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Structure Final
I'm 800% fucked
| Question | Answer |
|---|---|
| What is a fenster (or tectonic window)? | A structure (often a topographic low) where an isolated younger unit is the hanging wall in a thrust fault (classic dog collar) |
| What is a klippe? | A structure where an isolated older unit is the hanging wall in a thrust fault (sadistic dog collar) |
| What would repeating stratigraphy (two layers of one unit on top of one another) in a drill core suggest? | A thrust (or reverse) fault |
| "Stair stepping" is? | A feature common in thrust faults |
| What part of a thrust fault is the "ramp"? | the part of the stair step where it's diagonal |
| What part of a thrust fault is the "flat"? | the part of the stair step where it's fucking flat, genius |
| What is the "heave" of a fault? | horizontal offset |
| What is the "throw" of a fault? | vertical distance |
| What is the presence of mylonite indicative of? | a high strain zone |
| In a strike slip fault cross section, what does a circle with a dot in it indicate? | The wall is coming toward you |
| In a strike slip fault cross section, what does a circle with a cross in it indicate? | The wall is moving away from you |
| How do mylonitic rocks preserve evidence of how they were deformed? | deformation causes material to rotate. Rotation of rigid clasts in a matrix can lead to the development of asymmetrical fabric. The sense of shear is given by the ‘stair-stepping’ of these fabrics |
| If the tails on the porphyroclast are such that it's in a Z pattern, what does this indicate? | The top wall was moving to the left, the bottom wall was moving to the right |
| When you walk in the dip direction, where are you walking? | Upsection (into the future, geologically) |
| What are some examples of planar structures? | -bedding -faults -foliation -cross bedding |
| How do you find Rake (aka pitch)? | -described as an angle on the plane -can measure it with a protractor -count in from the direction that the arrow is pointing -count along the great circle from the outside, plot a dot -you could read the trend and plunge off the stereonet |
| What is a slickenline | A linear feature that lies on the same plane as the fault (same great circle as fault on stereonet). Any line that occurs on a shear fracture. |
| What are porphyroclasts? | large relict materials (minerals) in metamorphosed rocks |
| What is the brittle/ductile transition? | ~10-15 km underground, where stuff starts to flow. ductile shear zone/high strain zone – deep faults (stretchy pully thing instead of breaking) |
| What do contours parallel to contacts indicate? | Horizontal layers |
| What are some facing indicators for an igneous body? | flow top breccia (the top crusty bit gets brecciated while the underneath bit keeps moving), partially-filled amygdules, pillows (pointy bottom), chill zones |
| What do you call refolded folds? | anaformal sinclines |
| What is a pluton? | Discordant (cuts across existing rock bodies), intrusive igneous underground bodies, formed from cooled magma chambers |
| What is a dike? | A discordant, tabular shaped pluton, formed by filling of cracks/ |
| What is a sill? | A tabular, Concordant (parallel to preexisting stratification), pluton. |
| What is a laccolith? | It's the stink/river spirit from Spirited Away. Basically an overinflated sill (dome-like, concordant) |
| How are columnar joints formed? | cooling cracks from contractions of igneous lava flows |
| What is deformation? | change in shape of a material |
| What is metamorphism? | change in chemical structure through heat and pressure over time |
| What are a dip slope and an anti-dip slope? | -Dip slope (slope is same as topographic slope) -Anti-dip slope (strata dipping opposite to topographic) |
| Strike slip fault features | o can be right (or dextral) lateral SSF (what way it moved to your vantage point) o can be left (or sinistral) lateral SSF o sometimes SSFs are called Wrench Faults |
| Ways to tell what kind of fault you've encountered by looking at a drill core | Repeated stratigraphy could happen if the stuff was overturned, but it would be a different pattern. That’s for reverse. A Normal fault might be missing layers of stratigraphy. |
| Fault scarp | linear break in a slope that results directly from displacement along a fault. On either side of the slip surface, there may be damage zones (cracks around the fault) |
| Blind faults | faults that we can’t observe/see at the surface |
| What are cataclastic rocks? | Fault rocks - (formed by brittle processes) • Same look regardless of scale • Can be on the order of cm or mm Breccia can be produced by crushing rocks in a fault zone |
| BIFs are fun. What are they? | -gray is magnetite/specular hematite -red is chert |
