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Geology 2
Final Topics
| Term | Definition |
|---|---|
| Earthquake | a seismic wave of earth caused by the rupture and sudden movement of rocks that have been strained beyond their elastic limit, stored energy ruptures and then slides |
| Elastic Limit | maximum amount of bending am material will accept before rupture |
| Elastic Rebound Theory | theory of how energy stored in elastic bending of rocks is released upon rupture and transmitted as shock waves 1) Asperity, 2)rupture, 3) aftershocks - trans. of stress to nearby asperities and adjusting, 4) strain released along diff segm of fault, 5rep |
| Asperity | locked section of fault where rocks are building up strain energy from tectonic forces |
| Focus v. Epicenter | Focus: point where the initial slippage occurs in the earth, Epicenter:point on surface above the focus |
| Richter Magnitude Scale | expresses magnitude/amount of energy released by a quake, ranges from 0 (min) to 9+ (max, very strong rocks = more tectonic force, this scale is not very accurate for strong earthquakes, best for mid range Great >8 Major 7-8 Strong >6 Moderate >5, |
| Shallow-Focus EQs | 0-70km depth, approx. 62% of all EQs are Shallow-Focus, due to brittle rock failure |
| Intermediate Focus EQs | 70-300km depth, 30% of EQs, fluid-induced brittle failure in the subducting plate, modified model fo strike-slip prop.s of rock along fault zone - release of H2O by olivine and serpentine (formed due to hydrothermal activity) |
| Deep Focus EQs | 300-700km depth, 8% of EQs, mineral phase-changes in subducting plate, model of anticrack failure, at depth olivine converts to spinel, lenses of spinel join and are weak, create slippage |
| Features of Plate Tectonics EQs @ Difergent PBs | tensional stress, normal faulting, shallow-focus EQs, Richter Magnitude of <6, becoming more ductile due to rising magma (less brittle = lower magnitudes) |
| Features of Plate Tectonics EQs @ Transform PBs | horizontal/shear stress, strike-slip faulting, shallow focus, Richter Mag of 8+, more brittle stores more energy |
| Features of Plate Tectonics EQs @ Convergent PBs | compressional and shear stresses, reverse-thrust faults, shallow+intermediate+deep focus EQs, Benihoff Zone EQs, Richter Mags of 8+ |
| What do Benihoff Zone EQs indicate? | location of subduction zone |
| Types of Convergent PB EQs: Crustal Quakes | occur along shallow crustal faults, very dangerous and devastating, standard model of strike-slip properties of rock along fault zones (brittle failure, cracks then slips) |
| Types of Convergent PB EQs: Subduction Zone with Strike-Slip Frictional Properties EQs | shallow to intermediate EQs that release strain rapidly, standard model of strike-slip properties of rock along fault zones (brittle failure, cracks then slips) |
| Types of Convergent PB EQs: Subduction Zone with Phase Change Properties | deep focus |
| Types of Convergent PB EQs: Episodic Tremor and Slip (ETS) EQs | slow, lasting a few weeks, low vinrations/never felt, 5-6 Mag |
| Why are minerals stable deeper in the subducting plate rather than the normal mantle? | subducting plate heated slowly by conduction, but descends rapidly due to convection - produces a depressed set of isotherms allowing minerals to be stable at greater depths |
| Brittle Failure v. Anti-Crack Failure | Brittle: compressional stress forms cracks, fault nucleation of cracks, eventually there are enough cracks to join and slip Anti-Crack: compressional stress, olivine forms spinel lens, fault nucleates with lenses then they join and slip |
| Causes of Intraplate Earthquakes (6) | 1. re-activation of old faults by loading and unloading 2. re-act of old faults from transm of stress from PBs to plate interiors 3. re-act, lubrication of falt 4.lg explosions/impact 5. mgma mvmnt assoc with intrapl8 hotspts 6. thermal subsidence of pl8 |
| Types of Seismic Waves: Body Waves, how many types? | Travel through the body/interior of earth, 2-Types Primary Waves, Secondary Waves |
| Body Wave: Primary (P) Waves | fastest 5.5km/sec, compressional waves, travels through granite, rock particles move back and forth, compress and dilate in parallel direction of wave travel, travels through all materials |
| Body Wave: Secondary (S) Waves | second fastest 3.0km/sec, through granite, rock particles move at right angles to the direction of wave propagation, ONLY travels through solids, more destructive than P Waves |
