shrinking and the development of hexagonal columns T-intersections are common in unloading and result in orthogonal joint sets where the terminating joint is young than the throughgoing X-intersections occur when joints meet at acute angles but both are continuous

Answer 82

These are concentric bands around the origin that represent where the joint was **arrested** during propogation (slowed or ceased) They form slight lumps or decreased relief of the plumes intersecting them.

Answer 83

This is the concept that there is some maximum joints/volume of joints that will not be exceeded by the rock. Stress transition model states that when the joint saturation is exceeded the positive dilation switches the tensile stress to compressive. Stress-transfer model says that if undersaturated the next joint will form at the midpoint of the prior two

Answer 84

The economic value of joints is that they are conduits for hot fluids to precipitate metals and other valuable things. This also makes them good for geothermal and hydrocarbon storage. Joints also enable quarrying. Joints are also potent weathering agents and can become enlarged or contracted via deformation. They also act as conduits for groundwater and potential contamination

Answer 85

These are rounded fans that form from a localized stress perturbation. They record the propagation of the joint fracture.

Answer 86

This describes the presence of 2+joint sets in a rock body

Answer 87

These are smooth, planar features that cut through rock bodies and layers with ~0 displacement across the joint. These occur perpendicular to **tension** and are **brittle failure.** They tend to be continuous and through-going and occur at intervals of cm-km. In 3d they are elliptical and follow the path of maximum tension but are in a plane perpendicular to the primary tensile stress. They primarily occur in the uppermost few kilometers of the crust where tension can occur and occur in sets which are families of parallel, evenly spaced joints During the fracturing of the rock the propagation path minimizes shear at the joint tip and maximizes tensile stress.

Answer 88

Formationally joints are only from tension whereas shear fractures are from shearing. Shear fractures intersect at 60^o joints do not Shear fractures will have slickenlines

Answer 89

This is the idea that joints form due to tensile stresses which are most commonly from cooling or unloading.

Answer 90

This is understanding the motion of materials _during_ displacement not only their positions at t=0 and t\>0 but s(t). Thus, interpreting structures as a function of x,y,z,t with the goal to identify the displacement rate and path

Answer 91

The origin of the joint is always the nucleas for the plumose structure and the main face is perpendicular to the tensile stress. They are formed in some form of mode I jointing.

Answer 92

This is similar to buckling where there is one spot that shows a kink. There are z-folds (dextral) and s-folds (sinistral). They are defined by high anisotropic stress states post buckling in layers that have large amounts of cohesion. They can result of bending moments, dilation, in-kink rotation (torque), or shear.

Answer 93

These occur when the joint is arrested and the tensile stress is reoriented. This occurs near the surface which is how en echelon traces and fringes form.

Answer 94

These have arrows pointing from the oldest to youngest beds, they indicate the **facing direction**

Answer 95

This is the concept in faulting changing the net surface distance of an area. In normal faulting the crust is lengthened and thinned. It thrust faulting it is shortened and thickened. To determine the %stretch you find the ratio of the original map view length to the new length.

Answer 96

This is the study of how heterogeneity in the structure of a material changes the stress state. It posits that brittle materials have a **fracture toughness** given by σ_m and when the local stress intensity \> σ_m then a flaw is created to lower the localized stress to a **subcritical** state

Answer 97

Foliation = shaded triangle with dip Vertical foliation = shaded diamond Cleavage = a [ symbol with the dip inside in the direction of strike Vertical cleavage = I lines = dot with an area with the plunge angle

Answer 98

These are features that are 1D and are described as a vector with **trend and plunge.** Always be sure to indicate the direction of plunge (Ex: 18^o NW would be a line that is pointing NW in the downward direction)

Answer 99

This is ANY linear feature on a rock These are any preferred alignment of materials due to shear flow.

Answer 100

Lines plot as points on the stereonet. a plunge of 90 will be at the center.

Answer 101

This is a fault that has a curved surface which approaches horizontal with depth.

Answer 102

These are faults that shallow with depth. They are defined by a **rollover monocline** where thinning and rotation has deformed the beds, **'drag folds**' on the upper/lower surfaces, and **growth strata** (alluvium) thickening towards the fault surface. In comparison to domino faulting, the footwall remains stationary and "blocking" does not occur.

Answer 103

The outermost part of the Earth that create the "Solid" plates. It is composed of 4-9 km thick oceanic crust and 25-70 km continental crust. Oceanic crust is mafic and forms from the decompression melting of the asthenosphere. It commonly has igneous intrustions (gabbros and dikes) along with extrusive pillow basalts. It is younger than ~200 mya. Contintental Crust is very heterogeneous and the majority of it has been constantly deformed since the Precambrian. The oldest continental crust is \>4Ga

Answer 104

This is the maximum angle from sigma 1 where a plane will slip. It is determined by finding the intersect of mohr's circle and coloumbs failure. At this point the upper intercept of the circle with byerlees law shows the maximum angle from sigma 1 where a plane will slip. Anything beyond that and the rock will form a new fracture.

