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Igneous Rocks

Igneous Rocks. Fig. 7.16. 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. Koryakskaya

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Igneous Rocks

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  1. Igneous Rocks

  2. Fig. 7.16

  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.

  4. Koryakskaya Sopka Volcano, Eastern Russia Overview of Igneous Rocks • Form when minerals crystallize from magma • IntrusivePlutonic • ExtrusiveVolcanic • Magmas derived from below the Earth’s surface in the mantle • Magma is hot and buoyant

  5. Heat source?? Geothermal Gradient Composition Hot stuff It’s all about heat and density

  6. Igneous Rock Classification

  7. Plutonic Formed within the Earth Magma Reach Surface by uplift and erosion of the Earth’s Crust Volcanic Formed at the Surface Lava Intrusive Vs. Extrusive

  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

  9. Peanut Butter or Sugar Cookie Texture • Aphanitic • Fine –grained • Cooled quickly • Crystallized at the Earth’s surface • Porphyritic Aphanitic • Phaneritic • Porphyritic Phaneritic

  10. Aphanitic--peanut butter cookie

  11. Chocolate Chip Cookie Texture • Aphanitic • Porphyritic Aphanitic • Two stages of cooling • 1st cooled slowly within the Earth (larger cyrstals - Phenocrysts) • 2nd cooled rapidly on the Earth’s surface (fine-grained matrix) • Phaneritic • Porphyritic Phaneritic

  12. Porphyritic Aphanitic—Chocolate Chip Cookie

  13. Texture • Aphanitic • Porphyritic Aphanitic • Phaneritic • Coarse –grained • Cooled slowly • Crystallized within the Earth • Porphyritic Phaneritic Ooopps!! I must have eaten the Oatmeal Cookie

  14. Phaneritic—Oatmeal Cookie

  15. Oatmeal Raisin Cookie Texture • Aphanitic • Porphyritic Aphanitic • Phaneritic • Porphyritic Phaneritic • Two stages of cooling • 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)

  16. Porphyritic Phaneritic—Oatmeal Raisin Cookie

  17. Texture • Aphanitic • Porphyritic Aphanitic • Phaneritic • Porphyritic Phaneritic • Vesicular –voids left by trapped gas • Glassy • Pyroclastic

  18. Texture • Aphanitic • Porphyritic Aphanitic • Phaneritic • Porphyritic Phaneritic • Vesicular • Glassy • Very rapid cooling • Ions do not have time to from crystalline structures • Pyroclastic

  19. Texture • Aphanitic • Porphyritic Aphanitic • Phaneritic • Porphyritic Phaneritic • Vesicular • Glassy • Pyroclastic – welded shards of rock & ash ejected from a vent during an eruption

  20. Composition of Igneous Rocks • Silica (Si02) is primary ingredient of all magmas • Viscosity: Resistance to flow • Silica content • temperature

  21. Composition—Silica 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: • <45% silica  Very Low Viscosity

  22. Composition • Felsic-rhyolitic: • <900EC; Na, K, Al-rich • Light colored

  23. Composition • Mafic-basaltic: • >1100EC; Ca, Fe, Mg-rich • Dark Colored

  24. Composition • Intermediate-andesitic: • 900-1100EC; Na, Al, Ca, Fe, Mg, K • Salt & Pepper appearance Andesite Porphyry Diorite

  25. Hot Melting Crystallization Cold Bowen’s Reaction Series • Different minerals crystallize from magmas at different temperatures

  26. Magmatic Differentiation • Formation of more than one magma from a single parent magma

  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 SiO2, Na, and K • Marbles analogy

  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 rocksIncompletely melted chunks of country rock

  29. Magmatic Differentiation • Magma Mixing: Magmas of different compositions are mixed together • Resulting magma is of a composition intermediate between the parents

  30. Magma Mixing

  31. Magma Mixing

  32. Magma Mixing

  33. Fig. 7.21

  34. Composition Quiz • Which type of lava would flow most easily? • Mafic/Ultramafic • Which type of volcano would erupt most violently? • Felsic

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