GEN GEOL PHYSICAL
GEN GEOL PHYSICAL GEOL 1001
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This 84 page Class Notes was uploaded by Nia Greenfelder on Tuesday October 13, 2015. The Class Notes belongs to GEOL 1001 at Louisiana State University taught by G. Hesp in Fall. Since its upload, it has received 6 views. For similar materials see /class/222784/geol-1001-louisiana-state-university in Geology at Louisiana State University.
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Date Created: 10/13/15
Week 2 Geol 1001 armory 24201 The Solar System Formation 39 39 l 39 into an accretion disc 0 he Particles will rotate until being compacted into the center The ball at the center grows dense and hot The center will eventually become a sun v Fusion reactions begin the sun is born The 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 planetoids small planets 0 Soon a small planetoid collided with Earth Debris forms around the Earth The debris coalesces and forms the moon Then the atmosphere develops from volcanic gases When the Earth becomes cool enough Moisture condenses and accumulates and the oceans are born 0 Iourney to the Center of the Earth 0 The Earth is not a solid singular unit but is made up of concentric shells o The Earth has layers 0 There is slow movement within the Earth Comment JALl Cloud ofgases and energy create a sp ng sk 0 some liquid some plastic Grotherm 0 Temperature increases at the rate between 70 to 150 per kilometer into the east 0 Temperature and pressure change drastically as goingtoward center of the Earth 0 When nuclear explosion the energy is released in seismic waves 0 Some waves are straight bent fast andor slow I P waves primary I S waves secondary 0 Due to the waves they can determine what was the layer made of how hot it was and what was the pressure I Test Question 0 We know howthe Earth is made due to systemic waves 0 The center of the earth is as hot as the sun Earth39s Interior Layers o Crust Comment JALZ Test question Know which ones are the most dense in comparison to the others Don t need to know numbers 0 Continental 0 Oceanic o Mantel 0 Upper 0 Lower 0 Core 0 Outer Liquid 0 InnerSolid 154m izooo F a s ge 5370 km Earlh s tenler The Core I An ironrich sphere with a radius of 3471 km I 2 components with differing seismic wave behavior I Outer Core I Liquid ironnickelsulfur I 2255 km thick I Density 1012 gcm3 I Inner core I Solid ironnickel alloy I Radius of 1220 km I Density l3 gcm3 lLithospherel Comment JALS Know what this is Theigid h I k ml dlith ph CommentlJN l hospheredenswgt astheroaahersdensity 0 Makes up Earth39s tectonic plates 0 uppermost mantle crust 0 divided by Moho mohoric discontinuty Aethermosphere I Part of the upper most mantle rock movement asthemosphere and PLASTIC part of the mantle and upper most mantle Crust o It is relatively light 0 Crust divided into two parts 0 Crustal density controls surface position I lContinentalcrustl Comment JALS Composed ofsilica and 0 Less dense floats higher oxygen I ceanic crust l Comment JALS Composed ofiron and o More dense floats lower magnesum january 26201 1 CLASS CANCELED Geol 1001 january 28 2011 Plate Tectonics Basic idea of plate tectonics Earth39s surface is composed of a few large thick plates that move slow and change in size Intense geologic activity concentrated at plate boundaries Combination of continental drift and seafloor spreading hypotheses in late 1960s Plate tectonics explains 0 Global distribution of o Volcanoes o Earthquakes o Faults 0 Mountain belts 0 Features of seafloor 0 Evolution of continents and oceans Map ofthe continents 0 Each continent pretty much has its own plate and each plate moves around the earth 0 The major plates of the world 0 Pacific North American South American African Eurasian indo Australian and lone morel l Comment JAL7 Look up 0 Continental drift was originally proposed by Alfred Wegener a German meteorologist in 1912 o Wegner used several personal observations to support his idea and hypothesized that all of the present day continents were once part of a single supercontinent called Pangaea Early case for Continental Drift o Pangaea to present day spanning 225 million years 0 Puzzlepiece fit coastlines of Africa and South America has been long known 0 Wagner initially observed the potential fit of the continents Geological Evidence 0 Rock picture 0 Basalt ll Lava flows 0 Sandstone Shale Glossopteris fossils o Glacial till o In early 1900392 Wegener noted in South America Africa India Antarctica and Australia have almost identical ate Paleozoic rocks and fossils Comment JALS ISimilarlayersofrock Glacial Evidence foundin o o e The only way to explain thiswas ifthe continentswere once one o Wegener reassembled continents into the supercontinent Pangaea o Pangaea initially separated into Laurasia and Gondwanaland 0 These glacial features are best explained if the continents were part of Pangaea Paleomag39netism and Continental Drift Revived 0 Studies of rock magnetism determination of magnetic pole locations through time o Paleomagnetism uses mineral magnetic alignment direction and dip angle to determine the direction and distance to the magnetic pole when rocks formed Map of Lines of magnetic force Blackline geographic north pole red line magnetic Apparent polar wandering Fig 28 This proves plate tectonics because we assume Pangaea happened magnetics are more similar and can be explained o wauu39e curves for 439 quot suggest real movement relative to one another Seafloor Spreading And Sea oor Magnetization o The magnetic N and S switched aka the magma came up and pushed outward when cooled over time and the rocks switched This video is the evidence for continental drift as well Sea oor Spreading o In 1962 Harry Hess proposed seafloor spreading o Seafloor moves away from the midoceanic ridge due to mantrle convection Hot mantle rock rises under midoceaninc ridge 0 o Seafloor rocks and mantle rocks beneath them cool and become more dense from mid oceanic ridge When sufficently more cool and dense these rocks may sink back into the mantle at subduction zones 0 Downward plaunge of cold rocks gives rise to oceanic trenches Plates and Plate motion 0 Tectonic plates are composed of relatively ridgid lithosphere o Lithosphere thickness and age of seafloor increase with distance from midoceanic ridge I Plates quotfloatquot upon ductile aethenosphere I Plates interact at their boundaries which are classified by relative plate motion Evidence of Plate Motion 0 lPicturel Comment JALQ De cts rock ages and they varryfrom miccoene tolatej rass39c o The global dIstrIbutIon of seIsmIc and volcanic actIVIty Plate margins are outlined by seismic belts where 90 percent What Causes Plate motions o The plates are not stationary they are slowly drifting over the denser atmosphere 0 convection currents in the mantle quotdrivequot the plates along their path of movement 0 Picturesl n ics a hot pot then mg the process Comm JAL1039 One companng it to a picture depicti Plate Tectonics Week Three lemma31201 o Convection causes plate tectonics 0 Liquid plastic core heats up magma that surrounds the core Causing the magma to quotrisequot like boiling water hot water sinks cold water rises o 0 Ridge Push 0 Drive plate tectonics from hot spots 0 Rising magma parts the old oceanic crust and forms a new one when the magma cools down 0 Creates a mountain range in the ocean o Slab pull follows the mantle flow and the plates begin to pull down and become more dense and heavier which causes it to sink Work with ridge pull Plate boundaries 1 lDivergent margins Comment JALl All major oceans were caused y divergent creating underwater rnountain ranges At divergentplute boundaries plates move away from each other l and eventual ridge uplift Comment JALZ The sarrie thing is happening in 39 I Marked by 39 39 l 2 Convergent margins I Convergentplate boundaries plates move toward one another I Nature of boundary depends on plates involved oceanic vs continental 0 Ocean Ocean Comment JAL3 heavy metal i Comment JAL4 Look up there s three types Comment JALS They rrierge then oceanic 0 Types 0 iTwo continental plates converging O O V I u r i I Magma is generated at subduction zones where the dense oceanic plate is pushed 0 Ocean to ocean I i i I Two types of Crust o Crustal density controls surface position I Continental crust 0 Less dense floats higher I Oceanic crust o More dense floats lower 3 Transform margins crust sinks because it is neavercreating a ridge and volcanoes where convection is released through the v o voicanoes and that show you get ia e Comment JAL7 Where the rnantie submerges into the earth seduction zone is more de ned when two 2 continents are ernerging Continental crust is light because of silica and so when theyrrierge together they still attempt to rise Oceanic searioor is the heavy basaltic so it doesn t res39st sin ing C ment JAL6 They both searri to sink because of their baEltic weight causing inner water volcanoes creating islands Continental collision zones I Comment both seam to quotrisequot when this happens the tallest mountains in the world are formed Comment JALS Mount Everest in the Hi s I The creation of the Himalayas happen when India merged and the two plate rnaiaya Transform Plate Boundaries I At transform plate boundaries plates slide horizontally past one another Comment JALQ Can happen over night can cause earthquakes Mantie plumes and Hot spots I Monte plumed narrow columns of hot mantle rock rise through the mantle Comment JALlD Hawaii is the most famous o Stationary with respect to moving plates one 0 Hawaii was created because the plates shifted while the mantle plums continued o Divergent Plate boundaries February 2201 1 Rocks Rocks are earths materials made from minerals Most rocks have more than one kind of mineral 0 Example granite I Potassium feldspar 39 Quartz I Hornblende Some are monomineralic Limestone calcite Rock salt halite Glacial Ice Crystalline Structure 0 Atoms in a mineral are specfically ordered 0 Crystalline structure based on atomic patterens Polymorphs 0 Same composition but different crystal structure 0 Diamond and graphite are carbon polymorphs C 0 Diamond Strong covalent bonds hardest mineral o Graphite weaker Van der Walls bonds softest mineral Mineral Physical Properties Characccteristiiics deeetttermiiined by your five senses Used tooo ID mineras Properties depend upon 0 Chemical composition 0 Crystal structure Some are diagnostic o Pyrate I Cubic crystals high specific gravity striated crystal faces black streak metallic luster du brassy color sufer smell when crused erroneously mistaken for fools gold 0 Minerals have a unique set of physical properties Physical propelties 0 Common properties 0 Color I Color is diagnostic for some minerals o Olivine is olive green 0 Azurite is always blue Some minerals may exhibit a broad color range 0 Quartz clear white pink purple gray etc Color varieties often reflect trace impurities o Streak Color of a mineral crushed on unglazed porcelain Streak is often a useful diagnostic property 0 Congruent streak streak color same as mineral o Magnetite black mineraback streak o Incongruent streak streak color different than mineral o Luster The way the mineral scatters light Two subdivisions 0 Metallic looks like a metal 0 Nonmetallic O Vitreous glassy Satiny Silky Resi nous Pearly Etc 00000 O Harness I Scratching resistance of a mineral I Hardness compared to the Mohs Hardness Scale H Talc graphite Gypsum Calcite Flurite Apatite Orthoclase Quartz Topaz Loooximuuwa Corundum 0 ldiamondl Comment JAL11 Cari scratch any other mineral and is the hardness scale Specific graVIty 0 Related to density mass per volume H 0 Mineral wieght over weight of equal water Crystal Habit Crystal habit is the ideal shape of crystal faces dea growth requires ideal conditions Many terms are used to describe habit o e cubes octahedra blades hexagonal prisms dodecahedra etc Fracture some minerals lack planes of weakness Due to equal molecular bonds in all directions These minerals don39t have clevage they fracture 0 Ex Quartz displays a chonchodial fracture I Shaped like theinside ofaclam shell I Breaks along smooth curved surfaces I Produces extremly sharp edges Cleavage o Tendency to break along planes of weakness 0 Cleavage produces flat 0 Examples of clevage lDirectionl AW o o 2 directions at 90 degrees 0 2 directions not at 90 degrees ie 60 degrees 0 3 direction at 90 degrees 0 3 directions not at 90 degrees Mineral compositions 0 Only about 50 minerals are abundant o l985 of crustal mineral mass is from 8 elements Comment JAL13 Only 50 oftnemineralsor bAz 69 4000 are common 0 o O Si 277 l l Comment JAL14 Makes 0 AL 821 0 Fe 5 o Ca36 o Na28 o k26 0 Mg 21 0 all others 15 Mineral classes 0 miiinerals 39 quot39 quot bbbytheir 39 quoti n o silicates si 02439 rockforming mins o oxides 02 Silicate minerals o licates are known as the rockforming minerals 0 they dominate the Earths Crust o o The anionic unit is L Hquot hedron Comment JAL15 Present in all silicate 39 l o 4 oxygen atoms are bonded to llsilicon atom mmeras Comment JAL16 eally small Oxygen MUCH 0 Silicon Is tiny oxygen Is huge bigger Homework 1 Due 1000am on Monday February 7 2011 Note You will receive no credit for late submissions To learn more read your instructor39s Grading Policy Switch to Standard Assignment View Reading Quiz Chapter 1 Question 1 Part A Hint Al Which of these events is an exam le of anatural hazard A natural hazard is a threat to people or property in the shortterm or longterm future ANSWER E the 1906 earthquake E a possible eruption of Mount Rainier that would devastate Seattle Washington 3 a landslide that is about to happen in a remote area of Alaska E the 2004 Indian Ocean tsunami Correct Reading Quiz Chapter 1 Question 3 Part A Hint Al Which exam le below re resents relative a e dating Hint not displayed ANSWER 3 EDDIE L1 Angela is 15 years old and Karen is 7 years old Karen currently plays soccer Angela played soccer three years ago Angela is older than Karen Karen s birthday is August 2 Correct Reading Quiz Chapter 1 Question 4 Part A When a researcher publishes research in a national journal What part of the scienti c method is he or she most likely involved with Hint Al A national journal is a platform that scientists use to communicate to one another their most recent research ANSWER E a theory I curiosity I a law E a hypothesis Correct Reading Quiz Chapter 1 Question 8 Part A Which of the layers listed below is considered the brittle outer layer of the Earth Hint Al Hint not displayed ANSWER U oceanic crust E crust E asthenosphere U continental crust E lithosphere Correct Reading Quiz Chapter 2 Question 1 Part A Which of the following observations was included as evidence for Wegener s continental drift hypothesis Hint Al Hint not displayed ANSWER E trenches at subductlon zone boundaries E the jigsawpuzzle fit of the continents 3 ocean ridges E sea oor spreading Correct Reading Quiz Chapter 2 Question 2 Part A Which one of the following statements is TRUE Hint Al Hint not displayed ANSWER E Arock changes its magnetic field direction over geologic time as Earth39s magnetic field changes I Geomagnetic reversals cause the movement of the tectonic plates E Earth s magnetic field reverses over geologic time D Magnetic stripes on the ocean oor provide weak evidence for sea oor spreading Correct Reading Quiz Chapter 2 Question 3 Part A Beneath Earth39s lithosphere the hotter weaker zone known as the 7 allows for motion of Earth s rigid outer shell Hint Al Hint not displayed ANSWER E outer core I oceanic crust E crust 3 plate boundaries E asthenosphere Correct Reading Quiz Chapter 2 Question 4 Part A Which boundary is characterized as a long linear rise in the sea oor with shallow earth uakes and volcanic activity found along its length Hint Al Hint not displayed ANSWER transform boundary 3 E continenticontinent convergent boundary 3 subduction zone E divergent boundary Correct Reading Quiz Chapter 2 Question 5 Part A Deepocean trenches are formed by Hint Al Hint not displayed ANSWER E motion along transform faults E the subduction of lithosphere into the asthenosphere E sea oor spreading E the collision of continents Correct Reading Quiz Chapter 2 Question 6 Part A Where eo ra hically can you find transform faults Hint Al Transform faults move laterally when subjected to stress ANSWER E along the east coast of the United States 3 near the MidAtlantic Ridge near the MidAtlantic Ridge and along the San Andreas transform E plate boundary 3 along the San Andreas transform plate boundary Correct Read pages 60762 in your text Reading Quiz Chapter 2 Question 8 Part A Which of the following is one of the remarkable realizations associated with the discovery of sea oors readin Hint Al Hint not displayed ANSWER E The crust of the oceans is very young relative to the age of the continental crust E The crust of the continents is denser than the crust of the ocean I The Hawaiian Islands were formed by subduction E Mountains are denser than mantle Correct Reading Quiz Chapter 2 Question 9 Part A The Hawaiian Islands were formed as a result of Hint A1 Hint not displayed ANSWER sea oor spreadmg EU a mantle plume L1 oceanwontinent convergent boundary 1 oceanmcean convergent boundary Correct Quiz Chapter 3 Question 1 Hint not displayed ANSWER C It does not naturally occur 3 It does not have an orderly crystalline structure E It is an organic compound C It is not a solid substance Correct Reading Quiz Chapter 3 Question 4 Part A Two isotopes differ from one another because they have Hint Al Isotopes of an element have the same atomic number ANSWER E different numbers of electrons C more than one nucleus per atom E different numbers of neutrons E different numbers of protons Correct Reading Quiz Chapter 3 Question 6 Part A Which of the following characteristics is NOT considered a h sical ro ert of a mineral Hint A1 Hint not displayed ANSWER g C luster E hardness E silicate structure U streak Correct Reading Quiz Chapter 3 Question 7 Part A Out of the named 4000 minerals how many are abundant Hint Al Hint not displayed ANSWER E a few dozen 3 approximately 100 E none I almost all of them Correct Reading Quiz Chapter 3 Question 8 Part A Which of the following statements regarding a single silica tetrahedron is FALSE Hint Al