GEO 101-007 Chapter 4 Lecture Notes
GEO 101-007 Chapter 4 Lecture Notes GEO 101-007
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This 7 page Class Notes was uploaded by Jennifer Gintovt on Monday September 14, 2015. The Class Notes belongs to GEO 101-007 at University of Alabama - Tuscaloosa taught by Dr. William Lambert in Summer 2015. Since its upload, it has received 34 views. For similar materials see The Dynamic Earth in Geology at University of Alabama - Tuscaloosa.
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Date Created: 09/14/15
GEO 101007 91415 Chapter 4 Up from the Inferno Magma and Igneous Rocks Magma below the surface Lava above the surface Igneous Rocks Derived from the Latin word ignis meaning fire is one of the three main rock types the others being sedimentary and metamorphic Igneous rock is formed through the cooling and solidification of magma or lava Examples 0 Granite magma o Rhyolite lava Intrusive s Extrusive Igneous Rocks Where the igneous rock solidifies 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 with Depth Temperature and pressure increase with depth Crystallization Rate Molten material cools and solidifies quicker at the Earth s surface 0 Crystallization rate decreases with depth Crystallization Rate and Igneous Rock Temperature 0 Rhyolite o Finetextured Aphanitic Granite o Coarsetextured Phaneritic Igneous Rock Textures o A textural term for finegrained igneous rocks Mineral grains are too small to see with the naked eye microscope needed 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 no microscope 0 Indicates the molten rock solidified relatively slowly Minerals had time to grow 0 Formed in magma O GEO 101007 91415 Porphyritic Igneous Rock Texture Phenocryst a large crystal surrounded by a finergrained matrix in an igneous rock 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 Igneous Rock Chemistry and Properties Felsic Intermediate Ma c Ultrama c GEO 101007 91415 Magma Lava 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 TEMP and PRESSURE INCREASE with depth Melting and Freezing At what temperature does water freeze At what temperature does ice melt o 32 F or 0 C Rocks melt and freeze at specific temperatures too just a lot hotter than water How does magma form 1 Decompression 2 Addition of volatiles 3 Heat transfer from rising magma Decompression High amounts of pressure can prevent materials from melting at their normal temperatures GEO 101007 91415 Rock at great depths in the Earth s interior have tremendous amounts of pressure exerted on them Rock at great depths in the Earth s interior are often hotter than their melting temperature but remain a solid due to the pressure If for some reason the pressure is decreased on these rocks they will melt in a process called decompression melting Volatiles Volatiles are chemicals such as water H20 and carbon dioxide C02 that can mix with solid rock within the Earth s interior Volatiles help to break chemical bonds therefore adding volatiles to a quotdryquot rock will cause it to melt Also known as quot uxquot melting Heat Transfer 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 1 Source rock 2 Partial melting 3 Assimilation 4 Magma mixing Source rock Source rock composition 0 The composition of a melt magma re ects the composition of the solid from which it was derived Partial Melting 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 GEO 101007 91415 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 bread are ma c minerals 20 Felsic 80 Ma c If you remove raisins felsic minerals the remaining loaf is more bread ma c minerals 5 Felsic 95 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 Assimilation While magma slowly moves upward it may incorporate the chemistry of surrounding rock that completely melt due to the heat of the magma GEO 101007 91415 Magma Mixing If two or more bodies of magma with different chemistries combine in the subsurface the new magma will have a composition different from the original chemistries Why does magma rise to the Earth s Surface Like hot air in a hot air balloon causes the balloon to rise magma is similar to that hot hair 0 Magma is less dense than the surrounding rock 0 The pressure from overlying rock squeezes magma up toward the surface The resistance to ow High viscosity uid does not ow very well behaves like syrup Low viscosity uid ows easily behaves like water Temperature affects oil viscosity Change your oil when its hot as it will ow out easier How quickly easily does magmalava ow The viscosity ability to ow of a magmalava is a function of temperature volatile content and silica content Highest viscosity magma lava relatively low temperature low volatile content high silica content makes for explosive volcanoes Lowest viscosity magmalava high temperature high volatile content low silica content 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 9C 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 GEO 101007 91415 0 Felsic minerals high silica freeze last Fractional Crystallization 0 Crystal formation and settling The process progressively extracts iron and magnesium from the magma so the remaining magma becomes more felsic Bowen s Reaction Series 0 One mineral changes to another over specific temperature range pg 105 TemWa U39e Bowen39s Reaction Series C mP Si n Regimes rock types Potassium feldspar t 1 Felsic Muscovite mica t waitsmute i 39l39 Quartz Copyright 2005 Pearson Prentice Hall Inc
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