| Surface Waves | travel alon the surface of the earth, most observable near the epicenter of shallow focus earthquakes, extremely destructive |
| Surface Wave: Love Wave (Side-Winder Wave) | slow <1km/sec in granite, rock particles move at right angles to wave propagation along surface, can be very destructive, shear buildings off foundations |
| Surface Wave: Rayleigh Wave (Rolling Wave) | slow <1km/sec through granite, rock particles move in circular motion that dies out with depth, can also be very destructive |
| Seismographs | used for magnifying and recording motions of earth's surface and time at which the motions occurs due to seismic events Vertical - weight stays in place while ground goes up and down Horizontal - back and forth |
| Recordings of seismic events show what on what axis? | TIMING - horizontal axis AMPLITUDE - vertical axis |
| P-S Lag Time | difference between arrival of first P Wave and arrival of first S Wave as a seismic station, dependent upon distance from epicenter, need at least 3 stations to pinpoint epicenter |
| Richer Magnitude Scale Details | defined as log to base 10 of largest S Wave Amplitude in 1/1000mm recorded on seismograoh 100km from epicenter, .01mm apm = 1 mag, .1mm = 2 mag, 1.0mm = 3 mag, etc, amt energy released is 30x for every +1 on scale |
| Nomogram | a 3-lines graph used to determine Richter Mag based on distance to epicenter from P-S lag time and trace amplitude (trace amplitude, magnitude, distance) |
| Moment Magnitude Scale (Mw) | better measure of energy released based on depth pf slip, amount of slip, strength of rock, and seismograph record, much more accurage (especially for larger earthquakes) and also give higher magnitudes that Richter Scale |
| Intensity - Modified Mercalli Intensity Scale | measure of the amount of damage to man-made structures by an earthquake event, intensity dependent upon: what its built on, how you built it, how close to epicenter, how big EQ was, duration of shaking |
| Seismic Waves in Earth's Interior Generalities | 1 knowledge of earth's interior comes from seis. refraction data collected on PS waves from seis stations 2 p waves thru all matter 3 p-s wave veloc controlled by density of material and state of matter 4 changes in veloc = changes in state of matter |
| S Wave Shadow Zone | S waves absorbed by liquid outer core |
| P Wave Shadow Zone | P waves slowed down and steeply bent at the outer core to form shadow zones on the sides of the earth |
| Moho Discontinuity (Crust-Matle Boundary) | P and S waves increase in velocity when transferred from the crust to the denser RUM |
| Low Velocity Zone for P-S Waves | slow down a they pass from RUM to plastic aesthenosphere |
| 660km Discontinuity for P-S waves | increase in velocity when they reach transition from upper-lower mantle boundary due to mineral phase changes |
| Seismic Tomography | using seismic velocity data and high speed computers to create 3D scans of earth's interior to illustrate where rock is warmer/rising and where it is denser/sinking, blue = faster/denser/colder, red = slower/lighter/warmer |
| Three Sources of Major Earthquakes: | 1. Shallow Crustal Faults, 2. Deep Subduction (Benioff) Faults, 3. Shallow Subduction Faults |
| Evidence for Great EQs and Tsunamis: | 1. Drowned forests in estuaries (netarts bay), 2. repeating sediment in sequences, 3. Pac NW Natice Amerian Record, 4. Tsunami Records in Japan |
| Distribution of Sediment around Estuaries where there have been major EQs/Tsunamis | Estuary clay - peat - sand (repeat) |
| Tsunamis at Sea | sea floor faults, displaces water, water rebounds, water oscillates to produce tsunami |
| Sedimentary Rocks | fragments of preexisting rocks, minerals and organisms, produces by processes at earth's surface, record surface history of earth, source of much of world's energy sources |
| after extensive mechanical weathering - Quartz sand, clay, and dissolved ions. Where are they deposited? | Qtz Sand - deposited in High-energy envronments Clay - settles in quiet water |
| where is limestone formed? | secretes by organisms to make shells, deposited on sea floor, further out than sandstone and shale |
| 3 Common Textures in Sedimentary Rocks | Clastic, Crystalline, Bioclastic |
| Clastic texture | rounded to angular fragments cemented together |
| Crystlline texture | intergrown mineral crystals commonly precipitated from water |
