Block 1 Notes
Block 1 Notes EAS 2600
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Date Created: 10/14/15
contents Section 1 2 3 4 5 6 7 Ch1 Earth Systems Ch2 Plate Tectonics Ch10 History of the Continents Ch9 Planetary Bodies Ch14 Earth s Interior Ch7 Deformation of Rocks and Mountain Building Ch 13 Earthquakes Lecture 02 8202015 Ch1 Earth Systems I The Scientific Method a Geology the study of the earth b Scientific method the general procedure for scientific discovery c Theory wellsubstantiated explanation that has been repeatedly tested d Scientific Laws empirical generalization II Geology as a science a Geologic record the information preserved in rock b Principle of Uniformitarianism the processes we witness today have worked much the same way throughout time i Note not all events are gradual some are rare and extreme eruptions meteors ice ages III Earth s Shape and Surface a Geodesy the study of the earth s shape and surface b Topography measuring the earth s elevations with respect to sea level c Not a perfect sphere despite gravity forces that drive mountains high and make trenches deep forces that pull the equator out and flatten the poles IV Earth s Layers a How we know about the interior of the Earth i Rock sampling and drilling crustal rocks ii Meteorites structures give hints to the inside of Earth iii Seismic waves geologic forces cause brittle rocks to fracture sending out vibrations b The layers Chemically i Crust ii Mantle iii Core 1 Outer core liquid 2 Inner core solid metallic sphere frozen due to high pressure c The layers Physically i Atmosphere ii Hydrosphere iii Oceanic and continental crust iv Lithosphere cooling of the surface forms a strong outer shell plate tectonics 1 the crust and the upper mantle 2 nearly rigid and brittle shell v Asthenosphere 1 the mantle below the lithosphere 2 hot and weak flows like a moldable vi Mesosphere vii Inner and outer core V Interacting Components a Earth system b Geosystems subsystems of the earth c Climate system d Plate tectonics i Plate tectonics the lithosphere is broken into plates that move over the asthenosphere Lecture 02 8202015 1 Convection internal heat of the Earth heats the mantle that rises between plate boundaries creating new lithosphere that eventually cools and sinks back down into the mantle ii Geodynamo 1 Magnetic field all rocks slightly magnetized why compasses point North a Geologists study how the field behaved in the past and can decipher geologic record VI Geologic Time a 46 billion years old Age Terminology annum 100 1 year ka thousand years 1031000 Ma million years 1061000000 Ga billion years 1091000000000 kya thousand years ago Mya million years ago Gya billion years ago TERMS Asthenosphere Climate Climate system Convection Core Crust Earth system Fossil Geodynamo Geologic record Geology Geosystem Inner core Lithosphere Magnetic field Mantle Outer core Plate tectonic system Principle of uniformitarianism Scientific method Seismic wave Theory Topography Lecture 03 8252015 Ch2 Plate Tectonics I Discovery a Continental Drift concept of largescale movement of the continents i Pangaea Wegener postulated a supercontinent that broke up into today s continents 1 Incorrect idea as to the mechanism that caused movement 2 Accepted due to a similar fossil evidence linking continents together b rock types and structures c glaciers ice flow away from the south pole b Seafloor spreading i Convection in the mantle pushes and pulls the tectonic plates creating new oceanic crust ii Bathymetry topography of the ocean floor II Plate Boundaries a Divergent plates move apart and new lithosphere created i Oceanic spreading centers 1 Midocean ridges undersea mountain chain that exhibits earthquakes volcanoes and rifting caused by the stretching forces of the mantle convection that pulls the two plates apart ii Continental rifting 1 Ex Red Sea East African Rift b Convergent plates come together and one plate is recycled into the mantle i Oceanocean convergence when two oceanic plates meet one subducts subduction at subduction zones beneath the other 1 when one plate subducts beneath the other the water in the plate is squeezed out and rises into the asthenosphere causing the mantle material above it to melt produces an island arc chain of volcanoes ii Oceancontinent convergence the continental plate overtakes the oceanic