Exam 2 Geology
What is the history of the grand canyon?
clearly represents geological events over 1.7 to 1.8 billion years
what are sediment and sedimentary rocks important?
they are important hosts of energy, mineral, & water resources
How is sediment produced ?
weathering and erosion is transported by moving water, ice, and wind -the loose sediment hardens, or lithifies, into sedimentary rocks
what is an earthquake?
***an earthquake occurs when energy stored in rocks is suddenly released -most earthquakes are produced when stress build up along fault over a long time, eventually causing the fault to slip. >how do we describe an earthquake? -hypocenter: place where the earthquake is generated -epicenter: the point of the earth's surface directly above where the earthquake occurs (directly above the hypocenter) -seismic waves: radiate outward from hypocenter -seismic stations: waves arrive at closer seismic stations before farther stations >what causes most earthquakes? -normal faults \ -reverse and thrust faults / -strike-slip faults |/| >how do volcanoes and magma cause earthquakes? -an explosive volcanic eruption causes compression, transmitting energy as seismic waves -slope failures -movement of magma , it can push rocks out of the way, causing earthquakes -movement along faults (weight) >what else can cause seismic waves? -landslides -meteoroid impacts -explosions
how do earthquakes waves travel?
***earthquakes generate vibrations that travel through rocks as seismic waves -geophysical instruments record and process information on seismic waves -> data allow seismologist + geologist to understand where & we're earthquakes occur >kinds of seismic waves that earthquakes generate -surface waves -horizontal surface waves shears material -primary body wave (P-wave) compresses material; fastest wave -secondary body wave (S-wave) shears material >how seismic waves are recorded -seismometers: detects and records the ground motion during earthquakes -seismograph; modern seismic detector >how seismic records are viewed -seismogram (waves) -surface waves arrive last bc intense shaking -S-wave arrives later -P-waves arrive first
how does faulting cause earthquakes?
***most earthquakes occur because movement along faults -faults slip because the stress applied to them exceeds the ability of the rock to withstand the stress -rocks respond to the stress by either flex and bend or they break and slip >before, during, and after an earthquake -pre-slip & elastic star: stress increases and rocks experience elastic strain -slip & earthquake: fault slips, causing an earthquake -post-slip: stress drops during quake, followed by post-slip recovery of elastic strain: cycle starts again •"stick-slip" behavior because fault sticks then slips >how do earthquakes ruptures grow? •earthquake rupture starts in small area (hypocenter) then expands over time -starts as small parch below surface -migrates out, ruptures surface (fault scarp) -fault scarp lengthens
what happened during the great alaskan earthquake of 1964?
***the southern coast of Alaska experienced one of the world's largest earthquakes -magnitude if 9.2 (Mw) -triggered massive landslides -unleashed a tsunami -caused death + damage from Alaska to California >damages -landslids -sliding along clay -shaking + sinking >at sea during the earthquake -seafloor uplifted 4 to 5 m along faults -tsunami destroyed coastal areas >how geologist studied the earthquakes -mapped areas uplifted and subsides by earthquakes -generalized map of area -generalized cross section of megathrust
what do seismic waves indicate about earth's interior?
***the way seismic waves travel through Earth enables us to identify distinct layers and boundaries within the interior, including the crust, mantle, and core >how seismic waves travel through material -seismic waves radiates in all directions -at a boundary, wave will reflect or refract -from faster to slower material -from slower to faster material -rising waves from faster to slower >who seismic waves travel through earth's mantle + crust -a seismic wave bends as it travel through crust and mantle -curved paths permit us to find the depth to crust-mantle boundary (Moho) -close to EQ, paths through crust arrive first -farther, paths through faster mantle arrive first >how seismic waves used to examine earth's deep interior -size of core indicate by location of P-wave shadow zone -S-waves do not pass through outer core (so liquid)
How do we reconstruct Geological Histories?
***we reconstruct the sequence of geological events by using the various strategies of relative dating, correlation if rock units, isotopic dating, other... >How do we correlate units and events in two section of rock? -Physical correlation -Age correlation >why do some units change from one section to another? -facies change -layer eroded away -change in thickness -restricted event or environment
how down infer the relative ages of events?
**1st strategy is to determine the age of one rock relative to another, using a series of commonsense approaches collectively called "relative dating". 2nd geologist try to assign actual numbers, in thousand yo billions of years, "isotope dating". Also, fossils, allow to compare ages of different rock layers and to contract geological scale >5 principles of relative dating -1. (original horizontally) most sediments are deposited in horizontal layers -2. (superposition) a younger sedimentary or volcanic units is deposited on top of older units -3. a younger sediment or rock can contain pieces of an older rock -4. a younger or feature can cut across any older rock or feature -5. younger rocks and features can cause changes along their contacts with older rocks >
Why do we investigate Geological history?
**Geological history helps us evaluate the potential for geological hazards, explore for resources, comprehend the physical world around us, and understand changes in life and the environment over time >How do geological ages help us evaluate geological hazards -earthquakes (examine soils & rocks) -volcanoes (ages of lava & volcanic cones & how much they eroded/weathered) -flooding (determine floodplain and terraces)
what process form island arcs?
**Many islands occur in long arcs, that cross the seafloor. Islanders are associated with deep ocean trenches & dangerous volcanoes >How island arcs form -island arcs form where one oceanic plate subjects beneath another. -Subduction creates a trench and generates magma that forms an arcuate belt of volcanic island, such as Aleutian Islands & Java >what happens in front of & behind an island arc? -trench-rollback -back-arc basin >why island arc are curved -the earth is a sphere -more surface are on outside than at depth so a slab bends as it subjects
how and why did living things change through geologic time?
