chapter4 - Chapter 4 Igneous Rocks Key Terms and Concepts...

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    Chapter 4   Igneous Rocks
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        Key Terms and Concepts Igneous rock, magma, lava, extrusive, intrusive Bowen’s reaction series Textures: aphanitic, phaneritic, porphyritic, glassy, pyroclastic, pegmatitic Compositions: peridotite (ultramafic) basalt/gabbro (mafic) andesite/diorite (intermediate) rhyolite/granite (felsic) Generating magma: What causes rocks to melt? (PT phase diagrams) Lower Pressure (and even lower T) Add water (dehydration reactions) Raise Temperature Evolution of magmas (fractional crystallization, assimilation, magma mixing) Partial melting (What happens to silica content?)
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        General characteristics  of magma Igneous rocks form as molten rock cools and solidifies Magma-usually silicate melt Produced by partial melting of any type of rock Magma at surface is called lava
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        General characteristics  of magma Extrusive - at the surface volcanic lavas, ash, cinders, and other pyroclastic debris fine grained, cooled rapidly usually dry Intrusive - inside the earth plutonic sill, dike, batholith, laccolith, etc. coarse grained, cooled slowly often rich in volatiles
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        General characteristics  of magma Consists of three components: Liquid = melt Solids = minerals crystallizing ( phenocrysts ) Gases = Volatiles (H 2 O, CO 2 SO 2 ) dissolved in the melt or forming bubbles or vesicles depends on pressure
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        General characteristics  of magma Crystallization of magma On cooling, various minerals crystallize at different temperatures Somewhat predictable order Different textures can result from same magma (intrusive vs. extrusive, water content, etc.)
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    Bowen’s reaction series Figure 4.23
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    Igneous textures Texture - the size, shape, and arrangement of minerals Factors affecting crystal size Rate of cooling Amount of H 2 O Role of nucleation sites and element mobility
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This note was uploaded on 03/27/2008 for the course GEOL 101 taught by Professor Olinsky during the Fall '08 term at Texas A&M.

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chapter4 - Chapter 4 Igneous Rocks Key Terms and Concepts...

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