Answer 105

These are planar/elliptical faces with a large plumose and rib structure. The fringe is defined by smaller plumose structures on the outer edges of the main face that are slightly hackly.

Answer 106

thin lines are reserved for depositional and intrusion based contacts thick lines are used for faults

Answer 107

These are any traceable bed. They are critical to mapping and you can use dots or line-dot-line sequences to draw them for mapping.

Answer 108

This is the line/surface that defines the connection of the inflection points of the fold.

Answer 109

There are intragranular (within a grain), transgranular (accross 1+ grains), intergranular (along the grain edges.

Answer 110

These are the three kinds of loads that propogate at the joint tip and along the tipline. Mode I: Opening which is pure extension perpindicular to the fracture plane Mode II: Sliding which is pure shear parallel to the plane and in the plane Mode III: Scissoring this is shear within the fracture plane and motion parallel to the tipline but perpendicular to the upper and lower bed faces. There is also mixed modes of loading.

Answer 111

This is the lower bound of the lithosphere. It represents a compositional boundary **within** the lithosphere.

Answer 112

These are "regional tables/platforms" Where there is one life or decline. It looks like play-doh was layed over a cliff

Answer 113

1 kbar = .1 GPa

Answer 114

This is a foliation that occurs at ~12+ km in high shear zones where there is a brittle deformation of feldspar and garnet porphyroclasts (augens) and plastic deformation of quartz ribbons.

Answer 115

This has a line with a dot

Answer 116

These enable extension and relieve tension. They are caused by σ₁ = σ_v On the surface this is usually the weight of the rock. Normal faults are identified by the appearance of the hanging wall rocks being younger than the footwall indicating that the hanging wall moved down. It omits stratigraphic layers in the sequences when looking on the fault surface.

Answer 117

These are named by adding handedness to the normal name for the fault. Ex: Normal right handed fault

Answer 118

This is the concept of using 2d representations of 3d surfaces/objects.

Answer 119

This refers to **any** fold where a limb's stratigraphic up is not pointing towards the surface. If the fold is inclined the back limb can be overturned but the front limb can be non-overturned based on how you define back and front

Answer 120

These are folds where the bed thickness remains constant throughout the fold. It indicates lower temperature and shallower folding.

Answer 121

These are drawings showing how material moves during deformation. If it is pure shear then the particle paths are hyperbolic around the origin showing how the material moves down then is smooshed outwards. If it is simple shear the particles move in a more "translated" sense of motion where their paths are not precisely curved.

Answer 122

These are folds where the hinges are thick and the limbs are thin but consistent throughout the rock. This is common in high grade metamorphic rocks where there is high average ductility and low ductility contrast. This can be aided by "flattening" which is the dissolution of parts of the rock.

Answer 123

Physical elements are elements of structures we can directly measure (bed thickness, bedding...) Geometric elements are intangible elements of structures that we identify through analyzing physical elements.

Answer 124

If we plot limbs of a fold as planes to poles these will connect to create a great circle known as the pi circle which represents a plane perfectly perpindicular to the hinge line which will plot 90⁰ off the pi circle center

Answer 125

These are features that can be described as a 2d plane in space. They are described by a strike and dip

Answer 126

Planes with a dip of 90 degrees plot along the N-S line horizontal planes are on the primitive circle. The strike of a plane is the line connecting the two outer edges of the great circle

Answer 127

Given strike, apparent dip, apparent dip direction. 1. Make a tick at the strike and at apparent dip. Rotate the plot CC so the strike tick is at north. Draw the strike line (plane with dip=90) 2. Rotate CC so that the dip tick is in the E mark 3. From the inside out count out the apparent dip and draw the great circle. 4. true dip is found when strike is at N

Answer 128

the center is at the average principle stress. r = sigma 1 - center Any point on the circle as a plane within a rock is measured 2\*theta clockwise from sigma three (on the plot) where theta is the angle from **sigma one to the plane in the rock.** This is the same as 90-normal theta (from horizontal) or is the angle from the pole of the shear plane to sigma 1.

Answer 129

This occurs on the faces of joints and are feather like patterns propagating from the origin of the joint outward

Answer 130

These are folds that have a plunging hinge line.

Answer 131

Lines are projecting from the center to the outer edge so vertical lines are in the center of the plot and horizontal lines (vertical planes if planes to poles) are on the outer edge

Answer 132

There are two primary structures that form when porphyroclasts are in high shear environments. **Sigma structure:** This is where there is simple shear but the porphyroclast does NOT rotate. It looks like a tension gash. **Delta Structure:** this is where there is rotation and simple shear of the porphyroclast so the "tails" of the partial melt are non-linear.

