Geology Planet Earth - Lecture notes All PDF

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All notes for Geo 1050 Marquero...

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Stars and Galaxies -we are in milky way, over 300 billion other galaxies Distance to Celestial Objects -sun is only 93 million years -light year is the distance light travels in one year -closest star beyond the sun is 4 light years away Nature of our Solar System -our sun is medium sized, orbited by 8 planets -sun accounts for 99.8% of our solar systemm mass -two groups of planets in our solar system -terrestial: small dense rocky planets -mercury venus earth and mars -giant: large, low density, gas and ice giants -gas giants: jupiter, saturn -ice giants: uranus, neptune (frozen water, ammonia) Solar Sytem -terrestrial are four closest -all but 2 planets have moons -asteroid belt lies between mars and jupiter Forming the Universe -big bang caused expanding universe, 13.8 billion years -ball at the center grows dense and hot -fusion reactions begin, the sun is born -dust in the rings condenses into particles -particles coalesce to form planetesimals -planetesimals accumulate into a larger mass -irregularly shaped proto earth develops -interior heats up and becomes soft -gravity shapes the earth into a sphere -then a small planetoid collides with Earth -debris forms a ring around the earth -debis coalesces and forms the moon Formation of the Earth -atmosphere develops from volcanic gases -when earth becomes cool enough, moisture condenses and accumulates -oceans are born

Earth -an atmosphere (gaseous envelope) -hydrosphere (surface and near surface water) -lithosphere (earthy earth) Magnetic Anomalies -places where the magnetic field strength is either greater or less than the expected strength When a magnetometer is towed over a positive marine magnetic anomaly… The measured magnetic field is stronger than expected Sea-floor spreading explains the stripes -magnetic anomalies mimic layered lava flows -magnetic stripes form as lava cools at a mid ocean ridge -ocean crust spreads away from mid ocean ridge -reversals are recorded within the cooled basaltic lava -sea floor spreading is the mechanism of continental drift -drilling in the late 1960s recovered crust samples -ages increase away from the mid ocean ridge -ages are mirror images across the mid ocean ridge -strong supporting evidence for sea floor spreading -ocean cannot be over 200 million years old bc too dense bc too cold -youngest crust is adjacent to the mid ocean ridge Plate Tectonics -how Earth ages -earth’s outer shell is broken into rigid plates that move -moving plates change the face of planet earth -earth’s outer shell is broken into tectonic plates that move -tectonic plates are fragments of lithosphere -about 20 on earth in lithosphere -plates move at 1 to 20/cm yr -slow on our time, fast on earths -plates interact along their boundaries Boundaries -locations on earth where tectonic plates meet -identified by concentrations of earthquakes -associated with many other dynamic phenomena (volcanoes) -plate interiors are almost earthquake free

Divergent Boundaries -divergent - tectonic plates move apart -lithosphere thickens away from the ridge axis -sea floor spreading causes plates to move apart -magma wells up to fill the gap -magma cools, adding material to each plate Convergent Boundaries -tectonic plates move together -lithospheric plates move towards each other -one plate dives back into the mantle (subduction) -subducting plate is always oceanic lithosphere -subduction recycles oceanic lithosphere -subduction is balanced by sea floor spreading -earth maintains a constant circumference -old (~200 m years old) plates are more dense than mantle -flat lying oceanic plate does not subduct easily -all oceanic plates get subducted beneath the continents by the time it is 200 million years old -continent ocean boundary Transform Boundary -transform: tectonic plates slide sideways -plate material is neither created, nor destroyed -lithosphere slides past; not created or destroyed -many transforms offset spreading ridge segments -some transforms cut through continental crust -mid ocean ridge axis is offset by transform faults -geometric neccessity for a line spreading on a sphere -transforms bear strong evidence of sea floor spreading -abudant earthquakes common when offsets are opposed -earthquakes vanish when offsets are concurrent -continental transforms-chop continental crust Plate Velocities -plate vectors are determined gps measurements -knwoledge of plate motion is now accurate and precise Lightyear is distance light travels in one year Big bang theory 13.8 billion Formation of Solar System -small planetoid collides with earth -debris forms ring around earth