Hint not displayed ANSWER The atoms of the tetrahedron are strongly bonded together It has a net negative charge Cations can bond to it DUE F It has four silicon atoms l I Correct Reading Quiz Chapter 3 Question 10 Part A Minerals such as biotite are dark because of their Hint A1 Hint not displayed ANSWER 39 E II39OII content 3 ability to cleave U potassium content E ability to form in the mantle Correct Reading Quiz Chapter 3 Question 9 Part A The mineral uartz is an example of a Hint A1 Hint not displayed ANSWER smgletetrahedron structure I 3 sheet silicate E singlechain silicate E threedimensional framework silicate Correct I Reading Quiz Chapter 12 Question 2 Part A If you were to ll a bottle with clay iron lings water and air shake its contents and then let it sit what would you eXpect to see from bottom to top Hint Al Hint not displayed ANSWER 39 I clay iron water an 3 air water iron clay E iron clay water air I water air iron clay Correct Reading Quiz Chapter 12 Question 3 Part A The speed at which seismic waves travel through Earth s layers depends largw on Hint Al Hint not displayed ANSWER 3 the temperature of the material the composition of the material the amount of sodium in the material all of the above E the temperature and composition of the material Correct Reading Quiz Chapter 12 Question 8 Hint Al Hint not displayed ANSWER 39 E convection E radiation E conduction E primordial heat Correct Reading Quiz Chapter 12 Question 9 Part A Evidence su orting the conclusion that Earth39s mantle convects comes from Hint not displayed E large superplumes of hot rock rising from the coreimantle boundary C Earth39s magnetic eld E the geodynamo U a solid inner core Correct Score Summary Your score on this assignment is 831 You received 766 out of a possible total of 922 points G601 1001 Hesp january 21 2011 The Science of Geology 0 Geology is the science that science that persues an understanding of planet Earth 0 Physcial geology Materials composing Earth and processes waves glaciers winds etc 0 Historical geology Orgin of Earth and its development through time 0 Geology people and the enviroment 0 Natural hazards resources world population growth and the enviromental issues I New Zealand active faults very active sizemic waves resulting in earthquakes I Also many active and inactive volcanoes 0 Geological time o The magnitude of geologic time I Involves vast times millions or billions of years I Many geological process are very gradual o A 100 year process is considered very fast 0 Even a 1000 year process is considered fast 0 Earth was created 45 billion years ago 0 Some processes originating at creation are still occuring I Relative dating 0 Dates are placed in their proper sequence or order without knowing their age in years I Absolute dating 0 Accurate dates to events 0 Figure 19 o The nature of scientific inqury 0 Scientific method I Scientific method 0 Involves gathering facts through observation and formulation of hypotheses and theories 0 How or why things happen are explained using 0 Hypthesis a tentative or untested explanation 0 Theory a welltested and widely accepted view 0 The Rock Cycle part of the Earth system 0 The loop that involves the processes by which one rock changes to another 0 Figure 122 Birth of the Earth 0 Modern View of the Universe 0 Current concepts differ widely a 100 years ago I Earth is one of eight planets in solar system I The solar system is in the Milky Way galaxy I Our Sun is 1 of 300 billion stars in the galaxy o The expanding universe 0 Hubble 1929 I Development of the Expanding Universe Theory analogous to the llexpanding bread with rasins 0 Big Bang 0 When did the Expanding Universe begin I The best answer so far Big Bang I All of the mass and energy in the universe put into a single point I It exploded 137 billion years ago The Solar System I Earth shares the solar system with seven other planets 0 Planet a precise definition developed in 2006 0 Large solid body orbiting a star 0 Spherical o Clears orbital path 0 Our solar system also includes 0 The Sun an average star 0 Asteroid Rock or metallic fragments o Coments Fragments of ice orbiting the sun 222011 70800 PM 1212011 The Science of Geology Geology is the science that pursues an understanding of planet earth Physical geology materials composing Earth and processes Historical Geology Origin of Earth and its development through time 500 years ago our world was more different than today Geology people and the environment Natural hazards Volcanoes Ppl don t want to live next to dangerous places New Zealand has frequent Earthquakes Resources World population growth Environmental issues Geologic time The magnitude of geologic time Involves vast times millions or billions of years Many geological processes are very gradual Relative dating Dates are placed in their proper sequence or order without knowing their age in years Absolute dating Accurate dates to events Look over geologic time scale briefly Figure 19 The nature of scientific inquiry Scientific method Involves gathering facts through observations and formulation of hypotheses and theories How or why things happen are explained using Hypothesis a tentative or untested explanation Theory a well tested and widely accepted view The Rock Cycle Part of the Earth system The loop that involves the processes by which rock changes to another The Birth of Earth Modern view of universe Current concepts differ wildly from 100 years ago Earth is one of eight planets in the solar system The solar system is on an arm of the Milky Way Galaxy Our Sun is one of 300 billion stars in this galaxy The Expanding Universe Development of the Expanding Universe Theory analogus to be expanding bread Big Bang c When did the Universe begin 0 Best answer so far is the Big Bang 0 All of the mass and energy in the Universe was packed into a single small point It exploded 137 billion years ago and has been expanding ever since The solar system Earth shares the solar system with 7 other planets o planet 0 large solid body orbiting a star 0 has nearly a spherical shape 0 has cleared its neighborhood of other objects 0 O O o Our solar system also includes 0 The sun an average star 0 Asteroids rocky or metallic fragments o Comets fragments of ice orbiting the sun 1242011 Solar system Formation The nebular theory o The nebula condenses into an accretion disc 0 Energy is pulled toward center of the disc the particles concentrate towards the middle the ball at the center grows dense and hot fusion reactions begin the sun is born dust in the rings condenses into particles 0 particles coalesce to form planetesimals o Moon formation 0 small planetoid collides with Earth 0 debris forms a ring around the earth 0 the debris coalesces and forms the moon o atmosphere and oceans o the atmosphere develops from volcanic gases 0 when the earth becomes cool enough moisture condenses and accumulates oceans are born outgassing sweating of the earth 0 nebula forms sun particles continue to collide to form planetismals planetismals form planets one of the planetismals form moon earth cools down then atmosphere and oceans are formed Journey to the Center of the Earth notes posted o the earth is not a solid singular unit but it is made up of a series of concentric shells layers 0 slow movement of material in the earth 0 temperature increases with depth at a rate btwn 70 and 150 degrees F per kilometer into the earth 0 how did they know looked at behavior of seismic waves p waves primary s seismic o Earth s interior layers 0 Crust Continental Oceanic o Mantle Upper Lower inside of earth is just as hot as the sun 0 Core Outer liquid a Pressure decreases so it is more liquid Inner solid n Metallic but solid bc of pressure o The core 0 An iron rich sphere with a radius of 3471 km 0 2 componets with differing seismic wave behavior outer core a liquid iron nickel sulfer n 2255 km thick a density 1012 gcmA3 inner core a solid iron nickel alloy a radius of 1220 km a inmoodle o lithosphere 0 128 2011 TA Wegener proposed theort of continental drift Early case for continental drift pangea to present day spanning 225 million years c puzzle piece fit of coastlines of africa and SA have found that 0 Geological Evidence similar layers of rock are found in antartica Australia SA Africa and india formed bc Pangaea broke apart fossil evidence found in these areas in early 19005 Wegener noted south America Africa and Australia Antarctica and India have almost identical late palezoic rocks and fossils Glacial evidence o Wegener reassembled the continents in the supercontinent Pangaea o Pangaea initially separated into laurasia and Gondwanaland o These glacial features are best explained if the continents were part of Pangaea o It makes sense bc if we put them back together you can see the connection Paleomagnetism and continental drift reviewed studies of rock magnetism o determination of magnetic pole locations through time paleomagnetism uses mineral magnetic alignment direction and dip angle to determine the direction and distance to the magnetic pole when formed poles are magnetic N amp S o apparent polar wanderer curves for different continents suggest real movement relative to one another sea floor spreading and sea floor magnetization rocks come up as magma comes up rocks pushed aside Sea floor spreading in 1962 harry hess proposed seafloor spreading o seafloor moves away from the MOR dye to mantle convection 0 hot mantle rock rises under the MOR Seafloor rocks and mantle rocks beneath them cool and become more dense with distance from the MOR When sufficiently cool and dense these rocks may sink back int the mantle at subduction zones 0 Downward plunge of cold rocks gives rise to oceanic trenches Plates and plate motion Tectonic plates are composed of the relatively rigid lithosphere o Lithospheric thickness and age of seafloor incease with distance from MOR Plates float upon ductile asthenosphere Plates interact at their boundaries which are classified by relative plate motion The global distribution of seismic and volcanic activity the plate margins are outlined by seismic belts where 90 of the worlds earthquakes occur 0 O What causes plate motions the plates are not stationary they are slowly drifting over the denser asthenosphere convection currents in the mantle drive the plates along their path of movement 1312011 Plate tectonics o caused by convection o core is really hot and warms the magma o uneven distribution of heat The cells of circulation drive the movement of the plates on the earth o movement of hot rising mantle plume reaches surface and the cool descending plates create the uneven distribution This thus creates hot spots on earth s surface o slab pull also creates the plate tectonics slab pull ridge push 0 when the magma reaches surface it cools down and creats dense rock 0 warm material rises hotter lighter Cooler thicker Plate boundaries o divergent margins 0 plates move away from each other 0 marked by rifting basaltic volcanism and eventual ridge uplift basalt is a dark rock contains heavy minerals materials millions of years plate is rifting and it begins to fall thus forming a sea bc of the gap Atlantic ocean created this way sequence takes a narrow sea o convergent margins 0 plates move toward one another 0 what happens at the boundary depends on what type of plates are involved 0 they all have subduction zones area where plates are sinking subduction zones more defined with oceanic crust rather than continental n oceanvs ocean plate convergence o oceanic crust has a lot of basaltic o it tends to sink a oceanvs continent o oceanic sinks a continentvs continent o very rich in silica and lighter in comparison to oceanic crust thus they merge together and rise 0 Look at figures o transform margins 0 plates pass horizontally past one another this causes earthquakes actually they all cause earthquakes this can be quick process can be seen over night a farmers notice change in crop pattern 0 O O 0 Two types of Crust o crustal density controls surface position 0 continental crust less dense floats higher much thicker floats lower on the mantle o oceanic crust more dense floats lower o magma is generated at subduction zones where the dense Continental collision zones o India long ago was in the ocean but as time went on the continent collided with the Eurasian plate and it formed the Himalayas when it collided with the continent 0 India collided with Tibet then the mountains that were formed were actually former seafloor Mantle plumes and hotspots 2211 Minerals Mantle plumes narrow columns of hot mantle rock rise through the mantle Do not occur at plate boundaries occur in middle of mantle 0 Example Hawaii the hot spot shuts off bc the plate moves and another volcano forms 0 Hawaii islands form this way Plates moved The building blocks of rocks and hence of earth more than 4000 are known geologicdef of a mineral Rocks naturally occurring solid formed geologically definite chemical composition crystalline structure inorganic rocks are earth materials made from minerals most rocks have more than one kind of mineral Example Granite potassium feldspar quartz hornblende some are monomineralic only one mineral o limestone o rocksalt o glacialice Crystalline structure atoms in a mineral are specifically ordered ie limestone crystalline structure based on atomic patterns Polymorphs o Same composition but different crystal structure o Diamond and graphite are carbon polymorphs C 0 Diamond strong covalent bonds hardest mineral o Graphite weak van der Waals bonds softest mineral Mineral physical properties characteristics determined by your 5 senses used to ID minerals Properties depend upon o chemical composition o chemical structure some are diagnostic o some are hard lusterous have certain density they are special for that mineral o example pyrite FeSZ 0 cubic crystals high specific gravity brassy color mistaken for fools gold minerals have a unique set of physical properties o common properties 0 color 0 streak o luster o hardness 0 specific gravity 0 crystal luster o Color 0 Color is diagnostic for some minerals Olivine is olive green Azurite is always blue 0 Some minerals exhibit a broad color range Quartzclear white yellow pink purple gray etc 0 Color varieties often reflect trace impurities o Streak 0 Color of a mineral crushed on unglazed porcelean o Streak is often a useful diagnostic property Congruent streak streak color same as mineral n Magnetite black mineral black streak o Luster o The way a mineral scatters light 0 Two subdivisions o Hardnes o Scratching resistance of a mineral o Hardness compared to the Mohs Hardness Scale Incongruent streak streak color different from mineral n Chromite black mineral greenish brown streak Metallic looks like metal Non metallic Vitreasglassy Satiny Silky Resinous Earthy n n n n n 10 Diamond 9 Corundum 8 Topaz 7 Quartz 25 fingernail 1 Talc Graphite softest o specific gravity related to density mass per unit of volume 0 mineral weight over weight of equal water volume 0 pyrite heavy SG 50 Feldspar light o Crystal habit External shape Crystal habit Is the ideal shape of crystal faces Ideal growth requires ideal conditions Many terms are used to describe the habit O O O O Cubes Blades Octahedral Hexagonal prisms Compound forms Dodecahedra o Frctu re 0 O O 0 Some minerals lack planes of weaknesses Due to equal molecular bonds in all directions These minerals don t have cleavage they fracture Meaning they don t break into certain shapes Cleavage shape fracture no shape Example quartz displays conchoidal fracture Shaped like inside of a clam shell Breaks along smooth curved surfaces Produces extremely sharp edges o Cleavage O O O O O Tendency to break alone planes of weakness Cleavage produces flat and shiny surface Described by number of planes and their angles Sometimes mistaken for crystal habit Examples One direction a Mica Two directions 90 degrees a Potassium feldspar Two directions not at 90 degrees somewhat 60 degrees Three directions at 90 degrees a Halite Three directions not at 90 degrees a Calcite o Mineral compositions 0 You use as many properties as you want to identify minerals 0 Only about 50 minerals are abundant o 985 of crustal mineral mass is from 8 elements oxygen silicon n 743 of crustal minerals are 0 and Si a continental crust mostly comprised of these two rocks a oceanic crust has less than continental 0 Mineral classes Minerals are classified by their dominant anion o Silicates Most common mineral on earth Known as the rock forming minerals They dominate the earth s crust n Oxygen and silicon o Make up 947 of crustal volume o 74 of crustal mass the anionic unit is the silica tetrahedron n 4 oxygen atoms are bonded to 1 silicon atom a siicon is tiny oxygen is huge Chelsea Oliver Instructions To view the Glaciers and Glaciation Reviewing Glacial Features activity please advance to slide 52 Part A What is the term for a glacial lake formed in a depression as the result of the burial of a large piece of ice that later melted a kettle lake a tam a morainedammed lake an icescoured lake GREGG a pater noster lake Correct mam Correct A kettle lake forms in a depression created by the melting of a piece of buried glacial 1ce Part B Which of the following glacial features is not composed of stratified drift C an esker C an outwash plain E a kame E ground moraine C kame terraces Correct WW shmrw Correct Ground moraine is the unsorted unstratified glacial debris or till left behind on the landscape as a glacier retreats Part C What is the correct term for a valley that has been scoured by glacial erosion and later filled with seawater E a tam C a glacial trough C a hanging valley 393 a fjord E a Vshaped valley Correct WWW Right A glacially scoured valley that is later lled with seawater would be correctly identi ed as a fjord Part D Flow of glacial ice can be determined by the structure of some of the deposits left behind as glaciers have retreated Which of the following features can be used as an indicator of ice ow direction C a glacial erratic E a drumlin C ground moraine E a kettle lake C an esker Correct mama Correct Drumlins are a glacial feature that can be used to determine ice ow direction because the gentle side is always on the down ow side Part E The formation of a hanging valley occurs when which of the following