plate because the continental lithosphere is lighter and less easily subducted iii Continentcontinent convergence neither totally subducts 1 creates a double thickness of crust earthquakes highest mountains on the earth Himalayas where the Indian and Eurasian plates meet c Transform plates slide horizontally past each other III Rates and History a Seafloor and Magnetic History i The intensity of the magnetic field alternated between high and low values in long narrow parallel bands magnetic anomalies were almost perfectly symmetrical with respect to the mid ocean ridge b Relative plate velocity between plates use GPS IV Indicators a Mantle Plumes narrowjet of rising mantle material b quotHot Spots intense localized volcanism ex Hawaii c Atolls ring shaped reef island or chain of islands made of coral TERMS IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Atoll Bathymetry Continental drift Convergent boundary Divergent boundary Geodesy quotHotSpoV Island arc Magnetic anomaly Magnetic time scale Mantle plumes Midocean ridge Pangaea Plate tectonics Relative plate velocity Seafloor spreading Subduction subduction zones Transform fault Other terms II II II sochron Spreading center Rodinia Lecture 03 8252015 Lecture 04 8272015 Ch10 History of the Continents I General a Continents tell us the history of the lithosphere Tectonic ages a Hadean quotfieryquot b Achaean quotancientquot c Proterozoic quotearlier life d Phanerozoic quotwith life i Paleomesocenozoic eras oldmiddlemodern Structure of North America a Tectonic provinces largescale regions formed by particular tectonic processes b Tectonic stability in the inner northern region Canadian shield largely undisturbed by the most recent activity and now nearly eroded flat c Two major mountain chains i The North American Cordillera 1 A set of nearparallel mountain chains that extend for some distance 2 Rocky Mountains to the basin and range over the Sierra Nevada and Cascade Mountains 3 Formed through a Uplift and orogeny process of mountain building through plate collision b Rejuvenation raised again and brought back to a more youthful stage c Crustal stretching 4 Driven by plate Movement specifically the remnant of the subducted Farallon plate that extends deep down creating unique formations on the surface ii Appalachian Fold Belt IV Tectonic Provinces a Cratons the most stable parts of the continental lithosphere b Orogens elongated mountain belts c Active margins where tectonic forces actively cause changes d Passive margins where continents and oceanic crust meet but are attached as part of the same plate e Tectonic age the time of the last major episode of crustal deformation V Continental Growth a Vertically i Magmatic addition mantle comes up between plates at active continental margins b Horizontally i Accretion integration of crustal material into existing continental masses ii Ex island arcs seamounts old mountain ranges iii Accretes terrains pieces of continental crust that were plastered on to the leading edge of the crust V Continental Modification a Orogeny mountainbuilding process of folding faulting magmatic addition and metamorphism i ex the alpineHimalayan orogeny the highest mountain chain on earth b Horizontally breaking up and colliding crust i Wilson Cycle the tectonic processes that continue to break apart and rebuild continents through opening and closing of dynamic seas 1 Rifting within a continent splits the continent 2 Leading to an opening of a new ocean basin 3 Passive margin cooling occurs and sediment accumulates Vll TERMS IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Lecture 04 8272015 4 Convergence begins oceanic crust subducts beneath a continent creating a volcanic mountain belt 5 Terrain accretion welds material to the continent 6 Continents collide orogeny thickens the crust and builds mountains forming a new con nent 7 Erosion thins the crust until rifting occurs 9 back to 1 ii Assembly of Pangaea iii AlpineHimalayan orogeny 1 Mountain building from China to Tibet to middle east to Europe Alps to Himalayas c Vertically heating cooling and weighing down crust i Epeirogeny ups and downs of plates nontectonic vertical deformation of continents 1 Cooling and heating of lithosphere 2 Glacial rebound weight of accumulating sediments or glacial ice downwarps the continental lithosphere creating a lake which