Igneous Rocks

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Igneous Rocks

  1. 1. IGNEOUS ROCKS
  2. 2. Categories of Igneous Rock  Volcanic (extrusive)  Plutonic (intrusive)
  3. 3. Skaftafjell National Park, Iceland Columnar joints from because of cooling and contraction of magma. Fig. 4-CO, pp. 100-101
  4. 4. Table 4-1, p. 103
  5. 5. 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.
  6. 6. Classic Subduction Zone Subduction melts crust and makes mafic lava, rich in Al, Na, K, H20
  7. 7. 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
  8. 8. Bowen’s Reaction Series Fig. 4-9, p. 111
  9. 9. Table 4-2, p. 110
  10. 10. Mt. Rushmore National Monument, SD Carved in Harney Peak Granite. Fig. 4-2a, p. 102
  11. 11. Crazy Horse Memorial, SD Carved in Harney Peak Granite. Fig. 4-2b, p. 102
  12. 12. STEP 1: IDENTIFY THE ROCKS COLOR INDEX (CI)
  13. 13. Classification of Igneous Rocks Diagram shows the relative proportions of the main minerals and textures of common igneous rocks. Fig. 4-16, p. 117
  14. 14. 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.
  15. 15. 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
  16. 16. Mafic Igneous Rocks  Dark colored  46-85% mafic minerals  Plagioclase Feldspars, Olivine, and Amphibole dominate Hornblende in rock, Iron aluminum silicate, Lucas County Iowa
  17. 17. 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.
  18. 18. STEP 2: IDENTIFY THE MAIN ROCK FORMING MINERALS
  19. 19. Quartz (gray or pink) More info at - http://www.geo.umn.edu/courses/1001/min erals/quartz.shtml
  20. 20. Plagioclase Feldspars (white) This white feldspar shows two cleavages (top/bottom and sides) plus the fracture surface (front).
  21. 21. Potassium Feldspar (K-Spar) (pink) More info at - http://www.geo.umn.edu/courses/1001/min erals/potassium_feldspar.shtml
  22. 22. Muscovite (brown) More info - http://www.geo.umn.edu/courses/1001/minerals/muscovite.shtml
  23. 23. Biotite Mica (black) More info at - http://www.geo.umn.edu/courses/1001/minerals/biotite.shtml
  24. 24. Amphibole (dark gray) More info at - http://www.geo.umn.edu/courses/1001/min erals/amphibole.shtml
  25. 25. Pyroxene (dark green) More Info at - http://www.geo.umn.edu/courses/1001/minerals/pyroxene.shtml
  26. 26. Olivine (green) More Info at - http://www.geo.umn.edu/courses/1001/minerals/olivine.shtml
  27. 27. STEP 3: IDENTIFY ITS TEXTURE
  28. 28. 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
  29. 29. 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
  30. 30. Uneven cooling produces Porphyritic Textures Groundmass Fig. 4-14ef, p. 116
  31. 31. 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
  32. 32. 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
  33. 33. STEP 4: USE IGNEOUS ROCK FLOW CHART
  34. 34. Igneous Rock Flow Cart
  35. 35. Andesite is a fine- grained, extrusive igneous rock composed mainly of plagioclase with other minerals such as hornblende, pyroxene and biotite.
  36. 36. Basalt-Gabbro  Balsitic Lava: (45-52%) of silica + high percentage of Iron (Fe); typically occur at oceanic divergent pages
  37. 37. Utramafic Rock  Formed under highest temperatures  Composed largely of feerromagnesian silicates (high in iron)  Silica content is (=<45%)  Has a very low viscosity
  38. 38. Periodite Ultramafic rock made up mostly of olivine. Makes up most of the mantel. Fig. 4-17, p. 118
  39. 39. WHAT ARE THE LARGEST IGNEOUS INTRUSIONS?
  40. 40. Plutonic Variables  Composition  Size  Depth
  41. 41. Block Diagram of Igneous Intrusions B: > 100 km2 S: <100 km2 Fig. 4-24, p. 123
  42. 42. WHAT ARE THE MAJOR SHEETLIKE IGNEOUS INTRUSIONS?
  43. 43. Dikes and Sills D & S: most are mafic. Veins: most are felsic. L: inflated sills.
  44. 44. Dikes in the Field Herchenberg volcano, Eifel district, Germany Fig. 4-25a, p. 124
  45. 45. Sills in the Field Mafic sills in lighter-colored country rock, Santa Monica, CA Fig. 4-25b, p. 124

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