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112 Cards in this Set
- Front
- Back
- 3rd side (hint)
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What is the equation for stress? |
Stress=F/A |
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Explain Deformation |
the change in shape,position or orientation of a body under stress |
Shape |
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Give 3 Examples of Deformation |
Rotation, Translation, Strain |
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What is a characteristic of heterogeneous deformation? |
No change in shape |
shape |
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What is a characteristic of homogeneous deformation? |
Shape will remain the same and lines remain in the same orientation (parallel stay parallel and straight stay straight) |
Shape |
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Why will rocks deform in different ways? |
different Temperature and pressure due to different mechanical properties |
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What are two forms of structures that are tectonic/secondary structues? |
Brittle and Ductile structures |
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Explain a brittle structure |
*no loss of cohesion and will break in places EX Faults and Joints |
Faults and Joints |
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Give examples of ductile structures |
folds, foliations, lineation, ductile shear zones |
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It is true that faults can also form by slumping (which is a primary structure) |
True |
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What two rock forms are primary structures |
Sedimentary, Igneous |
Layering, Volcanic |
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Explain Microscopic view |
features are only visible with an optical microscope electron microscope |
small |
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Explain a mesoscopic view |
Can be directly observed with or without a hand lens and without extrapolation. |
Hand specimens to are but continuous outcrops |
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Explain a macroscopic view |
features that are several outcrops to whole mountain ranges in size. They are too large/ too poorly exposed to be examined directly in their entirety |
Must be observed indirectly |
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What are the 4 steps of Geometric Analysis |
1)Characterize the form of structure within a time sequence 2)establish geometry of rocks 3) Study the geometrical features and infer about large-scale structures from small scale observations 4) Provide a description that is mostly free from inference |
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Explain Kinematic Analysis |
After geometric analysis, an attempt is made to reconstruct the movements that took place during formation |
rotation, translation, strain |
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Explain Dynamic Analysis |
The reconstruction of stresses related to the movements that cause deformation of the structure |
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True or False, horizontal beddings are horrible markers |
False, Planar and horizontal bedding are the best markers because they are easily comparable |
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What does a change in younging direction indicate? |
Deformation (for example a fold) |
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What is grade bedding? |
the variation of grain size in a bed will create layers, with sediments that are coarser grained at the base and finer at the top |
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What causes grade bedding |
changes in energy of deposition environment |
A river flows into a lake, the water slows down and therefore energy decreases. The bigger sediments settle to the bottom and the lighter will remain on top |
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What is cross bedding? |
Surfaces that have thicker "master beds" that are oblique to the bounding surfaces of the "master beds"
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True or false: you can't tell the top or bottom of a cross bedding |
Trick question. Overall it is true, but erosion can occur that will cause the younger layer to cut through the older layer |
Erosion |
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True or false, the sedimentary layer or a disconformity is on the bottom |
false |
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Nonconformity, true or false, the layer of metamorphic rock is below the contact. |
True |
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What are 4 examples of graded bedding? |
Slide, slump, flow, shelf |
think turbinity currents from last year |
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What is a Flute clast? |
An assymetrical trough formed by "mini-tornadoes" (vortices) within a fluid that digs into the nconsolidated substrate |
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Explain the shape of a flute clast.Why does it look like that? |
When the vortex dies out it creates a form that gets shallower and wider at the downstream end |
"mini-tornadoes" |
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What is a load structure? |
Load structures will occur at the contact between a sand and mud layer. Because of density differences between the layers, sand can sink into the mud or mud inject into the sand |
Think Flames and differences in density |
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What is an important pre-existing factor for a load structure to occur? |
there must already be a pre-existing weakness for sinking or injection (or both) to occur |
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What is a dewatering structure? |
sediments that are oversaturated with water and underpressure that have been disturbed by and even will crack causing water containing sediments to fill it in and form a dyke/channel/fill |
water with sediments |
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What are the 3 types of contacts? |
Depositional, fault, intrusive |
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What are the differences between the 3 types of contacts |
Depositional-younger on top of older Fault-self explainitory Intrusive-lower rocks in the crust will inject into the crust (something intrudes into something) |
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Explain a disconformity contact in detail |
