GEOL 107 Exam 3 Study Guide PDF

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Kendall McCoach GEOL 107 Exam 3 Study Guide

Lecture Notes Features of the Ocean Floor 

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Mid Ocean Ridges o Where new ocean crust is created o Plates moving apart create gap at surface, magma from mantle rises to fill gap, magma is cooled (crystallizes) forming new oceanic crust o Seafloor spreading starts here o 70% of all earth’s volcanic activity occurs here Abyssal hills o Crust moving away from mid-ocean ridge is cooling and sinking  Therefore ocean depth is increasing o Faulted crust is slowly being covered by oceanic sediments  Mostly occurs at normal faults o Hills = very newest and tallest crust created Abyssal Plains o Crust continuing to move away from mid-ocean ridge is cooling and sinking  Therefore ocean depth is increasing o Crust completely covered by oceanic sediments  Smooth  Flattest portions of ocean floor o Plains = older, lower, and smoother crust Deep ocean trenches o Occur at convergent plate boundaries where oceanic lithosphere is being subducted o Long and linear o Deepest depths in oceans occur here Seamounts o Underwater volcanoes that occur individually or as chains Guyots o Flat topped seamounts – erosion by waves when seamount was near or at ocean surface Continental margins o Transition between deep ocean floor and land o Divided into three different zones  Continental shelf

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 Extends from shoreline to water depths of 100-300 meters  gentle slopes  can be exposed as land during glacial time periods  Continental slope  Extends from continental shelf to water depths approaching 3000m  Steep slopes  Submarine canyons can form here as a result of turbidity currents o Turbidity currents are sediment laden water currents that flow down a continental slope  Continental rise  Extends from continental slope to abyssal plain  water depths 3000 – 4000m  gentle slopes  slowing turbidity currents deposit material here called turbidite deposits Oceanic sediments o Two general origins  From weathered rock on land transported to oceans and deposited  Called terrigeneous sediments  Ex. Turbidite deposits  From chemical reactions in oceans that form sediments  Called pelagic sediments  Ex. Formation of calcite containing sediments from shells of marine organisms

Earthquakes 

Earthquake o Sudden release of energy by earth Stresses build up in rock due to plate tectonic forces acting on rock, when built up stresses overcome frictional forces preventing rock from moving in response to plate tectonic forces, rock suddenly moves, releases energy that built up Focus and Epicenter o Focus  Actual location where earthquake occurred  Defined by longitude, latitude, and depth o Epicenter  Surface location directly above where earthquake occurred  Defined by longitude and latitude position or common geographic name Earthquake waves o Energy released by earthquake travels away from focus  Travels as waves  Called seismic waves o

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 These waves displace rock material as they pass by Two major types of seismic waves

Body waves  Travel within earth  Two major types of body waves o P-waves  Compressional waves or primary waves  Travel by displacing rock material back and forth in direction that seismic waves are travelling  Fastest travelling seismic waves  Can travel through liquids o S – waves  Also called shear waves or secondary waves  Travel by displacing rock material perpendicular to direction that seismic waves are travelling  S – waves cannot travel through liquids (like magma or water)  They travel slower than P – waves  Surface waves  Travel along earth’s surface  Travel with combination of P-wave and S-wave motion  Because of complex motion, surface waves travel slower than P-waves or S-waves  They also cause more damage than P-waves and S-waves due to more complex, larger amplitude, motion Locating where earthquakes occur o Can use difference in velocities of P-waves and S-waves to locate where earthquake occurred o Involves use of seismographs to record ground displacements o 4 step process  Step 1: Measure difference in time travel between arrival of first P-wave and Swave at a seismograph station  Step 2: Plot difference in travel time determined in step 1 on standard travel time vs. distance curve  This determines distance that seismograph station was away from earthquake  Step 3: plot distance determined in step 2 as radius away from location of seismograph station  Earthquake has occurred somewhere on circle  Step 4: repeat steps 1 -3 at least two more times 

