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IV. Igneous Rocks Minerals Crystallized from Melts

IV. Igneous Rocks Minerals Crystallized from Melts. 1. The Rock Cycle 2. Formation of Igneous Rocks (and Bowen’s Reaction Series) 3. Classification of Igneous Rocks 4. Igneous Rocks and Plate Tectonics. Geological Materials Transformation Processes. The Rock Cycle. Igneous Rock

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IV. Igneous Rocks Minerals Crystallized from Melts

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  1. IV. Igneous RocksMinerals Crystallized from Melts 1. The Rock Cycle 2. Formation of Igneous Rocks (and Bowen’s Reaction Series) 3. Classification of Igneous Rocks 4. Igneous Rocks and Plate Tectonics

  2. Geological Materials Transformation Processes The Rock Cycle • Igneous Rock Solidification • Magma Partial Melting • Mantle Rock Fig 3.1 Fig 1.15

  3. % of Tot. # of atoms Fe/Mg:Silicon: Systematic SilicateMineralogy 29% 14% <20% 20% <3% 23% <2% 25% (0) 33% (0) 23% (0) 15%* Olivine Pyroxene Group • Fig. 2.9 • From bottom to top • Increasing Fe/Mg/Ca • Decreasing silica • Increasing density • Darker minerals Amphibole Group Mica Group Decreasing Silica Increasing Fe/Mg/Ca Quartz K and Na Feldspar Ca Feldspar Increasing Density

  4. % of Tot. # of atoms Fe/Mg:Silicon: Melting Points ofSilicate Minerals 29% 14% <20% 20% <3% 23% <2% 25% (0) 33% (0) 23% (0) 15%* Olivine Pyroxene Group >1000oC Mafic 45-52% • Fig. 2.9 • From bottom to top • Increasing Fe/Mg/Ca • Decreasing silica • Increasing density • Darker minerals Amphibole Group Intermediate 53-65% Mica Group Increasing Melting Temperature Felsic >65% silica Quartz K and Na Feldspar Ca Feldspar <700oC

  5. Melting ofGranite (Quartz, Na Plagioclase, Biotite) ~600oC ~700o ~800o Quartz Melts Na-Feldspar First Begins to melt ~900o ~1000o Biotite begins Magma is enriched to melt in Si, Na, Al (K) Silicic Melt

  6. Fig 3.13 Partial Melting and Magma E.g., Progressive Silica Enrichment Results in Silicic Magma Fig. 3.1, 3.12, 3.13 Enriched: O, Si, Al, Na, K, Depleted: Ca, Fe, Mg Gasses: (H2O, CO2) Poor in: O, Si, Al, Na, K, (<50%) Magma Partial MeltingRich in: Ca, Fe, Mg (>50% wght) Fig 1.15

  7. Solidification of Melts • Magma, Intruded or Extruded, • Solidifies (crystallizes) to form • Intrusive or Extrusive • Igneous Rocks Fig 3.12, 3.13

  8. E.g., Granite (Silicic, Intrusive Igneous Rock): Crystallized (Solidified) Silicic Melt Poor in: Fe, Mg, Ca, (<20%) Rich in: Silica (>70%) See Fig. 3.7a Biotite Quartz Na Plagioclase Igneous Rock

  9. Formation ofMagma • How are rocks melted?Pg. 61 • 1. Heating ■ 2. Depressurization • 3. Increase water content • 4. Increased silica content • Where do rocks melt? • Subduction zones (Silicic andIntermediate) • Mantle Plumes (“Hot Spots”) not only at Divergent Boundaries Mafic Hot and Low Pressure Hot and High Pressure

  10. Intrusive vs.Extrusive • Silicic (a.k.a, felsic) Magmas • Cool(<700oC) • Viscous(sticky, doesn’t flow easily) • Gaseous(steam of H2O and C02) • Silicic Rocks • Usuallyintrusive, course-grained, Silicic (Granite) to Intermediate (Diorite) rock forms plutons • If extrusive, fine-grained rocks formed by explosive volcanoes (fig. 4.21) Rhyolite or Andesite Volcanoes • Also injects surrounding rocks with silica laden steam Batholith made of Plutons Composite Volcano

  11. Dikes: Intruded near a pluton • Silica rich fluids are injected into cracks in all directions • Discordant: cutting across layers