conditions exists 3 A hanging valley occurs when two or more cirques are found on the same mountain peak A hanging valley occurs when a tributary glacier cuts its valley below that of the main trunk glacier an A hanging valley occurs when pater noster lakes are formed in tributary valleys A hanging valley occurs when a tributary glacier enters a larger glacier and hasn t cut the valley as deep as the main trunk glacier A hanging valley occurs when sediment in a valley is eroded below the elevation of a tributary glacier Correct mum FE Correct A hanging valley forms when valley glaciers melt and the elevation of tributary glacier valleys is higher than that of the main trunk glacial valley Which is the best definition of glacial snow line E the line diViding zones of accumulation and melting of ice at the surface of a glacier C the line diViding zones of snow and zones of rock at the base of a glacier E the line of latitude dividing zones of melting snow and zones of glacial snow E the line of latitude dividing zones of snowfall and zones of glacial ice formation Correct Part B Under what conditions will the front of a glacier remain stationary E Glacial fronts remain stationary when melting and snow accumulation are equal 3 Glacial fronts remain stationary when melting and snow accumulation are unequal E Glacial fronts remain stationary when friction exceeds gravity forces E Glacial fronts remain stationary when gravity forces exceed friction Correct m I view pan Part C Which way does ice ow in a glacier retreating uphill E downslope E upslope 3 both upslope and downslope E Ice does not ow in a glacier Correct Part D How would a snow line on a glacier move as a glacial front is advancing E The snow line would move downslope E The snow line would move upslope E The snow line would remain in approximately the same place Correct Part E How would you expect the front of a glacier to move if it undergoes a period of net accumulation followed by net wastage and finally a period of net accumulation E The glacier s front would move forward 3 We have no way of knowing without more information E The glacier s front would move forward backward and then forward again E The glacier s front would move backward forward and then backward again E The glacier s front would move backward Correct ContinueSee Score and Chelsea Oliver Part A Where do glaciers form C in places where more snow melts away in the winter than melts away in the summer I in places where more snow falls inthe summer than melts away inthe winter C in places where more snow falls in the winter than falls in the summer E in places where more snow falls in the winter than melts away in the summer Correct m Part B What is the snowline C the elevation below which snow persists throughout the year E the elevation above which snow persists throughout the year I the line marking the edge of a glacier and snowfree land C the latitude above which snow persists throughout the year Correct Part C What is the zone of wastage C the part of a glacier where water freezing exceeds snow melting E the part of a glacier where snow melting exceeds snow accumulation E the part of a glacier where snow melting exceeds water freezing C the part of a glacier where snow accumulation exceeds snow melting Correct lamensw Under what conditions Will the front of a glacier remain stationary E Glacial fronts remain stationary when friction exceeds gravity forces 3 Glacial fronts remain stationary when melting and snow accumulation are unequal C Glacial fronts remain stationary When gravity forces exceed friction E Glacial fronts remain stationary when melting and snow accumulation are equal Correct Part E What is an end moraine C a ridge of debris deposited by glacial meltwater E a at plain of debris deposited at the end of a glacier C a ridge of debris deposited at the end of a glacier C a at plain of debris deposited by glacial meltwater Correct tmvmm Part F How does an end moraine form E Pieces of rock are transported to the front of a glacier as ice within the glacier moves E Pieces of rock are pushed in front of a glacier as the glacier moves E Pieces of rock are transported to the front of a glacier as water within the glacier moves 3 Pieces of rock are pushed in front of a glacier as the glacier melts Correct m Part G Will plucking occur if a glacier is NOT advancing E No because glacial ice is still moving inside the glacier even if the glaciers front is not advancing E Yes because glacial ice is still moving inside the glacier even if the glaciers front is not advancing D Yes because snow accumulation and snow melting are equal when a glacier s front is not advancing E No because snow accumulation and snow melting are equal when a glacier s front is not advancing Correct PaItA Which of the following deserts is not considered a lowlatitude or subtropical desert E the Atacama Desert E C E E the Patagonian Desert the Great Australian Desert the Arabian Desert the Sahara Desert Correct Correct The Patagonian Desert is found in the middle latitudes of the Southern Hemisphere Part B The Great Basin located in the western United States is what type of desert IE3 E C C U a subtropical desert a middlelatitude desert a lowlatitude desert a polar desert a steppe rather than a desert Correct Correct The Great Basin Desert is located in the middle latitudes in the western United States Part C Which of the following statements is the best explanation for the occurrence of the Great Basin Desert in the western United States El n DE The Great Basin Desert exists because descending highpressure air masses do not contain any moisture Snow in the mountains surrounding the Great Basin melts very slowly The Great Basin Desert exists because it is a rain shadow desert Water is removed from the Colorado River before it gets to the Great Basin causing it to be dry Storms from the east rarely make it to the Great Basin while they still have moisture in them Correct Correct Mountain ranges to the west force clouds up over them causing any moisture that they may have to fall as precipitation before they reach the Great Basin Part D With the noted increases in global temperature what changes will be associated with Earth s climatic regions Deserts will expand into steppe and humid regions of the globe Current ice caps and glaciers will enlarge causing a lowering of sea level E Equot 3 With glacial retreat more fresh water will be available for agriculture E Because of the warmer temperatures more water will be available to the subtropical regions on Earth E Humid areas will expand and more food can be produced Correct Correct As the Earth warms circulation patterns will be modi ed and desert regions will expand Part E Which of the following provides the best explanation for the abundance of desert areas in the low latitudes C Rising air in these regions causes any available moisture to be carried away from the low latitudes There is no cloud cover in these regions In these regions air is cooled and compressed which precludes the transport of water in the atmosphere There is very little water to move in the atmosphere EB an Lowpressure systems in these areas prevent the formation of clouds that could carry water Correct Correct Because air is sinking in these regions it is compressed with very little available moisture so the underlying area becomes desert C quot Score and Prov Chelsea Oliver Instructions To view the Deserts and Wind Common Misconceptions about Deserts activity please advance to slide 31 Part A Which of the following statements about deserts is true E Water is the most significant agent of erosion in deserts C Deserts are lifeless C Deserts are always hot C Wind is the most important agent of erosion in desert regions E Deserts are dominated by sand dunes Correct m 7 WEIquot m WEE M7 Correct Water when available does produce the most signi cant amounts of erosion in deserts Part B Which of the following statements characterizes ephemeral streams U Ephemeral streams ow only at certain times of the year Ephemeral streams generally depend on groundwater in the desert to ow year round E C Ephemeral streams ow all the time in the desert E Ephemeral streams are streams that ow through deserts but have their origins outside of the desert U Ephemeral streams don t have any life in them Correct mlm Correct Ephemeral streams ow intermittently in the desert and usually depend upon rainfall for water Part C Most of the erosion that took place during the Dust Bowl years of the 1930s in the Great Plains of North America was the result of which of the following processes E ooding 3 urban development 3 livestock herding 3 heavy rainfall 393 wind Correct Correct In this instance once drought conditions were initiated wind blew the fme grained glacial deposits away from the Great Plains Part D In the desert environment how are ventifacts created E Ventifacts are produced by precipitation of mineral matter on the surface of a rock when water evaporates in a desert Ventifacts are formed as rocks are dissolved by groundwater and the particles produced are removed by wind activity 3 Ventifacts are produced by mass wasting when very small particles continue to drop off steep slopes and abrade the underlying rock Ventifacts are produced on the surface of a rock by the continued impact of very small Fl particles carried by the wind E Ventifacts are produced on the surface of a rock by the continued impact of very small particles carried by running water Correct mama Correct Ventifacts are produced by extremely ne windblown particles that abrade the surface of rocks in the desert and polish the surface Part E When desert pavement is produced in a desert why do the larger particles accumulate on the surface E Large particles fall from the nearby slopes due to mass wasting E The wind can move particles of only a very speci c size and it takes away these small particles concentrating the larger ones C Particles are cemented together as water evaporates C Wind is capable of moving the large particles to a site where they are deposited C Running water carries away all the smaller material Correct Correct When the wind blows no matter what the velocity there is only a certain size of particle that can be moved vocabulary word know for the test reference to something already taught 11707 Physical Geologx Deals with processes that operate at or beneath the Earth s surface Also with the materials rocks on which these processes operate What causes Earthquakes volcanic eruptions and where How and where are mountain ranges formed Geolo ic Time its immensit billions of ears is difficult to ras Consists of sun and 9 planets 2 groups of Ianets mercury Venus earth mars aka INNER PLANETS Ne tune aka OUTER PLANETS 7 L H l 1 3 r overs form planets co Fig 93 Earth warms decay of radioactive materials Inside earth continues today Early earth was partially molten Fig 94 Rocks are very poor conductors of heat Earth may have been uniform in composition inside and outside at first but became differentiated layered Once temp is hothigh enough iron falls down to center Falling releases energy and causes more heating Called icon catastrophe Big burp water and other gasses belched out Distances measured from surface of earth radius 6400 km Based on composition fig 15 A crust solid rock 0 40 km depth B mantle solid rock 40 2900 km depth C outer core liquid iron 2900 5100 km depth D inner core solid iron 5100 6400 km depth 11907 Figure 15 the layers of what the Earth is made out of Based on th melting KNOW LAYERS Chemical composition of the Earth Top Layer crust is most accessible and studied fig 17 Two elements the big 2 make up 75 of total Oxygen and Silicon O and Si Oxygen is main one These two plus another 6 make up the big 8 99 of the crust Aluminum AI Iron Fe Magnesium Mg Calcium Ca Potassium K Sodium Na FIGURE 18 know order of big 2 know names of all 8 Contrast with the composition of the whole earth Most abundant in order Iron Oxygen Silicon Magnesium Most of Fe in the core most of Mg in mantle As we go into the Earths interior it ets hotter Geothermal Gradient 1 39 39 39 u TN 13 ML toward out of low temperature Three methods Rate at which the temperature increases is known as a s 1 Consider heat transfer High temperature heat moves r rw rm wif Ll 111 Mwifo r but not for rocks ood for melts solids Q 12 g V 4 7 1 1c mu hef ids and ases also for rocks close to theIr melting pomt Convection through the is an efficient form of heat loss from the Earths hot interior 3 tutuzit tram 3 wau39trrjw39wac can travel through a vacuum Sun s heat figure 19 through the Earth s surface by thIs process but not important inside the Earth Outer cool rigid she lithosphere moves around underlying plastic of ductile layer Asthenosphere Moving into the beginning of chapter 2 This moves the continents and creates and destroys intervening oceans leads to plate tectonic theory Lithosphere is broken up into smaller pieces known as plates each of these is 100 km thick and varies in surface size and each act moves as an entity Figure 25 Some of these have on oceans at the iu A 7 Many examples seen at th 1 The middle of the Atlantic ocean mid Atlantic ridge separates South America and African plates The other plate rides on top denser plate usuay oceanic material is the one that bends and is subjected and the continental plate that is lighter rides on top and stays on top Examples 1 at west coast of South America Nazca plate is subducting under South American plate fig 29b 2 Pacific plate subducts under the Eurasian plate figure 2 9a 3 India in collision with Eurasian plate figure 29c subducted plate descends to depth hot eventually some of it melts to produce molten rock material magma and rises to surface to form volcanoes At near these boundaries get mountain bets formed rubbin of one ate aainst another roduces occasion I earth uakes quot 1 Xi 39H39TM Cvf fif T L wwgm hi 1 1 Best example IS fIgure 26 IS seen in southern California The San Andreas fault 210 pacific plate with sliver of California on it moves NW against rest of North American plate Rubbing of one plate against the other produces occasional earthquakes 1 2207 Rate of plate velocitymovement a few cmyr rate at which your fingernails grow actual values 2 20cmyr 1St approximation a points on a given plate move in the same direction and with same speed S Atlantic ocean 5000 km wide was created over last 120 mi years Africa and 5 America were joined as art of Panaea w continents and oceans Heightdepth measured from sea level varies considerably from place to place Continents average elevation 1km Highest at 9km Mt Everest Oceans avera reatest ones are associated with convergent plate boundaries 7 c S L 391er Deepest one 11km On average contine n ocean floor Light ow den ity 27 gcc continental crust floats higher than denser 32 gcc oceanic crust Floats on what Asthenosphere behaves like a bowl of Jell O with denser oceanic material sitting down Note at convergent plate boundaries heavier material oceanic bends and goes into interior subduction Continental material is too light to subducts cant push cork into water and keep down when 2 plates with continental material collide neither wants to subducts Ex India colliding with Eurasia Rocks are crumpled up into highest mountain chain Himalayas have over 1000 peaks higher than any other mountain chain Scientific method make observations do experiments to explain phenomenaobservations develop Hypothesis untested theory See if hypothesis can explain observed facts If so and holds up well for a long time we now have a theory This will continue to be tested against observations and experiments Flotation Archimedes Gravitation Newton Relativity Einstein Life on earth began quite early 4 bill yrs ago For long time remained fairly simple in form atmosphere consisted mostly of poisonous gases About 25 billion years ago oxygen began to collect in the atmosphere Some of this formed in ozone layer above earth protecting life forms from harmful incoming radiation About 600 million years ago life forms exploded on earth and from that time on fossils are common traces from life forms past Geological records show that particular times in past many life forms have gone extinct in a short period of time mass extinction events Causes are being investigated One 65 million years ago appears to have been caused by collision of 10 km meteorite with earth 60 of life forms became extinct Another 250 million years ago is mere enigmatic 90 of life became extinct A third today is mostly triggered by man s actions In geological past disposition of continents and oceans has been very different from today Thus 200 million years ago all continents were joined together forming super continent Pangaea This broke up due to plate tectonics divergent over last 200 mill yrs Created the Atlantic and Indian oceans and pushed continents into their present positions Heat engines 1internal heat inside earth Led to layering of earth and drives plate tectonics 2external ener from sun drives atmos here h dros here and biosphere Principle of geologic processes we see today have worked in much the same way through geological time By and large geological processes have operated slowlysteadily fig 14 Occasionally punctuated by collision with meteoritescomets These have immense consequences in very short period of time Create immense craters global fires burn vegetation throw up immense gas clouds Can radically affect global climate and faunal cause extinctions Most important formation of the moon 12407 Chapter 3 Minerals Definition 1 Naturally occurring 2 Solid inorganic 3 specific chemical composition 4 regular internal arrangement of atoms Rocks are aggregates of minerals Atom is the smallest portion of an element that has all the properties of parent element Look inside atom Figure 32 Center has nucleus small heavy around this circle small particles in orbits solar system Inside of nucleus have 1 Protons each has a positive electrical charge and mass one atomic scale 2 Neutrons no electrical charge mass one same as proton Circling in different orbits are electrons each with a negative electrical charge and mass very close to zero For any atom the number of protons in nucleus the atomic number of the element is balanced by an equal number of electrons in orbit Figure 32 