**different fossils occur in different rock units >how do fossils vary in age? -Cenozoic (recent life): mammals & grasses -Mesozoic (middle life): dinosaurs & flowering plants -Paleozoic (ancient life): crinoids, coral, clams, insects, certain fish, plants, & amphibians -Precambrian (before the cambrian period): simple creatures & fossils, such as stromatolites >what determines whether a species survives or become extinct ? -environmental setting -climate -reproductive strategy -adaptability -competition -predators and prey >evolution -refers to observable changes -2nd refers to theories that help explain the observed changes
what processes occur at mid-ocean ridges?
**Ocean ridges form where two ocean plates diverge. -magma ascending from the mantle erupts onto the seafloor or solidifies at depth, making new oceanic crust >what happens where plates spread apart? -solid rock and magma rises from the mantle to occupy the space between the plates -cooling + solidifying magma forms new oceanic crust >fast-spreading vs slow-spreading -rapid spreading allows the new oceanic crust to move far from the spreading center before it cools and subsides -slow-spreading: allows rocks near the strength enough to form large faults >what are black smokers and how do they form? -Black smokers are hydrothermal vents, where hot water from within the rock jets out into the seawater. AS the hot waters cools, the metals, sulfur, and other elements dissolved in the hot water form small crystals that make the water black and cloud
why are some regions high in elevation?
**Regional variations in elevation primarily reject the tectonic process that occurred in the region, and the nature of the crust and mantle depth. -a change in the surface can cause a region to be uplifted (rise in elevation) or to subside (drop in elevation) >controls on regional elevation -regions w/ thick crust are high -regions underlain by less dense crust are high -warm rocks are less dense and higher than cool ones >what causes variations in crustal thickness -differences in crustal thickness between regions reflect difference in their geological histories -such differences include: whether the crust is continental or oceanic, & whether it ha been deformed, eroded, or buried >ways to decrease regional elevation -structurally thin crust -erode material -cool crust or mantle >ways to increase regional elevation -shorten/thicken crust -add surface material -add magma at depth -heat crust or mantle
how do marine salt despots form?
**Salt deposits of marine origin occur along many continental margins, forming layers, irregularly shaped masses & structural domes -marine salt deposits only form in specific geological settings especially sites where sweater evaporates >settings that can deposit salt -broad flat areas adjacent to sea -bodies of water w/ evaporation -behind barred that restrict influx of seawater >structures that salt deposits form -salt domes -folded salt layers in salt domes -faulting and folding over weak salt layer >settings of salt structures along the Gulf Coast of the U.S. -thick layer of salt deposited during evaporation of seawater -subsurface flow of salt disrupts surface -pressure of overlying rocks causes salt to flow up and sideways >how salt forms near continental margins -formation of salt deposits requires that evaporation occur in water bodies w/ limited connection to the ocean so that water made salty by evaporation cannot simply flow into the open ocean. Sal accumulations formed in such marine settings are -> marine salt deposits
What is the Geology of continental Margins?
**The edge of a continent marks the transition between continental & oceanic crust, but this transition is typically concealed by thick layers of sediment > features & structures of continental margins -continental shelf -continental slope -continental rise ~> transition -the transition to deep ocean reflects progressively thinner continental crust & an abrupt change to oceanic crust -the thinned crust along most passive margins records rifting apart of the continent. Sediment on the continental margin varies greatly in thickness across the shelf, slope, rise & abyssal plain >what settings lead to underwater slope failure -turbidity currents (they are capable of eroding rock, even underwater -submarine canyons (turbidity current erode into continental slope + river and turbidity current eroded into continental shelf) -submarine fans & submarine landslides
what is the geologic history of the western united states?
**The western u.s experienced many changes in tectonic settings during its complex precambrian. >geologic evolution of the western U.S. -precambrian rifting -early paleozoic passive margin -middle paleozoic offshore arcs -late paleozoic collisions -settings at the end of the Paleozoic
how do mountains and basins form at convergent continental margins?
**at subduction zones beneath continents, various processes create mountains & basins -Basins can form in front of, and behind the mountain belt >how mountains & basins form in an ocean-continent convergent margin -along convergent boundaries, an oceanic plate subjects beneath a continental plate -subduction causes melting in the mantle beneath the continent & generally also leads to compression & thickening of the continental crust >continental collision -involves the convergence of two tectonic plates that each carry continental crust -the collision transmits large stresses to the plates on either side, forming thrust faults & thickening crust
hoe did continents join and split apart?
**continents shift their positions over time in response to plate tectonics -they have rifted apart and collided, only yo rift apart again >600 m.y. Ago: supercontinent of Rodinia -continents joined in Rodinia, centered over south pole >500 m.y Ago: Dispersal of Continents -most continents separated and moving apart >370 m.y. Ago: before Pangea -NAM about to collide with main part of Gondwana -island arcs off Asia (future terranes) >280 m.y. Ago:supercontinent of Pangaea -collision of Gondwana and NAM forming Appalachian mountains -tethys ocean between N and S parts of Pangaea
what processes occur in extensional and strike-slip settings?
**crustal extension on land or beneath the oceans produces normal faults & other characteristics.. -metamorphism occurs in extensional settings bc; shearing, heating near magmas, and the circulation of hot water near mid-ocean spreading centers >what type of deformation & metamorphism accompanies divergence: -continental drifting -onset of seafloor spreading -mid-ocean rifting >where do strike-slip faults & shear zones form & features? -shear stress -transform faults -shearing moves sideways -active fault offsets stream channels (san Andreas)
what are folds and how are they shaped?
**deformation can hold rock layers >main types of fold: -Anticlines: folds in the shape of an A -synclines: folds in shape of U or V -monocline: flat layers bend down (dip) in one direction and then flatten out again --\_ -Dome: layers lifted in circular area n -basin: formed by folding (opposite of dome u >geometry of folds -hinge: sharp fold (the tip) /\ -limbs () the curvy part (the legs) -axial surface: imaginary plane or curved surface /|\
what are some metamorphic features?