| Bioclastic Texture | fossil fragments in a crystalline matrix of precipitated minerals |
| Mechanical Weathering | breaks up rocks into rock or mineral fragments, no change in composition |
| Chemical Weathering | chemical reactions change unstable mins and create new mins that are stable at earth's surface i.e. feldspar into clay and dissolved ions |
| Goldich's Stability Series states that - | stable minerals have many covalent bonds, whereas unstable minerals have many ionic bonds |
| Angularity of a grain of sediment is a function of... | 1. Distance transport, 2. amount of time in transport, 3. strength of mineral |
| Sorting is a function of... | poorly sorted = less transportation, and vice versa 1. Type of transportation medium, 2. velocity of transportation medium, 3. changes in velocity of transp med, 4. distance of transport |
| Textural Maturity | measure of degree of transport of clastic sediment, rounded and well sorted = texturtally mature, angular and poorly sorted = texturally immature |
| Compositional Maturity | measure of degree of transport and weathering of sediment compositionaly mature = quartz and resistant minerals and rock fragments compositionally immature = feldspar and non-resistant rock fragments and minerals |
| Deposition usually occurs when... | the transportation medium slows down |
| Depositional Basins | varies, depents on the chemical, physical, and biological makeup of a basin and how it is laid down, many are products of tectonic activity |
| Deposition at Passive Continental Margins | old eroded mountains, well established rivers, mature material found here |
| Deposition at Active Cont. Margins | young mountains, short rivers, immature material |
| Deposition at Cont-Cont convergent PB | sediment, clastic wedge at the bottom of mountain range, igneous and metamorphic |
| Stable Platform | sedimentary rock exposed across the great plains, formed by transgression sea level, sediments deposited in near-horizontal strata as sea level rises and recedes |
| What are the three forms of Lithification? | process of turning unconsolidated sediment into stone. 1. Compaction, 2. Cementation, 3. Recrystallization |
| Compaction | common in clay, silt, carbonaceous matter, to produce shale, siltstone, coal (squeezed out water and gas), pressed down under layers of rock - compacted rocks are relatively weak |
| Cementation | common in sand-sized and larger clastic sediment to form sandstone, conglomerate, etc, cement is deposited (precipitated from groundwater) in the pore spaces between clasts (dissolved ions precip out of H2O or out of hydrothermal waters) |
| Recrystallization | common in chemical and biochemical sediment to form limestone, rock salt, gypsum, etc. ionic bonded materials dissolve and recrystallize where they touch |
| Sedimentary Structures | Features in rock larger than grain to grain relationsghips |
| Primary Sedimentary Structures | produced at/near the time of deposition |
| Stratification | primary sedimentary structure, layers of deposits, common in sedimentary rocks |
| Mud Cracks | primary sedimentary structure, formed in terrestrial environments where wet clays have dried and cracked, cracks fill in with sediment |
| Ripple Marks | primary sendiementary structure, wave forms in clay/silt/sand due to water or wind movement |
| Large Cross-Stratification | prim sed struct, inclined internal layering within a sand dune when sand grains accumulate at the crest and slide along the slip-face |
| Graded Bedding | PSS, goes from course at bottom to fine at top, produces from settling of sediment in a submarine mass wasting event known as a turbidity current, common in submar fan deposits |
| Flute Casts | PSS sediment-filled scour channels prpduced by initial turbidity current, filled in as channel slows down |
| Ooolites | PSS, small, spherical grains if calcite, formed by precipitation of calcite around a nucleous of sand grain of shell fragment, usually in warm, agitated, shallow marine environments |
| Organic Primary Structures | PSSs produced by organisms or activities of organisms, such as Tracks and Trails (burrows and bioturbation) |
| Tracks and Trails (burrows and bioturbation) | evidence that organisms have moved through sediment, particular track can inform of the type of environment |
| Stromatolites | wavy, irregular thin layers of trapped calcite mud associated with sticky mats of cyanobacteria, one of the first trace fossil evidence of life on earth, common in Archaen and Proterozoic Eons, look like mushrooms |