Hence seen from the outside atom has no electrical charge Thus each atom of oxygen has 8 protons silicon has 14 and carbon has 6 Weight of Atom depends on the number of protons P and the number of Neutrons N Atomic wei ht Isotoges forms of the same elements that have different atomic weights Thus carbon 12 GP 6N Carbon 136P7N Carbon 14 7P7N Many atoms lose or gain electrons quite easily If electrons gained atom becomes negatively charged called Anion If electrons are lost it becomes positively charged called Cation Important Ions Si4 A3 Mg2 Fe2 Ca2 K Na C4 Cations 02 54 Cl Anions figure 37 Sizes of ions important How they are stacked together to form minerals CationssmallI Anionbig Note Mg2 and Fe2 same size Na and Ca2 same size Ions are combined to form different compounds minerals All such minerals are electrically neutral charges from Cations must be offset by charges from Anions Bonds glue holding ions together can be of three types A ionic B covalent C van der waals Bonding takes place using outer orbit electrons Outer orbit having 8 electrons leads to stability Ionic Bonding Figure 34 look to forming sodium chloride salt halite Sodium Cation Na donor is electrically held to chlorine anion Cl acceptor NaCl formed an ions arranged around corners of cubes Outer shape of crystal reflects this form of cubes Other minerals can be made up of ions with higher charges EG Ca2 and 02 CaO Bond is strong CF Elmers all purpose glue Covalent Bonding figure 3511 some outer orbit electrons shared by different atoms Such bonds very strong Cf super glue Different atoms of carbon share outer electrons to form a 3 d structure called a diamond In another mineral graphite made up of carbon only C4 ions combine covalent in sheets and different sheets are held together by weak electrical forces van der waals bonding Diamond and graphite have very different properties but both make up of carbon only figure 311 They are called polymorphs two minerals having the same chemical composition but different atomic structures Minerals many thousands known are classified according to their anion group Table 31 Thus oxides sulfides chlorides NOT potassiumsodium iron cation minerals Reasons for this 1 follows chemistry 2 minerals with the same anion group are found are similar geological conditions Eg NaCl and KCl are both formed by evaporation of sea water Some ions combine to form Complex Ions Si4 and four 02 form SiO44 Silicate ion C4 and three 02 form CO32 carbonate ion 312 these complex anions combine with cations to form minerals 12607 Most important IS SIO44 forms tetrahedron Tda with Si at center and four Os at corners figure 9 3 Bonds between the Si and 0 ions are covalent cannot be broken apart Since Si and 0 together make up 75 of the earth s crust silicates are by far the most important group of minerals we study Silicates 39 SiO44 complex ions can link to cations to form minerals however they can Link directly to other SiO44 ions to form larger complex ions This direct linkage is called polymerization leads to numerous silicate mineral subdivisions A Isolated Tda SiO44 Tda not linked directly to each other but through Mg2Fe2 mineral group formed Olivine Tda link direction to form single chain not a mineral has negative electrical charge These chains linked to each other through cations Mg2 Fe2 Ca2 to form mineral group called pyroxene Two single chains link to form a double chain These double chains linked to each other through cations Group is called Amphibole double chains are elongated in one direction amphibole often occurs in rocks as needle shaped crystals D Many double chains link to form a sheet structure these sheets are linked together through cations Group called MICA often occurs in rocks in sheet form some of these sheets held together by van der Waals bonds very weak These bonds can be peeled apart Van der Waals bonds like post it notes Another important mineral group with sheet like structure is clay minerals E Tda can link into Three d Structure highest degree of polymerization Two important mineral groups B v C v i Quartz Si02 ii Feldspars contain Ca2 Na K Revision Silicates in increasing order of polymerization Isolated Tda Olivine Single chains of Tda linkaae Pvroxene Double chains of Tda linkage Amphibole Sheets of Tda linkaae MICA clavs 3 D Tda linkade Ouart feldspar Other mineral groups are much less complicated and less abundant get chlorides sulfides oxides etc Other complex ions such as Sulfates So44 Carbonates CO32 Phosphates PO44 Cannot polymelzatie hence much simpler 310 Important minerals Calcium Carbonate CaCO3 Calcite Calcium Sulfate CaSO4 Gypsum Calcium Phosphate Apatite Important Diagnostic Feature Identifying minerals table 34 Chemistm Iron most important Adds color redgreenbrownblack to minerals when present and also melting point along with Mg and leads to higher density Bonding Type Covalent bonded minerals are harder difficult to break and have lower densities Ionic bonded minerals in each case less SO Van der Waals bonds easily broken makes the mineral soft Physical properties used 1 Hardness MOH s scale Table 32 2 Cleavage break open the mineral exploiting plane of weak bonding eg platy cleavage breaking MICA apart along planes with van der Waals bonding 317318 3 Density minerals with covalent bonding have lower density Presence of iron raises the density of minerals 4 C stal form figure 38 Other less reliable properties Color can be very misleading minor trace impurities changes colors considerably Luster appearance in reflected light Fracture forceful breaking of the mineral Streak color of the powder left on unglazed porcelain sheet 320 Acid test often useful 316 Carbonates fizz releasing colorlessodorless as carbon dioxide Sulfides release gas smelling of rotten eggs HZS SOZ 1292007 Rocks Solid aggregates of minerals Look to 1 mineralogx what minerals it contains amp how much of each 2 Texture size and shape of mineral crystals and the way they are put together If crystals visible to the naked eye coarse grained not visible to the naked eye fine grained Mineralogy and texture tell us how the rock was formed Three rock families A igneous rocks formed by solidification of molten rock material magma fire formed rocks 39 39ntrusive magma crystallizes deep in the crust coarse grained interlocking crystals Extrusive rapidly cooled magma at the earth s surface fine grained interlocking crystals mmon minerals silicates mainly and a few oxides Table 35 B Sedimenta settled formed rocks Formed from sediments particles formed as preexisting rocks undergo weathering breaking down atnear the surface Figured 324 Sediments are soft altered by lithification into hard sedimentary rock Involves i compaction grains squeezed together by overlying material Cementation minerals precipitate binding grains together Two types of sediments a classic physically brokenaltered particles from preexisting rocks laid down by running watericewind minerals ALL SILICATES b Biochemica new chemical substances made from preexisting rocks dissolved during weathering precipitated from sea water Minerals carbonatessulfateschlorides table 35 Sediments and sedimentary rocks show bedding parallel layers as particles settle Since these rocks form by surface processes they dominate atnear the earth s surface 75 Igneous rocks dominate in the earths crust as a whole 95 C Metamorghic changed formed rocks Changed from exiting A and B Formed by subjecting preexisting igsymc rocks to high temperature and pressure deep within the earth 325 Rocks remain solid during this process are not melted but change mineralogytexturechemical composition Temperature gt250 degrees Celsius but lt800 Common minerals silicates and carbonates for all rocks quartz and feldspar most common important Subdivisions i regional metamorphism large region of rocks is affected by high temperature and pressure for long periods of time Often associates with regions where plates collide such rocks often show texture called foliation wavyflat planes produced by rock deformation Contact metamorphism small volumes of rock affected such as near igneous intrusions Where we see rocks Mostly at Outcrogs where underlying bedrock is exposed Sea cliffmountainscanyons etc Some of our knowledge comes from rocks recovered by drilling into continents and ocean bottom Rock cycle results from plate tectonics and climate Change igneous sedimentary metamorphic into each other Figure 326 Process may involve one or more steps and can take millions of years to complete 13107 Chapter 4 Igneous Rocks Look to 1 mineralogy and 2 texture Common minerals present Silicates table 41 Felsic no Mg or Fe present Quartz Qtz White Mica muscovite potassium Feldspar Ksp Plagioclase Feldspar Plag Mafic MgFe present Olivine OI Pyroxene Pyx Amphibole Amph Dark Mica Biotite In addition some amounts of Oxides present Magnetite Iron oxide Ionic substitution in minerals solid solution Mafic involve M92 and Fe2 substitute for each other ions same size and same charge Felsic Feldspars A3 substitutes for some Si4 to form AIO45 complex ions Also Ca2 and Na substitute for each other same sixe To get charge and size balance both charges occur together Ca2 gtNa A3 gtSi4 Total charge 5 5 This occurs in Plagioclase Feldspar family Note K and Na DO NOT substitute for each other size difference is large Therefore get separate family involving K Potassium Feldspars Texture figure 41 Coarse Grained cools slowly deep inside crust Intrusive or plutonic rocks Intrusive rocks force their way as magma into country surrounding rock Fine Grained cools quickly atnear the surface of the earth Extrusive or Volcanic rocks If very fast cooling chilling get glassy material Figured 43 Extrusive rocks can be either Figure 43 Lavas poured as liquids out of the earth s surface volcanoes B roclasts hot broken rock pieces thrown out of volcano When pyroclasts cool to form rock are called tuffs Classification of 16 rocks Look to Mg and Fe content and also SiOZ chemical content 1 Very high Mg and Fe Si02 40 Ultramafic rock 2 High Mg and Fe SiOZ 50 Mafic rocks 3 Int Mg and Fe Si02 60 Intermediate rock 4 Low Mg and Fe Si02 70 Felsic rocks Each of these can either be intrusive or extrusive Figure 44 and Table 42 Mineras Present Figure 44 Felsic Rocks Granite I intrusive and tholite g extrusive Ksp Plag Qtz Mica Intermediate Rocks Diorite I and Andesite g Pag Amph Mica Qtz Mafic Rocks Gabbro I and Basalt g single most important rock on the earth s surface Pag Pyx O Ultramafic Rocks Pedridotite I only no E Pyx OI In going from Felsic to Ultramafic 1 SiOZ content decreases and 2 Mg Fe content increases 3 Melting point rises 4 Viscosity decreases Table 42 222007 Viscosity measures the liquids resistance to flow High Viscosim clumpy like tar Low Viscosim runny like water Viscosity increases with A A decreasing temperature of magma eg engine oil B Felsic content of magma Derivation of magma melting of rocks Melting of rocks aided by 1 raising the temperature 2 addition of water to rocks 3 raising the pressure hinders melting table 43 Generally when rocks let only a small fraction does so partial melting some mineralsfractions melt Felsic minerals melt more readily at lower temperatures than mafic ones Hence when a rock undergoes partial melting the magma produced is more Felsic than the parent rock Parent Partial melt Ultramafic 9 mafic Mafic 9 intermediate Intermediate 9 felsic Plate boundaries and magma types Divergent mafic magma formed by partial melting of ultramafic upper mantle sea floor is made up of mafic rocks Convergent intermediate magma formed by partial melting of subducted mafic ocean plates Transform fault d no magma is generated Cooling of magmas cgstallization of rocks Assume very slow cooling of magma intrusive rocks Different minerals crystallize out at different stages of cooling temperature Thus fractional cgstallization occurs Some fraction of magma solidifies and then rest of magma may be removed Solid rock formed and the rest of the magma left both have different composition from starting magma Look to Bowen s reaction series Cool ma ma ve slowl in a dee chamber Comgosition of starting magma mafic the most common magma type Figure 45 Divide magma into two sections mafic and felsic parts Look to each separately but both go on at same time together Mafic discontinuous reaction series a minerals formed at different steps minerals show different structures All liquid magma as temperature falls very slowly 1 first solid mineral formed is Olivine 2 sits around sinks until at a fixed lower temperature reacts with the rest of the magma to form gyroxene 3 Pyroxene sits around until at fixed lower temperature reacts with the rest of the magma to form amghibole 4 amphibole sits around until at fixed lower temperature reacts with rest of magma if any left to form Biotite Felsic continuous reaction series 1 reaction occurs continuously every 1 degrees Celsius cooling 2 mineral structure unchanged continuous All liquid as temperature falls very slowly First solid mineral to form is CaRich Plagioclase feldspar As temperature falls this mineral reacts with the rest of the magma and becomes steadily more Na Rich ionic substitution Finally at much lower temperature if any magma left white Mica Muscovite K feldspar Quartz are formed Important points 1 Olivine Pyroxene formed by slow cooling large crystals No extrusive Ultramafic rock 2 After some early crystallization olpyxplag rest of magma is intermediate in composition 3 After more crystallization little magma left is felsic in composition figure 45 In principle we can form all major igneous rock types starting from a single mafic magma following Fractional CLystallization Generally not so need specific magmas to produce specific rocks 2507 Intrusive bodies figure 47 A tabular discordant vertical bodies dikes figure 49 B tabular concordant horizontal bodies sillis figure 49 concordant discordant with respect to surrounding sedimentary rocks which are often horizontally layerd C large gt100 km2 irregular plutons batholiths Often felsic in composition granitic All three have contact metamorphic zones around them Magma in invading surrounding rock may break off a piece of the rock at great depth If this piece is carried to the surface forms a strange unexpected rock piece called xeonith Figure 48 Geological proof of Bowens reaction series i palisades sill figure 45 top and bottom chilled margin are mafic gives composition of starting magma Olivine solidifies first falls to bottom see lowermost layer roxene and Plagioclase feldspar solidify next pyroxene falls to bottom E next layer up Plagioclase forms top layer Is the exact order of layers seen by geologist in field ii zoned cgstals formed by somewhat more rapid cooling Reactions do not have time to go through to completion Felsic case Plagioclase feldspar crystals have Ca and Al rich interior and Na and Si rich rims Mafic case Can have crystals with Olivine at the center rimmed by some roxene with a thin outer layer of amphibole Magma and spreading centers Partial melting of upper mantle peridotite forms mafic magma Rises and forms layer of Gabbro with dikes above and lavas of Basalt on sea floor These layers capped by five sections form Ophiolitic Suite figure 4111213 Later may be scraped up onto continents near subduction areas Are totally anomalous here generally expect felsic rockssediments on continents Magma rocks near subduction zones Wet mafic ocean floor capped by wet sediments undergo subduction Partial melting relatively easily giving magma that is intermediate in composition Magma may be gassy water carbon dioxide from melted carbonate sediments Figured 414 May form both intrusive and extrusive rocks islandmountain chains Intraplate volcanism Figure 411 many mafic cases thought to be caused by narrow hot spots plumes of molten material rising from deep 2900km within the earth EXAM 2 2122007 Chapter 12 Volcanism l l all Volcanism 1 is a fundamental process in building the Earth s crust 2 a major natural hazard in places 3 Analysis of lavas allows geologist to infer properties of the Earth s interior 4 gases escape into the atmosphere Types of Lavas Mafic Basalt Intermediate Andesite Felsic Rhyolite Basaltic lavas dark in color hot 1200 deg rees Celsius low can flow downhill at 10 kmhr A flood basalts erupt on flat terrain spreads out in sheets Successive flows build up plateaus Figure 1216 B other lavas on land called Pahoehoe and Aa figure 123 C Pillow lavas formed by undenNater eruption Ellipsoidal pillow like blocks 1m wide figure 412 eg formed atnear mid ocean ridges spreading centers tholitic lavas felsic light in color erupted at lt900 degrees Celsius High viscosity lavas tend to pill up into thick bulbous deposits figure 1211 Andesitic lavas properties in between basaltic and Rh olite Textures of Lavas Generally fine grained or glass 39 overlying rocks forming gyroclasts If very fine 2 mm in size called volcanic ash Other pieces may be much larges figure 128 When pyroclasts fall to the Earth and cool they form tuffs volcanic breccias rock made from solidified rubble roclastic flows hot ash dust gases ejected from volcano as glowing cloud rolls downhill at 200 kmhr Little warning can lead to great loss of lifeproperty figure 1210 These did most of the damage at Pompeii in 79 AD Erugtive styles Cl made up of many thin basaltic layers eg B mass of felsic lavas piled up atnear vent Eg top of C D E F ii Hip l i no longer able to support roof Volcanic structur collapses forming basin like depression often miles wide Lake forms fiure 121211 G i 39 quot 39 ll quot M 133i trileifi IE l 39quoti39WI ilrIg39 with M 2 m fig 5 Eg r l 1 1883 explosion heard in Australia thousands of km away Killed 30000 people tsunami Fissure Erugtions 1 On land form flood basalts figure 121516 Many cover 1 million sp Km apparently erupted quickly 2 At spreading centers form entire sea floor topped by pillow lavas 3 Ash flow degosits huge eruptions of pyroclasts cover large areas and 1km thick Never seen by man but in past occurred at Yellowstone il 1 39 Mix of waterrainice with pyroclasts or out townsVillage s Unpredictable Nevado del Ruiz 1985 killed 10000 Volcanic gases generally made of water vapor carbon dioxide sulfur dioxide oxides of nitro en If mainly gases heavier than air can form thick carpet in country side