**pressure and heat cause the rearrangements of existing materials & the formation of new minerals + new structural features >Rock cleavage -a type of discontinuity in the rock --__ >what is foliation & how is it expressed in rocks? -a foliated rock is a mineral that is aligned parallel to each other (forming layering texture) -ex: gneissic & schists >lineation in metamorphic rocks -def: aligned minerals or long, deformed pebbles -oriented minerals -shearing marks -stretched crystals
*how are ages assigned to rocks and events?
**done by using isotopic dating methods, most of which involve chemically analyzing a rock for the products of natural radioactive decay >how does radioactive decay occur -before decay, unstable parent atoms -half the parent atoms decayed to daughter atoms (time=half life) -after a second half of life, only 1/4 parent atoms remain -common radioactive decay series (possessing-> decays to argon) (carbon->decays to nitrogen) (rubidium ->decays to strontium) (thorium+uranium -> decays to lead) >measuring & calculating isotopic ages -mass spectrometer: used to measure the ratio of parent isotopes to daughter product in the rock or the mineral dated
How does Continental extension occur?
**during continental extension, continental crust is thinned and stretched horizontally, typically causing the region to subside. -continental extension also breaks the crust into faulted blocks , forming mountain ranges and sedimentary basins. >how do continents accommodate crustal extension? -when continental crust is extended, the upper parts responds by breaking into discrete blocks bounded by normal faults. -if the faults don't rotate during extension, only a small amount of extension can occur. -if the blocks & faults rotate, greater amounts of extension can take place -extension on non-rotating fault block •normal faults dip in opposite directions •moement along faults forms basins and mountains •over time, basins fill and mountains erode -extension on rotating fault blocks •normals faults all dip in the same direction •corner that is rotated up becomes a mountain •continued faulting tilts units more, extending crust >what happens when extension accompanies subduction? -some regions experience crustal extension and rifting in spite of being near a convergent boundary. -extension can occur behind or near the arc, where the crust is hot and weak -extension can accompany subduction of one oceanic plate beneath another oceanic plate or beneath a continental plate -large amounts of extension will form a new ocean basin behind the arc.
what is the evidence for the age of Earth?
**earth is 4.5 billion years old. -the advent of isotopic dating techniques finally provided the tool needed to demonstrate that earth is very old Evidence earth's history is NOT short -seasonal layers in tree rings -seasonal layers in varves (lake sediment) seasonal layers in ice cores -measured rates of modern plate movement are constant w/ long-term rates >where age of Earth comes from? -age of meteorites (4.55 billion) -dates Moon rocks (4.5 billion) -Oldest dates on Earth rocks (3.9 to 4.0 b.y rock) (4.3 b.y grains) -data from astronomy on age of Solar System & Universe
what causes earthquakes along plate boundaries and within plates?
**earthquakes formed along a plate boundary generally record the relative movement along this boundary (divergent, convergent, transform) >earthquakes along mid-ocean ridges -earthquakes are common along mid-ocean ridges, where two oceanic plates spread apart -most of these earthquakes form at relatively shallow depth & are small or moderate in size >how subduction causes earthquakes -it undergoes compression and shearing along the plate boundary -can produce very large earthquakes >how are earthquakes related to continental collision -during continental collision, one continental plate underthrusts beneath another. -colliions can be extremely complex, as different parts collide at different times and rates -collisions cause large tectonic stresses that shear and fault a broad zone within the overriding & underneath plates -as a result, earthquakes are widely distributed along the collision zone >how are earthquakes generated within continents -earthquakes can occur within continents, such as: continental rifts, continental transfer faults magmatic areas & reactive, preexisting faults
what are tectonic terranes?
**embedded within continents are pieces of crust that have a different geologic history than adjacent regions -tectonic terranes originate in a variety of tectonic settings >how to recognize a terrace and where they originate -a tectonic terrane is defined as being bounded by faults and having rocks, structures, fossils, and other geologic aspects >characteristics of tectonic terranes -major faults or shear zones separate terranes -different ages, fossils or rock chemistry -different sequence of rocks on either side of boundary -different tectonic settings for formation of rocks >original settings of terranes -island arc -oceanic island or plateau (hot spot) -accretionary prism -piece of continent -piece of seafloor *must be assed via subduction, collision, or strike-slip faulting
how do we study earthquakes in the field?
**geologist examine and measure faults in natural exposures and in trenches dug across faults -satellites & other tools allow faults to be studied in new ways >studying recent earthquakes in the field -dig trench study history of fault ruptures -measure offset of features and other evidence of past movement -document changes in topography >studying faults with satellites -ground displacement from repeated satellite measurements >studying the San Andreas fault -drilled into fault at depth to investigate rocks and conditions -studies of shallow trenches to document history
how are fossils used to infer ages of rocks?
**geologist use fossils to infer the ages of rocks and events, & help interpret the environment in which sedimentary layer accumulated >how fossils change in sequence of sedimentary rocks -can use overlap of two fossils to constrain age (G & H) -some spanned long time (g) -some species lived short time span so give narrow age range (fossil F) -fossils change up section in systematic way >how do we use fossils to correlate two sequences of rocks? -correlation: interpreted in which the units formed & where possible, fossils, especially idea fossils -stratigraphy: study sequences of rock, including the rock types, fossils, & inferred environments >principle of faunal succession -he noted that fossils changed systematically up through the section of rocks -was discovered by William Smith
how do we study geological structures and metamorphic features?