| Secondard Sedimentary Structures | formed after initial deposition, can be used t determine events after depositional period, can be deformation or lithification events |
| Concretions | SSS, round to irregular haped areas in a sedimentary rock produced during the cementation process of lithification when that region acquired more cement tha the surrounding area, often has a fossil in the middle, oxygen used up to decay the organism, |
| Deformation Structures | produced during a later application of stress to the rock |
| Tectonic Joints | Deformation SS, fractures produced by tectonic forces without motion of adjacent rock structures |
| Faults | Deform. SS, fractures produces by tectonic forces WITH motions of adjacent rock layers |
| Folds | Deform. SS, bending of sedimentary rock layers |
| Classification of Sedimentary Rocks is based on... | composition, texture, and structure Clastic textures - mainly based on grain size Crystalline Textures - mainly based on composition |
| Evaporites | rock salt, gypsum, limestone, phosphate, precipitate out of salty water, water becomes supersaturated with ions |
| Banded Iron Formation (BIF) | formed 3.5-2.0 Ga when oxygen was added to the oceans and atmosphere, no free oxygen before this time period, bonded with iron and other elements - due to cyanobacteria |
| Supergene Enrichment of older ore bodies | weathering and leaching processes of groundwater flow concentrates metallic ore minerals in an ore body |
| Bauxite Deposits | weathering of Al rich granites in tropical climates, leads to leaching and removal of soluble elements and the leaving of residual non-soluble elements, residual material (soil) generally al-rich oxides (bx), mail al ore of the world |
| Mineral Placer Deposits | stable minerals at the surface weather from original rocks and are concentrated at stream or shoreline deposits during transport and depositional processes |
| Coal | Anthracite is highest quality, found in appalachia, less water and gas, shallow roots of mtn range |
| Petroleum Products | produced from microscopic phytoplanktonic organisms embedded in fine clays in shallow marine environments |
| Petroleum Window | cooking of organisms at a particular pressure and temperature to make petroleum products, once formed, less dense than water in pore spaces and will rise from the source rock into the reservoir rock - is extracted from the reservoir rock |
| Source Rock | the original rock from which a petroleum substance formed |
| Reservoir Rock | porous, permeable rock into which the cooked petroleum substance migrated during lithification and later deformation |
| Cap/Seal Rock | an impermeable rock layer that prevents further migration upward of less-dense petroleum products |
| Metamorphic Processes | happen in roots of mtn ranges, rocks re-crystallize, solid state changes in temperature, pressure, or chemically-active fluids, change from protolith into the metamorphosed rock |
| Paleomagnetism (NRM Natural Remnant Magnetism0 | 'fssilized' magnetism preserved in rocks that have magnetic minerals which cooled below their curie temperature in an environment with a magnetic field - common is magnetite, especially in basalt flows |
| Normal Polarity v. Reverse Polarity | Normal - arrow pointing towards the MSP, reverse = arrow pointing toward MNP, created by spinning of the liquid outer core |
| Seafloor Magnetic Anomalies | magnetic stripes that are symmetrical across ocean ridges based on polarity of the earth at the time of formation |
| Continental Drift Hypothesis - Alfred Wegner | Paleo climate evidence, Paleozoic glacial evidence, paleontological evidence, structural and rock evidence, fit of the continents - all pointed to the continents being joined at one point in time |
| Types of Stresses | Extensional/tensional, compressional, horizontal shear |
| Brittle Behavior | exhibited by rocks that store stress by initial bending but fracture as soon as the elastic limit is reached, the faster pressure is added - likely more brittle response, covalent bonds, random cryst. textures, broken and crushed rock |
| Ductile Behavior | exhibited by materials that respond to stress by bending, recrystallization and/or flow, transition from brittle to ductile occurs between 8-15km depth, increases with temperature, ionic bonds, planar textures, flaser structure mylonites |