Hi 3 H rm lt Can use for geothermal energy clean system Global Pattern of Volcanism figure 121920 Ring of fire around Pacific Ocean caused b subducted plates leading to mainly Andesitic volcanism In areas two oceanic plates convergence In other areas mountain chain on continent formed eg Andes continental plate oceanic plate convergence Some volcanoes located atnear divergent plate boundaries Iceland intralate volcanoes and flood basalt areas thou ht to be linked to 3m 39 39 39 will fl figure 622 As Pacific plate has moved over the Hawaiian hotspot it has formed a chain of volcanic islands and seamounts figure 1221 Other island chains in pacific also formed in the same way Can calculate plate velocities from such hot spot tracks controversial Volcanism and human affairs Generally can not predict eruptions accurately short time frame box 121 Pyroclastic flows and lahars are most dangerous figure 1224 Many major cities are in danger Tacoma WA Naples Italy Collapse of Minoan civilization was caused b volcanic erution in Ae Exlosions on volcanic islands can trigger i 1n m 39 39 l me There is little time for warning costal areas Violent eruptions throw lots of dustash and gases into the atmosphere can cause plane engine to seize up Fine dust leads to spectacular sunsets for many years Can also cause minor global climatic changes cooling Examples seen in 18105 following big eruptions in Indonesia Others have scaled up from here If flood basalt eru tions release lots of asdust it can lead to dramatic onmate ohan A school or thou or so mob in Siberia and India respectively Positive as ects of volcanism 1 Examples in Mediterranean Sea area and Colombia Juan Valdez 2 Early atmosphere and ocean formed by volcanic eruptions 3 Geothermal energy possibilities almost limitless clean source of energy Figured 1227 ean7 n 711 These are then worn awa to ield source sediments l l 7 limo quot l al lo x ll we m Rocks minerals weather at different rates figure 161 Factors controlling weathering rate table 161 1 Parent rock eg granite Different minerals weather at different rates figured 73 feldsgar alters readil to cla mlnerals 2 3 soil formed by breakdown of rocks holds on to moisture Also houses plantsanimals that cause weathering 4 length of time the longer the time the more complete the weathering EMICAL AND WEATHERING OF TWO TYPES CH PHYSICAL i 39 l 7i i Feldspar especially Plag alter readily to form clay minerals Since feldspars are dominant clay minerals important component of sediments clays contain water Alteration occurs with pure water slowly speed up by dissolved carbon dioxide water is weakly acidic Acidic water will dissolve carbonates totally leaving no residue Calcium bicarbonate is soluble Different minerals show different types of stability to chemical weathering table 163 21607 Divide into 3 parts 1 Least stable non silicates halite and carbonates 2 intermediate all silicates generally Bowen s reaction series in reverse Minerals formed at highest temperatures alter easily those formed at lowest temperature quartz and clays least readily 3 Most stable non silicates formed by weathering Oxides and hydroxides rust layer formed from mafic minerals only gets thicker with time Thus different rocks with different mineral com onents chemicall weather at different rates 397 1 r v 39 no chemical reactions involved figured 163 r frost alternating heat and cold organism and helped by cracks joints in rocks Agents are wate figured 167 10 Special cases are exfoliation large sheets of rock peel off from the outcrop and spheriodal weathering curved la ers eel off boundaries smaller scale exfoliation and help each other figure 1637 10 imiortant compone a result of weatherin of outcrosbed rock An Dig ditch down in soil to reveal soil rofile la ers horizons Different types of sorl are formed from different starting rocks igneous sedimentary under different climatic conditions Where we have very hot humid weather acting on rocks for long time eg the tropics resultant soil tends to be poor for agriculture Support lush vegetation initially but no lasting ower Peole ractice slash and burn tactics record eg northern Arizona study of these unravels details of ancrent climates Thus Pa eosols indicate that oxygen was present in the atmosphere billions of years a o have also loaded soil in areas with salt pesticides toxic chemicals that slowly leak into ground water Raw material of sediments In addition to soil you get sand silt clay iron oxides detritus broken grains as major components going into detrital sediments formed elsewhere Also have dissolved calcium bicarbonate and in carried by running water that on arrival as destination lakesoceans can form biochemical sediments CHAPTER 5 Sediments and Sedimentary rocks Much of the Earth s surface including the seafloor is covered by sediments Most derived by weathering of rocks on continents All processes occur at or close to the Earth s surface low temperature and pressure Studying sediments and sedimentary rocks helps us to understand Earth s climate in the past changes in weathering processes General rocesses involved in order 1 Weathering of rocks 2 Erosion removal of material formed by weathering of rocks 3 Transport of material by rivers glaciers and wind 4 Deposition particles settle or precipitate out Sediment formed 5 Burial layers of sediment accumulate compacting older layers 6 Diagenesis pressure heat chemical reactions lithify harden sediments to form sedimentary rocks 1 and 2 both yield broken grains detrital or clastic material as well as dissolved material Products in Clastic parts depend on starting rock type and intensity of weathering Table 51 Feldspars alter relatively easily to clay minerals if sediment contains feldspar it denotes low amount of weathering At highest weathering amounts only quartz and clay minerals survive Give rise to the two main types of clastic sedimentary rocks sandstones quartz dominant and shales clays dominant Biochemical sediments form from seawater undissolved mineral remains of organisms as well as minerals precipitated form sea water Transportation most sediments are transported by water or currents Rivers play an important major role Strength of the currents is important Strong currents carry I coarse and fine detritus Moderately strong currents carry detritus mainly clay and material silt but not coarse sand which is deposited Weak currents carry only the detritus fine clay and when these are checked deposit fine mud deep oceans Distance of transportation affects both size and angularity of clastic particles figure 53 When transportation stops sedimentation beings As a current carr in article of all sizes slows biggest articles settle out first smallest ones last ravit ie if 39 7quotqu I Figure 53 2232007 Oceans and lakes may be regarded as mixing bowls input of material form rivers rain and glaciers Water is lost by evaporation over a short period of time lt 100 years amount of water in oceans remains constant But over long periods sea level may alter dramatically 100 million or more eg glacial epochs significant period Ocean water shows salinity caused by dissolved material Amount of salinity is balanced by addition of salts by rivers and removal by precipitation Of main interest to us Calcium bi carbonate Sodium chloride Sedimentam basins cover gt10000 km2 and contain thick accumulations of sedimentary rocks They are prime sources of oil and gases Basins figure 54 1 Following seafloor spreading breaking up a continent get long narrow rifts filled with sediments and igneous rocks 2 Later cooling of material near continents causes subsidence below sea level creating space to collect plentiful land derived sediments called thermal subsidence basins eg East coast of North America Load of collected sediments causes further depression subsidence creating more space to collect sediments Near continent can get thick 10 km thick sedimentssedimentary rocks Figure 54 Flexural basins occur when plates converge Weight of overriding plate causes underlying plate to bend down creating a flexural basin Oil reserves in Iraq occur in such a basin Sedimenta environment Defined by a geographic location characterized by combination of geological processes and environmental conditions figure 55 Location on continent near shoreline deep ocean Geological processes nature and strength of currents plate tectonic setting burial of sedimentgt volcanic activity Environmental conditions kinds and amount of water fresh saline topography mountainous coastal plain shallow or deep ocean Nature and amount of biological activity Clastic quot v cllvil On continents alluvial stream desert lake glacial At shoreline deltas beaches tidal flats Oceans on continental margin relatively shallow water or deep ocean sands and mud s are deposited These contain terrigenous sediments derived from land continent Bi 39 39 39 quot v envi show chemical and biochemical precipitation from sea water Most important carbonate environments marine settling with calcium carbonate the main sediment Many organisms extract CaCo3 from sea water to form shells When they die their shells accumulate to form sediment Commonly found in warm subtropical waters Evagorate environment formed where warm partially isolated sea water evaporates more quickly than it can mix with marine sea water Main product halite Sedimentam structures Bedding parallel layers of different grain sizes or compositional reflect successive depositional surfaces Bedding may be thin few mm or quite thick meters figure 51 Most bedding is nearly horizontal at the time of deposition Cross bedding sets of beds can be deposited by wind or by water Inclined at large angles lt35 degrees from the horizontal Are formed when grains are deposited on steeper down current slope of sand dune or sandbar Figure 57 Graded bedding each layer few cm thick progresses from coarse grains at the bottom to fine grains at the top Many such beds may lie on top of each other with a total thickness several hundred meters are called Turbidites formed b secial variet of ocean bottom current called turbit current ll r 7 47 Can distinguish between symmetrIcal rIpples formed at beach waves In both directions or asymmetrical ones formed by wave in single direction sand barsand dune figure 57 Found also in ancient rocks figure 58 and can infer conditions of deposition by using Principle of Uniformitarianism Bioturbation cylindrical tubes few cm in diameter extending vertically through beds figure 510 Are remnants of burrows and tunnels made by marine organisms In ancient rocks can deduce behavior of organisms and thus reconstruct sedimentary environment Diaenesis fi ure 512 after deposition and burial sediments undergo physical chemical changes and ii limm i 15 Burial temperature may rise to 150 degrees Celsius And comQaction occurs water squeezed out Most important for clayey sediments is cementation occurs minerals are precipitated in the open pores of the sediments Helps bind grains together Sediment Sedimentary rock Mud Shale Sand Conglomerate 226 07 Clastic look to particle size table 53 Large pieces bouldercobblepebble called conglomerate Medium pieces sand called sandstone Fine pieces silt called siltstone Very Fine pieces clay called mudstone shale Figure 515 Subdivisions of sandstones Contains 25 feldspar arkose Contains fair amount of clay greywacke These components tell us what was weathered and natu reintensity of weathering figure 516 Fine grained sediments siltstonesshale are deposited by the gentlest currents Shale often contains 10 carbonate andor organic material Relative to abundance of major sedimentary rocks 75 sand dominated rocks 10 carbonate rocks 15 Chemical sediments table 54 figure 517 Classification based on chemical com osition Most imortant are carbonates often made up of shells and skeletons of 39 392 If the rock contains Calcium carbonate 239 LD Imestonelchalk some magnesium included is dolostone Important occurrences figure 518 1 in reefs large ridge like structures made by corals carbonate platform shallow extensive flat areas eg Bahamas banks Evagorites precipitate inorganically from evaporating sea water in arid regions May contain carbonates sulfates and chlorides As evaporation precedes with little or no water input Calcium carbonate recr itates first next is calcium sulfate sum and fInall sodlum chlorlde hallte Many evaporite sequences very thick hundreds of meters Cannot be by total evaporation of deep ocean say Rather need a enclosed body of saline water with b constricted access to open sea c limited freshwater added by rivers d arid climate Water steadily evaporates level falls drawing in ocean water through access over long period of time evaporation of large amounts of saline water forming thick evaporate deposits eg Mediterranean sea figure 520 Chert bio chemically precipitated silica Phosghates from nutrient rich waters Iron formations generally in old rocks which is less oxygen present in the atmosphere Coal made up of diagenetically altered swamp vegetation Oil and gas not rocks formed from digenetic alteration of organic material in pores of sedimentary rocks Found mainly in sandstones and lime stones Only sedimentary rocks can contain fossils Chapter 6 Metamorphic rocks Produced when igneous or sedimentary rocks are subjected to high pressure and temperature for long periods of time inside of the Earth Can also metamorphose a metamorphic rock subtle changes only A good place is near convergent plate boundaries and especially deep inside mountain belts eg continent continent collision Going on today deep inside Alps Himalayas Will only see rocks perhaps hundreds of millions years later when brought to and exposed at the surface figure 63 The new rock develops new minerals and texture with all changes taking place in the solid state no melting However fluids water often play a major role Regional metamorghism large volumes of rocks subject to high pressure and high temperature for long periods of time many millions of years Deformation bending or breaking of rocks is not uncommon figure 63 Contact metamorghism smaller volumes of rock subjected to high temperature for shorter periods of time eg around cooling plutons Generally minerals in rocks formed at low temperatures change more readily during metamorphism eg cla mica Plates pushing past each other cause directed pressure force pressure in one of 3 dimensions more than in two figure 63 This directed pressure gives rise to new texture call foliationlineation in many metamorphic rocks Temperature increases steadily with depth inside of the Earth as does the pressure but not the same ever where Fiure F verae value is 30 degrees Celsius km for metamorphic conditions Pressure more difficult concept At depth of 15km rocks squeezed together 400 times more than at the surface of the Earth 22807 In P T space can define areas where we get lowI intermediate high grade metamorphic rocks Fig 62 Most regional metamorphic conditions are represented through central diagonal part of figure 62 Regional metamorphism eg cooking large turkey in oven Can have highlow grade temperature of cooking for long periods of time cannot stimulate increase in pressure Contact metamorphism eg frying a steak on skillet Relatively high temperature for short period of time Rocks subject to regional metamorphism when P and T are rising or holding steady we get prograde metamorphism Can go on for many millions of years during this stage get many mineralogical and textural changes in the rock Water comes out of rock and moves around facilitating changes Figure 69 Much later when the rock is moving towards the earths surface plate tectonicweathering P and T often quickly we get retrograde metamorphism Few mineralogicaltextural change as a low T inhibits changes b by rocks are dry Metamorphic textures result form directed pressure Platy minerals mica line up parallel t one another giving rise to streaky appearance foliation figure 64 As grade of metamorphism increases mica grains grow larger Thus shale first turns to slate then to schist then to gneiss Figure 64 Amphibole grains needle shape can also line up under directed pressure giving rise to lineation texture New minerals begin to grow slowly garnet being an important example figure 66 We need to be more specific than saying rocks are hig hintermediatelow grade metamorphic rocks Metamorphic facies grouping rocks under different grades of metamorphism from different parent rocks Thus different kinds of metamorphic rocks are formed from the same parent rocks under different grades of metamorphism Different kinds of metamorphic rock come from different parent rocks under the same grade of metamorphism Occurrence of certain index minerals in the rock help us in estimating the highest P and T that the rock was subjected to Better still to use groups of index minerals to define P and T conditions or facies of metamorphism Index minerals are formed are stable under only limited range of P and T conditions figure 67 68 Garnet is an important example Other minerals plagioclase feldsparquartz are stable under very wide range of P T conditions These cannot serve as index minerals The occurrence of certain newly formed green colored minerals chloriteepodite in low grade rocks helps us to define greenschist facies of Mm rock is foliated Table 62 At intermediate grade get amphibole developing in the rock mica may or may not be resent This is the amphibole facies rock is foliatedlineated At the highest grade of metamorphism mica and amphibole breakdown to form pyroxene see Bowen s reaction series temperature rising Rock becomes dry This is granulite facies non foliatedlineated T and P conditions of facies figure 67 Greenschist 450 degrees Celsius low ish pressure Amphibolites 650 degrees Celsius intermediate pressure Granulite 800 degrees Celsius high pressure Another important facies is called blueschist facies defined by low temperature 300 degrees Celsius and high pressure Rock is foliated and contains an unusual blue colored amphibole These unseal P T conditions are only met close to subduction zones All four belong to regional subduction zones Finally on facies diagram figure 67 get hornfels facies shows intermediate high temperatures very low pressure These are contact metamorphic rocks formed by heat transferred from plutons