**geologust usually begin the process by mapping, making obersvation, & by collecting other data & samples, & measuring orientation of features >how to determine when a fault was active? -overlap: demonstrates that the fault has not moved since the overlapping unity was placed -faulted units: a fault must be younger than nay units it cuts across -units deposited during faulting: if fault displaces the land surface & forms a fault scarp -tilting: can determine age from tilting -intrusion: dikes & plutons that cut across a fault & themselves unfaulted indicate that the fault is older than the intrusion >how do we investigate metamorphic rocks? -minerals that are present -observed sequence of minerals -mineral chemistry
what are the characteristics and history of continental hot spots?
**hot spots within a continental plate is marked by high elevations, abundant volcanism, and continental drifting -hot spots can facilitate complete rifting and separation of a continent into two pieces an can hero determine where the splits occurs, >what features are typical of continental hot spots? -hot spots are volcanic areas interrupted to be above rising mantle plumes -characteristics associated with high elevations, volcanism, & presence of rifts -ex: Afar region of East Africa & Yellowstone region of the western United States >how continental hot spots evolve 1. solid mass rises from lower mantle and meals 2.broad domain uplift and rift 3 arms 3.some magma escapes to surface 4.normal faults form basins 5.rifting along two arms forms new ocean 6.third arm fails to break up continent 7.failed arm low so occupied by major rivers 8.seafloor spreading continues
what is the potential for earthquakes along the San Andreas fault?
**is responsible for many destructive earthquakes -99% probability that California will have a magnitude if 6.7 or larger in the next 30 years -the san Andreas accounts for the largest quakes ex; san francisco
What are some milestones in the Early History of life on earth?
**life on earth began before there was much oxygen in the atmosphere -precambrian organisms evolved, started to photosynthesize, and eventually produced an oxygen-rich atmosphere >Cambrian explosion -stronmatolites -Trilobites -Bacteria -Brachiopods >4 causes possible for the Great Dying (largest extinction event in Earth history) -
How do we explore the sea floor?
**mapping the oceans requires remote observation of the sea floor bottom by bouncing sound waves off the seafloor + Geologist + Oceanographers collect samples of rocks on and below the seafloor by going down in small submarines or by using ships to drill holes through the & rock >4 methods used to explore the topography & rocks of the sea floor -sonar (use sound waves to map depths) -submersibles (allow for close observation of geologic features) -drilling (use ships to drill holes in ocean floor) -satellites > what can we learn from ocean drilling? - drill holes into the seafloor to retrieve samples for later study -can identify type of sediment or rock -fossils, geologic time scale -isotopic ages: rate of deposition = thickness/time span >how do we image what is below the ocean floor? -record sound waves -> geophones - seismic reflection profile: shows tilted, folded, & faulted layers
what are some milestones in the later history of life on earth?
**mass extinction at the end of the Paleozoic era provided evolutionary opportunities for new life forms >organisms that lived during the Mesozoic Era -Dinosaurs -Early Mesozoic: Tiassic -Middle Mesozoic: Jurassic -Late Mesozoic: Cretaceous >what causes dinosaurs to become extinct? -huge eruptions -asteroid struck earth >Cenozoic Era -age of mammals -dinosaurs went extinct here -Early Cenozoic: zebra, tiger, horses -Late Cenozoic: homo sapiens
how are different structures and metamorphic features related?
**metamorphism may accompany deformation a& form cleavage & other metamorphic structures that can be closely related to folds & other structural features >how fractures, holding, tilting, & shear zones related? -help accommodate deformation by: displacement on faults & shear zones can cause folding & tilting of layers that are displaced: >thrust faults and folds commonly occur together in regional belts >how cleavage is related to folds -cleavage is typically parallel to the axial surface of folds that formed during the same episode of deformation
How does metamorphism occur?
**metamorphism occurs when a rock becomes unstable (may be unstable bc of the way grains/layers are arranged) >what causes metamorphism -temperature increases: high pressure compress the rock & tectonic stress -contact metamorphism: caused by local heating of magma -regional metamorphism: increase in stress (tectonics or burial) >what causes regional metamorphism? -burial -subduction (two plates converge) -heat & hot fluids >what chemical process occur during metamorphism & deformation -recrystallization (cleavage & foliation) -remobilization (chemical) -pressure solution (fluids) >what physical processes can occur during metamorphism -deformation of objects -rotation -shearing
how do earthquakes cause damage?
**most deaths of earthquakes are caused by the collapse of the buildings or there structures -destruction and collapse may result from ground shaking during an earthquake or it can occur later due to fires, floods, or large ocean waves caused by earthquakes >what destruction can arise from shaking due to seismic waves -tsunami -structural damage -landslide -aftershocks cause further damage -bride failure on weak materials -rupture >destruction that can happen after an earthquake -tsunami and other flooding >limiting risks form earthquakes -improve building design (engineer for earthquake)
how does a tsunami form and cause destruction?
**most of the earth is covered by oceans, so many earthquakes, landslides and volcanic eruptions occur beneath sea -> each can generate a deadly tsunami >formation of tsunami -most from fault-related earthquakes on seafloor -waves radiate away from area of seawater displacement -fault movement uplifts or down drops seafloor, displacing water -waves inundate land then water withdraws, both water movements causing damage -waves become higher as they approach shore >other ways Tsunamis form -underwater landslides -volcanic eruptions >kinds of destruction that a tsunami can cause -death -destruction along coastlines where human populations are concentrated -chile had an earthquake and 15 mins later a tsunami
where do Mountain belts & high regions form?
**mountain belts and other regions generally owe their high elevations to thick continental crust >settings in which regional mountains belts form -subduction zone -continental collision -mantle upwelling Ex: West North America, Zagros Mountains, Tibetan Plateau, Andes >what happens during the erosion of mountain belts -early mountain building -erosion & isostatic rebound -erosion & uplift deep rocks to surface >what controls regional elevation in north america -thin lithosphere
Where does metamorphism occur?
