Midterm study guide
Midterm study guide Geol 105
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This 24 page Study Guide was uploaded by Abi Sommers on Sunday September 25, 2016. The Study Guide belongs to Geol 105 at 1 MDSS-SGSLM-Langley AFB Advanced Education in General Dentistry 12 Months taught by John Platt in Fall 2016. Since its upload, it has received 131 views.
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Date Created: 09/25/16
8/24 Global Tectonics Lithosphere includes upper part of mantle and crust that overrides the mantle represents departure from normal mantle w/in earth’s body Upper part of mantle increase in temperature as goes downward, mantle rocks that do melt and mantle rocks that do, partial melting Plate Boundary: Boundary between asthenosphere and lithosphere Global Topography and Bathymetry(topography below sea level) Seismic belts separated by large areas of planet where there are not earthquakes. Earthquakes are release of energy when crust shifts along a fault “Fault” means there must be some movement between stable areas, plates *Not until 1968 marine geologists found plates , spatial areas of earths crust shaping with respect to each other * Mid Atlantic Ridge is a boundary between two stable areas Plates can move, together, beneath, and past Divergence (together), Convergence (beneath), Transform Plate Motion (past) ● 1857 last movement of san andreas fault Coastal california slips past North America @ 55 kms per 1 million years *Continents have changed shapes and positions throughout time, reconstructions of Earth’s supercontinent pangea *Pangea built up of convergence of plates on other sides of the world When continental crust extends, confining pressure reduced Reduction of pressure allows existing high temp at depth to partially melt mantle Large volume of mole rocks (magma) rise up along axis of plate rifting, eventually new basaltic ocean crust *East africa shows early stages of same continental extension that led to evolution of rifted Red Sea in the north, one day could be as wide as the atlantic ocean *Volcanic mid ocean ridges and rises are direct expression of where hot mantle rises near to earth’s surface. Initial seafloor spreading happened between North Africa and North America Different parts of Atlantic Ocean opened before others Divergent boundaries Rifting and spreading along a narrow zone have created Mid Atlantic Ridge ; A mid ocean mountain chain where volcanoes and earthquakes are concentrated. *Central Atlantic between Eastern U.S and North Africa began to form first ,nearly 180 million years ago Breakup of pangea created 3 ocean basins Atlantic, Arctic and Indian Ocean Pacific was already there Generation of oceanic lithosphere along ridge and rise system known as, sea floor spreading, and process occurs at different rates 70% of earth’s crust formed in last 180 million years , only 4% of earth’s history 8/26 *Sea floor spreading hidden beneath oceans Iceland extensional plate boundary between Europe and N. American plates exposed at earth’s surface Iceland part of Mid Atlantic ridge Mid Atlantic Ridge enters at Thingvallir, one of first settlement areas in Iceland Island extending, divided by European plate and N. American plate Basaltic magma has built island by rising along vertical fractures Bardarbunga volcanic eruption 20142015 largest basalt eruption since 1700s. Added 1.5 km of lava over 6 mo. ^ Plate divergence Plate convergence : 3 types: Oceanic plate moves beneath oceanic plate Oceanic plate beneath continental plate Continental plate beneath continental plate Plate convergence and subduction Most common; oceanic plate goes below continental plate ● Juan de Fuca plate being subducted beneath U.S Pacific Northwest and Southern British Columbia, slow but fast enough to produce earthquakes. Vancouver, Seattle Portland all at risk. (last earthquake jan. 16 ,1700) subducting plate carries water rich ocean crust to beneath coastal N. America. Plate heats, dehydrates and water moves upward Earthquake hypocentre is starting point of earthquake from seismic waves travel outward Oceanic plate beneath Oceanic plate: Mariana Arc characterized by small islands Mountain systems w/in Alpine Mediterraneaniranianhimilayan orogenic belt. Belt created by collisions btwn eurasia and southern continental plates Earths most spectacular example of crustal deformation Alpine Himilayans Boundary today continuing tectonic activity *Parts of eastern medittereanean still have oceanic crust beneath them Highest elevation in the world is Tibet ; 15,000 feet. *Height of mass related to thickness ^ indian crust sitting beneath Asian crust India once part of supercontinent, as broke loose, began to move northward because attached to oceanic plate, being subducted to the North. Transform Plate Motion: two plates moving past each other, sometimes left slip, sometimes right slip *San Andreas transform fault 8/29 (Monday Week 2) Syllabus Material Covered The Earth