eg dykessills to surrounding rocks Rocks are sugary textured show no foliationllineation since there is no directed pressure involved and there is only a short heating time Two unusual regional metamorphic rocks containing one mineral each Quartzite formed by metamorphism of sandstone only quartz present Marble formed by metamorphism of limestonechalk only calcite present figure 65 Note regional metamorphic rocks are non foliatedlineated only if necessary minerals micaamphibole re not present Examples granulite marble quartzite All contact metamorphic rocks hornfels facies are non foliated lineated 322007 Chapter 8 geological time Geologists study phenomena on the scale of secminutes eg earthquakes to 100 of millions of years formation and erosion of mountain belts regional erosion Two types of measurement relative and absolute Relative dating Relative dating Important sedimentary rocks 1 principle of original horizontality sediments generally laid down in horizontal layers figure 84 2 principle of superposition in a set of undisturbed beds the one at the bottom is the oldest and the one at the top is the youngest 3 if beds are broken faults or intruded by igneous rocks these events occurred after deposition of sediments Figure 84 No single location has continuous sedimentation to get a full record must co relate rocks from different places Difficult over large distances Fossils as timegieces Rock record shows many different life forms most of which came into existence at some point in time in the past and then became extinct later on For each life form see evolution over time Thus given life form trilobite figure p 169 shows change of head shape number of segments and legs over millions of years Law of faunal correlation Rock that contain the same group of fossils showing the same features were formed at the same time Form good Correlation you need good fossils A common life form B widespread geographic occurrence C lived over relatively short period of time Such fossils are called index fossils Using above laws especially fossils can co relate rocks from all around the world figure 85 We find out that there are places in which sets of bed are missing This could be due to Missing beds were never deposited Beds were laid down but have subsequently been eroded away Boundaries marking these missing beds are called unconformities shown by wavy lines in figures Such marks of missing time may represent immense stretches of time and can be of three types Angular unconformity tilted sedimentary beds below and horizontally tilted beds on top Disconformitx horizontal sedimentary rock beds both below and above the unconformity Generally recognized by sharp change in fossil content across boundary Nonconformig igneousmetamorphic rocks overlain by sedimentary rocks All three are seen in wall of Grand Canyon 87 Can have very complex series of geological events 889 that have to be reconstructed form the rock record we see today Using all of these techniques on sedimentary rocks we build up the geologic column time scale with the oldest rocks at bottom and youngest at top 811 From basically four main units eras based on sharp fossil content differences Each of these then subdivided based on finer changes in fossil content Initially separated into two EONS The older one with very few good fossils Precambrian the younger one with good fossil content Phanerozoic life bearing Latter subdivided into three eras based on type fossils present Oldest Paleozoic old life dominated by fish and amphibians Next Mesozoic middle life dominated by reptiles Youngest Cenozoic recent life dominated by mammals 811 Each era of these is then subdivided into periods based on their refinement of exact fossils present Paleozoic era is divided into Permian oun est Carboniferous Devonian SilurianlOrdovician Cambrian oldest Mesozoic era divided into Cretaceous youngestJurassicTriassic oldest Cenozoic era divided into Quaternam younger Tertiary older 811 3507 Second Exam is chapters 12 16 5 6 8 look at test 2 and test 3 Boundaries between EonsEras represent sharp changes in fossil content Precambrian Cambrian bounda exgloration of life forms Paleozoic Mesozoic bounda 90 of life forms died out suddenly Mesozoic Cenozoic boundam 60 of life forms died out suddenly What caused these quick changes in life forms at the Earth s surface Were they catastrophic in nature When did they occur Note boundaries between various Periods also show difference in fossil contents Absolute radiometric dating Need some sort of geological clock Use radioactive materials General form Parent P unstable changes at a fixed rate to daughter D stable figure 812 If we can measure the amount of P and D in a rock mineral and rate of change is known we can figure out its age What does age mean For igneous rocks represents the time when it changes form a liquid to solid ie when the rock solidifies Examples of P D pairs used 1 Radiocarbon 14C changes quickly to nitrogen 2 an isotope of potassium K changes slowly to argon Ar 3 Isotopes of uranium U changes very slowly to isotopes of lead Pb More about rate of change Concegt of halflife figure 813 When the clock starts have only N at atoms of parents no daughters Time eg years it takes for half of the P to change into D called half life After one half life measured in say years have N2 atoms of parent only Missing N2 N N2 atoms have changed to daughter DP1 After two half lives have only N2x2 ie N4 atoms of parent and 3N4 atoms of daughter DP3 After three half lives have only N2x2x2 ie N8 atoms of parent and 7N8 atoms of daughter DP 7 And so on for more half lives Note at any given time the number of parents plus the number of daughter parents can neither be created nor destroyed but can change form Example A mineral contains 10 million atoms of P and 150 million atoms of D If the half life of this pair is 50 million years old what is the age of the rocks Note DP15 After 4 half lives have N2x2x2x2 ie N16 of parent and N N16ie 15N16 atoms of daughter DP15 So we are dealing with four half lives each of 50 million years old Rock is 50x4200 million years old More P D pairs table 81 For UPb half life 45 billion years used method to date fairly old rocksminerals 10 million years to 45 billion years For KAr half life 13 billion years use method to date rocksminerals few k years to 45 billion years For radiocarbon half life 6000 years Rocks do not contain much carbon Use this method to date once living material in the range 0 100000 years In this case the clock starts when the living material treeperson dies Now we use methods to calibrate geologic time scale Problem Geological time scale based on sedimentary rocks only and radiometric ages only gossible for igneous rocks Sedimenta rocks cannot be radiometricallx dated For sedimentary rock age is when sediment laid down fossil enclosed Detrital sedimentary rocks contain broken solid grains that have radioactive clocks ticking in them for a long time Best Method Date ash beds found mixed with sedimentary rocks These follow the Principle of Superposition Rocks above the ash bed are younger Rocks below the ash bed are older Figure to be shown in class 3 vvl In In In In In In In In In In H 100 Ma G F E Angular unconformity ash bed IIIIVI In In In In In In In In In In D C B A Ages AB gt300 Ma CDEF lt300 Ma gt100 Ma 300 Ma GH lt100 Ma Important examples of dating UPb method a Age of the earth 4500 million years based on dating of meteorites formed at the same time as the Earth b explosion of life forms at base of Paleozoic occurred 550 million years ago c faunal extinction event at Paleozoic Mesozoic boundary occurred 250 million years ago 372007 KAr method d faunal extinction event at Mesozoic Cenozoic boundary occurred 65 million years ago e man like creatures first appeared in East Africa 5 million years ago f correct age 1925 years obtained on ash material from Vesuvius eruption of 79AD death knoll for creation alists Radiocarbon method g Native American entire new world 30 thousand years ago h ice man froze to death in the Alps 5500 years ago i cloth on which Shroud of Turin is seen was made in 1300 AD Other important geological events dated 1 oldest rocks dated on earth 4200 million years older Records wiped out by big accretion events 2 oldest rocks showing signs of life algae on earth 4000 million years old 3 Appalachian mountains formed in complex series of vents 400 300 million years ago when Africa and Eu rope crashed into north America 4 current cycle of plate tectonics began 200 million a ago Pangea breaks up North America from Africa and Europe about 180 million years ago South America form Africa 130 million years ago Whole Atlantic Ocean created by divergent plate boundaries since 200 million years ago 5 India comes into hard collision with Eurasia 50 million years ago Himalayas rise rapidly in the last 15 million years big effect on climate Radiometric methods work ages obtained by these methods agree with those obtained by tree ring counting correct radiometric age obtained for 79 AD Mt Vesuvius eruption radiometric age always in right order ie agree with relative dating sea floor spreading plate velocities obtained from radiometric results in excellent agreement with those obtained by modern physics methods eg measuring distances using layers EXAM 3 FWP 3102008 Chapter 7 Rock deformation Looking at rocks in the field we see that they can be broken or faulted or bent folded by deforming forces Faulting shows brittle behavior of rocks folding shows ductile behavior This latter occurs only for rocks at considerable depth inside of the earth To understand structures formed by rocks in the field we need to measure the orientation of rocks in outer crops Measure p and strike of beds sedimentary rocks Strike is a compass direction eg N S NE SW whereas the Dip has a compass direction as well as an angle associated with it 723 Strike is the direction of a rock layer as it intersects the horizontal surface Dip is measured at right angle to this and measures the amount of tilting Note strike and dip directions are always at right angles Examples Horizontal bed dip 0 degrees Has no strike or dip direction Bed strikes NW SW Dip can either be NE SW and angle can be 1 or 90 degrees Use of dip and strike measurements to work out structure 74 Deforming force on rocks is called stress and the resultant change in shape or size is called strain Summary of deformation 77 Three types of stress compressionI extension and shear If rocks behave in ductile manner get folding stretching and shearing respectively In faulting movement of two blocks of rocks occurs across the fault plane This fault plane intersects the horizontal surface has both dip and strike If rocks break but no movement between the two blocks its called joint Brittle behavior faults figure 77 If rocks behave in brittle fashion get reverse faulting normal faulting and strike slip faulting respectively Faults are divided into dip slip and strike slip types In former movement occurs in direction of dip has vertical component In latter movement occurs in strike direction only horizontal movement Dip slip faults 7716 a normal fault caused by extension Found atlnear divergent plate boundaries b reverse fault caused by compression found at or near convergent plate boundaries Two dimensional figure Normal Faults extension bed missing Reverse faults compression bed repeated Block faulting two normal faults central part falls down to make a rift valley 716 In mountain building get extreme shortening blocks move tens of km along low angle lt15 degrees reverse fault Called Thrust Fault 71517 Strike slip faults are caused by shearing and are found atlnear transform fault boundaries can also have oblique slip fault caused by some amount of shearing and some amount of tensioncompression 31207 Brittle vs ductile behavior Deep behavior higher T amp P favors ductile behavior FOLDING Folds scale mm to many km fig 710 Axial plane divides the fold as symmetrically as possible 2 sides sets of beds are called limbs Folds can be upright or overturned Anticlines fold upwards Synclines fold downwards 710 We can recognize faults when both blocks of rocks are present by looking at offset beds What happens when 1 block has moved a vast distance or been eroded away Look for slickenslides or fault brecci to locate the fault plane Slickenslides striated or highly polished surfaces on rocks caused by movement of blocks on rocks Parallel striationsg rooves on the surface show the direction of movement Fault breccia finely ground up or crushed rock fragments atnear the fault plane Caused by grinding of 2 blocks of rocks against each other fig 714 Behavior of rocks may be intermediate between brittle and ductile When faulting occurs energy release as shock waves earthquakes chap 13 CHAPTER 13 EARTHQUAKES 2 blocks of rocks have opposing forces acting on them 131 Strain in rocks increases as stress increases until rock fails breaks 191 along fault plane and 2 blocks of rocks move in opposite direction Strain energy of rocks stretched rubber band is released as shock seismic waves earthquakes from point where fault originates called focus Point is vertically above this on Earth s surface is called epicenter 1312 Friction along fault plane now prevents further movement of blocks of rocks Continuing stress builds strain in rocks Repeating cycle Above is Elastic Rebound Theog Before main earthquake release of energy can get foreshocks minor earthquakes as rocks adjust to stress After main earthquake can get aftershocks as rocks make minor adjustment to stress 133 Seismic waves spread out from focus and travel through Earth Study of these waves behavior gives us detailed info about earth s interior Detecting ground movement Use seismometer to measure say distance between earth s surface and fixed point in the sky 134 If this changes earth s surface is shaking Need s such seismometers at any given place station to completely detect ground movement One detects vertical movement other 2 the horizontal part n s or e w these will pick up shaking of ground from distant earthquake 134 2 types of waves spread out from focus Body waves 135 These travel through earth s interior and are of 2 types Pwave involves compression of rock material involves push pul of material and is the faster primary of 2 body waves Since both solids and liquids resist compression amp waves travel through solids and liguids Swave slower than p wave involve shearing of material Liquids cannot be sheared and swaves cannot travel though liguids through solids only Surface waves travel only at or very near surface of Earth complex ground motion These waves are slower than body waves but shake ground severely135 Seismic wave velocities 5kmlsec Most of the damage following quakes are caused by the surface waves Severity of ground motion by seismic waves fas sharply with distance Only places quite near focus are liable to be damaged much further away we know the ground is shaking only bc seismometers are very sensitive instruments Locating the epicenter As body waves travel away from focus P waves outraces s waves The further away we go the more the s wave fas behind The time difference s p interval between the arrival of the pamps wave at station depends on its distance from focus Use records s p intervals from at least 3 different stations to locate the epicenter 136 Iquot 31607 Severity of earthquake is measured by its Richter magnitude Based on largest ground movement caused by seismic waves Scale not uniform In increasing one on the magnitude scale the amount of energy released by the earthquake goes up to thirty times Example how much more energy will a magnitude 8 earthquake release than one of 4 Answer about one million times 30x30x30870000 Every year we have about one million earthquakes of low magnitude Every 5 years we have a magnitude 8 earthquake and this releases about the same energy as all the previous year s earthquakes 138 Unless building etc built poor or on soft or squishy ground severe damage only results for earthquakes of say gt6 magnitude Can build bridges etc to resist severe shaking of big earthquakes nearby eg California and Japan Earthguakes and plate tectonic boundaries All three types of plate boundaries have eqs associated with them High magnitude ones are found atclose to convergent plate boundaries and transform plate boundaries 1312 Depth of focus is important measures distance between focus and epicenter If this lt100 km within lithosphere called shallow focus earthquake seen atlnear all three types of plate boundaries If this is gt100km below the lithosphere called deep focus earthquake seen atlnear convergent plate boundaries Major eqs At sea can generate tsunami can travel at 800 km an hour across the ocean and generate was 20m high when breaking at the shoreline 1317 These along with the ground slumping severe shaking of buildingsbridges cause most of the damage associated with earthquakes Major earthquakes occur in belts along convergent or transform plates boundaries In the US in Ca along San Andreas Fault and the NW corner of WA and Alaska near subduction zones Occasionally have earthquakes far from plate boundaries eg very severe ones at New Mad rid MO in 1810 and milder ones near Charleston SC Caused by movement along local faults Predicting Earthguakes Can use the following 1 ground tilting over time 2 sudden fall in level of water in wells 3 sudden release of radon gas 4 animal behavior None of these are close to being perfect and geologists can only make long range predictions over decades rather than specific ones eg July 2007 near LA Pumping liquid water down into fault plane caused lubrication and can hasten earthquakes CHAPTER 14 Exploring Earths Interior Direct observation down only 10 km from Earths surface To know deep structure use indirect methods Most useful of all is study of P and S waves travelinq throuclh the earth s interior We will also look at use of gravity measurements and heat flow form the Earth s interior and the Earth s magnetic field Use of seismic waves If the Earth were of uniform composition P and 5 wave velocity would increase steadily with depth leading to curved wave paths 142 However Earth has different layers and at these boundaries waves can be reflected or refracted 141 Will look primarily at refracted waves