**mountains within belts along convergent plate boundaries >conditions vary with depth & tectonic settings -contact metamorphism: low pressure & high temperature (occurs where magma forms) -regional metamorphism: high pressure & low-high temperatures -subduction-zone metamorphism: high pressure & low temperature
How do reefs & coral atolls form?
**reefs are shallows, mostly submarine features, built primarily by colonies of living marine organisms, including coral sponges, & shellfish. Reefs can also be constructed by accumulations of sheets & other debris. >in what settings do coral reefs form? -barrier reef -carbonate platform -fringing reef >how atolls form -1. Volcanic islands forms, followed by formation of feigning reef -2. Islands cools and sinks but reef continues to build upward toward light 3. Volcano sinks below sea level, leaving reef as stoll >regions with large reef -Caribbean regions -East Africa -Philipines
What process can deform and change a rock after it forms?
**rocks are heated and subjected to higher pressure as they are buried. -new condition causes deformation & metamorphism -both^ work together to reform rock into a metamorphic rock
How do rocks respond to stress?
**rocks can subjected to stress resulting from burial, tectonic activity, heating or cooling & other.. - strong stress= rock deforms >forces and stress -force: push or full, expressed as amount of acceleration experienced by a mass -stress: the amount of force divided by the area upon which the force is applied -if same amount of force is applied to two wooden pillars -> stress force/area >What kinds of stress affect rocks, and what is the strength of rocks? -confining pressure: same amount of stress from all directions ( -differential stress: different amounts of stress from different directions (is what deforms rocks) -strength of continental crust increases w/ depth, then weakens -rocks become progressively weaker as they get hotter -small stress: strong enough to be undeformed -increase stress: rocks remains undeformed if strength of rock is greater than differential stress -too much stress: failure= fractures/folds >how rocks & other earth materials respond to force & stress -if rocks/earth material is imposed to great pressure 3 things happen: -> displacement: move from one place to another ->rotation: tilt rock, or spin it ->strain: change in size/shape
what are fossils?
**rocks contain fossils= evidence of ancient life >what are fossils & how are they preserved? -shells/hard parts -bones -replacement -cast or mold -thin film of material -impressions -amber -constructed feature >traces of creatures in rock record -footprints -burrows of worms >what determines whether a fossil is preserved? -hard parts (more likely if creature has shell, bones teeth) -rapid burial (creature remains are left on surface)
what are some common metamorphic rocks?
**rocks that have been changed (or metamorphosed) by increased temperature and pressure are metamorphic rocks >what rocks form when sedimentary rocks are metamorphosed -shale -> slate-> schists-> gneiss -sandstone -> quantize -limestone ->crystalline marble >rocks formed when igneous rocks are metamorphosed -basalt & andesite -> greenstone -rhyolite -> metarhyolite -plutonic rocks -> deformed granite >origin of hornfels -a non foliated rock -can form from any kind of starting rock
how do continents form?
**tectonics constantly reshapes continents -pieces can be removed by rifting or added by accretion of tectonic settings terranes. -continents are also internally rearranged as areas are shortened during compression, stretched during extension, and shifted horizontally by strike-slip faults >how old is north america -the oldest parts of the precambrian shield formed as early as 3.8 to 4.0 billion years ago, but most of the continent was added later as a series of terranes, mostly during precambrian, paleozoic, and mesozoic time >ages of other continents -they contains precambrian shields that are flanked by belts of successively younger rocks and deposits
how did the Appalachian and Ouachita mountains form?
**the Appalachiand & Ouachita mountains lie inboard of the East Coast & Gulf Coast of the United States -the continental margin is not currently a plate boundary >Paleozoic Evolution of Eastern N. America -rifting -spreading -island arc >Paleozoic Evolution of Eastern N. America II -northern collision with continental fragment -collision with Gondwana, forming main Appalachian mountains
what features characterize the interiors of continents?
**the features of continents tend to be tectonically stable, largely because they are far from plate boundaries. -sedimentary rocks formed within continental interiors contain an important record of ancient rivers, lakes, wetlands, sea level variations, and changes in global and regional climate >features common in continental interiors -continental shield -continental platform -broad basin •sedimentary rock •unconformity •crystalline basement >process the affect continental interiors -stresses from far-off plate boundaries and other tectonic activity can cause uplifts and basins -stresses from far-off tectonic activity may form faults, folds, domes, and basins -global climate change or other processes cause sea level to rise and fall
how did sedimentary layers west of Denver form?
**the foothills of the front of denver range west of Denver, contain spectacular exposures od sedimentary rocks > the layers have been folded and tilted along the mountain from & form dramatic landscapes
who was the geological timescale developed?
**the timescale was devised by using fossils or by noting the absence of fossils. Geologists commonly establish boundaries between units at places in the rock section where fossils record major changes in the types of life >assigning numeric ages to timescale -geologist and chemist assigned numeric ages to the timescale by using carefully evaluated isotopic ages at key localities -date volcanic layer -date a dike or clasts - fossil-bearing > how is the timescale used to assign number ages to rocks and events? -these ages of periods could be sued to estimate number ages of fossil-bearing units that lack datable igneous rocks
can earthquakes be predicted?
**there is no reliable way to predict when one will strike >areas most likely to experience earthquakes -near plate boundaries -messy collision zones -subduction zones -continental rifts >areas in the U.S. most likely to experience earthquakes? -Alaska subduction zone -Cascade subduction zone -New Madrid area -San Andreas and related faults -Intermountain seismic belt -Hawaii >long range earthquake forecasting -is based primarily on the knowledge of when and where earthquakes occurred in the past -help determine locations and recurrence intervals of past earthquakes -USGS assigned probability to each main fault in San Francisco area >short-term earthquake prediction -lasers monitor movement along fault -predictions based on past history of Parafield segment
why are sediments and sedimentary rocks important to our society?