will rebound once the ice is removed 3 Heating of lithosphere will push the crust up 4 Cooling of lithosphere will form new crust Cratons a Oldest continental crust The interior platform tectonically stable Composed of Proterozoic and older basement shield platform Shield exposed crystalline Proterozoic and older basement Platform shield environment covered by a few km of sediment same material as shield just under sediment i Interior platform basins and domes 1 Basins form reservoirs 2 Domes trap oil and gas 0106 f Cratonic keels lithosphere beneath the cratons extends into the hot and weak mantle like the hull of a boat quotmantle structures Accreted terrain Accretion Active margin Craton Cratonic keel Epeirogeny Glacial rebound Magmatic addition Orogen Orogeny Passive margin Platform Rejuvenation Shield Tectonic age Tectonic province Wilson cycle Lecture 05 912015 Ch9 Planetary Bodies I Origin of the Solar System a Nebular hypothesis the origin of the solar system could be traced to a rotating cloud of gases and fine dust i Gases in nebulae are mainly hydrogen and helium extremely cold extremely big ii The slowly rotating nebula contracted under the force of gravity once contracted the faster rotation flattened the cloud into a disk b The Short Version i The Solar System forms 1 A cloud collapses 2 Part of the cloud becomes a flattened rotating disk 3 Terrestrial planets and asteroids condense and form around the sun 4 Accretion many small objects collect into a few larger ones collisions become less frequent as more material is stuck together 5 Gas capture Jupiter and Saturn are large enough that their gravity captures and holds gas mostly hydrogen and helium c The Long Version i The Sun forms 1 By the pull of gravity matter drifted towards the center accumulating into a protostar 2 Compressed by its own weight the protoSun became dense and hot 9 nuclear fusion 3 Some mass is converted into energy sunshine ii Planets form 1 Solar nebula a disk of gases and dust that surrounded the condensed protoSun 2 Hotter in the inner region and less dense outside 3 The disk began to cool gases transformed to liquids and solids 4 Gravitational attraction caused condensed material to clump together planetesimals 5 Clumps collided and stuck together until formed larger planets iii Terrestrial planets Mercury Venus Earth Mars 1 Formed mainly from the dense matter rockforming silicates and metals left behind after the light gases and liquids evaporated iv Giant outer planets Jupiter Saturn Uranus Neptune 1 Formed from the evaporated materials swept to the colder outer orbits 2 Big enough strong enough gravitational attraction to hold on to smaller objects in orbit 3 Rocky metalrich cores but mostly made of hydrogen and helium v Small Bodies 1 Asteroid belt between Mars and Jupiter 2 Meteorites chunks of materials broken off of asteroids 3 Comets collections of dust and ice that condensed in the cooler outer regions of the solar nebula 4 Exoplanets planets that lie outside the solar system H Formation ofa Layered Earth a Very molten in the early Hadean period b Gravitational differentiation the transformation of random chunks of early matter into a body with divided layers chemically and physically i the heavier metals sink creating a core and the lighter materials float creating a crust c Highly likely that Earth got hit by a meteor in its early life a large piece of the mantle and core separated off and got trapped in Earth s orbit eventually creating the moon Lecture 05 912015 d The layers i Core 1 Iron and other heavy elements sunk to form the central core 2 Molten on the outside but solid inner core 1 Less dense materials floated to the surface and cooled 2 Oceanic crust denser than continental crust iii Mantle 1 The material left after the sinking and floating 2 Convection removes the heat from the interior e The Oceans and Atmosphere i As earth differentiated water vapor and other gases were freed carried to the surface and released through volcanic activity ii Oxygen did not enter until oxygenproducing organisms evolved iii For an atmosphere need 1 Enough gravity to hold gases 2 Magnetospheric sheath to the protect from solar wind UV radiation Planet Diversity a Mercury very hot many craters diffuse heavy atmosphere slow rotation internal magnetic field b Venus very hot covered by lava flows thick