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Where circles drawn from solutions in step 3 intersect denotes location of earthquake epicenter o Most earthquakes occur at boundaries between tectonic plates o Some earthquakes occur at locations that used to be boundaries, or that in the future will become boundaries, between tectonic plates Earthquake intensity and magnitude o Size of earthquake measured by intensity and magnitude  Intensity  Measure of physical destruction caused by earthquake  Described by Modified Mercalli scale o Ranges from I to XII o Lower values = lower intensity while higher values = higher intensity  Magnitude  Measure of energy released by earthquake by looking at amplitude of seismic waves  Magnitude scales are logarithmic, not linear o Ex. Richter scale o As magnitude increases by a factor of 1, amplitude of seismic waves increases by factor of 10, energy released increases by factor of 30 Tsunami o Tsunamis are series of water waves caused by displacement of large volume of body of water such as ocean o Can be created by earthquakes  Also created by volcanic eruptions and underwater slides o Initial offset of ocean water travels to ocean surface, displaces water at surface as a wave  Generally small in amplitude but travelling very fast o As waves approach shallow water, velocity slows down, energy is concentrated and wave heights can dramatically increase  To greater than 30 m o Can travel throughout ocean basins Earth’s interior structure o Passage of seismic waves through earth can be modeled to determine interior structure of earth o Earth has 4 major layers  Crust  Outermost layer of earth  Two types of crust o Continental crust 

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20-40 km thick, less dense Felsic in composition  Ex. Granite, rhyolite Oceanic crust  0-10 km thick, more dense  Mafic in composition  Ex. Gabbro, basalt  

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Mantle  Thickest layer of earth o 2900 km thick  Ultramafic in composition o Ex. peridotite  Outer core  2300 km thick  Liquid  Mostly iron and nickel with some silica  Source of earth’s internal magnetic field  Inner core  1200 km thick  Solid  Mostly iron and nickel with some silica We know that outer core is liquid based in modeling of seismic waves  At angular distances greater than 104 degrees to 140 degrees no P-waves arrive at seismograph stations  Regions of no arrivals of S-waves and P-waves are known as shadow zones  S-wave shadow zone is created because S-waves don’t travel through liquids o Therefore outer core must be liquid  P-wave shadow zone is created because P-waves slow down when they travel through liquids o Therefore outer core must be liquid 

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Plate Tectonics 

Plate tectonics o Plate tectonics can be defined as a working model based on two fundamental principles  Outer shell of earth is divided into series of 12 or so individual lithospheric plates  These plates are in motion with respect to one another and with respect to underlying lower mantle  Plates move at velocities of 2-16 cm/yr

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o As fast as your fingernails grow Crust, Mantle – Lithosphere, Asthenosphere o Crust and mantle are defined based on composition – lithosphere and asthenosphere are defined based on strength o Lithosphere  Zone of strength  Apply a high enough stress and the lithosphere will break generating an earthquake  0-100 km thick beneath the oceans vs. 100-150 km thick beneath continents o Asthenosphere  Zone of weakness  Apply a high enough stress and asthenosphere will flow  200 km thick  Occurs beneath lithosphere o Lithospheric plates move on top of asthenosphere o Movements of lithospheric plates and their interactions create most of the major features on the earth’s surface  Also determines where most earthquakes will occur Plates Move Relative to Each Other o 3 types of relative motion and three boundaries associated with them  Away from each other  Boundary between these two plates is called a divergent plate boundary  Oceanic-Oceanic divergent plate boundaries o Features at oceanic-oceanic divergent plate boundaries  Plates moving apart at mid-ocean ridge create gap at surface  Magma from mantle rises to fill gap  Magma is cooled forming new oceanic crust  Plates cool as they move away from mid-occean ridge  Become thicker and denser and sink  Depth and age of ocean crust increases with distance from mid-ocean ridge  “Seafloor Spreading”  Stresses generate earthquakes  Small magnitude, shallow depth  Continental-continental divergent plate boundaries o Features present at continental-continental divergent plate boundaries

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Upwelling of magma from mantle causes continental lithosphere to upward Lithosphere will eventually break and begin to move apart Stresses generate earthquakes  small magnitude, shallow If continental pieces continue to move apart seafloor spreading may start  Takes millions of years

