GEO 101-007 Exam 2 Study Guide
GEO 101-007 Exam 2 Study Guide GEO 101-007
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This 19 page Study Guide was uploaded by Jennifer Gintovt on Monday September 28, 2015. The Study Guide belongs to GEO 101-007 at University of Alabama - Tuscaloosa taught by Dr. William Lambert in Summer 2015. Since its upload, it has received 226 views. For similar materials see The Dynamic Earth in Geology at University of Alabama - Tuscaloosa.
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Date Created: 09/28/15
GEO 101007 Test 2 Study Guide Chapter 4 Up from the Inferno Magma and Igneous Rocks Magma below the surface Lava above the surface Igneous rocks One of the three main rock types Formed through the cooling and solidification of magma or lava Examples 0 Granite magma o Rhyolite lava Intrusive igneous rock 0 Rock formed by the freezing of magma underground Extrusive igneous rock 0 Rock formed by the freezing of lava on the Earth s surface or ocean oor Temperature and pressure increase with depth Crystallization Rate Molten material cools and solidifies quicker at the Earth s surface Crystallization rate decreases with depth Crystallization Rate and Igneous Rock Temperature 0 Rhyolite o Finetextured Aphanitic Granite o Coarsetextured Phaneritic o A textural term for finegrained igneous rocks Mineral grains are too small to see with the naked eye 0 Indicates the molten rock solidified relatively quickly 0 Formed on the surface 0 A textural term for coursegrained igneous rocks Mineral grains are large enough to see with the naked eye 0 Indicates the molten rock solidified relatively slowly 0 Minerals had time to grow 0 Formed in magma Porphyritic Igneous Rock Texture Phenocryst a large crystal surrounded by a finergrained matrix in an igneous rock Grmdmagsim i x a Porphyritic a textural term for igneous rock that has phenocrysts distributed throughout a finer matrix Indicates two stages of cooling larger crystals grew at depth but before molten rock had solidified a volcanic eruption brought the material to the Earth s surface where the remaining melt solidified quickly Igneous Rock Chemistry and Properties MagmaLava Chemistry and Properties F elsic Intermediate Ma c Ultrama c 76 38 Iron and magnesium content Viscosity resistance to ow Explosive eruptions Mount St Hawaii Helens Magma Lava Chemistry Related to Igneous Rock Chemistry In general the chem of igneous rocks both extrusive and intrusive is highly related to the chem of the magma lava from which it crystallized o For example if you find a felsic igneous rock it crystallized from a felsic magma or lava So how do we get magma in the first place Magma forms in 3 steps 1 a High amounts of pressure can prevent materials from melting at their normal temperatures b Rock at great depths in the Earth s interior are often hotter than their melting temperature but remain a solid due to the pressure c If for some reason the pressure is decreased on these rocks they will melt in a process called decompression melting a Volatiles are chemicals such as water H20 and carbon dioxide C02 that can mix with solid rock within the Earth s interior b Volatiles help to break chemical bonds therefore adding volatiles to a quotdryquot rock will cause it to melt c Also known as quot uxquot melting 3 Heat transfer from rising magma a Rising magma brings heat from below and melts overlying or surrounding rock How do we end up with magma having different chemistry Felsic higher silica content Ultramafic magma lower silica content Ultramafic magma is mainly found at great depth and does not produce crustal rocks Intermediate magma is simply a mixture between mafic and felsic Felsic or silicic has the highest amounts of silica Mafic high amounts of magnesium and iron Factors controlling magma composition Source rock composition 0 The composition of a melt magma re ects the composition of the solid from which it was derived What happens if you slowly melt chocolate chip ice cream 0 The ice cream melts first but the chips are likely to remain solid until more heat is added This is the basic idea of partial melting At any given location in the Earth s interior only 2 to 30 of solid rock melts and forms magma More on this later but the felsic silicarich minerals melt first Therefore the new magma is more felsic than the original rock The remaining rock becomes more mafic Mafic rock may produce intermediate magma remaining rock may become ultramafic Pretend the raisins are felsic minerals and the If you remove raisins felsic minerals the bread are ma c minerals remaining loaf is more bread ma c minerals 2 Example 20 Felsic v Felsic 80 Ma c t 5 Ma c When a rock is exposed to higher temperatures the felsic minerals melt first leaving the remaining rock more mafic The new magma is more felsic than the original rock While magma slowly moves upward it may incorporate the chemistry of surrounding rock that completely melt due to the heat of the magma If two or more bodies of magma with different chemistries combine in the subsurface the quotnewquot magma will have a composition different from the original chemistries The resistance to flow uid does not ow very well behaves like syrup uid