**they are our main sources of groundwater, oil, natural gases, coal, salt, and material fro making cement and construction aggregate >sedimentary rocks are important bc they help us understand the geological history of earth + climate change + how life originated & changed through time -past events, sequence of life, & ancient life >sedimentary rocks help us understand earth's geological history -fossils in sedimentary rocks are the main record of how life originated and evolved -primary source of info about ancient environments, climate change, and past events >phrase sand and gravel -defined as resources, refers to sediment that commonly is excavated from pits and used in various types of construction -inclused clasts if various sizes, from clay, silt, and sand, to pebbles, cobbles, and boulders -the materials is sometimes used as it is, but more commonly is poured through large screens to sort the class by size
how to determine the location and size of an earthquake?
**using the combined seismic data from several instruments, seismologist calculate where an earthquake occurred and its magnitude ( how large it is) >how to locate earthquakes -seismologists maintain thousands of seismic station that sense and record ground motions 1.seismometer network sense a quake 2.select earthquake records 3.estimate station distance epicenter 4.triangulate the epicenter >how do we measure the size of the earthquake -measuring amplitude (measure S-wave amplitude for local magnitude) -magnitude (connect amplitude and distance on plot) >what can the intensity of the ground tell us about an earthquake? -we rely on reports of damage and shaking intensity as a way to classify the relative sizes of the earthquakes
what is the significance of an unconformity?
*def; buried surfaces called conformities, can represent large intervals of time missing from a rock sequence >3 types of unconformities -angular unconformities (represents gray limestone deposited under water -> limestone folded and eroded -> sediment deposited on top of eroded surface forming an unconformity) -nonconformities (form by non layered rock uplifted and eroded -> erosion surface bored by sediment) -disconformities (form from deposited of horizontal layers -> weathering erodes surface -> erode surface covered by later sediment)
where do most earthquakes form?
*earthquakes form where plate tectonics are most active -most earthquakes occur along plate boundaries -earthquakes can only happen in solid rocks -the deeper the earthquake happens, the less that happens on the surface -transform= shallow earthquakes -convergent= deep earthquakes -divergent= most shallow >where they occur -subduction zones -interior of some continents -other plate boundaries
what are different types of faults?
*faults are fractures along which rocks have slipped >how do we describe faults -dip: water flowing down \ -strike: horizontal line of water \- -dip-slip fault:one block moves up or down relative to the other block -strike-slip fault: slip occurs horizontally -oblique-slip fault: slips in oblique direction (slanted)\ >rocks above and below fault: -hanging wall: is above the fault (head) -footwall: where miners can walk >main types of faults: -normal fault: hanging wall moves downward relative to footwall -reverse fault: hanging wall moves up relative to the footwall -strike-slip fault: when rocks along a fault move with side-to-side motion ~left lateral: block on opposite side moves to left ~right lateral: block on opposite side moves to right >relative displacement of fault rocks -horst: -- -Graben: drops down down normal fault -\/-
How do fine-grained clastic rocks form?
*fine-grained consist f grains that are smaller than sand >characteristics -fine sediment is easily transported by water or wind -fine sediment can remain in transit until it reaches fairly quiet conditions in lake, sea, or floodplain -result: shale, siltstone >fine-grained rocks - fine-grained rocks consist of mostly clasts of fine grains of silt & clay -rock dominated by silt is siltstone (finest particles) -> can become shale when lithified >the land environments in which shale and siltstone form -they accumulate in several terrestrial (on-land) settings: -floodplains -wind -lake >environments near shoreline & further offshore where shale and siltstone form -shallow sea -lagoon -deeper sea -silt and clay in several shoreline and ocean environments -the ocean basins are vast, and clay covers more of the seafloor than any other type of sediment = shale is common sedimentary rock
How do carbonate rocks form?
*limestone and relate sedimentary rocks are called carbonate rocks bc they consist of carbonate ion combined w/ calcium, magnesium, other elements.. > most carbonate rocks form directly from water through chemical or biological processes >characteristics -limestone is common rock & exist in many varieties, all of which consist mostly of the mineral calcite -calcite can convert ti the mineral dolomite by the addition of magnesium, which produces the carbonate rock dolostone >environments in which limestone form -most limestone forms in marine environments -BUT can be deposited around springs, in lakes & as coatings & other features on the floors, roofs, and walls of caves >where carbonate rocks form -most carbonates rocks form in marine settings: reefs, & other shallow-water environments on the continental shelf -ALSO, from on low-dying mud flats & along shorelines dominated by carbonate sand >how dolostone forms -made of dolomite mineral -resistant to weathering & erosion >how carbonate rocks are expressed in the landscape -limestone is very common + distinctive rock that covers areas of North America -recognized by gray color, well-bedded, pock-marked erosion texture -pillars:areas that are less fractured/ more difficult to dissolve -sinkholes: if the rood of such a cave collapses, a sled depression (can damage buildings, roads, & utilities)
How do changing environments create a sequence of different kinds of sediment?
*most sedimentary rocks are in a sequence, w/ multiple layers formed now on top of another. >the layers in a sequence may all be the same rock type, but more commonly include a variety of rocks >what happens when environments shift through time -result in a sequence of sedimentary rocks -transgression: common change is for seas to advance across a region, covering more land with time, due either to a rise in sea level or a lowering of land -section formed during transgression: ->limestone ->mudstone ->sandstone ->older units >what happens when sea moves out -when the sea retreats and more land is exposed -regression: occurs when sea level becomes lower or the land is uplifted -section formed during regression ->sandstone ->mudstone ->limestone >why sedimentary layers end -bc a facies ends (limit of environment) -bc it is deposited only within a channel
Where does sandstone form?
