Lecture 9_Major Elements

Lecture 9_Major Elements - Chapter 8 Major Elements GEOL...

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Unformatted text preview: Chapter 8: Major Elements GEOL 320 -- Petrology S i O 2 C a O Na 2 O K 2 O T i O 2 M n O MgO H 2 O P 2 O 5 Major elements: Major elements: usually greater than 1% usually greater than 1% SiO SiO 2 Al Al 2 O O 3 FeO* MgO CaO Na FeO* MgO CaO Na 2 O K O K 2 O O H H 2 O O ✦ primary control for mineralogy & primary control for mineralogy & crystallization/melting behavior crystallization/melting behavior ✦ control viscosity, density, diffusivity of control viscosity, density, diffusivity of magmas and rocks magmas and rocks Element Wt % Oxide Atom % O 60.8 Si 59.3 21.2 Al 15.3 6.4 Fe 7.5 2.2 Ca 6.9 2.6 Mg 4.5 2.4 Na 2.8 1.9 Abundance of the elements in the Earth’s crust Minor elements: Minor elements: usually 0.1 - 1% usually 0.1 - 1% TiO TiO 2 MnO P MnO P 2 O O 5 CO CO 2 ● substitute for an element in a primary mineral ● higher concentrations can result in an accessory mineral (ex: zircon, rutile) Element Wt % Oxide Atom % O 60.8 Si 59.3 21.2 Al 15.3 6.4 Fe 7.5 2.2 Ca 6.9 2.6 Mg 4.5 2.4 Na 2.8 1.9 Abundance of the elements in the Earth’s crust Cathodoluminescence (CL) image of the mineral zircon (ZrSiO 4 ) showing internal concentric growth zonation (J. V. Jones, Univ. of Minnesota Trace elements: usually < 0.1% usually < 0.1% everything else everything else ✦ substitute for major or minor elements substitute for major or minor elements ✦ extremely low concentrations do not permit extremely low concentrations do not permit formation of a separate phase formation of a separate phase ✦ examples: Pb, U, Ni, Co, Cr examples: Pb, U, Ni, Co, Cr Element Wt % Oxide Atom % O 60.8 Si 59.3 21.2 Al 15.3 6.4 Fe 7.5 2.2 Ca 6.9 2.6 Mg 4.5 2.4 Na 2.8 1.9 Abundance of the elements in the Earth’s crust Why Bother Studying Major, Minor, and Trace Elements? • their behavior can tell us a great deal about igneous processes • major elements can be used to classify rocks • the chemical control that these elements exert can affect the physical properties of crystal-melt systems • provide insight into melt evolution Analytical Methods: Wet Chemical Analysis • rocks and minerals had to first be dissolved and diluted • minerals had to be physically separated from the rocks and in quantities that were measurable • titration of resulting liquid • calculations of ion concentrations • time-consuming • low levels of precision (only majors and minors could be analyzed Pre- 1920’s and 1930’s Analytical Methods: Instrumental Modern Spectroscopic Techniques Energy Source Absorption Detector Sample Emission Detector Output with absorption trough Output with emission peak Absorbed radiation Emitted radiation Figure 8-1. The geometry of typical spectroscopic instruments. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall....
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This note was uploaded on 04/07/2008 for the course GEOL 320 taught by Professor Milam during the Winter '08 term at Ohio University- Athens.

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Lecture 9_Major Elements - Chapter 8 Major Elements GEOL...

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