Toward each other  Boundary between these two plates is called a convergent plate boundary  Oceanic-oceanic convergent plate boundaries o Features/processes at oceanic-oceanic convergent plate boundaries  Subduction – oceanic lithosphere beneath oceanic lithosphere  One oceanic plate is denser than the other  Deep ocean trenches  Volcanoes on non-subducted oceanic lithosphere  Create volcanic chains called island arcs  Earthquakes  Small to large magnitude, shallow to deep focal depths  Oceanic-continental convergent plate boundaries o Features/processes at oceanic-oceanic convergent plate boundaries  Subduction – oceanic lithosphere beneath continental lithosphere  Deep oceanic trench at subduction zone  Deepest parts of the ocean  As oceanic plate subducts reheated and placed under higher pressure it “dewaters” and surrounding material melts, less dense melted material rises towards surface and may erupt forming volcanoes on continental lithosphere  Stresses generate earthquakes – small to large magnitude, shallow to deep focal depths  Continental-continental convergent plate boundaries

Features/processes at continental-continental convergent plate boundaries  Two plates with continental lithosphere collide  Light, felsic, continental crust is not subducted  High elevation mountains  Not volcanic  Earthquakes  Small to large in magnitude, shallow to intermediate depths  No volcanoes, no deep earthquakes  Slide past each other  Boundary between these two plates called a transform plate boundary  Features/processes at transform plate boundaries o As plates try to slide past one another, frictional forces prevent them from doing so o Earthquakes – small to intermediate in magnitude, shallow to intermediate depth  No subduction, no volcanoes, no deep earthquakes Continental Drift and Wegner/Holmes o Theory of plate tectonics is relatively new  Proposed in the 1960’s o Initial ideas of plate tectonics began with hypothesis of continental drift described by Alfred Wegener in early 1910’s o Continental drift hypothesis proposed that about 250 million years ago all major continents were joined together in a large land mass  Pangea  Since 250 million years ago the continents have drifted apart to present day positions Evidence Supporting Continental Drift o Geographic “fit” of now separated continents o Geology of no separated continents very similar o

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Joining of continents in one large land mass could explain large glacial event Very strong evidence supporting continental drift however no plausible explanation (at the time) for driving force behind continents shifting  Sir Arthur Holmes in late 1920’s proposed thermal convection as a driving force for continental drift  Thermal convection is transfer of heat by physically moving hot “stuff” to colder areas and colder “stuff” to warmer areas  Continents “ride” on top of upper mantle convective currents

With technology available post-WWII great deal more was learned about ocean basins and integrated with continental drift and earthquake locations to form theory of plate tectonics  Technology used – sonar, magnetometers Evidence that led to development of plate tectonics o Evidence supporting seafloor spreading  Mapping of world-encircling mid-ocean ridge  Where new oceanic crust created  Lots of mapping started after WWII using echo-sounders  Age of oceanic crust increases away from mid-ocean ridge  Discovered by correlating marine magnetic anomalies with known times of reversals of Earth’s magnetic field  Generated by complex interactions of moving currents of liquid iron/nickel in Earth’s outer core  Moving free electrons generate magnetic fields  Mapping of Ocean Basins  Lots of mapping started after WWII using echo-sounders  Depth increases away from mid-ocean ridges o Non-random world-wide distribution of earthquakes  Most earthquakes occur at boundaries between tectonic plates o Explanation for apparent “wandering” of earth’s magnetic poles  Paleomagnetism – measure magnetism that rocks/minerals acquired in past  key is that geomagnetic poles have either been located near north geographic pole or near south geographic pole o not in-between  plots of paleomagnetic poles appear to show that poles have “wandered” with time  can explain apparent polar wander by keeping poles fixed, and allowing for movement of continents to move with respect to poles  “Drift” Seafloor Spreading o New ocean crust created at mid-ocean ridge, moves away, gets older, colder, denser, sinks  depth increases away from mid-ocean ridge  70% of all of earth’s volcanic activity occurs at zones of seafloor spreading Reversals of Earth’s Magnetic Field o In early 1900’s, reversals of Earth’s internal magnetic field were discovered and ages of reversals estimated  Bernard Brunhes, French Geophysicist, 1906 

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 Monotori Matuyama, Japanese Geophysicist, 1929 Geomagnetic Time Scale

