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IgMet Exam 1 Study Guide

by: Cody Totten

IgMet Exam 1 Study Guide Geol 3223

Marketplace > University of Oklahoma > Geology > Geol 3223 > IgMet Exam 1 Study Guide
Cody Totten
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About this Document

This study guide covers the first 4 chapters of the book, and any additional material that is on the first exam. The questions are modeled after those on previous year's exams.
Igneous and Metamorphic Petrology
Dr. Barry Weaver
Study Guide
Geology Igneous Rocks Magma Crystallization
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This 5 page Study Guide was uploaded by Cody Totten on Thursday February 18, 2016. The Study Guide belongs to Geol 3223 at University of Oklahoma taught by Dr. Barry Weaver in Spring 2016. Since its upload, it has received 295 views. For similar materials see Igneous and Metamorphic Petrology in Geology at University of Oklahoma.


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Date Created: 02/18/16
Igneous and Metamorphic Petrology Exam 1 Study Guide: Chapters 1-4 Write a balanced equation for the reaction of Hypersthene to Olivine used in the CIPW Norm calculation: (Fe,Mg)SiO = 3 (Fe,Mg) SiO + 2 SiO4 2 Write a balanced equation for the reaction of Albite to Nepheline used in the CIPW Norm calculation: 2 NaAlSi O3= 8a Al S2 O 2 42Si8 2 Write a balanced equation for the reaction of Orthoclase to Leucite used in the CIPW Norm calculation: 2 KAlSi O3= 8 KAlSi O + 22Si6 2 When calculating the CIPW Norm, what minerals are mutually exclusive? Quartz and Olivine, Quartz and Nepheline, Nepheline and Hypersthene What major element oxides are assigned to the following minerals in the CIPW Norm calculation? Apatite: P O and CaO 2 5 Ilmenite: TiO ,2and FeO Titanite: TiO , CaO, and SiO 2 2 Orthoclase: K O2 Al O 2 a3d SiO 2 Albite: Na O, Al O , and SiO 2 2 3 2 Acmite: Na O,2Fe O ,2an3 SiO 2 Anorthite: CaO, Al O , and SiO 2 3 2 Corundum: Al O 2 3 Magnetite: Fe O and FeO 2 3 Hematite: Fe O2 3 Diopside: FeO, MgO, CaO, and SiO 2 Wollastonite: CaO and SiO 2 Hypersthene: FeO, MgO, and SiO 2 Quartz: SiO 2 What normative minerals coincide with silica oversaturation, silica saturation and silica undersaturation? Silica oversaturation = Quartz normative Silica saturation = Hypersthene normative Silica undersaturation = Nepheline normative What type of magma displays high concentrations of Na O and K O2relative t2 SiO 2 Alkaline magma What type of magma displays low concentrations of Na O and K O relative to SiO ? 2 2 2 Sub-Alkaline magma What are the two types of Sub-Alkaline magma and how are they different? Tholeiitic magma: low concentration of Al O r2la3ive to SiO and s2ows Fe-enrichment Calc-Alkaline magma: high concentration of Al O rel2t3ve to SiO 2 What types of magma are seen at each type of tectonic environment? MOR = Tholeiitic, Subduction Zones = Calc-Alkaline, Hotspots = Alkaline In the Fo-En-Qz system, how does equilibrium crystallization differ from fractional crystallization? In equilibrium crystallization, the crystals are in equilibrium during their formation, and remain so as the composition of the melt changes. This means that once the system reaches the peritectic point, Forsterite will react to form Enstatite, before continuing towards the eutectic point. The fully crystallized magma chamber will be of a uniform composition throughout. In fractional crystallization, the crystals are no longer in equilibrium with the system after their formation. They settle out, removing the crystals from the magma. There will be no reaction of Fo to En, the peritectic point will be ignored, and the system will continue to track to the eutectic point. The magma chamber will be stratified, with Fo crystals at the bottom and grading upwards towards Qz crystals at the top. What are the effects of pressure on the Fo-En-Qz system? As pressure increases, the temperature of the liquidus surfaces will increase and the peritectic point will move towards a less SiO ri2h composition until at very high pressures it becomes a eutectic of the Fo-En system separated from the En-Qz system by a thermal divide. The solidus temperatures also increase, and the end magmas become more mafic/ultramafic. Considering the Di-En system, what happens when the temperature drops below the solvus? Exsolution of Di in En crystals and En in Di crystals occurs, and these two end members are no longer stable in solid solution at low temperatures. Be able to use the lever rule to determine percentages of crystal and liquid phases and their compositions in both binary and tertiary phase diagrams. What effect does water have on magma? Water is a depolymerizing volatile that breaks the silicate network of magmas. It decreases the viscosity of silicate magmas and decreases the temperature at which crystallization begins. It also stabilizes the crystallization of hydrous phases over anhydrous phases (amphibole over pyroxene). The presence of water also pushes the eutectic of a melt to a more SiO2rich composition. What effect does CO have on magma? 