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Transcript
Igneous Rocks Warm-up Compare and contrast rocks and minerals. Overview of Igneous Rocks Form when minerals crystallize from magma IntrusivePlutonic ExtrusiveVolcanic Magmas derived from below the Earth’s surface in the mantle Magma is hot and buoyant Koryakskaya Sopka Volcano, Eastern Russia It’s all about heat and density Heat source?? Composition Geothermal Gradient Hot stuff Intrusive Vs. Extrusive Plutonic Formed within the Earth Magma Reach Surface by uplift and erosion of the Earth’s Crust Volcanic Formed at the Surface Lava Igneous Rock Classification Composition Texture Felsic Intermediate Mafic Ultramafic Course-Grained Granite Diorite Gabbro Peridotite Porphyritic Course-Grained Fine-Grained Porphyritic Porphyritic Porphyritic Granite Diorite Gabbro Rhyolite Andesite Basalt Porphyritic Fine- Porphyritic Porphyritic Porphyritic Grained Rhyolite Andesite Basalt Texture Related to the cooling history of the rock Really Fast = no grains glassy Fast = Small/ microscopic grains Fine-Grained Slow = large grains Course-Grained Complex = Mixture porphyritic Why?? Other textures: Vesicular: trapped gases in lava Pyroclastic: ash and rock fragments formed explosively Texture Fine-Grained Cooled quickly Crystallized at the Earth’s surface Porphyritic Fine-Grained Course-Grained Porphyritic Course-Grained Peanut Butter or Sugar Cookie Fine-Grained--peanut butter cookie Texture Fine-Grained Porphyritic Fine-Grained Two stages of cooling – 1st cooled slowly within the Earth (larger cyrstals Phenocrysts) – 2nd cooled rapidly on the Earth’s surface (fine-grained matrix) Course-Grained Porphyritic Course-Grained Chocolate Chip Cookie Porphyritic Fine-Grained —Chocolate Chip Cookie Texture Fine-Grained Porphyritic Fine-Grained Course-Grained Cooled slowly Crystallized within the Earth Porphyritic Course-Grained Oatmeal Cookie Course-Grained—Oatmeal Cookie Texture Fine-Grained Porphyritic Fine-Grained Course-Grained Porphyritic Course-Grained Two stages of cooling Oatmeal Raisin Cookie – 1st cooled slowly within the Earth (larger crystals Phenocrysts) – 2nd cooled faster but still slow enough that crystals fully develop – within the Earth (coarse-grained matrix) Porphyritic Course-Grained — Oatmeal Raisin Cookie Texture Fine-Grained Porphyritic Fine-Grained Course-Grained Porphyritic Course-Grained Vesicular –voids left by trapped gas Glassy Pyroclastic Texture Fine-Grained Porphyritic Fine-Grained Course-Grained Porphyritic Course-Grained Vesicular Glassy Very rapid cooling Ions do not have time to from crystalline structures Pyroclastic Texture Fine-Grained Porphyritic Fine-Grained Course-Grained Porphyritic Course-Grained Vesicular Glassy Pyroclastic – welded shards of rock & ash ejected from a vent during an eruption Composition of Igneous Rocks Silica (Si02) is primary Composition of Earth's Crust by Mass ingredient of all magmas Viscosity: Resistance to flow O-46.6% Silica content temperature All Others-9% Si-27.7 Ca-3.6% Fe-5.0% Al-8.1% Composition—Silica Content Felsic: Feldspar & Silica >65% silica High Viscosity Intermediate: 53-65% silica Intermediate Viscosity Mafic: Magnesium and Iron (Ferris) 45-52% silica Low Viscosity Ultramafic: <45% silica Very Low Viscosity Composition Felsic-rhyolitic: <900EC; Na, K, Al-rich Light colored Composition Mafic-basaltic: >1100EC; Ca, Fe, Mg-rich Dark Colored Composition Intermediate-andesitic: 900-1100EC; Na, Al, Ca, Fe, Mg, K Salt & Pepper appearance Andesite Porphyry Diorite Complete the following table by identifying which of the characteristics in the left-hand column are present in volcanic and/or plutonic igneous rocks by stating yes or no for the appropriate number. One characteristic has been completed as an example. Characteristic May form from mafic magma Form at Earth’s surface Have texture Made of small grains Granite is an example Form as a result of melting Present at Earth’s surface only after erosion Contains minerals Classified based on color Dark-colored examples have low silica content Contain visible grains Volcanic igneous Plutonic igneous rocks rocks 1. 3. 2. 4. 5. 7. 9. 11. 13. 15. 17 19. 6. 8. 10. 12. 14. 16 18. 20. Bowen’s Reaction Series Hot Melting minerals crystallize from magmas at different temperatures Crystallization Different Cold Magmatic Differentiation Formation of more than one magma from a single parent magma Magmatic Differentiation Crystal Settling: crystallized minerals have a density greater than the magma and settle to the bottom due to gravity Because Fe and Mg are first removed, melt becomes rich in SiO2, Na, and K Marbles analogy Magmatic Differentiation Assimilation: magma reacts with the “country rock” which is adjacent to the magma chamber Magma composition is altered according to the composition of the assimilated country rock Inclusions are rocks Incompletely melted chunks of country rock Magmatic Differentiation Magma Mixing: Magmas of different compositions are mixed together Resulting magma is of a composition intermediate between the parents Magma Mixing Magma Mixing Magma Mixing Fig. 7.21 Composition Quiz Which type of lava would flow most easily? Mafic/Ultramafic Which type of volcano would erupt most violently? Felsic