 Record of when reversals of earth internal magnetic field have occurred Marine Magnetic Anomalies o As oceanic crust created at mid-ocean ridge cools below the Curie temperature, magnetic minerals in crust acquire magnetization aligned with earth’s internal magnetic field  If magnetic field is same as today (normal polarity) this slightly increases magnetic field at that location  If magnetic field was opposite of today (reversed polarity) this slightly decreases magnetic field at that location o Marine magnetic anomalies generated by subtracting earth’s internal magnetic field from measured total magnetic field at a given location  Total magnetic field includes magnetization of oceanic crust o In early 1960’s as plate tectonics and seafloor spreading were being proposed and published, Canadian geologist Lawrence Morley and British geophysicists Fred Vine and Drum Matthews independently proposed that if seafloor spreading was occurring then crystal rocks surrounding mid-ocean ridges should show record of earth’s magnetic field reversals as these rocks cooled through Curie temperature when they formed  Morley’s two submitted manuscripts were rejected, Vine and Matthews were first to get published o Based from initial observations of magnetic profiles collected over Mid-Atlantic Ridge by anti-submarine ships in British Navy during WWII o Interpretation of Marine Magnetic Anomalies used to establish age of oceanic crust Hot Spots o Absolute plate motion – motion of lithospheric plates with respect to deep interior of Earth  Absolute plate motion can be determined by studying volcanoes produced by hotspots o Hot spots are areas within lower mantle where melting occurs – these melting zones are fixed in their positions o Magma from hot spots rises up through mantle, asthenosphere and lithosphere and forms volcanoes on lithospheric plates  These plates are in motion o As plates move repeated volcanic activity related to hot spot magma produces line of volcanoes that shows direction of plate with respect to hotspot  Hawaiian Islands are example of hot spot volcanoes showing absolute plate motion

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By determining ages of volcanoes and measuring distance between them, you can calculate the rate of absolute plate motion

Rock Deformation 

Rock Deformation – Folds and Faults o Stress- force applied per unit area o Strain- deformation produced by stress

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Three types of Deformation o Elastic Deformation  Apply stress, rock deforms, remove stress, rock returns to original form, no net deformation o Ductile Deformation  Apply a stress, rock deforms, at high enough stresses rock permanently deforms by flowing  Fold features are formed by plastic deformation o Brittle Deformation  

Apply a stress, rock deforms, at high enough stresses, rock permanently deforms by breaking Fault features are formed by brittle deformation  2 major types of fault features o Vertical displacement faults  Normal fault  Hanging wall goes down relative to footwall  Due to crustal stretching  Reverse fault  Hanging wall goes up relative to footwall  Due to crustal shortening  Slope of fault is steep  Special type of reverse fault called thrust fault o A low angle reverse fault o Horizontal Displacement faults  Strike-slip fault  No vertical motion  One block slides sideways past the other  Fault surface is nearly vertical  Left lateral strike slip fault and right lateral strike slip fault o Based on relative movement of rocks on either side of fault o Left lateral fault

Rocks across fault appear to have moved left Right lateral fault  Rocks across fault appear to have moved right 

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Strike and Dip o Orientation of rock layers defined by attitude (strike and dip) o Strike 

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Horizontal line in plane of bedding  Expressed as a compass direction  Intersection of rock layer with a horizontal plane

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Expressed as direction and angle Compass direction in which rock layer is inclined from horizontal angle between horizontal plane and bedding plane  Direction of dip is always at right angles to the direction of strike Ductile Deformation and Folds o Two major types of folds  Circular folds  Folding about a central point  Domes o Circular fold in which rock layers dip away from central point of folding  Basins o Circular fold in which rock layers dip toward central point of folding  Linear folds  Folding along an axis  Monoclines o Linear fold in which rock layers dip away from nearly horizontal layers  Anticlines o Linear fold in which rock layers dip away from axis of folding  Synclines o Linear fold in which rock layers dip toward the axis of folding  

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Renewable and Non-Renewable Energy Sources  

Renewable energy sources regenerate and can be sustained indefinitely Five renewable sources used most often o Biomass o Water

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o Geothermal o Wind o Solar Non-renewable Energy Sources o Energy sources are considered non-renewable if they cannot be replenished in a short period of time o Four non-renewable energy sources used most often are  Oil and petroleum products  Gasoline, diesel fuel, heating oil and propane  Natural gas  Coal  Uranium  Nuclear energy  Uranium ore is mined and converted to fuel used at nuclear power pla...