Answer 133

These are structures that form during lithification/deposition. These commonly include assymetric intraformational folds (magmatic flow deformation) and soft sediment deformation structures

Answer 134

This includes structures that form because of the internal/inherent nature of creating rocks. This includes bedding, flow layering, intrusions... They are described using contact type, lith/mineralogy, texture, resistance, and color. Stratigraphic up can be identified with ripple marks, cross beds, mudcracks, and pillow structures which are all primary structures

Answer 135

Normal faults have sigma 1 radial (like gravity) and sigma 3 laterally. They dip at ~60 Thrust faults have sigma 1 laterial and sigma 3 radial. These dip at ~30 Strike slip has sigma 1 and 3 lateral and sigma 2 radial. The wedge being pushed by sigma 1 has an inner-angle of 60 and dip at ~90.

Answer 136

This is the concept that when a rock is subjected to far field stresses that create tensile points in the structure this creates a variety of microcracks and the joint eventually forms by propagating along the microcracks perpendicular to tensile sterss.

Answer 137

The relative path of deformation of any material may differ dramatically. This means that the start/end state do **not** characteristically define the strain state of the rock.

Answer 138

This is false tachylite (lightning rocks). It forms from the frictional melting of rock. Not grinding or fracturing. It is generally glassy to crystalline and fills sills/gaps within the **generation surface**

Answer 139

This is a type of plane strain where one direction is extended and the other is compressed. It is co-axial deformation where there is not a rotation in the principal **stretching** axes. This also means that the compression to extension ratio is relatively 1:1. The change in area is also zero.

Answer 140

This is a measure of the acute angle of a line in a plane measured In the plane. ALWAYS note the direction that the lineation is moving down towards.

Answer 141

On a regional level folds can be described as anticlinorium and synclorium. These can be considered first order folds that have localized anti/synclines superimposed onto their structure

Answer 142

Across the globe, similar patterns of continental extension related to orogenic collapse is correlated with the presence of metamorphic core complexes. In NA these occur in the basin and range extensional system from Mexico through Canada. They tend to be domal arches ranging from 25 to 60 km in length, bounded by low angle normal faults, and display a unidirectional sense of shear, this is **simple shear**

Answer 143

Within a series of partially connected normal faults the **relay** **ramps** refer to the inclines between tip points.

Answer 144

These are joints that form perpindicular to the principle stresses and represent the dilation of the surface above/below the nuetral axis

Answer 145

the viscosity of the lower lithosphere is ~10²³ poise The viscosity of the upper asthenosphere is ~10²¹ poise

Answer 146

This is the mechanical behavior of rocks. It has three end-members, elastic, plastic, and viscous. **Elastic strain** is defined by recoverable deformation through the hysteresis loop where stress is related to strain by hookes law in a linear fashion as defined by E. **Plastic Behavior** is defined by materials having an irreversible change in shape. Ductile rocks have undergone plastic deformation and are at a point where changes in strain occur continuously even if stress is constant. Below the critical stress E=infinity so there is no change in strain with stress. **Viscous Behavior** is described by "solid-state flow" where small proportions of melt and long time scales enable materials to act quasi-fluid like where differential stress = viscosity x strain rate

Answer 147

These are the toole marks used to describe slickenlines. They often accompany crystallographic reorientation

Answer 148

These are strike, slip mini faults which form +-30^o from sigma 1

Answer 149

The planar feature dips to the right so if you put your right hand down dip your thumb points in the direction of strike

Answer 150

This is the amount of differential stress required to cause failure in the brittle regime or flow within the plastic regime.

Answer 151

This is "domino-style" or "bookshelf" faulting defined by fault dip **decreasing** with increased slip.

Answer 152

**S-surfaces** (planes of schistosity/foliation/flattening) this is the plane of S₁ perpindicular to sigma 1 and **C surfaces** which are usually linear and form planes of maximal shear. They bisect the intersetion of sigma one and S₁ To identify: look at the relatively repetitive and planar surfaces of micas within the higher grade fabrics these will correspond to the C-surfaces and 45 degrees from that will be the curvy S-surfaces.

Answer 153

These are a type of analytical plots for analyzing azmuth and dip vs depth of a drillhole. They can show faulting or folding via cusps.

Answer 154

Penetrative planar layers of mica and lath-shaped minerals

Answer 155

These are structures that are the result of deformation after the rocks are formed. It is the primary focus of the class. They include things like joints, veins, faults, folds, cleavage, lineations, and microstructural deformation.

Answer 156

This is a measure of rotation due to shear ## Footnote γ = Δx/y = tan(ψ) where ψ = the angle of the roation of an internal element.

Answer 157

This is an area that can be small or large and is described by many sub-parallel interconnected slip surfaces. These form at depth where rock is more plastic than brittle.

Answer 158

This describes offset over a zone that can represent cm-km width. This represents basal faulting where temperature is high enough to cause plastic deformation. They tend to form mylonites.