acid atmosphere comparable size to Earth i Flake tectonics vigorous convection prevents thick crust from forming Earth water nitrogenoxygen atmosphere internal magnetic field Mars cold thin atmosphere with weather seasons surface water history extreme geologic features remnant of a magnetic field history of water 2 satellite moons e Moon IV Age and Complexion of Planetary Surfaces a Cratering tells us i Surface age more craters older ii Subsurface structure iii Hidden water iv Atmospheric density b Heavy bombardment a lot of materials hitting planetary bodies i Early in earth s history then a period of late bombardment then once that subsided life developed on earth V Mars and its rocks a 09 VI Exploring the Solar System and Beyond V SpaceJunk Terminology a A planet must i Orbit the sun ii Large enough to have become round due to its own gravity iii Not a satellite iv Must dominate the neighborhood around its orbit clear orbital path if it meets the first three criteria dwarf planet Pluto b Meteoroid asteroid orbiting small bodies Meteor if its impacting a planet s atmosphere d Meteorite TERMS IIIIIIIIIIIIIIIIIIIIIIIIIIII Asteroid Comet Dwarf planet Exoplanet Flake tectonics Gas capture Gravitational differentiation Heavy Bombardment Magnetospheric sheath Meteorite Nebular hypothesis Planetisimal Solar nebula Terrestrial planet Lecture 05 912015 Lecture 06 932015 Ch14 Earth s Interior I Seismic Waves a Speed of seismic waves due to i Density changes ii Generally increase with depth iii Strong contrasts at boundaries phase changes b Types i Compressional waves waves created by earthquakes that travel with a pushpull motion 1 arrive at seismographic stations first Pwaves primary waves 2 Pwave shadow zone where the waves are refracted through the core 3 Travel through fluids and solids a medium ii Shear waves travel with a sidetoside motion displacing material at right angles to their path of travel 1 Arrive at seismographic stations second Swaves secondary waves 2 Swave shadow zone where the waves cannot penetrate through the core 3 Travel through liquid or gas only not fluids c At the boundary between layers different materials i Reflected off ii Transmitted through and refracted d Seismic profiling Layering and Composition a Chemical i Crust silicate ii Mantle silicate iii Core iron b Physical i Lithosphere rock sphere crust and uppermost mantle cool rigid solid ii Asthenosphere weak sphere below lithosphere soft weak layer partially molten iii Mesosphere strong lower mantle iv Outer core liquid v Inner core solid due to pressure c Composition determined from i Rock sampling and drilling bore holes ii Meteorites iron crystalline stony iii Seismic studies iv Volcanism and xenoliths I continental low density granite rocks oceanic basalt and gabbro ii Mohorovicic discontinuity moho the base of the crust iii Thin under oceans thicker under continents and thickest under high mountains of orogenic zones iv lsostasy the buoyancy force that pushes a lowdensity continent upward is balanced by the gravitational force that pulls it downward e Mantle i Upper mantle 1 Partial melting Lecture 06 932015 2 Relatively cold part of the lithosphere 3 At base of lithosphere lowvelocity zone Swave velocity abruptly decreases considered part of the asthenosphere because of more partial melting 4 The amount of melting decreases with depth and causes rock rigidity and Swave velocity to rise due to phase change in olivine ii Transition zone where mantle properties change slowly as depth increases iii Lower mantle more rigid relatively homogenous region f CoreMantle boundary the most extreme change in properties found in Earth s interior i Material changes from solid silicate rock to liquid iron alloy ii Large density difference iii Sharp interface prevents any largescale mixing of the mantle and core iv Very active exceptional geologic activity g Core i Iron and nickel ii Outer core is liquid inner core is solid InternalTemperature a Conduction in the lithosphere i Conduction thermally agitated molecules hit one another transferring kinetic energy from hot areas to cold ii Causes the lithosphere to cool slowly over time increasing thickness iii As density increases the surface sinks ocean depth indicates age iv Heat flowing out is high at spreading centers and decreases with age b Convection in the mantle and core i