Slide 1

Igneous Rocks Slide 2 Fig. 7.16 Slide 3 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 Volcanic igneous rocks Plutonic igneous rocks May form from basaltic magma1.2. Form at Earths surface3.4. Have texture Made of small grains5.6. Granite is an example7.8. Form as a result of melting9.10. Present at Earths surface only after erosion11.12. Contains minerals13.14. Classified based on color15.16 Dark-colored examples have low silica content1718. Contain visible grains19.20. Slide 4 Overview of Igneous Rocks Form when minerals crystallize from magma Intrusive Plutonic Extrusive Volcanic Magmas derived from below the Earths surface in the mantle Magma is hot and buoyant Koryakskaya Sopka Volcano, Eastern Russia Slide 5 Its all about heat and density Heat source?? Geothermal Gradient Composition Hot stuff Slide 6 Igneous Rock Classification Composition Texture Felsic Intermediate MaficUltramafic Phaneritic GraniteDioriteGabbroPeridotite Porphyritic Phaneritic Porphyritic Granite Porphyritic Diorite Porphyritic Gabbro Aphanitic RhyoliteAndesiteBasalt Porphyritic Aphanitic Porphyritic Rhyolite Porphyritic Andesite Porphyritic Basalt Slide 7 Intrusive Vs. Extrusive Plutonic Formed within the Earth Magma Reach Surface by uplift and erosion of the Earths Crust Volcanic Formed at the Surface Lava Slide 8 Texture Related to the cooling history of the rock Really Fast = no grains glassy Fast = Fine-grained aphanitic Slow = Coarse-grained phaneritic Complex = Mixture porphyritic Why?? Other textures: Vesicular: trapped gases in lava Pyroclastic: ash and rock fragments formed explosively Slide 9 Texture Aphanitic Fine grained Cooled quickly Crystallized at the Earths surface Porphyritic Aphanitic Phaneritic Porphyritic Phaneritic Peanut Butter or Sugar Cookie Slide 10 Aphanitic--peanut butter cookie Slide 11 Texture Aphanitic Porphyritic Aphanitic Two stages of cooling 1 st cooled slowly within the Earth (larger cyrstals - Phenocrysts) 2 nd cooled rapidly on the Earths surface (fine-grained matrix) Phaneritic Porphyritic Phaneritic Chocolate Chip Cookie Slide 12 Porphyritic AphaniticChocolate Chip Cookie Slide 13 Texture Aphanitic Porphyritic Aphanitic Phaneritic Coarse grained Cooled slowly Crystallized within the Earth Porphyritic Phaneritic Ooopps!! I must have eaten the Oatmeal Cookie Slide 14 PhaneriticOatmeal Cookie Slide 15 Texture Aphanitic Porphyritic Aphanitic Phaneritic Porphyritic Phaneritic Two stages of cooling 1 st cooled slowly within the Earth (larger crystals - Phenocrysts) 2 nd cooled faster but still slow enough that crystals fully develop within the Earth (coarse-grained matrix) Oatmeal Raisin Cookie Slide 16 Porphyritic PhaneriticOatmeal Raisin Cookie Slide 17 Texture Aphanitic Porphyritic Aphanitic Phaneritic Porphyritic Phaneritic Vesicular voids left by trapped gas Glassy Pyroclastic Slide 18 Texture Aphanitic Porphyritic Aphanitic Phaneritic Porphyritic Phaneritic Vesicular Glassy Very rapid cooling Ions do not have time to from crystalline structures Pyroclastic Slide 19 Texture Aphanitic Porphyritic Aphanitic Phaneritic Porphyritic Phaneritic Vesicular Glassy Pyroclastic welded shards of rock & ash ejected from a vent during an eruption Slide 20 Composition of Igneous Rocks Silica (Si0 2 ) is primary ingredient of all magmas Viscosity: Resistance to flow Silica content temperature Slide 21 CompositionSilica Content Felsic: Feldspar & Silica >65% silica High Viscosity Intermediate: 53-65% silica Intermediate Viscosity Mafic: Magnesium and Iron (Fe) 45-52% silica Low Viscosity Ultramafic: Composition Mafic-basaltic: >1100 E C; Ca, Fe, Mg-rich Dark Colored Slide 24 Composition Intermediate-andesitic: 900-1100 E C; Na, Al, Ca, Fe, Mg, K Salt & Pepper appearance Andesite Porphyry Diorite Slide 25 Bowens Reaction Series Different minerals crystallize from magmas at different temperatures Melting CrystallizationHotCold Slide 26 Magmatic Differentiation Formation of more than one magma from a single parent magma Slide 27 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 SiO 2, Na, and K Marbles analogy Slide 28 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 Slide 29 Magmatic Differentiation Magma Mixing : Magmas of different compositions are mixed together Resulting magma is of a composition intermediate between the parents Slide 30 Magma Mixing Slide 31 Slide 32 Slide 33 Fig. 7.21 Slide 34 Composition Quiz Which type of lava would flow most easily? Mafic/Ultramafic Which type of volcano would erupt most violently? Felsic