as a System: Earth’s core made of iron, partly liquid partly solid, generates magnetic field ( Geo Dynamo) Sun produces solar wind, made up of charged particles ( protons and electrons), creates electric current which generates magnetic fields Solar winds come from wind, go into magnetic field, field lines bend around and follow direction of solar wind Magnetosheath deflects solar wind Charged particles from solar wind on solar atmosphere Impact of solar wind on upper atmosphere has potential to destroy atmosphere which protects from solar radiation Without magnetic field and solar wind, would be constantly bombarded by solar radiation Core generating magnetic field, allowing for life on earth * Life sequestors carbon, keeping Earth’s surface cool Greenhouse effet, Co2 in atmosphere helps keep heat in and is contributing to global warming Without life, Earth would be like, Venus, with poisonous atmosphere, no oceans or liquid water or plate tectonic, no magnetic field ( maybe because no plate tectonics) Climate System involves interactions among atmosphere hydrosphere, cryosphere (icey layer), biosphere, and lithosphere System receives heat and matter from space, energy from the sun and material falling into the Earth ( Called an Open System) 8/31 The Scientific Method: Based on the empirical method can understand the world by developing scientific explanations for observations Scientific explanations considered valid only if account for observations What we observe has physical explanation, even if beyond present understanding ● We assume basic physical laws are the same at all places and times Hypothesis: Tentative explanation of observations and experiments Theory: Set of linked hypotheses that survived repeated challenges and accumulated a substantial body of observational support Scientific Model: Predictive description of some aspect of nature based on hypotheses and established theories ● Science advances by continued testing and challenging of ideas against observations and measurements Scientific Method Continued: No explanation is closed to question Theories can never be proved A hypothesis theory, or model is confirmed by repeated observations and experiments gain credibility Longer a theory holds up to all scientific more confidently it is held One of most important tests of scientific explanation is to compare its predictions with observations Earth ’ s crust varies in thickness and density Curst is a compositional layer lying above the mantle Oceanic crust is thin and dense Continental crust is thick and has lower density Isostasy : The Floatation Principle ( example of a theory0 Crust “ floats” on underlying denser mantle Topography controlled by thickness and density of crus t The Floatation Principle : A floating object displaces its own mass of fluid. If fluid has higher density than object, volume of displaced fluid is less than volume of object. So part of object stands above surface of the fluid (freeboard) This means thicker block of same material will stand higher than thinner block. Thick crust stands higher than thin crust For same reasons, block of denser material stands lower than block of less dense material, it has to displace a larger volume of fluid ● “ The Present is the key to the past” 9/2 LAB ISOSTASY : balance between gravitational forces pulling down earth’s crust. ; the equilibrium that exists between parts of the earth's crust, which behaves as if it consists of blocks floating on the underlying mantle, rising if material (such as an ice cap) is removed and sinking if material is deposited. Crustal substance V Gravitational Force V Crustal rebound ^ Buoyancy force ^ Pressure from glacial ice causes crustal subsidence, melting of ice causes crustal rebound Airy: Mountains are higher because they are thicker ( have big root like an iceberg) Volume (thickness of crust) is variable density is constant Pratt : Mountains are higher because they are less dense than other crust (float higher on mantle) Density of crust is variable Volume (thickness of crust) is constant Airy isostasy: all crust has same density, high mountains occur where crust is thickest Blocks of crust have same density Blocks of crust have different thickness Continental blocks either higher than ocean blocks because thicker than ocean blocks 9/2 Lecture Most rocks are aggregates, made up of grains Granite is a rock made up of several dif. Types of mineral grains *Rock is a complex material made of many different grains Minerals are much simpler ● Individual grains often have a simple chemical composition, and crustal structure composed of a mineral Example : Quartz is a mineral, a sand grain usually crystalline SiO 2’ Minerals Naturally occurring substance Solid Fixed chemical composition A particular crystalline structure ( Olivine: Mg 2SiO 4 main constitute of Earth’s upper mantle ) Minerals to know ! Gold Au Diamond C Graphite C Halite NaCl Queartz SiO 2 Calcite CaCO 3 Magnetite Fe3O 4 Mica silicate