GSU GEOL 1122K - Chapter 4 Reading Quiz (12 pages)

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Chapter 4 Reading Quiz



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Chapter 4 Reading Quiz

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Pages:
12
School:
Georgia State University
Course:
Geol 1122k - Introductory Geosciences Ii
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Wet igneous rock melts at a lower temperature than the dry version of that same rock because the addition of volatiles in wet rocks lowers their melting temperature they occur on the seafloor where temperatures are already cold dry igneous rocks are made of more felsic minerals wet igneous rocks form at shallower depth in the Earth The presence of volatiles helps break chemical bonds resulting in a lower melting temperature for the wet rock SEC 4 2 A black fine grained tabular intrusion between two layers of horizontal sedimentary rock must logically be a basaltic sill granitic sill basaltic dike granitic dike Only basaltic sill fits the description granite would be light colored and a dike would cut across existing layers SEC 4 3 Figure 4 9 After an explosive volcanic eruption on an island the surrounding sea is full of light gray floating rock What must it be rhyolite pumice obsidian basalt Pumice is a felsic vesicular rock that contains abundant vesicles which makes it less dense than water SEC 4 4 Figure 4 16a An igneous rock has a medium gray fine grained groundmass with large crystals of plagioclase Which of the following statements about it is FALSE It could logically be porphyritic andesite The lava flow that produced it got quenched in ocean water The plagioclase crystals are called phenocrysts It began to crystallize at depth from intermediate composition magma then rose to the surface and became a lava flow Not only would water quenching create a glassy texture but this explanation also doesn t touch at all on the origin of the large crystals SEC 4 4 Bowen s reaction series shows that minerals crystallize in a random order with no particular pattern involved allows a geologist to predict what minerals will be found in a given igneous rock is an attempt to explain the logic of formation of sedimentary rocks explains why some compounds use ionic bonds and others have covalent bonding Bowen s reaction series was deduced through laboratory procedures that cooled molten rock the crystal formation in the igneous rocks produced frequently followed a predictable order SEC box 4 1 Bowen s reaction series shows the sequence in which different sulfate minerals form during the progressive cooling of a melt creates a progressively more mafic melt has a continuous track in which there is observed a progressive change from sodium rich to calcium rich amphibole was established by laboratory experiments in which mafic melt was quenched in mercury Bowen s reaction series shows the sequence in which different silicate minerals form not sulfate minerals from a mafic melt Through crystallization of mafic minerals the melt becomes more felsic not more mafic It has both a continuous and discontinuous track and was developed by lab experiments SEC Box 4 1 Figure Bx4 1b Granite is an extrusive igneous rock is felsic in composition logically could be found in a lava flow is the coarse grained equivalent of andesite Granite is a felsic intrusive and therefore coarse grained igneous rock It is often found as plutons rather than lava flows which are extrusive The coarse grained equivalent of andesite is diorite SEC 4 4 Figure 4 15 How does subduction trigger melting Flux melting of the asthenosphere above the subducting slab creates a rising melt The down going slab melts as it reaches hotter temperatures deep in the Earth The overriding slab insulates the subducting slab increasing temperature and causing melting The subducting slab is made of felsic minerals and therefore melts at lower temperatures Flux melting the addition of volatiles occurs as the down going slab adds water to the surrounding asthenosphere this acts as a catalyst for melting SEC 4 5 Figure 4 4 Identify the FALSE statement Early Earth had numerous heat sources for igneous activity including conversion of the kinetic energy of meteorite impact to heat energy conversion of the kinetic energy of iron alloy sinking toward Earth s center to heat energy decay of all of its radioactive elements almost none remain today the compression of mass into a smaller volume Radioactive decay was a heat source for early Earth but it did not exhaust Earth s supply of radioactive elements There are many radioactive elements left and they re still decaying and heating Earth s interior SEC 4 2 Identify the FALSE statement Hot solid rock in the Earth may be even hotter than surface lava because of the pressure of overlying rock may melt if volatiles such as water and carbon dioxide are added may melt if heat is transferred to it from hot mantle rock rising up into the crust maintains uniform composition as it melts and becomes magma Magma composition evolves as rock melts due to partial melting and assimilation processes SEC 4 2 Identify the FALSE statement Large igneous provinces LIPs are places where huge amounts of mafic magma have been erupted or intruded represent special events in Earth s history that may have been caused by super plume activity occur only along continental margins may have profound impacts on the environment including land ocean and atmospheric processes LIPs may occur on the seafloor or on land along margins or in the interiors of oceanic plates or continents SEC 4 5 Identify the FALSE statement Pegmatites have intruded at great depth and cooled very slowly can contain crystals up to tens of centimeters across occur in tabular intrusions called pegmatite dikes are an igneous rock type distinguished by their unusual grain size Pegmatites have cooled quickly but are surprisingly very coarse grained because they form in water rich melts that allow atoms to move around quickly and develop large crystals SEC 4 4 Identify the FALSE statement Magma moves upward toward the Earth s surface because it is less dense than the surrounding rock slowly working its way up through cracks and narrow conduits more quickly as it cools and therefore becomes less viscous because the weight of overlying rock creates pressure that squeezes it up The hotter the magma the less viscous it is and the faster it flows SEC 4 3 Interpret this diagram to find the FALSE statement Point A represents rock that fits the following description Its temperature is about 1700 C It is mantle rock It is under about 100 000 bar 100 kbar of pressure Its physical state is molten Since rock at point A is on the left side of the solidus line it is solid The region to the right of the liquidus line represents molten rock Between the two lines the rock is a mixture of


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