Concentrate in depths where the P and 5 wave velocity does not steadily increase with depth Rather velocity will A decrease with increasing depth show sudden step increase with depth Shadow Zones Caused by depth of seismic wave velocity with increasing depth occurs at mantle to outer core boundary Figure 142 Note 1 S wave shadow zone is larger almost half of Earth 2 P wave shadow zone in doughnut shaped and smaller 3 shadow zones are areas where no direct P and S waves can arrive BUT reflected waves do arrive in these areas Can get time frame of reversals by a measuring magnetism normal or reversed of lava flows around the world and b finding out when the lava was erupted by carrying out K Ar dating Thus get the geomagnetic polarity time scale figure 210 and 1415 magnetic field flip flops between N and R states Origin of Earth s magnetic field As temperature is greater than 600 degrees Celsius curie point at 50 km depth cannot have a bar magnet buried deep inside then Earth Note that electric current in crustmantle rocks do not conduct electricity However the outer core is made out of iron which is a good conductor of electricity Electric current in the outer core have been flowing for many billions of years and cause the Earths magnetic field To reverse the direction of the Earths magnetic field just reverse the direction of the electrical current 32607 CHAPTER 2 10 Plate tectonics Most of the teaching in these chapters is done with the aid of gures tables supplied on a handout Problem Different chapters seem disconnected How to form big picture unifying essential parts History In 19205 Weg ner meteorologist suggested continental drift Continents have moved around in the past and in the late Permian times formed super continent Pangea Northern part Laurasia N America and Eurasia H 1 213 Southern part Gondwanaland made up of Africa S America India Australia Antarctica From Triassic time Pangea started to split apart and parts began to move slowly to where they are now Proof for continental drift came from 1 fit of continental edges H 2 2 Paleoclimatology glaciations 3 continuity of rock formations and common fossils across oceans figures 212 best example is the way that South America puzzles in with Africa 4 Continuity of structures eg mountain belts across oceans figure 22 Generally ideas not well received especially in N America and Europe Also Wegner could not supply energy sourcesforces to move continents Idea died with Wegner s death in 19305 The idea was revived in new form in 19505 19605 The new form is called Plate tectonics continents do move but not across oceans but rather oceans are created and destroyed over time Concept of sea floor sgreading critical 1 detection and mapping of mid ocean ridges sonar 2 high amounts of heat flowing out near these ridges 3 existence of symmetrical magnetic stripes on sea floor H 3 All are neatly explained by arguing for diver ent late boundaries sea floor 5 readin where molten rock material comes out pushing plates apart H 4 If divergent boundaries exist and the Earth is not expanding we must have convergent glate boundaries elsewhere and one glate must be subducted Slack in motion at other places taken up by transform fault boundaries figure 25 Definition of plate both vertically and horizontally comes from seismology For a given plate all points move at the same velocity FIRST APPROXIMATION Table H5 of great importance summarizes many important things about plate tectonics Divergent glate boundaries figure 26 1 topographically form mid ocean ridges mountain ranges thousands of km long 1000 km wide and 1 2 km high 2 mafic magma extruded under water form pillow lavas H6 3 over time hot material is pushed away from mid ocean ridge and becomes colder H 7 Hot material near boundary is light sits up Later becomes colder and denser sits down Gives shape to oceanic crust near spreading centers and creates mid ocean ridges H 7 4 oceanic crust in general forms part of H 6 5 age of oceanic floor depends on distance from ridge axis H 8 3282008 A present oceanic crust created since breakup of Pangea Oldest oceanic crust is 200 million years old 6 details of rifting of continents to be taken up later Convergent glate boundaries main topographic feature deep sea trench parallel to subduction line a depressed belt in the sea floor up to 11 km below sea level Deep sea trenches represent the deepest parts of the oceanic floor 1 Can be of three types depends on what type of crust on either plate H5 26 OCEANOCEAN denser plate subducts OCEANCONTINENT oceanic plate denser subducts CONTINENTCONINENT neither wants to sub duct 2 Benioff zone marks top of subducting plate located by noting line of earth quake foci near boundary 1312 Old cold dense oceanic crust subducts steeply easily but young oceanic crust warm light subducts at a shallow angle less readily H5 3 Li ht material continental crust resists subduction a wet sediments very light gets sliced up near subduction zone stacked up like deck of cards called melange H10 610 b Continental crust light resists subduction When Indian plate came into collision with Eurasia initially oceanic crust was subducted at first inertia Continental material squeezed sideways under Tibet lifting it high in the air Highest mountains are made of light material sedimentary rocksgranite c Often at subduction zones incoming small pieces of continental crust do not sub duct but are plastered onto the continent forming disglaced susgect terranes H11 Fig 1012 Much of Western North America consists of complex series of suspect terranes incoming from the Pacific Ocean over the last 100 million years Figure 1011 Fate age of crust Oceanic crust dense will eventually sub duct and disappear age 0 200 million years old Continental crust light eternal will not sub duct age 0 4500 million years old Transform fault boundaries On continents take up the slack in motion often between divergent and convergent plate boundaries See San Andreas Fault H12 In oceans offset mid ocean ridges Eg the Kane Fracture Zone H13 These take up the slack in motion caused by different parts of the same oceanic plate moving at different velocities Plate Velocities are not necessary for all points on a given plate On a sphere spreading occurs round a spreading pole H14 Points that are farther away move faster than those near the spreading pole On oceanic sections of plates this slack taken up by transform fault boundaries H13 plate here weaker and faulting results where necessary On continents plate stronger thicker and slack in motion not taken up so easily This may result in strain accumulating far from the plate boundaries causing intra plate earthquakes New Madrid Different plates have very different velocities 1 20 cmyr Why 1 Bigger plates move more slowly cf Nazca and South American 2 Plates with lots of continental material on them more weight move more slowly Nazca and South American Plate 3 Plates with at least one end being subducted pulled move faster Pacific and North American Plate Calculating Plate Velocities H11 a Use distance of magnetic reversal on sea floor from the ridge axis and corresponding age H4 Gives value averaged over some million years b Use say laser beams to measure actual distance between two cities on different plates over 30 years Changes over this period measure velocity averaged over 10 30 years H15 Recently noted that velocities calculated by a and b agree generally to within 1 Gives quantitative proof of sea floor spreading Plate tectonics in the remote past If we look to continental blocks H212 we find large blobs of rocks that have not suffered deformation for NZ billion years They are called cratons Surrounding and holding cratons together are long elongate sections of rocks that have suffered intense deformation These are called orogenic belts and represent remnants of mountain belts formed when two continents cratons crashed into each other Shows that plate tectonics in some form has been going on for many billion years Wilson Cycle 1018 Over long periods of time billion years oceans open and close repeatedly Thus North America AfricaEurope were separated by an old Atlantic Ocean Iapetus over 500 million years ago This ocean closed 300 million years ago plastering North America to AfricaEurope creating Appalachian Mountains Later 200 million years old onwards these continents broke apart creating the present Atlantic Ocean During initial stages of splitting of continents spreading occurs at triple junctions three rift arms meeting at 120 degrees H13 One of these arms generally fails to develop fully the failed rift Tens of millions of years later these failed rifts house major rivers H14 What powers plate tectonics 214 Energy comes from the internal heat of the Earth 1 Drag on the base of the lithosphere 100km deep caused by convection cells whole or part of the mantle 2 Pushpull model Push comes from oceanic crust at mid ocean ridges Light material sitting up slides down under gravity M comes from old dense oceanic crust that sinks back into the deep mantle at subduction zones M is probably the bigger force of the two 3 Role of hotspots concentrated jets of hot material rising from 2900 km down is controversial 215 Chapter 9 Early History of the Earth and Moon Universe is thought to be 14 billion years old Origin of Solar System Nebular Hypothesis Formed from nebula 91 mainly gas hydrogenhelium and dust Rotating cloud flattens into disk gravity pulled most material into center proto sun formed 92 Temperature rose inside sun to millions of degrees nuclear engine fired up This continues today process same as in hydrogen bomb Einstein some mass converted into energy Remainder of material in nebula continued spinning In some places gravitation causes clumping of material As these clumps grow they pull in more material accretion Finally sweeps out most of the remaining material 92 Inner terrestrial planets Mercum Venus Earth Mars 93 Small rocky quite dense Formed close to sun so most volatiles boiled away Radiation from Sun blows away light gases hyd rogenhelium Occurs about 456 by ago Outer Jovian planets Jupiter Saturn Uranus Neptune 93 Much bigger more gas relatively low density Saturn would float in water Contain rockmetals but enough gravity to hold on to lots of gases eg hydrogenhelium Lots of small lt100km size bodies left over Rocky ones called asteroids Gassy ones orbiting far out called comets Sometimes these bodies come into near Earth orbit and can lead to collisions 32807 Differentiation of Earth Earth heats up rapidly after birth caused by a accretion process b compression c radioactive decay inside Very early big collisions also cause extra heating One at 45 billion years of mars sized body causes a formation of moon b earth s rotational axis tilt c outer layers to melt 94 Oldest rocks on moon 447 billion years old dated radiometrically Heavy material iron falls to center creating molten core Least dense material floats to surface forming crust Recent work shows some very little crust formed in presence of water 43 44 Billion years ago Between the core and crust have mantle left behind material consisting of more Fe and Mg than crustal rocks 95 Earth s ocean and atmosphere Light material gases escape during heating process form early oceans and atmosphere Some say lot of water brought in by accreting comets Others say most water is released form the Earth s interior Latter process continues today from volcanoes releasing gases 96 Composition of early atmosphere very different form today eg little or no free oxygen Diversity of planets table 91 Late hea bombardment Around 39 billion years ago very heavy bombardment of inner planets by asteroidscomets Accretion process wipes out most of earlier evidence resets radiometric clocks Known again from direct dating of moon rocks This is why few rocks on Earth give radiometric age gt4 billion years In early stages of Earth much more heat escaping form interior probably cause more vigorous convection Plate tectonics different from that of today 915 Bombardment accretion continues today Estimated 40000 tons added to Earth annually equal to cube of rock 20m on edge mostly dust size particles But once in a while bigger body collides with Earth Craters left on continents 918 These collisions can have immense effects at surface affecting life table 92 Can cause or contribute to global faunal extinctions resist impulse to blame all extinctions on asteroid impacts CHAPTER 10 EVOLUTION OF CONTINENTS Most continents have stable interior not deformed for many billions of years called cratons shields 101 Much made up of strongly metamorphosed rocks Around them and often holding them together have elongated belts of strongly deformed rocks orogenic belts The Appalachian Fold Belt Formed by plate tectonics primarily atclose to convergent plate boundaries From west to East have 104 a valley and ridge province folded and thrust sedimentary material shows compression form south east 400 500 million years ago b Blue Ridge province are eroded interior of mountains highly metamorphosed rocks thrust over at least 300 million years Again shows compression c Piedmont metamorphosed rocks intruded by granite thrust over Shows compression again above 400 300 million years ago d Coastal plain undisturbed sedimentary material formed after slitting of Pangea after 180 million years ago Offshore have thick sedimentary deposits on continental shelf In other places see continental accretion at work eg west coast of N America 1011 Over last 200 million years have added lots of material brought in by convergence process Can involve plastering on A light continental material B material from island areas C material brought in by strike slip transform faults D Suturing of material following Wilson cycle Also on east coast of North America have accreted terrains Thus Florida probably brought in from Africa side when Pangea assembled Later when Pangea split up this continental material was left on N American plate The Himalayan Orogenx As Indian subcontinent moved form deep in southern hemisphere Gondwanaland ocean between it and Eurasia closed Near Northern edge large islands are formed As continental India came into hard collision 50 million years ago motion northward drastically reduced Island arcs etc are deformed mashed into Eurasia causing gross shortening raise high mountains Section of India underlies Tibet crust is 60 100 km thick also caused China and Mongolia to be squeezed eastwards 1016 like squeezing toothpaste out of tube Northward movement of Indian plate continues today GPS measurements but must cease eventually Probably forms most important plate tectonic event of last 50 to 100 million years 41607 Water inside the ground beds that store and transmit water are called aguifers Such beds have high porosity empty pore spaces in rock ability to hold water and high permeability these pore spaces are interconnected ability to transmit water from one place to another 177 At the other extreme rocks that have lowintermediate porosity and low permeability are termed aguicludes 177 Can result from cementing of pathways between pores or from presence of clayey material Table 172 lists porosity and permeability of various rocks generally sedimentssedimentam rocks only are aguifers In a simplified manner most sandstones and limestones are aquifers and shales are aquicludes Almost all ig neousmetamorphic rocks with very low porosity are aquicludes At very deep levels inside the Earth the high pressure squeezes the rock lowering porosity Water moves very slowly 1cmyr and can dissolve minerals in rocks At these depths water is salty 1721 Groundwater Table As water percolates into the Earth top part soil has some pores filled with waters others with air This is called the unsaturated zone At a lower level are open pores are filled with water only this is called saturated zone 178 Boundary between these two zones is called the groundwater table and is marked by the level of water in a well If the groundwater table hits the surface of the Earth hilly areas a natural spring is formed 176 Aquifers may be unconfined or confined For the latter the aquifer is both overlain and underlain by an aquiclude Given the rig ht set of conditions can get an artesian well water flows out of well under pressure and comes out at the surface 1710 With alternating aquifers and aquicludes can also get a perched water table lying above the main water table 1711 In dry seasons shallow wells may go dry 179 Pumping out of water from wells results in a cone of degression in the water table 1712 Rate of groundwater flow Generally groundwater moves very slowly from one part of an aquifer to another In gravelly beds is 20 cmday high end Much lower than in rivers 20 cmsec Rate of groundwater flow is controlled by Darcy s Law and depends on a Permeability of material b the Hydraulic Gradient 1715 Since groundwater flow rate is very slow If an aquifer is over pumped wells can go dry locally Also if groundwater is contaminated it could be very slow to recover An example is shown in 1714 common for big cities near the coastline Pressure of freshwater keeps saltwater offshore If too much pumping saltwater intrusion occurs draws salty water from wells Solutions a Pump millions of gallons of freshwater down the well push back saltwater margin impossible b Shut down pumping for many years Currently over 70 of the Earth s inhabitants do not have access to sufficient fresh clean water As we continue to use water wastefully and groundwater levels fall will have serious water shortage in parts of the USA Then either import water from elsewhere Canada or develop cheap technology to purify salt water Freshwater will become the most important liquid for survival over the next 50 100 years As oil reserves fall in the next 20 years first liquid crisis will relate to energy sources Erosion by groundwater Most noticeable where limestone occurs atclose to the Earth s surface Groundwater slightly acidic dissolves rock limestone away creating sinkholes underground caves disappearing streams Karst Topography 171819 In caverns stalagtities grow down from the geiling stalagmites grow up from the ground Eventually join to form columns 1717 Quality of groundwater Many natural contaminants are removed by filtration through sandy layers However not so for