mineral Feldspar silicate mineral (KAlS3O 8) Olivine silicate mineral Crystal Structure All minerals have crystalline structure Controls shape, appearance, and physical properties of the mineral Atomic Bonding in Crystals: Ionic Bonding There are cells in which electrons are located and electrically charged Electrons spin, get together with opposite polar “ spins” Salt is soluable, lots of ionic materials have easily breakable bonds and low densities * Exchanging of electrons Atoms not forced to be next to each other, can float off Covalent Bonding Each carbon atom linked to four others Atoms linked together by covalent bonding where they share electrons instead of exchanging them Atoms forced to stay close to one another, therefore tends to be stronger than ionic bonding Covalent bonding in carbon leads to creation of diamonds Polymorphs: Graphite and diamond are polymorphs of carbon ; have same composition but dif. Crystal structure * Crystal structure is critical in defining the mineral Graphite: So soft because covalent bonding in sheets of cells Sheets of carbon atoms have properties like metals so atoms can migrate through, and is electrical conductor Silicate Minerals silicate linked to 4 oxygens, oxygens then bond to other oxygens Tetrahedron; Si and O atoms are covalently bonded Silicate minerals make up most of planet Silicates constructed of SiO4 tetrahedra The tetrahedra may be linked into chains, sheets or frameworks. Metal ions maintain charge balance Bonding in Quartz: Silica tetrahedra linked covalently in framework, sharing oxugen atoms, formula for quartz SiO2 ● Mica is silicate ○ Has silicate and oxygen, aluminum and potassium ○ Sheet structure : silicate layer, aluminum hydroxide layer, aluminum atom, silicate layer , potassium ions Properties of Minerals: ( will learn more in lecture) color, streak, hardness, crystal shape and symmetry, cleavage, density Color may be misleading: many minerals are colored by trace impurities Sapphire and ruby are both corundum ( Al2O3) ● Garnet : prof’s fave mineral, cubic symmetry, silicate mineral Week 3 Notes 9/7 : Answers to last week’s pop quiz: 1. What term best describes the part of Earth that forms the tectonic plates? Lithosphere 2. The radius of the Earth’s core is about one sixth radius of the earth. False 3. Which is not correct? Earth’s mantle is made of liquid rock 4. Plate material is formed at divergent boundaries and destroyed at convergent boundaries. True 5. Boundaries of plates most clearly indicated by : distribution of earthquakes 6. The sun is the principal energy source that drives plate tectonics. False 7. Which statement is not correct : plate boundary in central california is a subduction zone 8. The East African Ridge and Mid Atlantic Ridge are both expressions of divergent plate boundaries. True Earth Materials II : Rocks Rocks : Rock Description: Mineral assemblage Grain size ( size of crystals) Texture Organization and structure ● These all give info that allow us to interpret how the rock formed Texture: Crystalline texture grains may have crystal faces and interpenetrate may result from growth of grains granite Sedimentary (Clastic) texture Rounded or angular grains Do not interpenetrate Separated by matrix Pebbly sandstone and conglomerate sediment deposited by rivers Clastic means segmented Granite: The main constituent of the continental crust An igneous rock , a crystallized rock made of mainly quartz and feldspar rich in Si , Al, Na, K Oxygen is most abundant element ! Peridotite: Main constituent of Earth’s mantle Crystalline texture Peridotite made up of mainly olivine ( also pyroxene, sometimes garnet) Mainly Si (less than in the crust) and Mg Oxygen is most abundant element! Classification of rocks by texture and origin I . Igneous rocks Crystalline texture Crystallize from a melt (magma) 2. Sedimentary rocks Clastic texture (mainly) Grains deposited by flowing water or wind 3. Metamorphic rocks Crystalline texture Growth of minerals in the solid state Form by modification of other types of rock Igneous rocks: Igneous rocks form by solidification from a liquid ( magma, molten rock). Magma may crystallize within the crust ( intrusive igneous rocks), or flow out at the surface as lava ( extrusive (volcanic) igneous rocks Intrusive igneous rocks Basalt dike, New Zealand Magma may be emplaced into the crust , forming igneous intrusions The magma cools more slowly (years to millions of years) Crystals have time to grow Rocks are medium or coarse grained, with a crystalline texture Plutonic rocks Granite, Sierra Nevada large crystals are kfeldspar large intrusion of igneous rocks called plutons cool very slowly, coarsegrained ● Interpretation based on observation of the great size of the rocks Sedimentary Rocks : Grains transported by rivers, currents, tides, waves or wind are deposited to form clastic sedimentary rocks. ( Bedded conglomerates, Fish Canyon, California) Metamorphic Rocks : Start as one thing and end