*occur in many environments such as: river channels sand dunes on land, & submarine canyons beneath the oceans >characteristics of sandstone -mostly composed of sand-sized grains -moderately to well sorted -quarts is the dominant mineral in most sandstone >environments where sandstone forms -sand dunes -floodplain (flat area w/ grass + trees) -desert dunes -rivers >how sandstone forms along shorelines -most beaches are dominated by sand= beach deposits become sandstone -sand also dominates many parts of deltas (especially the channels + shallow-water parts) >how sandstone form in offshore environments -sand accumulates at sites father from shore, in deeper water -sand is derived from the erosion of continents, islands, reefs, & barrier islands but may be carried to deeper water by turbidity currents
What sedimentary environments are near shorelines and in oceans?
*oceans and their shorelines are dynamic environments with wind, waves, and ocean currents transporting sediment eroded from the coastline or brought in from elsewhere >Beaches -are stretches of coastline along which sediment has accumulates -most consist of rounded gravel, cobbles, or boulders >Lagoon (the sheltered water) -water near the shoreline may be sheltered by offshore reefs or islands -near-shore parts of lagoons contain sand, mud & stones derived from land -outer parts might have: sand & pieces of coral eroded from a reef >deep seafloor -generally receives less sediment than areas closer to land -its sediment is dominant by fine, windblown dust & by remains of mostly single-celled marine organisms >costal dunes -commonly form where sand & finer sediment from the beach blown or washed inland & reshaped by the wind >Tidal Flats flats -most tidal flats are covered by mud and sand or are rocks >submarine deltas -the muddy or sandy front if the delta may be unstable & material can slide down the slope, sending sediment into deeper water >barrier islands -
Where Do Breccia and Conglomerate Form?
*they both include clasts in a matrix of finer material, which can be sand, clay, slit or mix of all 3 >breccia -contains angular clasts -suggest minimal transport -forms from thick slurries of mud & larger clasts that originate in mountains (mudflows/febris flows) >conglomerate -contains rounded clasts -suggests longer transport -forms if steep mountains streams deposit sediment along the mountain front
how do we study sedimentary sequences?
*we do this by observing a sequence of rocks and noting characteristics that provide clues to the environment in which each rock unity formed >then interpret the past environment by comparing these characteristics to sediment in modern environments >studying a sequence of rocks allows us to infer how conditions changed over time >attributes of sedimentary rocks that are indicators of environment -color of rocks -clasts size, shape, and sorting -thickness of bedding -types of bedding (large-scale cross beds in well-sorted sandstone indicates deposition by wind) -mudcracks (most have been deposited on land and in environments where wet sediment could dry out) -fossils (provide info of temp., salinity, & clarity of water >interpret/observe sequence of sedimentary rocks -observing sequence of layers
what are the characteristics of clastic sediments?
*when clastic sediment becomes sedimentary rock, the name assigned to the rock depends on the side and shape of the clasts >size -boulders} -cobbles }Gravel -sand {sand} -clay {mud} >shape (tells us how far rocks have traveled) -angular clasts -rounded clasts (traveled the most) >sorting -poorly sorted (clasts near their source are usually poorly sorted/angular/large -moderately sorted -well-sorted (ex: sand on dunes) *farther from source means smaller, rounder
what are some major world earthquakes?
-Chile -Turkey -Taiwan -Nicaragua -Armenia -Japan
what were some major north american earthquakes?
-Northridge -Hebgen lake -Mexico -San Francisco -Alaska -Charleston -NEW MADRID biggest one
what are nonelastic sedimentary rocks and how do they form?
-nonclastic rocks form when dissolved chemical precipitate from water >Limestone -when cemented together, shells & coral skeletons form a variety of rock known as limestone (made mostly of calcium carbonate & easily seen fossils) -limestone forms through a combination of biological and inorganic processes >accumulation of plant materials -plant debris can accumulate in greta thickness in wetlands & bogs, where it partially/wholly decays & can be compacted into sedimentary rock >halite -precipitated mineral
How is palaeomagnetism used to study the ocean floor?
> Describe how earth's magnetic field is generated -liquid outer core contains convection currents -normal magnetic field (red needle on top) -reversed magnetic field (red on bottom)
What sedimentary environments occur on land?
>Mountain environments (characterized by steep slopes) -most have high elevation -erosion is vigorous on such steep slopes & provides abundant sediment -the sediment can be transported out of the mountains & into other settings >streams & rivers in mountains (braided river) -typically have steep gradients -streams & rivers leave mountains = develop a braided appearance > Sand Dunes -wind picks up & moves sand grains & finer particles >Glaciers -snow becomes compacted to ice, which flow downhill as ^ -as glaciers move, they erode underlying materials & carry sediment away > Gentle meandering river - rivers that flow over gentle terrain commonly meander gracefully -Flood plains of meandering rivers are built, layer upon layer, by mud and sand carried by floodwaters >Lakes -some lakes are allays filled with water, but others dry completely when the water evaporates or the it seeps into underlying materials
Why do sedimentary rocks have layers?
>beds -may be a single thick layer or may include many smaller layers (ex: limestone or sandstone) **almost all sedimentary rocks contain layers >types of layers -thick layers -thin layers -gradational boundaries -sharp boundaries -graded beds: (visibly thick layered) -cross beds: (angular to other beds) -parallel beds: layered (pancake looking) >how layers in sedimentary rocks form -discrete event -change in current -sediment supply -sea-level change -climate change
what types of rocks do clastic sediments form?