Answer 159

1. ) structural traps for oil and gas 2. saddle reef deposits which are lode quartz precipitating in the low P of the fold axis 3. Strata-bound deposits: These are commonly Pb-Ag deposits

Answer 160

Turncation of units, mismatched ages of units, repeated stratigraphy, and/or missing data

Answer 161

These are folds where the limbs thicken/thin evenly between layers. Usually hinges are thick and inflection points are thin. It indicates mid ductility.

Answer 162

This is an end member of strain defined by noncoaxial deformation. This is shear in a typical form where the principle stretching axis rotates over deformation. It is where the primary force/s are parallel and separated by some distance, not in line/co-axial. It is characterized by elements being deformed along a line parallel to the direction of shear.

Answer 163

These are fine parallel laminae

Answer 164

These are toole lines that show displacement along faults and record the displacement history of the fault. They are generally straight, fine, delicate. They may cement breaking material from the other wall to create hooks, lumps, or spikes.

Answer 165

These are polished surfaces or mineral coating that form from the displacement and associated heat

Answer 166

Crystals that form during the displacement of material along a fault with the aid of stylolitic pressure dissolution. This generally creates a pock-marked surface of rods and cones.

Answer 167

This is a term that describes the actual relative **displacement.** **separation** is the measure of the apparent relative displacement.

Answer 168

This includes the slip direction, magnitude, and sense. It is the displacement vector.

Answer 169

Using mohrs circle, coloumb failure, and byerlees law we can define the space where slip will occur before a new fracture forms to accommodate failure. If a mohrs circle intersects byerlees law at stresses below coloumb failure then any pre-existing fracture within that orientation will slip before failure occurs. If the plane is oriented such that mohr's circle intersects the coloumb failure criterion **before** the plane intersects byerlees law or the coloumb failure then a new fault is formed.

Answer 170

These are ridge like growths that form on the fault surface due to asparities during the translation. It acts as a low pressure area for displaced material. The smooth way is the direction of slip. These generally have **chatter marks** which are the cliffy parts of the lineations

Answer 171

1. ) plot hole collars 2. ) plot layer intercepts 3. ) make contours with the knowledge that faults displace contours

Answer 172

1. ) choose the transect (usually perpendicular to the strike of the main features) 2. ) Create topographic profile by "Draping" the transect line onto the "surface" 3. ) Transfer the station point information and other relevant knowns onto the profile. Usually this starts with the dip of beds near the surface while making sure to account for apparent dip. 4. ) Construct interpretation 5. ) QA/QC by making sure that conservation of mass holds (midpoint L = C1)

Answer 173

1. ) draw the dipping plane in map view (x-y) 2. ) Use a cross section perpendicular to strike to find the contour line at some depth d where x = d/tanθ and θ is the dip. x will be real normal distance and will need to be converted to map units 3. ) At whatever angle you are looking to cross the structure the apparent dip is found by measuring the distance from the contour z=0 to the created contour at z =d. This is x₂. 4. ) convert x₂ to real units and θ₂ (apparent dip) = tan^-1 (d/x₂)

Answer 174

1. ) in map view draw the two intersecting planes 2. ) Draw two subsurface contours at depth = d for each plane with dips; θ₁ θ₂ and distances from the drawn line in map view given by d/tanθ = x_1,₂ 3. ) draw these contours 4. ) find the map distance from the original intersect to the new intersect. Measure this distance (x₃) 5. ) the plunge of the line of intersection is given by tan^-1(d/x₃) and the trend is determined via measuring

Answer 175

This is a type of deformation defined by a change in the **volume** of a rock body (dilation) or a change in the shape (distortion). It is a form of non-rigid deformation which results in a change of the spatial arrangement of the materials of a rock. If we know the size of the body at t=0 then we can quantify strain.

Answer 176

This a form of structural analysis based in descriptive analysis that only analyzes distortion and dilation

Answer 177

This is the analysis of strain of a rock body that defines how every line passing through the centroid changes in length and angle during deformation.

Answer 178

tan ϕ_d = tan ϕ (S₃/S₁) where ϕ_d = the angle between S₁ (max extension) and some line AFTER deformation and ϕ is the angle between the same line and S₁ before deformation Where the line is arbitrarily drawn based on field measures and S1 is considered a direction in which the maximum strain occured.

Answer 179

This is an ellipse or ellipsoid that shows the finite stretch of the material in every direction. It models what would happen to a sphere in that state of strain.

Answer 180

This is the extension/time. In real geologic terms we cannot match the incredibly slow timescales of tectonic which acts as a caveat to lab experiments.

