Geology 101 Igneous RocksII_2007

Geology 101 Igneous RocksII_2007 - -Experimental...

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Igneous Rocks II
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Origin of Magmas Solid rock is at equilibrium with its surrounding Changes in the surroundings cause solid rock magma [melting] Raising T Lowering P Changing composition
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Lowering P Mantle convection moves deep mantle rocks upwards Raising T Hot mafic magma intrudes into the crust Changing composition Adding small amounts of water
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How do rocks melt? Heat: Geothermal Gradient Temperature of most Silicic magmas [600-800 o C] -about the base of crust Temperature of Mafic Magmas [1100-1200 o C] -upper mantle conditions
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Magma Differentiation Magmas, and the resulting igneous rocks, show a wide range of compositions Source Rock variations cause major and minor variations in the magma Magma Mixing Assimilation
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Partial Melting Individual minerals in source rock melt at different T Magma is enriched in many elements, especially SiO 2 How do we know this? Norman Bowen [1887-1956]
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Unformatted text preview: -Experimental Petrologist-developed Bowen’s Reaction Series Bowen’s reaction series • Fractional Crystallization – Individual minerals precipitate from magma at different T – Magma is enriched in many elements, especially SiO 2 – Magma may migrate [buoyancy] Bowen’s reaction series Plate Tectonic Setting of Igneous Rocks • Divergent Plate Boundaries – Partial melting of mantle produces basaltic magma • Convergent Plate Boundaries – Subduction produces partial melting of basalt, sediments, parts of mantle – Andesitic and rhyolitic magma – Ascending magma assimilates lower crustal material Plate Tectonic Setting of Igneous Rocks • Mantle Plumes – Partial melting of plumes of mantle material – Basaltic magma is produced – Rising magma produce • Intraplate island chains • Flood basalt [ Columbia River Basalts ]...
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This note was uploaded on 10/26/2009 for the course GLY 123 taught by Professor Vogl during the Spring '09 term at University of Florida.

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Geology 101 Igneous RocksII_2007 - -Experimental...

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