>conglomerate >Breccia (gravel-sized clasts) >Sandstone (sand-sized clasts_ >Shale (mud-sized clasts) >how clastic sediments become clastic sedimentary rocks -1st compaction: sediment is buried beneath more sediment materials or other materials, increasing pressure pushes clasts together -2nd cementation: pore spaces are commonly filled with water containing dissolved materials, which precipitate to form minerals that act as a natural cement that holds the pieces of sediment together >common natural cement -calcite -silica -clay minerals -iron oxides
What are major features of the Deep Ocean?
>features -seamount (isolated mountains) -abyssal plain (much of the ocean floor) -oceanic trench -accretionary prism -island arc -mid-ocean ridge >Age of seafloor, depth of seafloor, & sediment thickness -the thickest sediment is along continental margins -Deepest seafloor is oldest -mide-ocean ridges less deep because young -aye increases systematically out from ridge -age patterns truncated at trenches because of subduction
how did smaller seas near Eurasia form?
>formation -north sea: Continental drifting during formation of Atlantic -Persian Gulf: loading by thrust sheets during collision -Red Sea: rifting then early stages of seafloor spreading
How do local mountains form?
>how mountains are formed by volcanism -by pilling volcanic material on a preexisting surface -lava flow= loft/ steep mountains >how faults build mountains -thrust faulting (Denali) -normal faulting (death valley) >how folding builds mountains -folding can warp & uplift earth's surface as well as the underlying rock layers -uplift & erosion of folded, hard layer can create a topographic high >how differential erosion forms mountains -granite pluton resists erosion -hard rock layer resist erosion
How do Oceanic Islands, Seamounts, and Oceanic Plateaus form?
>how oceanic islands and seamounts form? -eruptions of lava into seafloor -volcano rises above the sea as an island -top of mountain beveled off by waves: crust cools & island subsides below sea >how oceanic plateaus forms -some large regions of the seafloor rise a kilometer or more above their surroundings forming -> oceanic plateaus 1.rising mantle plume at hot spot 2.submarine flood basalts pour onto seafloor 3.plateau forms over several millions years >distribution of hot spots, linear island chains, & oceanic plateaus -Hawaii -Tahiti -Azores -Ontong Java Plateau
how do we study ages of landscape?
>how we infer age of a landscape -landscape surface younger than rocks on which it is carved -landscape surface older than rocks deposited on top >how does a typical landscape form? -preexisiting rock covered by sea -sea deposits layer of sediment -environment changes, deposited more rock -deposition stops -area eroded by rivers, etc. -continued erosion
how do we investigate deep processes?
>investigate deep conditions -study rocks with deep origins -use computers to model processes -replicate deep conditions in a laboratory >how seismic waves help us explore earth's interior -seismic observation from different directions (granite, sedimentary rocks) -interpretation by comparing observed with what was expected if all same material >what process are occurring in the mantle and the core-mantle boundary -seismic velocities of the lowermost mantle vary from place to place -seismic wave velocities increase abruptly at the Moho (crust-mantle boundary) when they pass from the crust down the mantle -velocities vary within mantle due to major changes in mineralogy and increasing density with depth, and because of upward and downward flow of mostly solid mantle material
how do we explore earth's subsurface?
>physical samples -exposures of deep, unlisted rocks -magma that brings up pieces of deeper rocks -mines & drilling >geophysical surveys -electric surveys -magnetic data -gravity data -gravity model -seismic-reflection data
how do rocks respond to changes in stress, temperatures, and fluids?
>respond to stress -depends on 3 main factors: magnitude of stress, pressure & temperature + amount of fluid present in the rock >how rocks respond to differential stress -compression: when stress buses in on rock -tension: when stress is directed outward -shear: on edges of rock in opposite directions -shallow levels: rocks fracture -deeper levels: rocks flow >how rocks fracture -joints: crack where rock has pulled apart. Joints form when stress pulls a rock apart -fault: have slipped past one another -stresses that form joins: burial and tectonic forces/ cooling and contraction/ unloading >how a fault forms -cylinder rock: small stress -rock bulges: increase stress -failure : too much stress -fault: slip of one rock |\
where do Basins form?
>settings where basins form -passive margin -continental rift -normal faulting -foreland basin -strike-slip faulting -regional subsidence >Major basins -Cenozoic basin -Mesozoic basin -Paleozoic basin *basics formed along the San Andreas fault >The Michigan Basin -a deep basin beneath Michigan contains a fairly complete column of sedimentary rocks deposited during the early parts of the Paleozoic Era
How did smaller seas of the pacific form?
>smaller seas of the pacific -Bering Sea: New subduction -Sea of Japan: Back-arc rifting -Philippine Sea: Back-arc spreading >how the gulf of California formed -1. subduction along west coast, to later become a coastal transform fault -2. transform boundary & spreading centers jump inland, carving off the Baja
Where do clasts come from?
def: most sediment is pieces of other rocks known as clasts, other from water when dissolved material is precipitated by chemical reactions A. >physical weathering -physical breaking of rock -4 major causes: near-surface fracturing frost and mineral wedging thermal expansion biological activity >chemical weathering -includes several types of chemical reaction that affect a rock by breaking down minerals, casing new mineral to form B.>there are many different products of weathering because: -type of material (exposure to earth' surface have various compositions that affect how they respond to physical and chemical processes -different parts of material (sediment rocks contain more than on mineral & each reacts differently to weathering) -importance of fracturing (fractures permit water, air, and organisms to invade the rock, which causes more chemical & physical weathering) C. >how do transportation and erosion affect sediment? -once weathering has loosened pieces of rock, the pieces can be transported by rivers, glaciers, wind, and other forces. -during, transportation, larges clasts are broken & abraded to produce smaller ones