Answer 181

This is the displacement between two marker beds at a fault surface

Answer 182

This shows three main parts: An elastic part given by mohrs failure criterion where stress is linearly related to strain by youngs modulus and brittle deformation dominates. At these depths joints then faults occur. At the lower depths, quartz becomes plastic (T300-350 C) The yield strength (~10-15 km) indicates the elastic-plastic transition and is where earthquakes nucleate (greatest stress). It is also where von mises failure begins. After this an exponential decay of strength occurs marked by the brittle-ductile transition. It begins with flexural flow fold then plastic flow (qtz) and viscous flow (strain dependent so stress is constant)

Answer 183

This is simply the upper half of mohrs circle plotted vertially so normal stress is considered proportional to depth where P=30 Mpa\*h (km)

Answer 184

This is force that tends to deform a body. The difference is that deformation is a function of how force is distributed over an area. It is used to describe all of the tractions on all surfaces that have the origin at the point of interest. It is the tensor that describes the force/area acting within a **volume** of rock.

Answer 185

The bending of a group of rocks is just like the bending moment of a structure where the upper areas experience stretching (normal faulting) and the lower layers have compression (thrust faulting). In a cross section of a thick folded layer the uppermost layer is likely to have P-solution based boudinage and T-joints. The mid-layers will have X-joints and conjugate normal/thrust faults. The lower layers are likely to have increasingly dense slaty cleavage.

Answer 186

This is L_f/L_oit is the ratio of the final length to the initial length and denoted by S S₃ = the minimum finite stretch S₁ = the maximum finite stretch

Answer 187

These are the plastic elongation of mineral due to shearing or constriction. It occurs very commonly with calcite

Answer 188

1. Identify geometry: orientation, shape of the rock units, and nature of contacts (via mapping) 2. ID kinematics: movement during deformation and includes, translation, rotation, distortion, and dilation 3. ID dynamics related to deformation because of stresses/forces generated by tectonic processes.

Answer 189

Study of the architecture of Earth's Crust from deformation

Answer 190

This is a delta structure because there is clearly rotation. The tails indicate clockwise rotation hence the sense of shear is top to the right.

Answer 191

These are subsurface topographic maps of the geologic planes.

Answer 192

These are sharp zigziags in the rock that are the result of pressure dissolution. In pressure dissolution S₁ = S₂ =1 but S₃\<0

Answer 193

These describe the geometry and topography of subsurface features.

Answer 194

These are when folds get folded. Oftentimes instead of having limbs that go straight like a parabola they will have slight bends and wiggles that are synforms(U shaped) and antiforms (Upside down U)

Answer 195

This is when the youngest layer in on the innermost hinge of the fold. Alternatively, it is a fold that is convex in the direction of the oldest beds.

Answer 196

This is a way of describing an anticline where the youngest layers are on the outermost hinge but at the lowest elevation. It is usually convex up but the youngest layer is at the base.

Answer 197

These are "cross fold" joints that form parallel to the principal stresses for a tectonic regime on a regional scale. They generally form because pore pressure is perpindicular to the principal stresses and thus propagate parallel to the principal stresses

Answer 198

These are rocks that are foliated and/or lineated due to having flowed in a solid state. They are shear zone rocks. S tectonites have schistosity (foliation) only due to flattening (pure shear). It is likely smashing play-doh L: Lineation only where there is shearing and/or constriction. Like a pasta maker LS: Foliation and lineation from general shear. The most common tectonite.

Answer 199

This postulates that the rock starts in some stress state in the compressive regime but P_f slowly builds and pushes sigma 3 into the tensile regime and a joint forms when it intersects the Coloumb Envelope of Failure. This repeats and creates several plumose structures

Answer 200

Stylolites: Pressure solution of limestone "dimples": pressure solution "drilling" of one cobble into another. Passive folds: folds that have been "chopped" parallel to the main fold axis (large cleavage) Cleavage

Answer 201

This is finding the strike and dip of a plane based on three elevations. 1. ) Draw the triangle in map view that represents the three points where z1\>z2\>z3 2. ) Using map scale find the distance from z1 to z3 in map scale. This is x1-3 3. ) θ1-3 = sin^-1 (z1-z3)/(x1-3) 4. ) Contruct a simple line given by z = z1-tanθ x 5. ) z2 must lie on the line between z1 and z3. so z2 = z1-tanθ x. Solve for x. This is the hypotenuse of a triangle from z1 at θ. Use xsinθ = horizontal distance. 6. ) This horizontal distance can be plotted on map view between z1 and z3. The line connecting z2 and this point is the strike of the plane. 7. ) Use this line to find the strike at z1 then measure the perpindicular map distance between the contours. 8. ) θ = tan^-1(z₁-z₂)/x = true dip

Answer 202

These are shown with little teeth on the hanging wall

Answer 203

These are faults that relieve contraction/compression. The hanging wall moves up relative to the footwall which is shown by having older rocks on younger rocks or having higher grade on lower grade. It also repeats stratigraphic sequences.

