Ch4 - Chapter 4 Igneous Rocks Crystallization from melts...

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Chapter 4 Igneous Rocks Crystallization from melts Read pp. 77-99
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Basalt columns, Devil’s Pile National Monument, Sierra Nevada
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When magma cools, it breaks into hexagonal columns
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Striations left by glaciers
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Outline I. Formation of igneous rocks A. How does magma form Temperature and melting Pressure and melting Water and melting II. Classification of igneous rocks A. By texture 1. Coarse grained - intrusives 2. Fine grained - extrusives 3. Glassy
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Outline cont. B. By silica content 1. Felsic - example: granite 2. Intermediate - example: andesite 3. Mafic - example: basalt 4. Ultramafic - peridotite III. Crystallization from melts A. Fractional crystallization B. Magmatic differentiation C. Bowen’s reaction series Continuous series Discontinusous series
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Outline cont’d V. Igneous activities A. Volcanism (next chapter) B. Plutonic activity 1. Tabular pluton - dikes and sills 2. Massive pluton - batholiths IV. Where do magmas form? A. Mid-ocean ridges - mafic B. Subduction zone - mafic to intermediate C. Mantle plumes - mafic D. Lower continental crust - felsic
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What is magma? Magma is molten rock, together with suspended mineral grains and dissolved gases, that forms when temperature rises sufficiently high for partial melting in the lower crust and upper mantle (asthenosphere). Temperature of the magma is 700-1200 degrees Celsius.
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How do magmas form? Rock melting depends on 1.Temperature A mineral melts when temperature exceeds its melting point 2. Pressure Melting temperature of mineral increases with pressure 3.Water content -- Melting temperature of mineral decreases with water content.
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II. Classification of igneous rocks Igneous rocks are classified by A. Texture A. Course-grained = intrusive B. Fine-grained = extrusive B. Chemical Compositions (silica content) A. Three distinct types of magma
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Ch4 - Chapter 4 Igneous Rocks Crystallization from melts...

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