other pollutants such as gasoline heavy metals PCBs pesticides fertilizers If groundwater has become contaminated and recharge is fast can clean up situation but expensive For aquifers where flowrecharge is slow clean up may not be done ever after decades 1720 Box 231 41807 In many areas groundwater or melted snow water comes close to hot rocksmagma at depth Water is super heated up and ascends to escape from geysers Old Faithful can serve as cheap clean almost limitless source of energy Iceland New Zealand Chapter 18 StreamsRivers Run off after rainfall goes into streams and rivers These carry water and huge amounts of clastic and dissolved material towards the oceans If flow is relatively slow streamlines are parallel to one another laminar flow If flow more rapid streamlines cross turbulent flow 1813 In general fast moving streams pick up and carry particles detritus When the current slows sediment is dumped coarse particles first and fine clays last 1815 Sediment Load A flowing stream carries a load partly as bed load partly as suspended load 1814 Suspended load finer particles is always moving downstream Bed load consisting of bigger particles moves downstream by hops and skips process called saltation A river s ability to carry particles of different sizes is called its competence and depends only on the stream velocity The total weight of sediment it carries is called its capacity and depends on both its stream velocitv and the volume of water the river is carrvinq Large rivers carry more sediments than small streams higher capacity On river bed erosion is occurring larger pebblesboulders can scour the bottom leaving potholes 181 1 ChannelsI Floodplain A river flows through a valley the area between the tops of the slopes on the two sides At the bottom is the channel the trough through which water runs At low water level water only fills the channel But at flood stage water may fill almost entire valley In broad valleys have a floodplain the flat part of the valley filled when a river overflows its banks In such areas we get meanders oxbow lakes and natural levees Meanders Over broad floodplain river channel takes a sinuous path This is created over decades for low velocity low sediment load streams The current is faster on the outside of curves causing further erosion of the outer bank 18319 On the inside bank current is slowest and sediment is deposited to form point bars Slowly curved path becomes more marked and eventually at major flood stage the river cuts off the loop 18319 creating a crescent shaped body of water the oxbow lake Some streams have many channels not one which rejoin and separate braided streams 183 Common where large variation seasonal in volume of water carried as well as high sediment load Levees 184 Created naturally when at flood stage river overflows channel onto floodplain Velocity is checked and sediment is dumped Over decades these levees become higher confining river to its channel except for very high floods 42007 Stream Discharge In the volume of water flowing down a river past BTR say per second varies widely with stream for most rivers Discharge depends on increases with width of river channel depth of river channel stream velocity When very high River flows its banks flooding Levees often ineffectual Allowing house on 100 year flood plan is asking for trouble Longitude Profile a streams bed level depends on topography hardness of bedrock climate and stream flow Most rivers bed height is above sea level show a consistent profile from headwaters to mouth This is called the longitudinal profile and is concave upward 1822 In part controlled by the ultimate level to which the stream bed can be eroded For most rivers this is sea level the base level Climate has a major effect on long profile high rainfall causes high weathering erosion of soils high discharge causes erosion of river bed The long profile of a river will change when the base level temporary dam or final sea level changes 182324 If the stream reaches an equilibrium sate between erosion and sedimentation in its course it is called a graded stream Where a stream emerges from the mountains onto flatland the velocity is checked suddenly Much sediment is dumped in a cone or fan shaped body alluvial fan Increased erosion or uplift causes a river to cut into its floodplain Terraces older floodplain often paired on either side are created 1826 Drainage networks A ridge of high few meters to km ground separates any two streams called the divide Rain snow fall on each side funnels down into the streams A drainage basin is the area of land that funnels all its water into the streams draining that area 185 The divide can be on local or continental scale In the lower 48 states the continental divide runs along regional high ground mostly the Rockies Rain fall to the west finishes up in the Pacific Ocean east Atlantic Gulf of Mexico Other less important divides separate water destined for the Atlantic versus the Gulf Appalachian Mountains Water destined for the Great Lakes versus the south Mouths of rivers Most rivers flow into the ocean eventually Current is checked sedimentation occurs building up the delta In this area slope of a river bed is very gentle stream breaks up into many channels distributaries These carry water and sediment downstream Morphology of delta 1817 A Sand deposited at he top of the delta make up horizontal togset beds B Down current silt and fine sand deposited in beds gently slopping towards ocean the foreset beds Resemble cross beds C Sea ward of this we have deposition of fine clay in thin horizontal bottomset beds Growth of the deltas As the delta grows outward the river takes a longer route to get to the ocean This is mechanically inefficient and the river seeks a new channel to shorten route to base level 1818 Over thousands of years verified by radiocarbon dating the river delta sweeps sideways backwards and forwards Over the last 80 years the Mississippi is forced Corp of Engineers to send most of its water down the main channel past BR and NO On it own the river would send more watersediment down the Atchafalaya This system is basically unstable 4302007 Carbonate shelfs deposits common in shallow warm seas In instances after carbonate layer laid down algae grew on it As more carbonate rains down algae grows up throw carbonate to get to sunlight After a long time a layered carbonate structure stromatolite is formed Similar structures found in old rocks up to 35 billion years old suggesting simple forms of life like algae existed on earth at that time Waves Wind blowing over oceans creates waves Water particles at the surface move in circular orbits figure 202 Radius of orbit reduces with depth wave motion ceases at some depth says D As wave approaches land shallow water depth may be less than D Water particles held up from executing circular motion Causes erosion of sea bottom and gives rise to surf figure 202 Extreme case is tsunami approaching land Builds up to surf 20 meters high due to velocity of tsunami 800 kmhr in open ocean Also causes wave front to bend when nearing shoreline Tides Cause by gravitational attraction of the Moon more important and then sun on ocean water Thus water closest to the moon is raised up to high tide at antipodal point water is left behind and this caused by the moon and sun aid each other get high high tides sgring tides When moon and sun are at right angles to each other first and third quarter their tides work against each other Get low tides low tide fall tide Position of shorelines strongly affected by global temperatures During last glacial geriod sea level was 160 m lower than now eastern shoreline of USA much further out During last 18000 years interglacial timeI sea level has risen 160 meters cover much of the continent shelf Sea level still rising today How much is natural and how many due to human activities Need to consider effect of green house gases carbon dioxide methane and water vapor These gases allow visible light from sun to reach earth Plants use this light photosynthesis and emit lower energy light infrared Latter is absorbed by greenhouse gases cannot escape to outer space Causes heating of earth Since industrial revolution C02 content of atmosphere has risen markedly figure 1516 As has global temperature Analysis of air bubbles in Antarctic ice cores shows that during warmer interglacial periods air contained higher amounts of C02 methane Before civilization 1511 Increasing use of fossil fuels in all countries releases lots more C02 into the atmosphere Right now USA with 5 of the world s population uses3 times more energy than China and India with 45 of the worlds population As third world countries get more industrialized they will use much more energy However oil reserves are being depleted Hubert s peak figure 23910 Wars over oil supplies More C02 and methane pumped into the atmosphere each year Earth s surface atmosphere is warming up Sea level will rise further drowning coastal areas What can or should be GEOL Intro and Ch1 8252010 63400 PM Geology Study of the Earth Introduction 0 Earth s Interior 0 Surface 0 It s history 0 Origin and history of life 0 Natural resources 0 Hazards Overlaps with and draws from Physics Chemistry Astronomy and Biological Sciences 0 Multidisciplinary Physical Geology 0 Concerned with 0 Earth materials changes and processes within and at the surface of the earth The earth is constantly changingdynamic Natural Resources 0 Oil metal rocks Natural Hazards o Earthquakes o Tsunamis o Volcanoes o St Pierre destroyed by eruption of Mt Pelee in 1922 0 Some effect the climate globally Tambora1851Laki o Interactions o The eruptions from Tambora and Laki demonstrate interactions between various components ofthe earth system ManMade hazards o Chemicalindustrial pollution 0 Nuclear waste Chapter 1 The Earth System Keypoints 0 About the earth system 0 All parts of our planet and all of the interaction of those parts comprise the Earth System 0 Earth is an open system 0 Geosystems include climate plate tectonics and the geodynamo The Scientific Method fig 11 0 The goal explain how the universe works 0 Steps 0 1 Observation and experimentation o 2 Development of an hypothesis or multiple hypotheses as tentative explanations 3 Testing challenging and experimentation to eliminate hypotheses or revise them Scientific theory is a successful hypothesis A Scientific model is based on hypotheses and theories 0 O O Topography g 13 0 Topography elevation change on the earth s surface 0 Ertosthenes measures the earth s size 0 Used the angle of shadows in Alexandria and Syene to find the earth s radius Surmised there was some curvature to the earth and assumed it was a sphere o Uniformitarianism 0 States that the same processes we observe today have been operating throughout Earth s history The cycle of uplift erosion transport deposition solidification into rock and renewed uplift requires a great deal oftime for its operation The earth is 455 billion years old 0 The geologic record 0 Process comparison slow versus rapid The rocks at the bottoms ofthe grand canyon are 1720 billion years old a The rocks decrease in age as you ascend The explosive impact of a meteorite created this 12 km wide crate in just a few seconds 0 Spacial scales atoms to solar systems Discovery ofa layered Earth 0 Seismic waves illuminate Earth s interior 0 O o Compressions and shear waves behave differently and are bent or absorbed at layer boundaries within the Earth Earth s interior is layered according to density 0 Surface rock density is less than 35 gcm3 0 The whole earth s density is 55 gcm3 0 The core s density must be about 8 gcm3 Refraction at boundaries 0 when the densities of the different material that the waves travel through change it bends the wave itself Re ection at boundaries 0 Angle of Incidenceangle of reflection Seismic waves are generated by earthquakes Body waves travel through the earth They are reflected and refracted at boundaries between layers in the earth The layers 0 Crust o Mantle 0 Outer core liquid iron 0 Inner core solid iron The Crust 0 Continental crust thicker density28 gcm3 0 Oceanic crustthinner density 30 gcm3 0 Floats on mantle which has a higher density Lithosphere o composed of all ofthe crust and uppermost mantle o rigid and cooler in temperature 0 around 100 kilometer thick Asthenosphere o The part of the mantle below the lithosphere o Warmer ductile material Abrupt changes in density between Earth s major interior layers are caused by changes in the chemical composition of those layers 0 Crust Mainly Silicon and oxygen Mantle similarto crust but with a lot more magnesium Outer coreMostly iron lnner core Only iron and nickel O O O o Temperatures within the earth 0 Temperatures increase with the depth in the earth Variation ofT with depth 2 de nes the geothermal gradient or geotherm o Mantle Convection Similar to boiling water Moves hot material upwards where it then cools and sinks back to the bottom When Mantle is heated it becomes less dense and can float upwards It then cools becomes more dense and sinks back down 8252010 63400 PM Homework 2 Notes Geology 1 PartA 0 Part B 0 Part C 0 Part D 0 Part E O PartA O PartB 0 As a result of partial melting magma originates in I The mantle and crust When lava erupts at Earth s surface what type of rock is produced I Extrusive Magma that reaches the surface cools quickly has finegrained texture and produces extrusive rocks Pyroclastic debris from a volcanic eruption can include I Ash and cinders Why does magma have a tendency to rise after its formation I It is less dense than the surrounding rock As rock melts the density decreases This process causes the magma to rise Most igneous rocks never reach the surface However igneous rocks other than those formed in volcanoes are found exposed on many parts of Earth How do you account for this phenomenon I They formed at depth and have been exposed by uplift and erosion Most igneous rocks are primarily composed of I Silicate minerals Silicate minerals are the most common minerals in Earth s crust and therefore make up the bulk of most igneous rocks though minerals from many other important groups may also be present The light silicate minerals include I muscovite orthoclase feldspar plagioclase feldspar and quartz These are all lightcolored minerals and are found in granitic rocks PartC O PartD O PartE O 3 PartA O PartB O PartC 0 What element is principally responsible for making olivine pyroxene amphibole and biotite dark I Iron Iron is common in mafic rocks and minerals in fact quotmaficquot refers to the high iron and magnesium content of these materials chpt 3 page 66 Basaltic igneous rocks contain which of the following minerals I pyroxene and calciumrich pagiocase feldspar A geologist sends you a sample that was collected in the field You find that it is a graycolored igneous rock containing amphibole and intermediate pagiocase l feldspar 39s Reaction Series as a guide how would you describe its Comment C1 Ultrama cr olivine high 1 temperature 1 tocrystallize compOSItIon Basaltic pyroxene and calcium ricn feldspar I Andesiticlintermediate amphiboleand Andesmc plagioclase feld ar 6 I Amphibole and intermediate pagiocase feldspar occur in the Vanitic39lasttwv allizeiPotassiumie dSPa aquotd andesitic temperature regime Com ment C2 3 N L Bowen was the rst to dernonstrate how a single magma body could generate a variety ofl gneous rocks Which of the following igneous rocks contains no minerals Obsidian Obsidian cools so quickly that the individual ions in the lava do not have time to organize into a crystalline structure What is the term used to describe a very large widespread and deep intrusive body of igneous rock I Batholith In what type of igneous feature would you find rocks with a vesicular texture I Surface of lava flow lavarVESlCULAR wnen magma solidi es atdepthr COURSE GRAl ED Because escape of gas from lava is possible only at or close to the Rapid cooling oflava GLossv Form surface or by upper crust FINE GRAINED surface of Earth lava flows may possess vesicular texture Part D 0 Working in the field you see a thin darkcolored igneous sill across the valley Without seeing the sill up close what texture would you expect it to possess I Finegrained Part E 0 Working in the field you come upon a lightcolored finegrained igneous rock that contains some very large darkcolored crystals How do you account for this complex mineralogy I The dark crystals formed first undergoing slow cooling and the remainder cooled quickly The compositional differences imply that the darkcolored coarsergrained minerals formed first at a slow cooling rate and the lightcolored finergrained minerals cooled later and more quickly 4 PartA o What is the classification of igneous rocks based on I Composition and Texture Part B o Basalt is an igneous rock that can be identified by its small crystals What are they composed of I pyroxene and calciumrich plagioclase feldspar Basalt is a mafic finegrained igneous rock that contains pyroxene and calciumrich plagioclase feldspar Part C oAn igneous rock that contains quartz and potassium feldspar would have a mineralogic content placing it in the range of I granitic or felsic rocks Part D o What is a coarsegrained rock composed of intermediate plagioclase feldspar and pyroxene I Diorite Diorite is a coarsegrained rock with intermediate plagioclase feldspar and pyroxene 4 Part E o What is a finegrained igneous rock composed primarily of very small crystals of potassium feldspar and a few large crystals ofquartz I rhyolite porphyw PartA o What lies underneath volcanic features on Earth s surface I magma chambers and volcanic conduits Part B o What is the difference between a dike and a sill I A dike intrudes across sedimentaw layers and a sill intrudes between sedimentary layers Part C o What is a volcanic conduit called after the conduit has solidified and been exposed by erosion I Volcanic necks Part D 0 Why are volcanic rocks often exposed at Earth39s surface as hills ridges and mountains surrounded by areas of lower elevation I Volcanic rocks are often more resistant to erosion than surrounding rock Part E o What is a magma chamber called after the conduit has solidified and been exposed by erosion I Batholith
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