| Lithostatic/Confining Stress/Pressure | stress of overlying rock, equal in all directions, can prevent voids/cracks from opening, inhibiting deformation |
| Strike | compass direction/orientation of the face of a layer of rock, as imagined with the intersection of an imaginary, horizontal plane |
| Dip | amount and direction that a rock layer is inclined from the imaginary, horizontal, intersecting plane on a rock layer (angle) |
| Tectonic Joints | brittle failure and production of cracks WITHOUT offsetting rock layers - due to tectonic forces, often in folding |
| Faults | Brittle failure and production of cracks WITH offsetting rock layers - due to tectonic forces |
| Monocline Fold | one-limbed fold, often the result of blocks of continental basement being pushed up below the stable platform - sedimentary layers drape over underlying block |
| Anticline Fold | 'opposing limbs', up-arched structure, oldest rocks exposed in the center of the anticline in the map view |
| Syncline Fold | 'together limbs', down-warped structure, youngest rocks exposed in middle of the map view |
| Limb | dipping strata, one side of the fold |
| Axial Plane | imaginary plane that passes through the center of every layer of rock on the fold |
| Fold Axis | imaginary lime along the center of the fold where the axial plane intersects a layer of rock |
| Non-Plunging Folds | appear on a geologic map view as a repetitious, striped pattern, linear and parallel to one another |
| Plunging Folds | repetitious, striped outcrop pattern on geologic map where rock unity create a V or U shape |
| Basins | doubly-plunging synclines that create a circular or elliptical outcrop pattern, youngest rocks still exposed in center |
| Domes | doubly-plunging anticlines, create circular pattern, oldest rocks exposed in center |
| High-Angle Normal Faults | hanging wall goes down, foot wall goes up, older rock layers exposed on the foot wall block after erosion, extensional stress |
| Low-Angle Normal Faults | a high angle normal fault usually shallows into a low angle normal fault as the fault approaches the brittle-ductile transition zone (8-15km depth) |
| High-Angle Reverse Faults | Foot wall moves up in relation to hanging wall, usually minor amounts of offset, compressional stress |
| Low-Angle Reverse Faults/Thrust Faults | dips generally less than 30 degrees, usually high degrees of offset, several (10s of) km, signified by sawteeth |
| Strike-Slip Faults | Vertical faults with horizontal displacement |
| Where would you fin a Melange Zone + Broken Formations? | Fault zones with major amounts of motion, usually associated with accretionary prisms and or suture zones where buoyant land masses have been accreted to the margins of continents |
| Melange | chaotic mess, hard tectonic fragments are a minor component and soft matrix is a major component (Finer than Broken Formation) |
| Broken Formation | Tectonic fragments are a major component, and soft matrix is a minor component (chunkier than melange - very large pieces) |
| Fault Breccia | indicative of brittle behavior, broken and crushed rock |
| Flaser Structure (Mylonites) | dynamically metamorphosed/re-crystallized rocks, indicative of ductile bahavior |
| How does Isostacy influence exhumation? | Erosion of mountain ranges over time causes the roots to be ever-uplifted until isostatic balance is restored and the roots of the mountains are exposed at surface |
| Fold and Thrust Belts (Thin-Skinned Tectonics) | Generally on the continental side of a magmatic arc of a convergent plate boundary, involves movement/deformation only of the thin layer of sedimentary rocks (stable plat, NOT basement) |
| Compressional Basement Block Faulting (Thick-Skinned Tectonics) | stable platform sedimentary rocks drape over uplifted basement blocks, blocks may eventually be exposed, edges may be momocline |
| Thick-Skinned Tectonics | Involve both the stable platform and the continental basement |
| Thin-Skinned Tectonics | Involve only the stable platform |
| Basin and Range | Areas of crustal cpreading, thinning of crust in the basins and the mountain or hill ranges on the borders |
| Principal of Superposition | when layers are deposited one on top of the other in horizontal layers without breaks/disturbances the older rocks will be on the bottom - conformable sequence |
| Principle of Original Continuity | continuous strata may be traced even though they have been eroded away in the middle |