The beds of rock sequences above and below the unconformity are parallel to one another but there is a measurable age difference between the two beds. This represents a period of nondeposition and or erosion |
non-deposition |
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Explain a nonconformity in detail |
Explains unconformities at which the strata is deposited on a basement of older rocks aka plutonic or metamorphic |
Ex. Unconformity btw Cambrian strata and precambrian basement in grand canyon |
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What is a conformable contact? |
layer or layer of sedimentary rocks with no time gaps |
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What does unconformable mean? |
a gap in the record of deposition |
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What is a diagenesis structure? |
the process by which sediments are lithified into sedimentary rocks aka represents a physical and chemical change that occurred during burial of the structure |
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What will differential compaction result in? |
a pitch and swell of structures |
compaction both laterally and vertically |
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Give an example of compaction |
the compaction of mud leads to the development of a preferred orientation of clay resulting in a shale bed |
shale |
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Explain what a pressure solution is |
The concentration of a material can cause a stress that causes another mineral to dissolve leaving behind an odd structure |
Ex. Calcite may dissolve and clay material are left behind |
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What is a penecontemporancous fold/fault? |
The re-sedimentation of loosely held sediments |
Swirls |
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What type of structure is slumping? |
Penecontemporaneous (original bedding more or less maintains cohesion) |
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What is a primary Igneous structure? |
Magma can be emplaced either on the surface (extrusive) or within the crust (intrusive) creating an primary igneous structure |
felsic and mafic |
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What are types of igneous structures |
volcanic neck, radial dykes, batholith, dike, ring dike,sill, stock |
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what is a sill? |
A sill is a sheet intrusion that parallels the pre-existing stratification in stratified sequence. It is roughly subhorizontal in unstratified sequences |
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What are migmatites and what are they formed of? |
Migmatites are a structure associated with intrusive rocks, they are formed of cooled partial melting rocks
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What is a cooling fracture? |
columnar jointing, associated with shallow intrusions and extrusive flows, hexagonal,the long axes or columns are perpendicular to isotherms |
Devils Tower |
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What are the 2 measures of strain? |
Elongation Stretch |
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What is the equation for elongation? |
e(E)=delta(l)/lo |
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What is the equation for stretch |
s=l/lo=1+e |
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If a mineral is buried deeper, what will happen to it? |
volume will decrease and chemical composition may or may not change |
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What are the 3 types of principal strains? |
principal directions of strains principal strains principal planes of strain |
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What are the 5 types of homogenous strain? |
a)General Strain (X>Y>Z) b) X>Y=Z(Cigar) Axial symmetrical extension c) Axial symmetrical shortening X=Y>Z (pancake) d)Plane strain X>1>Z(no length change in Y) e)Simple Shortening 1>Z X&Y have no length change (**must be a decrease in volume) |
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What is total strain? |
Comparing the initial length to the final length |
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How to you get finite strain? |
compare two lengths that are beside eachother |
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What is coaxial strain? |
pure shear |
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What is non-coaxial strain? |
simple shear (not all are simple shear) |
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What is simple shear? |
thickness doesn't change, individual layers do not deform (also no change in third dimension) |
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True or false, all non-coaxials are simple shear |
False |
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describe pure shear |
as an object deforms the long and short axis do not rotate or change orientation making them coaxial and therefore pure shear |
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What is a body force? |
results from action of a field at every point within a body. It can work at a distance and depends on the amount of material affected |
gravity, magnetic |
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What is a surface force? |
acts only on surface, operate across a contact area between adjacent parts of a body and these forces originate when one body pushes or pulls on another |
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Why are body forces and surfaces forces closely related in the earth |
body forces give rise to spatial variations or gradients in the surface forces |
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What is a compressive force |
Pushing and is possitive |
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What is a tensile force |
pulling and is negative |
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What is the equation for stress |
sigma=F/A |
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If there is a large area, relatively, how big will the stress be? |
small |
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What amount of stress will be applied to a small area? |
large |
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What are the two resolutions of stress vectors? |
Normal (perp) and shear stress (parallel) |
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What is the equation for sigma(n)? |
