Igneous Rocks
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Igneous Rocks

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    Igneous Rocks Igneous Rocks Presentation Transcript

    • IGNEOUS ROCKS
    • Categories of Igneous Rock  Volcanic (extrusive)  Plutonic (intrusive)
    • Skaftafjell National Park, Iceland Columnar joints from because of cooling and contraction of magma. Fig. 4-CO, pp. 100-101
    • Table 4-1, p. 103
    • Magma Composition  Felsic Lava: high percentage (>63%) of silica, and trapped gasses; highest viscosity, lowest temperatures; rich in iron (Fe) and (Mg)  Intermediate Lava: (52-63%) of silica  Mafic Lava: (45-52%) of silica + high percentage of Magnesium (Mg); typically occur at subduction zones; rich in aluminum (Al), sodium (Na), potassium (K) and water.
    • Classic Subduction Zone Subduction melts crust and makes mafic lava, rich in Al, Na, K, H20
    • Volcanic Monitoring, Hawaii Viscosity: controlling factors include temp., silica content, volatile content, shear stress, and crystallinity. Temp: Lava can range from 1000 to 1200 C. Fig. 4-1, p. 102
    • Bowen’s Reaction Series Fig. 4-9, p. 111
    • Table 4-2, p. 110
    • Mt. Rushmore National Monument, SD Carved in Harney Peak Granite. Fig. 4-2a, p. 102
    • Crazy Horse Memorial, SD Carved in Harney Peak Granite. Fig. 4-2b, p. 102
    • STEP 1: IDENTIFY THE ROCKS COLOR INDEX (CI)
    • Classification of Igneous Rocks Diagram shows the relative proportions of the main minerals and textures of common igneous rocks. Fig. 4-16, p. 117
    • Felsic Igneous Rocks  Light colored  0-15% mafic minerals  Quartz and Potassium Feldspar dominant Oriskany Sandstone from Hancock, West Virginia: also known as “glass sand” contains light gray quartz crystals.
    • Intermediate  Light colored to gray  16-45% mafic crystals  Plagioclase Feldspars dominate Feldspars can be split into two main groups, the Alkali Feldspars and the Plagioclase feldspars
    • Mafic Igneous Rocks  Dark colored  46-85% mafic minerals  Plagioclase Feldspars, Olivine, and Amphibole dominate Hornblende in rock, Iron aluminum silicate, Lucas County Iowa
    • Ultramafic Igneous Rocks  Very dark in color.  86-100% mafic minerals.  Olivine and pyroxene are dominant crystals This is a rock called peridotite (= olivine and pyroxene), which forms much of the upper mantle.
    • STEP 2: IDENTIFY THE MAIN ROCK FORMING MINERALS
    • Quartz (gray or pink) More info at - http://www.geo.umn.edu/courses/1001/min erals/quartz.shtml
    • Plagioclase Feldspars (white) This white feldspar shows two cleavages (top/bottom and sides) plus the fracture surface (front).
    • Potassium Feldspar (K-Spar) (pink) More info at - http://www.geo.umn.edu/courses/1001/min erals/potassium_feldspar.shtml
    • Muscovite (brown) More info - http://www.geo.umn.edu/courses/1001/minerals/muscovite.shtml
    • Biotite Mica (black) More info at - http://www.geo.umn.edu/courses/1001/minerals/biotite.shtml
    • Amphibole (dark gray) More info at - http://www.geo.umn.edu/courses/1001/min erals/amphibole.shtml
    • Pyroxene (dark green) More Info at - http://www.geo.umn.edu/courses/1001/minerals/pyroxene.shtml
    • Olivine (green) More Info at - http://www.geo.umn.edu/courses/1001/minerals/olivine.shtml
    • STEP 3: IDENTIFY ITS TEXTURE
    • Rapid cooling of extrusive lava produces an Aphanitic Texture Faster cooling from extrusive magma, produces small minerals with a fine-grained texture Fig. 4-14ab, p. 116
    • Slow cooling in plutons produces Phaneritic Texture Slower cooling from plutons where the rate of growth exceeds the rate of nuclei formation forms relatively large mineral grains that can be seen. These visible course-grained minerals have a phaneritic texture. Fig. 4-14cd, p. 116
    • Uneven cooling produces Porphyritic Textures Groundmass Fig. 4-14ef, p. 116
    • Other Textures Glassy texture Gasses expand Fragmental texture because magma and leave a formed by explosive cooled extremely vesicular texture. eruptions. quickly. Fig. 4-14g-i, p. 116
    • Volcanic Breccia Consists of poorly sorted mixture of fine grains and larger angular fragments produced by especially violent eruptions, volcanic landslides and mudflows near volcanoes. Fig. 4-15, p. 117
    • STEP 4: USE IGNEOUS ROCK FLOW CHART
    • Igneous Rock Flow Cart
    • Andesite is a fine- grained, extrusive igneous rock composed mainly of plagioclase with other minerals such as hornblende, pyroxene and biotite.
    • Basalt-Gabbro  Balsitic Lava: (45-52%) of silica + high percentage of Iron (Fe); typically occur at oceanic divergent pages
    • Utramafic Rock  Formed under highest temperatures  Composed largely of feerromagnesian silicates (high in iron)  Silica content is (=<45%)  Has a very low viscosity
    • Periodite Ultramafic rock made up mostly of olivine. Makes up most of the mantel. Fig. 4-17, p. 118
    • WHAT ARE THE LARGEST IGNEOUS INTRUSIONS?
    • Plutonic Variables  Composition  Size  Depth
    • Block Diagram of Igneous Intrusions B: > 100 km2 S: <100 km2 Fig. 4-24, p. 123
    • WHAT ARE THE MAJOR SHEETLIKE IGNEOUS INTRUSIONS?
    • Dikes and Sills D & S: most are mafic. Veins: most are felsic. L: inflated sills.
    • Dikes in the Field Herchenberg volcano, Eifel district, Germany Fig. 4-25a, p. 124
    • Sills in the Field Mafic sills in lighter-colored country rock, Santa Monica, CA Fig. 4-25b, p. 124