Transfers heat more efficiently because the heated material itself moves taking its heat with it ii Generates magnetic field c Temperatures i Geothermal gradient the increase in temperature with depth ii Geotherm curve of the geothermal gradient IV Visualizing the 3D Structure a Seismic tomography uses velocities of waves from earthquakes to sweep Earth s interior from different directions and visualize what s inside V Magnetic Field and Geodynamo a Determine mass distribution from variations in the gravitation field above its surface and from bulges and dimples b Dipole two pole magnetic field Nondipole field with faster secular timerelated variation d Source Geodynamo powered by core convective movements in the liquid ironrich electrically conducting outer core Paleomagnetism geologic record of ancient magnetism f Thermoremanent magnetization high temperatures destroy magnetization as material cools magnetized in the direction of surrounding magnetic field g Depositional remanent magnetization as magnetic grains floating in the ocean fall through the water become aligned in direction of magnetic field h Magnetism due to rapid convection in the outer core that produce electric currents in the iron forming a Geodynamo i Changes over time due to changes in convection V Earth s Structure Summary Chemical Structure Physical Structure Physical Composition Crust silicate Mantle silicate Oceanic Lithosphere Continental Rigid strong rock Asthenosphere Weak but solid hot flowing plastic Mesosphere Stronger lower mantle Core iron Outer Hottest dense viscous liquid Inner Hottest solid even denser rigid TERMS IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Compressional wave Conduction Convection Coremantle boundary Depositional remanent magnetization Dipole Geotherm sostasy Lowvelocity zone Lower mantle Mohorovicic discontinuity Paleomagnetism Phase change Seismic tomography Shadow zone Shear wave Thermoremanent magnetization Transition zone Upper mantle Lecture 06 932015 Lecture 07 982015 Ch7 Deformation of Rocks and Mountain Building I Plate Tectonic Forces a Deformation predominantly horizontal folding faulting shearing compression dilations i Factors that influence deformation a Rockmineral type b Water content c Temperature d Pressure depth e Strain rate ii Tensional forces divergent boundaries a Stretch and pull rock formations apart iii Compressive forces convergent boundaries a Squeeze and shorten rock iv Shearing forces transformfault boundaries a Push two parts of a rock formation in opposite directions b Stresses i Normal stress compression or tension ii Shear stress rightlateral or leftlateral I Normal strain compaction or dilation ii Shear strain rightlateral or leftlateral iii Strain rate speed rate at which strain occurs iv Convergent strain creates fold and thrust belt Mapping Geologic Structure a Outcrop where subsurface rock is exposed and rock formations are visible b Strike compass direction of a line formed by the intersection of a rock layer s surface with a horizontal surface parallel to rock sheets horizontal orientation c Dip perpendicular to strike angle of decline from horizontal vertical orientation d Use geologic maps and geologic cross sections to show rock formations Hi How Rocks Deform a Brittle normal faulting reverse faulting strikeslip i Elasticity under small strain rock will bend but when stress is released will bounce back to its original shape ii Failure strain accumulates to a point where the rock breaks earthquakes b Ductile folding stretching shearing i Plasticity smooth continuous deformation but does not spring back to original shape permanent deformation c Extensional deformation tensional deformation where ductile lower crust is stretched but brittle upper crust faults with highdip angles Pressuredependent strain Ratedependent deformation type of deformation depends on strain rate i High strain rate brittle ii Low strain rate ductile f lsostasy less dense crust floats atop more dense and mobile mantle i lsostatic adjustment a Erosion lithosphere lifts up b Sediment deposition lithosphere downwarps Lecture 07 982015 ii Large mountains have quotdeep roots icebergs IV Basic Deformation Structures a Fault fracture that displaces rock on either side brittle deformation i 2 types a DipSlip fault rock slips up or down 1 Normal fault hanging wall block moves down