  12. Extrusive vs. Intrusive • Mafic Magmas • Hot(>1000oC) • Non-Viscous(runny, flows easily) • “Dry”(no H2O or C02) • Mafic Rocks • UsuallyExtrusive, Fine-grained, Mafic (Basalt) rock forms oceanic crust, Shield Volcanoes and Basalt Floods • If Intrusive, course-grained mafic rocks are formed Gabbro. • If intrusive, Dikes and Sills more common. (Plutons don’t form)

  13. Mafic Sill: Intruded between layers • Mafic magma is less viscous and hotter so • Does not form plutons but • Cuts along layers (Sills) or even across layers (Dikes) • Also Baked Zones of adjacent country rock and Chill Zones within the intrusion

  14. Igneous Rock Classification Intrusive(Plutonic) Extrusive(Volcanic) • E.g., Basalt and Gabbro have two minerals • Pyroxene • Ca-Feldspar Fig. 4.10 Volume Percent of Minerals Continental CrustOceanicMantle Crust

  15. Frame- Double Single Iso. work Sheet Chain Chain Igneous Rocks and Silicates Fig. 2.9 The Igneous Rock Classification parallels the systematic Silicate Minerals Classification Fig. 3.11 and Fig. 4.10 Volume Percent of Minerals

  16. Igneous Rock Classification SilicicIntermediateMafic Granite Diorite Gabbro Rhyolite Andesite Basalt Fig. 3.7 (Porphyritic) Intrusive Extrusive

  17. Bowen’s Reaction Series Temperature of Crystallization Low Silica Magma Two series of minerals formed during crystallization of magma Intrus. Extrus. Gabbro Basalt Diorite Andesite Granite Rhyolite 1200oC 1000o Frame- Double Single Isolated work Sheet Chain Chain 750o High Silica Magma

  18. Crystallization ofGabbroandBasalt ~1,450oC ~1,400o ~1,350oThe remaining melt is enriched in silica (Int-Felsic) Ca-Feldspar Olivine Olivine converts Forms Forms to Pyroxene ~1,300o ~1,250o GabbroBasalt Remaining silica crystallizes into Ca-Feldspar. Intrusive Extrusive Cooling: Slowly Quickly Mafic Melt If melt is extracted Ultramafic Rock will be formed

  19. Crystallization ofDioriteandAndesite If cooled slowly in the magma chamber then extruded, Andesite Porphyry will be formed ~1,400oC ~1,300o ~1,200o Ca Feldspar Olivine converts Ca Feldspar Forms to Pyroxene absorbs Na ~1,100o ~1,000o DioriteAndesite Pyroxene converts Remaining silica Intrusive Extrusive to Amphibole forms Na-Ca Fldspr. Slowly Cooled Quickly Cooled Intermediate Melt

  20. Crystallization ofGraniteandRhyolite ~1,200oC ~1,100o ~1,000o Na-Feldspar Pyroxene Pyroxene dissolves forms and grows forms to form Amphibole ~900o ~750o GraniteRhyolite Amph. dissolves Remaining silica Intrusive Extrusive to form Biotite forms Quartz Slowly Cooled Quickly Cooled Silicic Melt

  21. Crystallization ofGraniteandRhyolite

  22. Global Distributions of Rock Types And relationships to plate tectonics • Dark Blue: Oceanic crust  Basalt Fe,Mg,Ca Rich (Si,Al,Na,K poor) • Light blue: New oceanic crust  new Basalt being formed along Mid-Ocean Ridges • Red regions: Mountain ranges  Felsic-Intermediate igneous and metamorphic (green

  23. Global Distributions of Rock Types And relationships to plate tectonics • Dark Blue: Oceanic crust  Basalt Fe,Mg,Ca Rich (Si,Al,Na,K poor) • Light blue: New oceanic crust  new Basalt being formed along Mid-Ocean Ridges • Red regions: Mountain ranges  Felsic-Intermediate igneous and metamorphic (green

  24. Pacific Northwest

  25. Pacific Northwest

  26. Mount Hood

  27. Ship Rock, New Mexico Volcanic Stock and Feeder Dikes

  28. Volcanic Stock Feeder Dike

  29. Devil’s Post Pile, California Devils Tower, Wyoming

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