Answer 204

120-180 = gentle 70-120 = open 30-70 = tight \<30 = isoclinal

Answer 205

The tip of a fracture is the place where the fracture propgates from. The tipline in the axis that connects the tips at the upper and lower bounds of the rock

Answer 206

This is stress in vector form where normal stress is normal to the plane and shear is parallel to the plane

Answer 207

These are discrete or broad areas where steeply dipping faults shear past one another. They accommodate for shear. Oceanic transfer faults are very important because they enable spreading centers to have different rates of spreading.

Answer 208

This is defined by all the point matter within a rock being displaced along equal and parallel displacement vectors. This means that the internal distances between elements remains constant but their absolute location in space changes.

Answer 209

Transposed rocks are rocks with lenses parallel to the main cleavage planes. It is layering due to deformation. The process begins with folded bedding which become elongated similar folds. These eventually get "chopped up" by pressure solution and the relict hinges become lenses within the rock parallel to cleavage.

Answer 210

Transpressive motion represents oblique compression and transtensive motion represents oblique tension

Answer 211

Slaty cleavage, crenulation cleavage (cuts older folding),

Answer 212

Syntexial veins describes veins where material precipitates from the walls to the center Antiaxial veins have crustal that precipitate from the center to the walls (the center crystals are oldest.

Answer 213

Previous continental (passive) margins from the breakup of pangea. These are major petroleum systems (like the artic) Mid-ocean ridges: commonly symmetric mountain chains with graben structures or asymmetric with detachment fault Continental rifts associated with hot mantle upwelling (East Africa, Rio Grande). They include high angle normal faults that become listric at depth. They are shaped like a shield. Highly elevated regions of Earth (Tibet) due to gravitational collapse. Continental extension zones (basin and range) where a mix of back-arc basin extension and transtension from the san andreas create graben structures.

Answer 214

Phyllitic foliation: sheeths of small micas Schistose foliation: coarser grained micas without banding Gneissic foliation: This has clear banding that formed during deformation and metamorphism Migmatite: This looks like guts. It occurs when partial melting occurs (T\>650 C)

Answer 215

Bedding planes, fault planes, joints, dike, walls/cuts, veins, foliations.

Answer 216

There are ductile rock bodies which accommodate deformation without losing cohesion of internal strength by distributing deformation throughout the rock's volume. An example of this would be the asthenosphere. Brittle rock bodies accommodate deformation by a near loss of cohesion along discrete fractures (residual frictional cohesion) Elastic rock bodies have deformation linearily related to the stress load as described by Hooke's Law

Answer 217

Strike-slip: dip is ~90 with motion parallel to the strike Dip slip: slip along inclined surface with the hanging wall and footwall (normal and thrust faults) Oblique slip: inclined translation with dip ~30-60. Rotational Faults: These are faults where one block moves about an axis relative to the other.

Answer 218

Progressive strain is the motion of every point throughout the deformation path instantaneous strain: a snapshot of strain at some dt Finite strain: The final result of deformation

Answer 219

**Differential stress** is the diameter of mohrs circle. It causes **distortion** **Mean stress** is the average of the principle stresses. It causes **negative dilation.** **Deviatoric stress** is the radius of the circle. It causes **distortion.**

Answer 220

mineral lineations slickenlines line of intersection between two planes

Answer 221

This is any pause in deposition and/or erosion This includes nonconformities: young ig or sed on old meta or ig angular unconformities: sedimentary layers over sed layers at a different orientation disconformity: Parallel beds of similar composition usually id'ed using dating.

Answer 222

These are the most common form of joints and oftentimes form sugar cube joints due to Poisson effect and dilation. ## Footnote This is a type of unloading jointing where the ellipsoid shape of the pluton creates radial and tangential stresses for jointing. An example of this is half dome. If the rock being exhumed is a pluton (oftentimes having an elliptical shape) it will create joints that are radial and tangential to the ellipsoid. these are **exfoliation joints**

Answer 223

This is common within flexural folding where the upper and lower surfaces of a fold experience shear. It is said to be verging to a direction based on the degree to which the tops/bottoms are sheared.

Answer 224

V(sphere) = (4/3)\*pi\*r³ V_e = (4/3) pi a\*b\*c and r = (abc)^1/3

Answer 225

This is a failure envelope describing failure at high confining pressures. At these depths, lithostatic pressure dominates and failure occurs at about 45 degrees therefore 2theta = 90 and the critical stress becomes constant.

Answer 226

Heterogeneity in the rock mass creates localized stresses that then create the joints. They are created due to thermal tension, unloading, or exfoliation (unloading for igneous rocks/plutons)

Answer 227

The geotherm increases to about 25 C/km

Answer 228

When a fault first forms (theta = 30 from sigma 1) only the **differential stress** and not the average stress decreases. It ten slowly increases until it intersects byerlees law and will slip along that fracture. As the differential stress increases the angle between sigma 1 and theta increases (measured by the upper intercept) which corresponds to a lower angle of dip for a normal fault. This continues to increase **until** mohrs circle intersects coloumbs failure criterion (at 2\*theta = 60) and a new fault forms, relieves stress, and the process repeats.