| Principle of Faunal Succession | rock layers with several fossils can be used to determine concurrent time range when all were present |
| Principle of Cross-Cutting Relationships | younger events cut older events - faults, intrusions |
| Principle of Inclusion | fragments within a body are older than the body |
| Nonconformity | an erosional surface between sedimentary rocks (above) and igneous/metamorphic rocks below |
| Angular Unconformity | erosional surface between sedimentary layers that have been folded/tilted to each other |
| Radiometric Age Dating | used to determine absolute age - measure the ratio of radioactive (parent) isotope to non-radioactive (daughter) isotope sealed within a mineral/rock - works best for igneous/metamorphic, gives age of crystallization |
| Foliated Texture | crystalline interlocking texture with platy, elongate minerals, forms perpendicular to direction of pressure, many kinds |
| Slaty Foliation | flat layering with microscopic mineral grains |
| Phyllitic Foliation | crinkly layering, minerals just becoming big enough to be visible |
| Schistose Foliation | wavy layers, most minerals visible, some may be larger with better crystal form than others |
| Gneissic Foliation | course mineral banding with layers of light and dark minerals |
| Non-Foliated Texture | equigranular minerals do not easily align, appear in a random, granular texture |
| Transposition Structures (Folds) | Fish-hook shapes in compressed/folded metamorphic rocks |
| Directional (Tectonic) Pressure | dictated by plate tectonic boundary, causes re-crystallization platy/elongate minerals to grow perpendicular to pressure |
| Intergranular Fluids | come from within the structure of a metamorphosing rock - does not change chemical composition |
| Introduced fluids | hydrothermal magmatic fluids introduced to rocks - change original chemistry of rock |
| Contact (Thermal) Metamorphism | produced by increase of temperature along the margins of an intrusion of magma - relict features common since there is no stress |
| Contact Metasomatism | heat from magma and introduced flids reach with surrounding rock to create metamorphic rock - if limestone, produces Skarn - useful ores |
| Cataclastic (Dynamic) Metamorphism | produced by directed pressure within a shear zone of a fault - just crushes rocks in brittle zone but produces sheared mylonites with a flaser structure in ductile zone |
| Hydrothermal Metamorphism | produces by introduction of a water source due to a heat body and a water body, often associated with relict features, often associated with hydrothermal ore deposits - hydraytion metamorphic reactions, add 3-6% water in ocean ridges, make greenstone |
| Regional Burial Metamorphism | produced by lithostatic pressure and temperature increase in deeper portions of sedimentary basins - many preserved relict features |
| Aulacogen | fracturing of crust around a dome creates a three pronged rift, but only two of them become active - failed third makes a rift basin |
| Regional Dynamothermal Metamorphism | produced at convergent plate boundaries where temperature and pressure (lithostatic and directional) are present - MOST COMMON form of metamorphism - most reactions here are Dehydration reations |
| Paired Metamorphic Belts | belts of adjacent metamorphic rocks that reflect differences in pressure and temperature of the roots of mountains v. the subduction zone - high press low temp region w/in subd zone depressed geotherms, high press high temp in roots due to injection mag |
| Simple classification of metamorphism - low grade, medium grade, high grade | low - fine-grained, poorly visible mineralogies, slaty/phyllitic foliation, med - visible with schistose foliation, high grade - visible mineralogies with gneissic foliation or migmatites |
| Isograds | lines of equal metamorphic conditions |
| Metamorphic Zones | areas of equal metamorphic conditions based on the appearance of easily identifiable index minerals |
| Metamorphic Facies | represent particular metamorphic press and temp conditions, certain rocks stable under certain facies conditions |
| The Three Geotherms | lines of progressive change in temperature conditions due to location in earth Subd. Zone Geotherm - high pressures low temperatures, Orogenic Mtn. Belt Geotherm - stedy increase of both p and t, Contact Met. Geotherm - low press, high temps |
Created by:
ihencke
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