up as another Garnet amphibolite with garnet, hornblende, and feldspar Metamorphic rocks have a crystalline structure Mineralization: Water flows through pore spaces and fractures in rock Dissolves material Precipitates it as cement, and in fractures ( veins ) minerals deposit by fluids include quartz calcite many economically valuable minerals ( gold, silver, ore materials ) 9/9 Lecture (Monday’s quiz will not include this info) Exam Question of the Day : The theory of isostasy states that : D. Topography (surface elevation) is controlled by the density and thickness of the crust Extrusive igneous rocks : Magma extruded at surface solidifies to form fine grained or glassy volcanic rock; lava flows Glass is a noncrystalline solid Volcanic lava can cool to form a glass Some volcanic rock has “fine grained” or microscopic crystals Columnar jointing in basalt lava columnar joining in basalt County Antrim, Northern Ireland every point within lava flow pulls away for others points and breaks up into columns ( mud cracks and column jointing in lava produced by same physical process) ● If magma is ejected violently, may be deposited as ash ( pyroclastic rocks) Mt. St. Helen ash cloud Intrusive igneous rocks : 3 types ( important definitions! ) Dike a tabular intrusion that is discordant with surrounding rock Pluton a large intrusion ( usually discordant, but so big, hard to see) Sill a tabular intrusion that is concordant with the surrounding rocks Where and why does melting occur within the Earth? Where 1. At midocean ridges 2. In mantle plumes 3. Above subduction zones 4. In zones of mountain building Magmatism at midocean ridges: Melting is a result of decompression of mantle rock rising beneath ridge Occurs at 3060 km depth Melting of mantle peridotite Magma cools to form 6km thick ocean crust Forms distinctive sequence of intrusive and extrusive rocks Locally preserved on land : ophiolite Lava cooled fast, fine grained called : basalt Coarse grained Intrusion called : gabbro Melting at midocean ridges Melting of mantle peridotite beneath MOR Produces basalt magma : Low content of SiO2 High content of Fe and Mg melting is attributed to decompression, as the asthenosphere rises towards the surface ( see lecture diagram) Convection is the manner heat is conducted ;Hot material rises, cool material sinks, transaction occurring by transferring of heat Quiz Monday! Lab Week 3 ● The Earth’s mantle is higher because of isostasy 3 kinds of plate boundaries 1. Divergent ←- --> 2. Convergent > < 3. Transform > ←------ Divergent boundaries ; plates move apart; new seafloor is made Hot material within mantel reaches top and cools down at sea floor Forms new material and rocks at sea floor , new material pushes old apart, to left and right, creates mid atlantic ridge Convergent boundaries ; one plate is subducted (the denser plate) the Andes Mountains are an example of this 3 types of Convergent boundaries; OceanContinent collision (andes mountains and peruchile trench) Continentcontinent collision ( himalayas and tibetan plateau) Ocean ocean collision ( japanese islands and japan trench) Transform boundaries ; plates slide past each other along strike slip faults San andreas fault is an example of this The Pacific plate has been grinding horizontally past north american plate for 10 million years Hot spots Not related to plate tectonics Chain of volcanoes formed above a stationary magma chamber in mantle Can be used to determine plate motion rates and directions Hot spots are beneath active volcanoes 9/12 (Continuing last week’s lecture) Where does melting occur? 1. Below mid cean ridges 2. In mantle plumes 3. Above subduction zones 4. In zones of mountain building 2. Magmatism in mantle plumes Plumes rise from the coremantle boundary at nearly 3000 km depth Rising plumes start melting at depths of 100km Produce basalt magma Magma similar to magma at mid ocean ridges Magmatism often occurs away from plate boundaries May occur in ocean basins Oceanic island volcanoes Low viscosity basalt forms shield volcanoes (Hawaii) *Mauna Loa, Hawaii : A shield volcano Plumes can occur beneath continent ( Yellowstone Plume) Continental flood basalts Basaltic magma has low viscosity and flows long distances Magma types: Basalt Andesite Viscosity : the way we quantify ability of fluids to flow Water has much higher viscosity than air (i.e moving hands through air vs. through water) 3. Subduction zone magmatism Melting at 100200 km depth in the Earth’s mantle. Melting is a result of addition of water ( carried down subduction zone) to hot mantle peridotite Most abundant magma is andesite Richer in silica, alkali metals and water than basalt Subduction zone in magmatism can occur in both oceanic and continental settings Magma is waterrich, and causes explosive eruptions Magma is silica richhigher viscosity than basalt Creates tall volcanoes ( stratovolcanos) Interlayered lavas and pyroclastic Mt. Shasta, N. California Magma intruded into