Answer 229

They are shovel shaped. where there is maximum displacement at the center and this approaches 0 with decreasing distance to the **tip point/line** where the displacement = 0

Answer 230

Theta is always =30^o

Answer 231

The hanging wall is extended as a function of slip along the surface. This means that as displacement increases towards the center of the fault the hanging wall slumps inward to create a **syncline** which plunges **into** the fault. In the footwall, the removal of overburden creates a bulge aka a **syncline** which plunges **away** from the fault surface.

Answer 232

Generally rocks within Earth will experience gravitational loading, thermal loading due to dilation, displacemement based loading, and pore pressure.

Answer 233

When doing structural topographic maps, faults cutoff topographic lines.

Answer 234

Rotation is the translation of material about a central point. It is described by the radians of rotation It occurs most common within overlying rigid deformation (where rigid faulting underlies a more ductile upper layer that deforms. It also occurs with listric normal faulting, kink folding, and mylonation.

Answer 235

Theta is measured **from** the plane of interest to the maximum stress.

Answer 236

**Yield Strength** is the point when strain softening starts to occur. This is not the peak stress but the point slightly below it. **Ultimate Strength** is the point of maximum stress **Rupture Strength** is the point where slipping occurs (instant drop in stress without change in strain)

Answer 237

Detachment faults are low angle (\<30^o) which form underneath graben systems and at the interface of the brittle crust and the metamorphic core complexes. In the latter case they are marked by **chloritic alteration** (green color) which forms due to fluid alteration during the process of exhumation. They can be confused with thrust faults.

Answer 238

This is underlayed by 500 m to 2 km of mylonitized orthogneiss/metasedimentary rocks with potentially undulatory foliation. Deeper than this is the **injection complex** which has a series of leucogranitic dikes cutting the mylonitized gneisses. As they approve the shear zone they become oriented parallel to the detachment surface.

Answer 239

Starting at the detachment fault (low angle fault separating brittle crust from core complex) chloritic breccia (green breccia between cm and 10s of m thick) cataclasite resistant layer (~1 m)\ mylonitic shear zone (gneisses with hundreds to km of m thick) injection complex (dikes in the gneisses) undeformed core

Answer 240

The combination of ductile flow of the weak, hot lower crust/moho region and tectonic unloading causes the core complex to act like a bubble in oil.

Answer 241

This is a way of thinking about how core complexes form. It shows the breakaway and detachment of the upper crust as the lower crust upwells and is fed by the moho/upper mantle.

Answer 242

These are lobe-like plunging antiformal corrugations that occur on the detachment fault side of metamorphic core complex. They plunge into the direction of the footwall recession. They are basically the result of stretching.

Answer 243

There are generally two types of rifts: wide rifts and narrow rifts with indiviual characteristics based upon the moho temperature and the crustal thickness. Core complexes from in wide rifts where moho temperature is high (high ductility) and crustal thickness is high

Answer 244

A half graben basin is flanked on both sides by high mountains with high-angle normal faults and has sedimentation/depocenter in the middle where growth strata increase in thickness towards the mountain range. Supradetachment basins are wider and the depocenter becomes **thicker** away from the mountains unlike the growth strata of half-grabens. They are flanked by a low angle fault with basins that are far from the mountains.

Answer 245

**porphyroblast systems** (delta and sima types) mica fish (lenses of mica that form in the directions of stretching) SC fabrics (C fabrics are linear and show highest shear) Fractured grains (like a toppled loaf of bread)

Answer 246

They start as half-grabens with a structural low adjacent to the normal fault high. This low causes isostatic rebound at depth that starts to "bulge" the half graben basin into a basin high. At depth this causes the normal fault to flatten. The flattening of the normal fault initiates the onset of breakaway faults in the growth strata. The continual decline of the hanging wall repeats this process, and the basin high continues to enlarge until you reach the point where there is a detachment fault at the surface.

Answer 247

They are found at convergent margins where topographic highs create normal faulting and the topographic lows are dominated by thrust faulting

Answer 248

These **Andean/cordilleran-style** thrust belts are characterized by a trench, forearc, arc, plateau, retroarc thrust belt, and foreland basin. The plateau is the highest point along the figurative cross-section given and is a point where normal faulting occurs. It has a weak lower crust due to the high heat of the upwelling magma. This means that it is more easily squeezed upwards where it cools and collapses.

Answer 249

**Alpine/Himalayan-style** convergence is similar to the ocean-continent collision except that a trench does not form and there is a generally thickening of the crust that causes isostatic rebound in the plateau region. There is a similar collapsing a double sided thrust belts though.