| What are the types of deformation? | -the total package -translation – movement from one point to another -rotation – changing position about an axis -distortion/strain – shearing, stretching |
| In which geologic era were skolithos most abundant? | Cambrian |
| What are strike, dip, are direction? | bearing from N, angle relative to horizontal, map direction |
| What is a good rule to remember about strike and dip? | strike and dip are perpendicular. If it’s pointing north, it can’t dip north |
| How do you find strike with the brunton? | Hold it horizontal at the surface and level it. Like, be looking at yourself in the mirror. |
| How do you find dip with the brunton? | Hold it with the whole edge on the surface, flush. Definitely have the mirrored bit pointed in the dip direction. Move clinometer. |
| How do you find direction with the brunton? | Have sighting arrow point in the direction of the dip. And like...look at it |
| How do you find trend with the brunton? | line up sight with direction, close one eye, level it, be above it. |
| How do you find plunge with the brunton? | same as dip |
| 2 big components of geologic maps? | -topography plays a role in the pattern -also the underlying structure |
| What are the types of contacts? | o Stratigraphic/Sedimentary contact o Igneous/Intrusive contact o Tectonic/Fault contact o Erosional/Unconformable contact |
| What are some facing indicators for a sedimentary body? | graded bedding, cross bedding, bottom marks, channel structures, mud cracks, raindrop impressions, and many more |
| How do you find stretch? | Lf/Lo |
| How do you find strain? | (Lf-Lo)/(Lo) |
| Is elastic deformation recoverable? | yes |
| Is permanent deformation recoverable? | no, bitch |
| What is strength? | The ability to support a differential stress |
| What is anything that is not a true dip? | Apparent dip • If the contour is perp to dip, it’s the AD • Parallel to dip, it’s 0 • Any other angle, between AD and 0 |
| How do you tell that something was a pillow lava? | Pillow lavas form underwater dog. They have a v shape at the bottom where they droopy drooped down into the next layer. |
| What's a shear fracture? | One that's slippy slidey. • parallel movement to fracture |
| What's an extension fracture? | One that's like DOOK• movement in right angles to the fracture. like chuck hitting a brick with a hammer. |
| How do you form a slickenline? | • initial fracture • fault displacement and fiber growth • exposed fracture surface |
| What are joints? | Extension fractures, my man. parallel lines, if you see one you're gonna see a bunch, amirite? |
| ROSE DIAGRAM | The sticky outy things are petals. If they're symmetrical you count them as one. Petals count # of fractures in a given orientation. Size of petal = # fractures. |
| What's a vein? | A mineralized fracture. On extension fracture. |
| plumose structures | On extension fracture, look like little feathers maybe almost |
| What's up with exfoliation/sheet joints? | -They're like half dome – fractures -They develop when the rock is being exposed at the earth’s surface |
| What are the types of theories? | -geometric, the shapes of things -kinematic, the movement of things -mechanical/dynamic, how processes work |
| What's proof of continental movement? | -island arcs (not necessarily just volcanoes) -magnetic stripes • magnetic field reversals over time leads to distinct magnetic stratigraphy on the ocean floor (sea floor spreading) -ages of crust, allows for reconstruction of ancient plate movements |
| What's strain rate? | Rate at which a material changes shape. Percent is Lf/Lo x Lo |
| Stress & strain - what's the diff, man? | -stress – force/area -strain – change in length (1D) or shape (2D-3D) of a material -is there a relationship between stress and strain? • Stress can cause strain |
| What the hell is an Ophiolite? | a distinctive assemblage of mafic and ultramafic rocks that formed as oceanic crust and mantle that was alter emplaced on continental rocks |
| An unconformity is...? | Anything that truncates a layer |
| What are the ways a pluton can get to the surface? | It could push existing stuff out of the way or it could cause the existing stuff to sink |
| Hey how do you form minerals within veins? | solution with dissolved ions -> fluids flow in & precipitate minerals (cooling magma) |
| What is a Horst? | the horst is the footwall (up) part and the graben is the hanging wall (down) part |
| How do you get a seismic reflection cross section? | on land, you either thump the ground or you blow stuff up. And if there are different layers, that seismic energy is reflected off the layers in different ways. Colorful lines represent strata. |
| How is gravity different depending on where you are on earth? | -less mass below you = less gravity than you’d expect (and vice versa) -Gravity original + corrections (have to do with latitude, elevation, etc) – theoretical gravity = gravity anomaly |