crust below arc volcanoes forms groups of plutons Sierra Nevada batholith Addition of crustal melt creates a range of compositions: Extrusive Basalt Andesite Dacite Rhyolite Intrusive Gabbro Diorite Granodiorite Granite ● Phenocryst : big crystals inside a rock Magmatism in zones of mountain building In areas of thickened continental crust, like Himalayas, melting of crustal rocks produces granitic magma 9/14 (&16) Lecture The Volcanic System Melt source Magma chamber Dikes and sills Central and side vents Surface accumulations : Lava Pyroclastic flows Ash Falls Lahars ( volcanic mudflows) Types of Extrusive Rock Lowviscosity magma ( basalt) : Pahoehoe Aa (blocky lava) Pillow lava ( ropey lava) Form from underwater lava flows, mainly basaltic High Viscosity magma (andesite rhyolite) Tuff (ash) Pyroclasitc Welded Tuff Rhyolitic texture Ash particles still partly molten and soft when deposited, so they become flattened and weld together Volcanic Breccia Eruptive Styles and Volcanic Landforms Fissure Eruptions Magma may be extruded from an elongate fissure, which forms a dike at depth Cinder conesfire fountaining Volcanic fissures with cinder cones in Iceland Flood basalts Flood Basalts of the Columbia River Shield volcanoes lava flows Shield Volcano on Mauna Loa (low viscosity basalt lava) Olympus Mons, Mars, Largest volcano in Solar System: 17 km high. Stratovolcanoes pyroclastic eruptions Fujiyama, Japan (high viscosity andesite lava) Volcanic domes viscous lava Mount Shasta, N. California Calderas Diatremes volcanic pipes Pyroclastic Ejecta Ash ( tephra) Tuff Bombs Breccia Pyroclastic flows Pyroclastic flows can be produced by a lateral blast from a side vent, or the collapse of a vertical ash cloud erupted from the central vent LAB Minerals : Naturally occurring Solid Fixed chemical composition Particular crystalline structure 7 useful properties to ID Minerals: Color Most visible and most deceiving property of a mineral Hardness Mohs scale of Hardness Diamond Corundum Topaz Quartz Feldspar Apatite Fluorite Calcite Cypsum Talc Luster How mineral’s surface reflects light Metallic Nonmetallic Streak Color of substance after it has been ground to a fine powder Very diagnostic, can help distinguish between very similar looking minerals i.e magnetite and hematite Crystal Form ( habit) Many possible habits Atomic structure is reflected at a scale you can see! Cleavage and fracture minerals break along flat cleavage lanes or curved fracture planes cleavage happens along planes of weakness fracture happens when there is no plane of weakness cleavage smooth, fracture rough Miscellaneous properties magnetic properties, reactive with HCI (avid) 9/19 Exam question of the day: Volcanoes above subduction zones are more explosive than those above hot spots (mantle plumes) because they are C. richer in SiO2 and contain more dissolved water ● Quiz on Wednesday, 9/21 ● Midterm next week Sedimentary Rocks: Sedimentary rocks are formed from sediment deposited on the Earth’s surface Sediment includes: Solid particles of rock or mineral material Material precipitated out of solution Biological materials Sedimentation can take place on land, in lakes and rivers, or beneath the sea Sedimentary rocks cover 75 % of continental area, and nearly all the ocean floor ● Persian Golf, a sedimentary basin Sedimentary Rock Cycle : Weathering and erosion of preexisting rock Transport of sediment by water, wind or ice Deposition Burial Lithification: processes that convert sediment into rock Types of Sediment : 1. Clastic Sediments Particles of preexisting rocks and minerals Course grained sediment ( gravel > conglomerate) requires a high energy transport mechanism Steep,fastrunning rivers ( alluvial deposits) Debris flows Storm waves on beaches Glaciers (till) Medium grained sediment ( sand >sandstone) requires a medium energy transport mechanism wind Rivers Deltas Fair weather beaches Tidal Flats Submarine turbidity currents Fine grained sediment ( clay > shale) requires a low energy transport mechanism slow moving rivers lakes, lagoons, Floodplains deep sea Sedimentary structures Bedding Scours and channels Crossbedding Ripples Graded bedding Bioturbation Mud cracks Evaporites: Precipitates formed with increasing concentration Calcite, dolomite, gypsum, halite and other salts Form in areas with restricted circulation of water and hot climates Playa lakes in deserts Rift valleys Narros seas (red Sea) Crystalline texture ( because crystalize out of the water) 9/23 Lab Phaneritic : Aphanitic: Porphyritic: large and small crystals together: change in cooling rate Glassy: no crystals! Cooled too fast for them to form Chemical compositions Lot of silicone: felsic Not a lot: ultramafic RememerL Granite phaneritic , feslic Diorite phaneritic , intermediate (after felsic) Gabbro phaneritic , mafic Periodite phaneritic ultramafic Rhyolite aphanatic , felsic, Adnesite aphanitic, intermediate
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