ows easily behaves like water Factors controlling the rate of magma cooling Magma at the Earth s surface cools quickly Depth of magma intrusion magma deep in the Earth better thermos cools slower than shallow magma Shape and size of magma intrusion larger bodies of magma cool slower than smaller bodies 0 Intrusions with a large surface area cool more quickly more area for magma to lose heat Circulating water ground water passing through the magma removes heat like a car radiator Water freezes at 32 degrees Fahrenheit 0 9C Magma freezes at much higher temperatures 600 to 1200 QC Magma contains many different elements that eventually form various minerals each of which freeze at a different temperature Mafic minerals high Mg and Fe freeze first Felsic minerals high silica freeze last h pg 105 Chapter 5 The Wrath of Vulcan Volcanic Eruptions The year without a summer 1816 Iune 67th 1816 6 inches of snow in NY state 1815 Eruption of Mount Tambora Indonesia Temperature 39 39 39 Composition Regimes Bowen 5 Reaction Senes rock types Intermediate diorlteandestte I39IC Potassium feldspar I Felsic Muscovute mica graniterhyolite l 139 Quartz Copyright 2005 Pearson Prentice Hall Inc 4000 feet of mountain was removed by eruption Additions to the atmosphere is thought to have lowered global temperatures Volcanic Eruptions affect us all Ash cloud so dense that solar radiation is re ected back to space resulting in short term global cooling or Water vapor and C02 create greenhouse effect resulting in warming Water vapor and other gases SOZ HCl HF produce acid rains that kill crops and livestock Mt Vesuvius Pompeii Italy City buried under 1320 feet of volcanic ash after Mt Vesuvius eruptio9n in 79 AD Another eruption is not a matter of quotifquot but rather a matter of when Surrounding population approximately 3 million Origin of the term Volcano Vulcano Italy 0 Vulcan God of Fire Lava ows sheets or mounts of lava that ow onto the ground surface or sea oor in molten form and then solidify Review Viscosity resistance to ow 0 Melts with a high viscosity do not ow easily Review Factors affecting viscosity temperature volatile content silica content Hot lava with a high concentration of volatiles and low concentration of silica ows easily 1 Basaltic mafic chemistry low silica content 2 Andesitic intermediate chemistry medium silica content 3 Rhyolitic felsic chemistry high silica content Basaltic Lava Flow and Features Basaltic mafic lava ows have very low viscosity when first emerging from the ground due to high heat and low silica content Typically ow less than 10km the empty space left when a lava tunnel drains this happens when the surface of a lava ow solidifies while the inner part of the ow continues to stream downhill Hawaiian term a lava ow with a surface of smooth glassy ropelike ridges Hawaiian term a lava ow with a rubbly surface Columnar jointing a type of fracturing that yields roughly hexagonal columns of basalt when a dike sill or lava ow cools glassencrusted basalt blobs that form when magma extrudes on the sea oor and cools very quickly pressure plays role Andesitic Lava Flow Andesitic intermediate lava ows have higher viscosity due to higher silica content vs basaltic lava ow Typically ow less than 10 km Rhyolitic Lava Flow Rhyolitic felsic lava ows have highest viscosity due to highest silica content also tend to be coolest Typically ow less than 12 km 0 Lava quotdomequot forms Very blocky Dionisio Pulido Farmer who experienced an earthquake that quickly formed into a volcano on his farm Pyroclastic debris from basaltic eruptions weak eruptions Latin for little stones Pea to plumsized fragments of glassy lava and scoria aka cinders Apple or largersized fragments Solidify while still in the air May become streamlined during ight Pyroclastic debris from andesiticrhyolitic eruptions explosive eruptions Two types of lapilli may also be produced Volcanic Ash Some ash reaches high altitude and falls back to earth like snow gravity quickly returns some ash to the ground as a pyroclastic ow or glowing avalanche A few more terms unconsolidated loose deposits of pyroclastic grains regardless of size Ash or ash mixed with lapilla that has been buried and transformed into solid rock Mobile mixtures of ash coarser debris and water Crater vs Fissure Eruption At a crater eruption lava spouts from a chimneyshaped conduit At a fissure eruption lava erupts as a curtain along a crack Volcanic Caldera Formation As an eruption begins the magma chamber in ates with magma During an eruption the magma chamber drains and the central portion of the volcano collapses downward The collapsed area becomes a caldera Later a new volcano may begin to grow within the caldera Three types of Volcanoes 0 Not explosive basaltic mafic lava relatively safe 0 sputters tephra out basaltic lava but more gas content relatively safe 0 Very explosive rhyolitic felsic lava dangerous Effusive Eruptions Mainly basaltic lavas low viscosity shield volcanoes Explosive eruptions Mainly rhyolitic lavas high viscosity stratovolcanoes Volcanic activity is NOT random Stratovolcanoes occur at convergent plate boundaries Shield volcanoes above hot spots Cinder cones develop at continental rifts each