-debris turns into moon Atmosphere -99% of athmosphere is below 50 km -weight of overlying air increases density and pressure of air below -sea level pressure= 1 atm -everest= .3km Continental Drift -wegeners idea was debated and ridiculed -most scientists did not believe him -lack of a mechanism for drift a major criticism -wegener died in 1930 at the age of 40 -lacking an advocate, the drift hypothesis faded -his idea was revived in the 1950s -drift hypothesis needed new and different evidence -provided by paleomagnetism study of the fossil magnetic field Polar Wander -paleomagnetic signatures of similarly aged rocks in different continents is recorded -polar wander paths are constructed for each continent -apparent tendency of the north or south magnetic pole to vary in position over time is called polar wander Interpretation of Marine Magnetic Anomalies -magnetic anomalies result from seafloor spreading in conjunction with magnetic polarity reversals -positive marine magnetic=earth displaying normal polarity -negative marine magnetic=earth displaying reverse polarity Lithosphere= rigid, rock, brittle, does not flow Athenosphere=ductile, flows

Mineral -no liquids Silicate Minerals -known as the “rock forming mineral” -dominate earth’s crust -oxygen and silicate -make up 94.7% of crustal volume -74.3% of crustal mass Rapid cooling (quenching) forms glass… not a mineral -obsidian is a rock -it is a volcanic glass that forms when silica-rich lava cools very quickly -obsidian consists of a solid mass of glass through and through Polymorphs -minerals with the same composition; different structure -polymorphs reveal the importance of bond type -diamond and graphite are carbon polymorphs © -diamond: strong covalent bonds; hardest mineral -graphite: weak van der waals bonds; softest mineral Magma Formation -geothermal gradient-the earth is hot inside -crustal tempterate averages 25c/km of depth -at the base of the lithosphere T: ~1280C -geothermal gradient varies from place to place Crystalline Igneous Textures -rock texture reveals cooling history The geotherm is the rate of change of temperate with depth in the Earth’s interior As a rock is moved up in the Earth, it is subjected to slightly lower temperateures and much lower pressures, as it begins to melt Because of its physical properties, magma tends to move upward, away from where it formed If magma is more felsic, viscosity is more as well

Volcanic Materials -the products of volcanic eruption take three forms -lava flows: molten rock that moves over the ground -pyroclastic debris: fragments blown out of a volcano -volcanic gases: vapor and aerosols that exit a volcano Lava Flows -lava can be thin and runny or thick and sticky -flow style depends on viscosity, which depends upon -composition, especially silica, fe, and mg content -temperature -gas content -crystal content Classification is based upon composition and texture -composition- felsic, intermediate, mafic, and ultramafic -texture -High silica/ low FE and MG are called -silicic, felsic, rhyolitic

Basaltic Lava Flows -mafic lava: very hot, low silica and low viscosity -pahoehoe: hawaiian word describing basalt with a glassy, ropy texture -forms when hot basalt forms a skin -with the flow, the skin is rolled into ropy ridges and furrows -A’A’: hawaiian word describing basalt that solidifies with a jagged, sharp, angular texture -forms when hot flowing basalt cools and thickens -with flow, lava crumbles into shards and fragments -Pillow basalt -round blobs of basalt cooled in water Andesitic Lava Flows -higher sio2 makes andesitic lavas viscous -unlike basalt, they do not flow rapidly -they mound around the vent and flow slowly -outer crust fractures, creating rubble -andesitic lava flows remain close to the vent Rhyolitic Lava Flows -rhyolite, with the highest si02, is the most viscous lava -rhyolitic lava rarely flows -rather, lava plugs the vent as a lava dome

Explosive Pyroclastic Debris -intermediate and felsic magmas erupt explosively -more viscous than basaltic magma (from sio2) -contain more gas -produce large quantities of volcanic ash and tephra (pyroclastic material) Magma Chamber -located in the upper crust -usually an open cavity or area of highly fractured rocks Craters --bowl shaped depression atop a volcano -up to 500m across, 200m deep -form as erupted lava piles up around the vent -summit eruptions -located within the summit crater -flank eruption -located along the side of a volcano Caldera -gigantic volcanic depression -one to ten km acoss, larger than a crater -steepsidewalls and flat floors -form from massive eruptions -volcano collapses -crater lake, oregon -yellowston national park Volcano Types Shield Volcanos -mauna loa -very wide Cinder Cone -conical piles of pyroclastic debris -smallest type of volcano -slopes are at angle of repose -often symmetrical with a deep summit crater Stratovolcanoes -large, cone shaped volcano -composed of alternating layers of lava and tephra -often symmetric, can be odd shapes from landslides, etc