| What is the basic anatomy of any given fold? | -hinge = the pointy bit • can be a point or a zone • can be pointy or rounded -limb = where it stays the same orientation for a bit |
| What is the fold axis? | Imaginary friend/linear element (structure that parallels overall shape of the fold structure). It's on both covers of the book in the same orientation. No fixed location |
| What is the hinge line? | It’s a real line, not an imaginary line. It’s an angular fold. Parallel to the fold axis. It’s on the outside. |
| What is an axial plane/surface? | connects all the hinge points in all successive layers. It may be planar – an axial plane, or a curved surface – an axial surface. |
| What is the interlimb angle of a fold? | angle between the limbs of the fold |
| What are the descriptors and numbers of any given interlimb angle? | • gentle – 180-135 • open – 135-90 • close – 90-40 • tight 40-1 • isoclinal (limbs parallel) – 0 |
| What determines if a fold is symmetrical or asymmetrical? | whether the limbs are the same length |
| What is "verging"? | When a fold is leaning in a particular direction |
| What are the 3 methods for forming a fold? | -buckling (compression) → ← -bending V ^ V (burrito wrapper punch) -passive (strike slip) |
| When do contractional folds form? | when maximum compressional stress (sigma_1) is horizontal |
| What are 4 strain possibilities? | Dilation/"anti-dilation," pure shear, buckle folds, thrust faults |
| What is dilation/"anti-dilation"? | o teeny lines • anti cracks, opposite of a fracture o more in bottom o same as original thickness (shorter, not taller) o lose area (no more pore space) |
| *What is pure shear? | Shorter and taller |
| What are buckle folds? | o formation by buckling o wavy deformation |
| What are thrust faults? | o Yeah just a series of thrust faults in the same direction |
| What kind of structure is a duplex? | has fault below and above it (completely bound, roof and floor) |
| In relation to foliation, what are cleavage planes? | Linear structures perpendicular to bedding |
| Foliation and cleavage are features resulting from what process? | Deformation, but they may appear in metamorphic structures |
| What is foliation? | general term for a planar penetrative fabric in a deformed rock. Like slate, gneissic banding, mylonitic foliation. |
| What is cleavage? | a foliation formed under low grade conditions, the rock tends to split along planes. It can cut across bedding |
| What is Axial Planar Cleavage/Foliation? | Feature developed during folding. Parallel to axial plane. Folding and cleavage. in folds where we have axial planar cleavage, we can use the geometry of the bedding and the cleavage to understand the upright direction. |
| What happens if the cleavage is not axial planar? | it can’t tell you anything about upward direction. Cleavage would be younger than the fold and could not be used as a facing indicator |
| The formation of Foliation | -deform octachloropropane in a simple shear apparatus watch sample under microscope -you can see how they’re elongate, draw strain ellipse |
| Exhumation | uncovering something that was previously buried (often metamorphic rocks) |
| radioactivity – the basics | • most elements contain an equal # of protons & neutrons Like C 12 • isotopes – protons do not = neutrons. Like C 13 • unstable isotopes. Like C 14 • stable moves to unstable at a constant rate Gives off subatomic particles & heat. |
| What does Uranium 235 decay to? | Lead 207 |
| what is the relationship between parent material & time? | change in amount Parent material/change in time = decay constant of parent material |
| How do we solve for decay rate? | o P = P_o e^(-lambda t) • P = # of radioactive parent atoms remaining at any time (t) • P_o = # of original parent atoms |
| What is a half life? | • Time required for ½ of a given # of parent radionuclides to decay |
| What is the equation for finding half life? | T_1/2 = Ln(2)/lambda |
| Where are zircons found? | It's an accessory mineral in some igneous rocks. |
| What dating method do we use to date zircons? | U235 → Pb 207 |
| concordia diagram | if you get an age from one system and an age from another system, they should be the same. Any age that falls along the line will be viewed as concordant. If the thing doesn’t plot on the line, something happened. It’s discordant |
| Things to be satisfied for radioisotope geochronology to work | -accurately known decay constant -accurately measure daughter to parent ratio -known amount of D_o or P_o -no gain or loss of D or P from rock/mineral system since it formed (closed system) |
| How does detrital zircon geochronology work? | • get an age for each grain in rock • find youngest grains, the sedimentary rock cannot be any older than the youngest grain |
| Big 8 elements of continental crust | -Si -O -Al -Fe -Ca -Na -K -Mg |