volcano type can occur in other settings volcanoes that are erupting have erupted recently or are likely to erupt soon volcanoes that have not erupted for hundreds or thousands of years but have the potential to erupt again volcanoes that were active in the past but have shut off entirely and will never erupt again Example Devils Tower Wyoming Predicting Eruptions 0 As large volumes of magma moves up from below rock moves and cracks releasing energy that can be detected as small earthquakes 0 An increase in earthquake activity might suggest a future eruption 0 As large volumes of magma moves up from below more heat is brought near the surface 0 Melting snow on volcano summit might suggest a future eruption 0 As large volumes of magma moves up from below the volcano will actually bulge o Measurable bulging of volcano might suggest a future eruption 0 As large volumes of magma moves up from below more gases and steam will vent from the volcano 0 These gas increases might suggest a future eruption Volcanic eruptions remain largely unpredictable Despite all our advances in technology we are not able to give proper warning of upcoming volcanic eruptions Millions of people risk their lives every day due to their proximity to active volcanismincluding this guy Chapter 6 Pages of Earth s Past Sedimentary Rocks Illustrates the different processes and paths as Earth materials change both on the surface and inside the Earth Principles Key to Geologists the principle that the same physical processes observed today are responsible for the formation of ancient geological features the principle that younger layers of sediment are deposited on older layers of sediment thus a sequence of strata the oldest layer is at the base Sedimentary Rocks Sedimentary rocks tell us more about the history of Earth than any other rock type 0 Sedimentary rocks can tell us about I Past life plants and animals I Past environments rivers lakes and oceans I Pages of Earth s pastquot Sandstone Classes of Sedimentary Rocks based on mode of origin Consists of cementedtogether solid fragments and grains from preexisting rocks 0 Example sandstone Formed from material such as shells produced by living organisms 0 Example coquina Formed from carbonrich relicts of plants 0 Example Coal Formed from minerals that precipitate directly from water solutions 0 Example Limestone Clastic Sedimentary Rocks formation fundamental steps are involved with the formation of clastic sedimentary rocks 0 rock fragments clasts detritus formed by the disintegration of bedrock in response to physical and chemical weathering o breaking of bedrock into smaller pieces chemistry of rock is not changed o bedrock is broken down as chemical reactions change chemistry of preexisting rock 0 Both physical and chemical weathering can break bedrock down at the same time Clastic Sedimentary Rocks Formation Physical Weathering Breaking of rocks into smaller pieces How does this happen 0 expansion of water in cracks by freezing wedging the rock apart 0 as pressure is decreased due to removal of overlying rock by erosion igneous metamorphic rock expands and fractures in large sheetlike layers 0 rapid heating and cooling of a rock s surface resulting in more rapid expansion and contraction of the rock surface than the rock interior 0 the cracking and expansion of rocks as a result of plant growth and animal activity Clastic Sedimentary Rocks Formation Chemical Weathering those processes which occur when air and water chemically react with rock to alter its composition and mineral content 0 Includes dissolution hydrolysis and oxidation 1 o The dissociation of a mineral into its constituent ions as it dissolves in water 2 o The chemical reaction of a mineral with molecular oxygen 02 resulting in decomposition of the mineral I Example Oxidation of Fe in minerals resulting in the formation of hematite Fe203 3 0 Water reacts with a mineral to form a new mineral with water as part of the crystal structure I Example weathering of feldspar minerals by hydrolysis to form clay minerals Clastic Sedimentary Rocks Formation Factors affecting rates of weathering fractures in rock gt Calcite dissolves in weakly acidic solutions gt Silicate minerals weather in same order as order of crystallization Bowen s Reaction Series 3 Chemical weathering most effective in warm moist climates Clastic Sedimentary Rocks Formation 0 Combination of processes wind water ice gravity that separate rock pieces from bedrock and carry it away is breakdown of the bedrock the erosion is separating and removing those pieces from bedrock o The movement from one location to another of clasts from one location to another by wind water or ice 0 Process by which sediment clasts settles out of the transportation medium water ice wind 0 Transportation of loose sediment into solid rock Typically involves burial of sediment compaction loss of waterair and cementation calcitequartz Clastic Sedimentary Rocks Classification Five useful characteristics for describing clastic sedimentary rocks Clast Size 0 Size refers to the diameter of clasts making up a rock I Largest coarsest to smallest Finest Boulder cobble pebble sand silt clay Clast Composition 0 Refers to the make up of