Eruptive Style -effusive eruptions -produce lava flows -explosive eruptions -blow up Controls on Eruptive Style -viscosity-controls the ease of lava flow -basalt- low viscosity lava flows away from vent -felsic- high viscosity lava builds up at the vent Tectonic Settings -plate motion is a dominant control on volcanism -volcanic types are linked to tectonic boundaries Volcanic Hazards -lava flows- lava threats are mostly from basalt -pyroclastic flows -clouds of ash and gas that race downslope -ride ver a carpet of superheated air -eases passage of the flow -volcanic fragments fall around the volcano -blast- rarely, explosions are ejected sideways -landslides- eruption related slope failures -eruptions cause landslides, vice versa -lahars- mudflows result when ash is moved by water -material is more dense than water -carry away everything (people, houses, bridges) -earthquakes-moving magma causes earthquakes -gas- volcanic gases are poisonous

PRE EXAM 1 POST

Metamorphic Processes -metamorphic change occurs slowly in the solid state -several processes are at work -1. Recrystallization: minerals change size and shape -2. Phase change: new minerals form with same chemical formula, diff crystal struct -3. Neocrystallization: new minerals with changes in temperature and pressure -initial minerals become unstable and change to new minerals Causes of Metamorphism -agents of metamorphism -heat (t), pressure (p), differential stress, hot water -not all agents are required, they often do co occur -rocks may be overprinted by multiple events Heat (temperature, t) -metamorphism occurs as the result of heat -200-850 C -upper t limit is melting, it varies based upon rock mineral composition and water content -heat energy breaks and reforms atomic bonds -sources of heat -geothermal gradient -magmatic intrusions -compression Pressure (P) -p increases with depth in the crust -270-300 bars per km (1 bar is almost 1 atm=14.7 psi) -metamorphism occurs mostly in 2 to 12 kbar range -t and p both change with depth -mineral stability is highly dependent upon T and P -this stability can be graphed on a phase diagram -changes in t and p lead to changes in minerals Differential Stress -forces applied to a rock surface that are stronger in some directions compared to others -commonplace result of tectonic forces -two kinds of differential stress: normal and shear -normal stress: operates perpendicular to a surface -tension: pull apart normal stress -compression: push together normal stress -preferred mineral alignment is called foliation -foliation imparts a layered or banded appearance -rocks commonly break parallel to foliation planes

-foliation develops perpendicular to compression -minerals flatten, recrystallize and rotate Foliated Metamorphic Rocks -slate: fine clay, low grade metamorphic shale -has distinct foliation called slaty coverage -develops by parallel alignment of platy clay minerals Earthquake Size -size is described by either intensity or magnitude -mercalli intensity scale- degree of shaking damage -roman numerals assigned to different levels of damage -damage occurs in zones -damage diminishes in intensity with distance -magnitude: the amount of energy released -maximum seismogram motion -nromalized for distance -small earthquakes are frequent -abt 100,000 magnitude 3 earthquakes/year -large earthquakes are rare -32 magnitude 7 earthquakes/year Earthquake Focal Depths -shallow -along the mid ocean ridge -lower magnitude earthquakes -transform boundaries -shallow part of trenches -continental crust -intermediate and deep earthquakes occur along the subduction trace -intermediate: 20-300km downgoing plate still brittle -deep: 300-670km mineral transformations -earthquakes rare below 670km (mantle is ductile) Continental Earthquakes -earthquakes in continental crust -continental transform faults (san andreas, anatolian) -continental rifts (basin and range, east african rift) -collision zones (himalayas, alps) -intraplate settings (ancient crustal weakness

Intraplate Earthquakes -5% of earthquakes happen away from plates Earthquake Damage -ground shaking and displacement -R waves cause ripple waves which are like waves Tsunami Behavior -tsunamis race at jetliner speed across the ocean -they may be almost imperceptible in deep water -low wave height Earthquake Prediction -predicition would help reduce catastrophic losses -we can predict general time periods (ten to hundreds of years) -they cannot be predicted short term (hours to months) Mountains -mountains provide vivid evidence of tectonic activity -manifestations of geologic processes -uplift -deformation -metamorphism -frequently occur in elongate, linear belts -constructed by tectonic plate interactions in a process called orogenesis -building involves deformation, jointing, faulting, folding, partial melting -orogenesis causes deformation thru bending, breaking, tilting, squashing, stretching, shearing -orogeny is a term that refers to the process of mountain building -born and have a finite lifespan -young mountains are high, steep, and growing upward -middle aged mountains are dissected by erosion -old age mountains are deeply eroded and often buried Deformation -deformed terrane passes into undeformed terrane -undeformed: horizontal beds, spherical sand grains, no folds or faults -deformed: tilted beds, metamorphic alteration, folding and faulting -results in one or all of the following -translation: change in location -rotation: change in orientation -distortion: change in shape Brittle vs Ductile Deformation