Answer 250

From low to high elevation. The **foreland** is the inner-continental basinward part of the belt and made of younger, lower grade rocks. It will be in front of an **emergent imbricate fan** which has newer thrusts at lower elevations. This merges with the plateau aka the **hinterland** where the **duplex roof** exists (the first thrust fault) These are underlain by younger thrusts too. This is where the highly sheared, old, and high-grade rocks exist. All of this sits **above the decollment fault** which is the "main fault" that the other faults feed into. It is relatively flat but dips towards the hinterland. It represents a decoupling within the crust There are usually turned over antiformal folds in the hanging wall and synclines in the footwall.

Answer 251

The first ramp thrusts over the flat which then eventually begins to thrust too. This increases the dip of the dip of the earlier thrusts and also makes the youngest faults those that are closest to the foreland. Like normal faults, thrusts cut up-section (originate at depth). They are connected like stair-steps with ramps and flats that progressively reach the surface. This is because they take advantage of planes of weakness (parallel to bedding)

Answer 252

These are usually in the hinterland which is the oldest fault. This means that it has had the greatest amount of displacement and uplift. This correlates to a greater amount of erosion which exposes the oldest rock. The elevated hinterland is important to the development of large thrust belts where the weight of the elevated rock helps to push the younger foreland thrusts.

Answer 253

These are thrusts that form over relatively stationary and stagnate ramps. They "cut" the rock along the fault and slide along the thrust.

Answer 254

Thrust sheets generally refer to large interior thrusts. The thrusting layers can be eroded to expose the younger material below, **windows**, and there can be parts that become seperated from the main sheet. These are **klippes**

Answer 255

These are foreland features of thrust belts where they can form "lobes" that overlay the interior rocks.

Answer 256

There are **fault-bend** folds where layers bend over the thrust. The upper layers will be thinned. It is similar to a rollover monocline. **fault propagation folds** These are rock layers that fold ahead of the propagation tip. These create the turned over antiformal folds in the hanging wall. The syncline axis in the footwall is near the propagation tip. During Continental continental collisions there are also "snake head folds" which occur in relatively weak, less brittle crust where a large lobe basically plops onto the footwall.

Answer 257

This is the uppermost thrust. It forms the earliest and is rotated to steeper and steeper dips as it overrides the foreland material. These occur when the inactive fault is thrusted above the active ramp to be on the surface of the previously adjecent layers.

Answer 258

There are generally several thrust sheets that layer onto one another. In the foreland are the youngest thrusts and the hinterland has the oldest thrusts. The lower layer where "decoupling" occurs is the floor fault and the roof fault is the boundary between the thrusted layers and the overlying rock. A horse is where the thrusted layer interfaces with the inclined layer below.

Answer 259

The integral of the frictional forces needed to forces 100's of km of thrust sheet onto another rock is beyond the magnitude of conventional tectonics. The rock would shatter before thrusting in this matter. The caveat is water pressure. Water pressure acts as a negative weight and enables the thrust sheet to more effectively slide onto the material below it. It decreases mean stress without changing differential stress (drives the process) Additionally, thrust sheets move in piecewise dislocations. movement and strain is **not** homogeneous.

Answer 260

These are depressions that form on the frontside of fold-thrust belts (in the foreland) where the topographic load of the fold-thrust belt causes lithospheric flex. Foredeeps seperate the fold-thrust belt from the forebulge.

Answer 261

The key concept to understanding convergence in this context is that oceanic plates simply "fall" like a weak noodle. **advancing subduction zone** refers to when the rate of falling is less than the horizontal displacement of the plate. This causes for retroarc thrust sheets. See the Andes for an example (the pacific plate has the maximal spreading rates) **retreating subduction zones** refer to when the spreading rate is less than that of the falling rate of the plate. This leads to the trench moving oceanward and the development of backarc **extension** See the West coast (also influenced by transtension)

Answer 262

This refers to the "subduction rate" of the plate and is related to the rate at which the oceanic plate sinks while horizontal translation occurs. when convergence rates exceed subduction the trench advances towards the continent and retroarc thrusts form. When convergence rates are less than subduction rate the trench moves oceanward and the continental crust is extended. This is a retreating trench.

Answer 263

Gravity. The differing rates of convergence and divergence lead to strike slip faults through.

Answer 264

**releasing bends** are transtensional pull apart basins **restraining bends** are high relief transpressive thrusts and folds. Slip along thrusts and related fault mechanisms due to uneven strike-slip mechanisms leads to transverse ranges and seismeic hazards.

Answer 265

Strike slip systems generally have a curvy architecture that branches from a main fault at depth to a series of roughly parallel surface scarps. **extensional flower structures** are those that form in transtensive basins. They are generally a series of listric normal faults very similar to classic horst and graben structures. **contractional flower structures** are convex down structures that are like pimples. They form thrusts.

Answer 266

Because they are deep there is a large area of surface displacement and because friction is really the only resisting force the slip rate is high.

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