due to tensional forces 2 Reverse fault hanging wall block moves up due to compressional forces 0 Thrust fault lowangled reverse fault b StrikeSlip fault rock moves horizontally along fault plane transform faults are large strikeslip faults that cut through the lithosphere ii Hanging wall the rock above on top of the foot wa iii Foot wall the rock below the hanging wall b Folds when a planar structure gets bent mostly from compressional deformation which shorten and thicken the crust ductile deformation i Anticline bent upwards into arches ii Syncline bent downwards into troughs iii Horizontal fold horizontal fod axis plunging fold axis at an angle iv Symmetrical vs Asymmetrical vs Overturned fods tilted beyond vertical v Circular structures formed from fods a Basin bowlshaped depression of rock where beds dip towards a central point youngest rocks in core b Dome broad circular upward bulge of rock layers oldest rocks in core c Joint crack in a rock along a fault line where there has been no appreciable movement Key Distinctions Stress force exerted over a surface Nm2 PSI Strain the measure of deformation from stress lengthlength mm TERMS Strike Strikeslip fault SyncHne Tensional force Thrust Anticline Basin Brittle Compressive forces Deformation Dip Dipslip fault Dome Ductile Fault Fold Foot wa Formation Geologic cross section Geologic map Hanging wa Joint Normal fault Shearing force IIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Lecture 08 9102015 Lecture 09 9 152015 Ch 13 Earthquakes I What is an Earthquake a Earthquake occurs when brittle rocks under stress suddenly fail along a fault line b Elastic rebound theory stress is continuously placed on rocks at faults after an earthquake the stress is released and the rock rebounds to previous position i Elastic energy accumulates over time and then is released radiating in seismic waves ii Fault slip distance of the displacement iii Recurrence interval time between ruptures implied that it should be constant c Fault rupturing i Focus the point at which fault slipping begins ii Epicenter geographic point on earth s surface directly above the focus iii Aftershocks large earthquakes trigger smaller earthquakes iv Foreshocks small earthquake that occurs before the main shock near its focus d Occurrences i Cold rocks subduction zones because plate that subducts has a lower temperature Methods of Studying a Seismograph records seismic waves i Suspend small mass to record movements felt on the surface b Waves i Pwaves come first compressional travel through all mediums ii Swaves come second updown travel only through solids slower than pwaves iii Surface waves come last slowest iv Body waves through the earth c Locating the Focus i Measure time intervals to determine distance d Measuring magnitude i Richter scale numerical size to represent severity of earthquake by largest ground movement 1 Corrected for distance from focus ii Mercalli intensity scale 112 number scale iii Seismic moment directly related to the physical properties of the faulting 1 Area of faulting by the average fault slip 2 Can be measured more accurately than Richter e Fault mechanism the orientation of the fault rupture and the direction of the slipping i Tells us whether it was normal reverse or strikeslip fault right or left lateral Faulting Patterns a Divergent boundaries i Normal faulting from tensional forces b Transformfault boundaries greatest activity i Strikeslip faulting from shearing forces c Convergent boundaries largest earthquakes i Horizontal compression along huge thrust faults d ntraplate earthquakes i Small percentage within plate interiors ii Relatively shallow mostly occur on continents on old fault lines zones of crustal weakness IV Hazards and Risks a Faulting and shaking i Liquefaction destabilization of saturated soil b Landslides in mountainous areas c Tsunamis i Can be created by 1 Oceanic earthquakes 2 Submarine landslides 3 Volcanoes large caldera blowout 4 Meteors d Fires gas lines break V Prediction TERMS IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Aftershock Earthquake Elastic rebound theory Epicenter Fault mechanism Fault slip Focus Foreshock Intensity scale Magnitude scale P wave Recurrence interval S wave Seismograph Surface wave Tsunami Lecture 08 9102015 Lecture 09 9 152015
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