-brittle deformation: rock breaks by fracturing, occurs in the shallow crust -ductile deformation: rock deforms by flowing and folding -transition between the 2 occurs at 10-15km depth Causes of Deformation -types of stress: compressional (squeezing), tensional (pulling apart), shear (sliding past) -tectonic collision produces horizontal compression -large scale -most common type of deformation Strain -changes in shape caused by deformation -stretching (pulling apart) -shortening (squeezing together) -shear (sliding past) Geologic Structures -geometric features created by deformation -folds, faults, joints, etc. -often preserve information about stress fields Fault Orientation -dipping fault: fault with an inclined fault plane -on dipping fault, the blocks are classified as the -hanging wall block -footwall block -standing in a tunnel excavated along the fault -your head is near the hanging wall block -you are standing on the footwall block Dip Slip Faults -sliding is up and down the fault plane -therefore, blocks move up or down the slope of the fault -two kinds of dip slip fault depend on relative motion -reverse fault: hanging wall moves up -thrust fault: special type of reverse fault -normal fault: hanging wall moves down

Strike-Slip Faults

-fault plane is vertical; fault blocks move sideways -classified by the relative sense of motion. To find this: -right lateral: opposite block moves to observer’s right -left lateral: opposite block moves to observer’s left -large strike up faults may slice the entire lithosphere Folds -layered rocks may be deformed into curves called folds -folds occur in a variety of shapes, sizes, and geometries -often occur in a series -may result in extremely complex geometries -orogenic settings produce large volumes of folding rocks -special terminology is used to describe folds -hinge: portion of maximum curvature on a fold -limb: less curved “sides” of a fold -axial plane: imaginary surface defined by connecting hinge of successfully nested fold Fold Identification -anticline: arch like fold -limbs inclined away from the hinge -syncline: trough like fold -limbs inclined toward the hinge -monocline: fold like a carpet draped over a stairstep -generated by blind faults in the basement rock -these faults do not cut through the surface -displacement folds overlying sedimentary cover Forming Folds -folds develop in two ways: flexural slip and passive flow -in flexural slip, layers slide past one another -it is like the movement when a deck of cards is bent -passive flow folds form in hot, soft, ductile rock at high temperature -horizontal compression causes rocks to buckle Modern Orogenesis -modern instrumentation can measure mountain growth -global positioning systems (gps) measure rates of -horizontal compressions -vertical uplift

Causes of Mountain Building

-continental collision follows ocean basin closure -brings two blocks of continental lithosphere together -complete subduction of oceanic lithosphere -buoyant continental crust shuts down subduction Causes of Orogenesis -continent continent collisions -buoyant continental crust will not subduct Causes of Mountain Building -continental rifting creates mountains -normal faulting creates fault-block mountains and basins -decompressional melting adds volcanic mountains Orogenic Collapse -the himalayas are the maximum height possible -there is an upper limit to mountain heights -erosion accelerates with height -weight of high mountains overwhelms rock strength -deep, hot rocks eventually flow out from beneath mountains -the mountains then collapse downward like soft cheese Folds -fold often occur in series -may result in extremely complex geometries -orogenic settings produce large volumes of folded rock -deformed rock often experiences multiple events Forming Folds -folds develop in two ways: flexural slip and passive flow -flexural slip, layers slide past one another -it is like the movement when a deck of cards is bent

Geologic Time

-understanding time permits assigning an age to -rocks, fossils, geo structures, landscapes, tectonic events, change -deep time: immense span of geologic time -concept is very vast, hard for people to grasp -human history is minuscule against geologic time -two ways of dating geological materials -relative ages: based upon order of formation, older vs younger -numerical ages: actual number of years since an event, age is # Principle of Uniformitarianism -processes observed today were the same in the past -we can observe lava flowing and cooling into solid rock -ancient lava flows are the products of volcanic eruptions Principle of Original Horizontality -sediments settle out of a fluid by gravity -causes sediments to accumulate horizontally -sediment accumulation is not favored on a slope -hence, tilted sedimentary rocks must be deformed Principle of Superposition -in an undeformed sequence of layered rocks: -each bed is older than the one above, younger than the one below -younger strat...