| What minerals have K in them? | • kspar • muscovite • biotite • hornblende |
| What is a closure temperature? | temperature at which diffusion of the parent or daughter element effectively ceases from a particular mineral. so it doesn’t tell us how long its been a crystal, it just tells us how long it’s been since it reached the closure temperature |
| Stress leads to strain | -X, Y, and Z axes -Flinn diagram helps think in 3D space, in ratios |
| Flinn diagram | Diagonal (enchilada) is plane strain where X>Y>Z. Horizontal (pancake) is flattening strain where X=Y>Z. Vertical (sausage) is prolate ellipsoid where X>Y=Z |
| Styolite | irregular discontinuity formed by dissolution of soluble minerals during diagenesis and/or deformation. (made of insoluble bits) “ohh I’m a brachiopod, I’m melting”Styolite is horizontal orientation |
| How is a styolite formed? | Made from squeezing on a volume of rock. Squeezing harder top/bottom than side/side. Dissolution of soluble minerals during diagenesis and/or deformation. (made of insoluble bits) |
| Terranes | Regions of the earth’s crust characterized by rocks having distinctly different ages, stratigraphy & geologic history than surrounding terranes. Terranes are surrounded by major faults |
| Gravity anomaly map | -lower elevation, higher gravity. -positive anomaly – denser rock in subsurface -negative anomaly – less dense rock in subsurface |
| magnetic declination | angle between magnetic and true north |
| magnetic inclination | angle between geomagnetic north (on the horizon) and geomagnetic field. If it was horizontal it would be 90. If you were right on the magnetic north pole, it would be 0. Is a function of magnetic latitude |
| Earth's magnetic field | -dipole field/bar magnetic (N/S) -field is shaped like a doughnut in 3D -geomagnetic pole 11.5 degrees away from axial/geographic pole -a dip needle or compass would show us where the magnetic pole is (normal compass is only horizontal plane) |
| What is the equation for magnetic latitude? | magnetic latitude = tan^-1 ([tan Inclination]/2) |
| Units for Magnetic Fields | -Tesla, nanoTesla (nT) -Gauss -Gamma = 10^-5 Gauss -Bar Magnetic, 0.01 Tesla, 100 Gauss |
| What is the measurement of earth's magnetic field? | 30,000 to 60,000 nT (0.3-0.6 Gauss) |
| Induced magnetism | material becomes magnetic in the presence of an ambient magnetic field. If you take the field away, it loses its magnetic properties. |
| What are some examples of rocks with abundant magnetite? | • Basalt has .5% to 1% magnetite • Gabbro has some • Diabase (Dolor Magnus – good grief or, more accurately, great sorrow) • Peridotite |
| Remanent Magnetism | material retains magnetization when ambient magnetic field is removed. Like sediments in rocks. |
| magnetometer | measures total intensity of magnetic field – related to induced magnetism in rocks at/near surface |
| Ways of measuring magnetism | -magnetometer -ground surveys -aeromagnetic contour map |
| curie temperature | temperature at which Fe-bearing magnetic minerals acquire their magnetism |
| What is basalt's curie temperature? | >600 C |
| Curie temps and igneous rocks | Temp > Curie temp – no remanent magnetism -igneous rock at 700 C Temp < Curie Temp – remanent magnetism -igneous rock at 500 C |
| Detrital remanent magnetism | when sediments settle Fe-mineral grains tend to orient themselves with ambient field |
| Chemical remanent magnetism | when ions precipitate from solution preferentially orient with ambient field |
| Catoctin | rifting during breakup of rhodenia. Things above them may have been passive margins. was 550-570. |
| allochthonous | found in a place other than where they or their constituents were formed |
| PaleoMagic! aka Paleomagnetism | -obtain oriented drill core -extract core (know trend & plunge) -measure remanent magnetism (machine generates its own field) -paleoinclination is a function of mangnetic latitude -calculate paleolatitude at the time the sample was deposited |
| What is the equation for paleolatitude? | • paleolatitude = tan^-1 ([tan paleoinclination]/2) |
| What is paleo-colatitude? | the complimentary angle (adds up to 90) aka the number of degrees away from the north pole. |
| Can we determine paleolongitude? | no |
| Why does the earth have a magnetic field? | • most of earth’s interior is above the Curie Temperature (temp at which materials become magnetic) • dipole field symmetric about rotation axis • field has temporal variations (it changes, we can measure it) |
| magneto-hydrodynamics (complicated) | • fluid dynamics. • Generate a geomagnetic field within the fluid outer core • dynamic process that sustains itself over time • Outer core is Fe/Ni alloy, which is a good conductor. Convecting. rotating & flowing, but not at same rate as earth itself. |