FN/A2=Fcos(theta)/A2=sigma(cos^2(theta)) Where A2 is the area that the force is applied to |
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What is the equation for Fn? |
Fn=Fcos(theta) |
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What is the equation for Fs? |
Fs=Fsin(theta) |
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What is the equation for sigma (s)? |
Fs/A2=sigma1/(2sin(2theta)) |
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In 3D, what is stress representated as at a point? |
ellipsoid |
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In 2D, what is stress represented as at a point? |
ellipse |
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How many sigma (n) and sigma (s) components are there when a stress is experienced on the side of a cube> |
1 sigma n and 2 sigma s |
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What is the equation for sigma(#) n |
sigma#cos^2(theta) |
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what is the equation for sigma# s? |
sigma#/(2sin(2theta)) |
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true or false sigma1>sigma3>sigma 2? |
false sigma1>sigma2>sigma3 |
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Triaxial? |
all sigmas have same non zero value |
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biaxial (planar)? |
sigma3=0, sigma1 &2>0 |
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Uniaxial(compression)? |
sigma3&2=0 and sigma 1>0 |
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Uniaxial (tensile)? |
sigma3>0, sigma 1&2 =0 |
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Biaxial |
sigma3<0 and sigma2=0 and sigma1>0 |
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Hydrostatic (lithostatic) |
sigma1=sigma2=sigma3=p |
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Whatis the equation for deviatoric stress? |
total stress-mean stress |
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what is a stress field? |
a body describedby mapping out components of stress at all points |
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When is a stress field homogeneous? |
when all ellipsoids have same shape and orientation at all points |
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What is a stress trajectory? |
lines that are every where parallel to principal directionsof stress |
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True or false: strictly homogeneous materials are common |
false, rare |
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Is statistically homogeneity scale dependent? |
yes |
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What is isotropic? |
material has same property in all directions |
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What is unisotropic? |
looks different depending on the direction |
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Explain elastic behaviour |
the strain is recoverable and there is no permanant distortion although, the strain and deformation will occur instantly. Once the stress is taken away the deformation will disappear instantly |
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Explain hydrostatic compression |
under stress that has some value in all directions |
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what is bulk modulus? |
the amount of stress needed to change a certain amount of volume |
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what isthe modulus of rigidity |
how easily/difficult it is to shear the rock |
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Explain ideally viscous behaviour? |
resulting strain rate is proportional to the applied stress. (strainis permanent and not recoverable) |
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Explain ideally plastic behaviour |
material doesn't deform if stress is below a critical value and cannot maintain a stress greater than the critical value. At the critical value, it continuously deforms in a permanent manner |
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Explain brittle behaviour |
rocks deform by developing marked discontinuities across which there is often a break in cohesion |
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Explain ductile behaviour |
rocks deform by distributing strain in smoothly varying manner throughout deforming mass |
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What are the factors that affect brittle/ductile behaviour? |
temp, confining pressure, material, strain rate (opposite effect to that of temperature), pore-fluid pressure (effect opposite to confining pressure) |
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What is ductility |
capacity for undergoing permanent change of shape without fracturing at scale of observation |
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What is a cylindrical fold? |
when the fold axis is parallel to the hinge line |
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what is a non cylindrical fold? |
no fold axis, hinge line is curved |
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True or false, for parallel folds, true thickness is the same everywhere |
true |
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true or false, for a similar fold, the apparent thickness is not the same everywhere along the layer |
false |
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what is an intrafolial fold? |
its is an isolated tight fold closure in rocks that otherwise are not obviously folded. It occurs in areas of intensive folding |
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What are the different classes 1A, 1B, 1C 2 and 3? |
1:parallel fold
A:<90 B:perpendicular to plane C:>90 2:similar fold 3:isogons converge |
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Explain what deviatoric stress is, also how is it represented on the Mohr's cirlcle |
Deviatoric stress is the stress value that determines if a shape change will occur or not. The larger the stress the greater distortion (shape change). On the Mohrs circle, deviatoric stress is the radius of the circle (sigma1-sigma2)/2. The proper representation of the circle is to move it to the origin. |
Not a hydrostatic component of the principal stress |
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Explain what mean stress is,how is it represented on the mohrs circle |
Mean is the hydrostatic component of the principal stress. It represents the tendency to produce dilation (deltaV/Vo) On the Mohrs circle, mean stress is the center point of the circle(sigma1+sigma2)/2. |
Hydrostatic component of principal stress |