clasts in sedimentary rock what the pieces are made of I Clasts are often individual minerals grain of quartz or rock fragments multiple minerals Angularity and sphericity o Angularity indicates the degree to which clasts have smooth or angular corners and edges 0 Sphericity refers to how close the clast is to being a sphere ball Sorting o The degree to which the clasts in rock are all the same size or include a variety of sizes I sedimentary rocks have particles the same size I sedimentary rocks have various size particles Character of cement 0 Simply describes the type of cement glue that helps hold the clasts together Cement is typically calcite or quartz Physical characteristics of clastic sedimentary rocks tell us about the processes the components of the rock went through from weathering to lithification o Observing these processes today helps us to understand the Earth s history Clast Size Clast Character Rock Name Alternative Name Coarse to Rounded pebbles and cobbles Conglomerate very coarse Angular clasts Breccia Large clasts in muddy matrix Medium to Sandsized grains Sandstone coarse Quartz and feldspar only 0 Quartz sandstone Quartz and feldspar sand quartz gram 0 Sandsized rock fragments 39 Arkose Quartz sand and sandsized rock Lithic sandstone fragments in a clayrich matrix 39 Wacke informally called greywacke Fine Siltsized clasts Siltstone Very fine Clay andor very fine silt Shale if it breaks into platy sheets Mudstone if it doesn t break into platy sheets Biochemical Sedimentary Rocks Various Types rock composed of primarily calcium carbonate which is either calcite or aragonite and once made up the shells for once living organisms rock composed of primarily cryptocrystalline quartz very very small grains which was once the shell of silicasecreting plankton Cold water environments Organic Sedimentary Rocks Primarily coal Chemical Sedimentary Rocks Bonneville Salt Flats ocean has right ingredients in it that once it starts to evaporate it becomes more salty and eventually creates a at bed of salt once the water completely evaporates preexisting rock and may deposit new rocks 0 Mammoth Hot Springs Yellowstone hot water seeping through the ground that dissolves away Sedimentary Structures A characteristic of sedimentary deposits that pertains to the character of bedding and or the surface features of a bed a single layer of sedment or sedimentary rock with a recognizable top and bottom 0 Bed surface marks I Mud cracks dry clay that has contracted over time and creates cracks I Trace fossil ex Footprints left by something that have almost been cast into rock the boundary between two beds several beds together the overall arrangement of sediment into a sequence of beds Ripple marks shows the movement of the current in the past Cross bedding movement of sand over a dune or ripple that creates a new dune crest a submarine underwater avalanche of sediment and water that speeds down a submarine slope a layer of sediment deposited by a turbidity current in which grain size varies from coarse at the bottom to fine at the top A shows the distribution of formations past environments Each color represents a specific formation Chapter 7 Metamorphism A Process of Change What type volcano is Olympus Mons Shield Largest known volcano in solar system Mars What is a Metamorphic Rock Metamorphism Example Igneous Metamorphic Rock Rock Metamorphism occurs without the rock first becoming a melt or sediment Hot water can also play a role NOT MELTING THE ROCK Granite Gneiss pressure the original rock from which a metamorphic rock formed In the example above granite is the protolith ames Hutton Father of Modern Geologyquot Developed the principle of uniformitarianism Was puzzled by certain rocks that seemed to have been formed as other rocks do but had been distorted in structure Rock Metamorphism Basics Solid state change due to change in preexisting rock s environment 1 Temperature change 2 Pressure change 3 Compression and shear become relevant 4 Hot water hydrothermal uid added to the system 5 Or a combination of one or more Environmental change produces new minerals that did not occur in protolith andZor produces a new texture Changes to Protolith Environment Increase temperature addition of heat helps to break chemical bonds allowing atoms to move and form new bonds which means new minerals Increase pressure tremendous pressures can cause atoms to pack more closely together sometimes forming new minerals Increase pressure and temperature certain minerals are stable at specific temperatures and pressures 0 Changing these variables promotes new mineral formation Exposure to very hot water hydrothermal uid from slide 16 metasomatism the process of changing a rock s chemical composition by reactions with hydrothermal uids Compression and Shear force is applied down on an object example gravity force is applied to the sides of an object example convergent plate boundary force is applied in opposite directions on an object example pushing a deck of cards to one side or the other 339 Results of Compression and Shear o Equant Grains roughly same dimensions in all directions 0 Inequant Grains dimensions are not the same in all directions 0 Preferred