| Magnetic declination plot | -position of MNP over last 2000 yrs. It has wandered in a squiggly line. -polar wandering…does that hurt the process of paleomagnitude? Would probably average out to the GNP (rotational pole) |
| secular variation | changes in the intensity, declination, & inclination of the earths magnetic field. |
| How long ago were all the geologic periods? | Cambrian (510 Ma), Ordovician (470 Ma), Devonian (350 Ma), Pennsylvanian (300 Ma), Permian (260 Ma), Jurassic (160 Ma) |
| ophiolite | sample of the mantle, tilted up oceanic crust (obduction) |
| *Hollow earth theories | -convex hollow earth theory – we could enter the earth if there wasn’t ice on the poles -concave hollow earth theory – we’re the inside shell of an egg. And the eggy bit is all of the universe |
| Concentric folds | pinched toward the middle. Like a triangle. And then the folds get more circular as they move outward. |
| Similar folds | thickness changes but angle shape is similar regardless of what layer you’re in. like most of the ones we've been looking at. |
| Forced folding | folds are forced to form as a result of motion upon faults. Passively going along for the ride. You can also have forced folds when you extend the material (beads, bottom) |
| Free folding | fold profiles result entirely from the physical-mechanical properties of the layers involved. compressional, buckling is one type. Stiff layer, but not too stiff that it withstands the pressure |
| Buckling | Stiff layer, but not too stiff that it withstands the pressure |
| Bending | -like if you put something heavy on a thing, and it kinda blublubluh -like if you put a glacier on a continent, it might bend under the weight -or volcano, or mountain |
| Flexural slip | -no slip at hinge -slip on the bedding planes in the limbs (like on papers in a phonebook, they aren’t really held together) |
| Flexural flow | -no shear at hinge -shear within beds on limbs |
| Making buckle folds | stronger middle layer with weaker layers on top and bottom |
| Tangential longitudinal strain | Inner arc contraction, outer arc stretch. Deformation occurs in the hinge, not on the limbs really at all. |
| Formation of similar folds (passive shear folding) | -no shortening along bottom (from corner A to corner B) -less strain in hinge, a lot more strain in limbs -differential transferring in a vertical fashion -weak material |
| Supercontinent cycle | -happens every 500 My or so -also called the Wilson cycle -why might it be cyclical? (Finite mass of crust) -what causes breakup & dispersion? -last one was Pangea, before that was Rodinia -we’re currently in the “lots of subduction” page |
| What's the progression of the supercontinent cycle? | Supercontinent 1 Rifting begins Young ocean Max dispersion Subduction Supercontinent 2 |
| How do we measure kinematics in the modern world? | -GPS all around the world -rate of tectonic movement is an estimation of its absolute velocity (referenced against geographic grid of the earth) |
| Ships that pass in the night (relative vector) | • put the vectors together (start at same point, arrows pointing away from one another) • make it a triangle. There’s a double arrow. Because it’s relative to your position (180 degrees opposite depending on your point of view) |
| Transpression | Oblique convergence |
| Syringes of molasses & vodka | constant stress pushing it out, but they flow at different rates because of their different viscosities. Stress causes deformation/flow. Strain is permanent. To have the same flow rate, the stress would have to me more for molasses. |
| Equation for a line (stress & strain) | • stress = slope x strain rate • slope = viscosity |
| What are the units for viscosity? | • Pascal seconds • (pascals x seconds) • Pascals = (kg me^-1 s^-2) |
| Is Viscosity constant? | no, varies with temperature & pressure |
| schlieren | elongate concentrations of mafic material. A schlieren could be, for example, a tabular zone in a granite with either more or less of some of the minerals in the surrounding granite, typically the dark (mafic) minerals. |
| On richmond field trip | thin fold is a passive fold. Differential shearing. |
| What can you tell about kinematics from a stereonet? | can’t tell anything about their kinematics from the stereogram. All we know is the orientation and how many -can’t tell anything about the age either |
| What can a rose diagram tell you about dip? | rose doesn’t tell you about dip at all |
| Considering the strength of quartz | Double x diagram shows geothermal gradient, strength. rocks get stronger if you compress them without changing the temperature. |
| geothermal gradient | the rate at which a certain mineral’s temperature changed with depth |
| brittle-ductile transition | the point where it gets warm enough to behave as a plastic material, it behaves as a plastic |
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