2 CO i2 a polymerizing volatile that helps to like the silicate network of magmas. It increases the viscosity of silicate magmas. The presence of CO a2so pushes the eutectic of a melt to a more alkaline composition. What are the 4 aluminous phases of mantle peridotite, at what pressures and in which tectonic environments are they found? Plagioclase: <10 kbar, Mid-Ocean Ridges Spinel: 10-25 kbar, Continental Crust Garnet: >25 kbar, Continental Crust What two processes cause mantle melting? Upwelling, which causes a decrease in pressure and allows decompression melting to occur. This is a MOR and mantle plume process. Lowering the solidus curve, which occurs when volatiles are present in a magma. Volatiles lower the temperature at which the mantle melts. This occurs at subduction zones. What is non-modal melting? When mantle peridotite melts, the first melt produced is of the eutectic composition, which is usually different that the bulk composition of the rock. This means that certain phases (the aluminous phases and clinopyroxene) will melt out in greater percentages than in the bulk composition. What is a primary magma? A primary magma is a magma that has a primitive mantle composition, with a magnesium number of > 70 What types of textures will be produced by small degrees of undercooling, large degrees of undercooling, and very large degrees of undercooling and why? At small degrees of undercooling, a phaneritic texture will be produced because the nucleation rate is slow and the crystal growth rate is moderate. This means that few nuclei will form and crystals will be able to grow to larger sizes. At larger degrees of undercooling, an aphanitic texture will be produced because the nucleation rate and the crystal growth rate are both high. This means that there will be many nuclei and the crystals will run into each other before they can grow large. At very large degrees of undercooling, a glassy texture will be produced. The nucleation and crystal growth rates are both low, so there will be few nuclei and few crystals will be able to grow. What is assimilation and why does it occur? Assimilation is the contamination of a magma by the incorporation of a whole rock wall pieces (stoping) or partial melt from rock walls. This is due to the fact that crystallization is an exothermic process and releases heat energy into the surrounding rock. Assimilation-Fractional Crystallization can greatly affect the composition of magmas, especially mafic magma moving through continental crust. What are the three main groups of trace elements and how are they differentiated? The three groups are Large Ion Lithophile Elements (LILE), Rare Earth Elements (REE), and High Field Strength Elements (HFSE). They are distinguished by ionic radius and ionic charge. The LILE tend to have lower ionic charge and higher ionic radius, the REE have an ionic charge of 3+ (with the exception of Eu, which can also have a 2+ charge) and moderate ionic radius, and the HRSE tend to have smaller ionic radius and higher ionic charge. What is the bulk distribution coefficient? The bulk distribution coefficient assesses the compatibility of a particular trace element in a multi-mineral assemblage, taking into account to contribution of each mineral. It is given by the equation: D = W (K )a+ Wd,a ) + b (K d,b … c d,c What does it mean for an element to be compatible? Incompatible? A compatible element is one that can readily substitute into a mineral phase based on its ionic charge and radius. Compatibility is given by K = C / C . A compatible element d xl liq has a K d 1. In incompatible element is one that does not readily substitute into a mineral phase. A compatible element has a K < 1d What is the magnesium number (mg#) of a magma? How does it change as crystallization proceeds? The mg# is the ration of Mg to Mg+Fe in a magma. As crystallization occurs, more Mg is included into crystals, while the magma becomes more silica rich. There is less Mg in the melt, so the mg# decreases.


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