Orientation alignment of inequant grains 0 The arrangement of grains formed as result of metamorphism specific new minerals grow only under metamorphic temperatures and pressures parallel alignment of platy minerals such as mica and or the presence of alternating lightcolored and darkcolored bands Metamorphic Processes 1 339 Changes the shape and size of grains without changing the mineral chemistry grains ten to get bigger but not always 339 Changes one mineral to another mineral of the same composition but different crystalline structure atoms rearrange 0 v Results in new minerals that differ different chemical composition from those of the protolith 4 339 In the presence of water grains are dissolved on the sides undergoing more pressure and precipitate new mineral where the pressure is lower water helps atoms move easierquicker 0 v Grains change shape texture without breaking due to compression at high heat and soft plasticlike nature of rock Two Fundamental Classes of Metamorphic Rocks 1 metamorphic rocks distinguished by their component minerals grain size and by the nature of their foliation Ex Gneiss metamorphic rocks primarily divided up by their component minerals what it is made of Ex Quartzite Common Examples of Foliated Rocks 1 Slate I Finegrained foliated metamorphic rock I Protolith shale or mudstone high clay content I Relatively low pressures and temperatures I Strong foliation slaty cleavage breaks easily into sheets 2 Phyllite I Finegrained with foliation caused by the preferred orientation of very fine grained white mica I Protolith slate neocrystallization of clay to produce white mica I Relatively low pressures but higher temperatures I Silky sheen called phyllitic luster 3 Metaconglomerate I Same metamorphic conditions as slate and phyllite pressure solution and plastic deformation atten pebbles and cobbles into pancakelike shapes I Alignment of clasts pebbles cobbles defines foliation I Protolith conglomerate 4 Schist I Mediumtocoarsegrained I Foliation schistosity which is defined by the preferred orientation of large mica akes I Forms at higher temperatures than phyllite I Various protoliths 5 Gneiss I Typically composed of alternating light and dark bands with each band having a specific composition mafic vs felsic minerals I Foliation is gneissic banding which gives it a stripped appearance I Protolith had alternating beds of sandstone and shale or caused by extreme amounts of shearing rock ows like plastic I Various protoliths 6 Migmatite I Extreme conditions where gneiss may begin to melt but the partial melt quickly freezes resulting in part igneous part metamorphic rock Examples of Mica I Range of colors but has perfect cleavage in one direction sheetlike I Can be associated with metamorphic rocks Nonfoliated Metamorphic Rocks Common Examples 1 Hornfels I Contain a variety of metamorphic minerals which is based on minerals found in protolith and the temperature pressure of metamorphism 2 Quartzine I Protolith is pure quartz sandstone quartz grains recrystallize creating new grains sugary texture 3 Marble foss111ferous hmestone marble 3945 quott 31 I Protolith is limestone which recrystallizes so that fossil shells pore spaces grains and cement become a solid mass of calcite e Degree of Metamorphism I Metamorphic grade indicated the intensity of metamorphism or the degree of metamorphic change 0 Low or high grade lrcteasing pressure Geologic Setting of Metamorphism 1 Contact thermal gt Temp of the protolith rises due to heat transfer from nearby magma gt Hydrothermal uids also play a role in metamorphosis gt The zone of alteration that is in C onta Ct M etamorphism Aureole contact w1th the magma 15 called f z metamorphiccon tact aureole gt Does not involve increase in pressure and differential stress gt Metamorphic Contact Aureole zone of alteration that varies in width depending on the size and shape of the magmatic intrusion as well as the amount of hydrothermal circulation present 2 Burial gt Metamorphism due only to the consequences of very deep burial 8 15km gt Temperature and pressure increase with depth gt Lowgrade metamorphism 3 Dynamic gt Occurs at faults surface on which one piece of crusts slides at great depth gt10 Km Mylonite gt Minerals in warm rock recrystallize get smaller and form the highly foliated metamorphic mylonite gt Form due to shearing alone 4 Dynamothermal regional gt Occurs during mountain building convergent plate boundary gt Some rock is pushed up mountains while some rock is pushed down Increased temp with depth Increased pressure with depth Increased compression and shear due to convergence gt Grade of metamorphism increases with depth gt Eventually mountains are eroded away and metamorphic rocks formed at depth rise and are visible at the Earth s Surface gt LARGE SCALE 5 Hydrothermal gt Chemical alteration caused when hot ionrich uids circulate through cracks gt Common at midocean ridges 6 Subduction Zones gt Produces metamorphic rock called blueschist gt Rare combination of high pressure but low temperature 7 Shock gt Shock waves caused by highenergy events such as a meteorite impacts can change minerals quartz changes to coesite
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