Igneous rocksQuestions to ponderPowerPoint PresentationIgneous RocksSlide 5Slide 6Slide 7Igneous Rocks –TextureSlide 9Slow cooling – Intrusive (plutonic)Slide 11Rapid cooling – Extrusive (volcanic)Slide 13Igneous Rocks – CompositionSlide 15Slide 16Other Special TexturesSlide 18Rocks with Porphyritic texture are called PorphyriesMagma is generated by the melting of rock. The type rock that is melted controls the composition of magmaHow does the mixing of crust potentially control the magma composition?If basaltic oceanic crust melts by subducting under granitic continental crust, what would you expect to be the resulting magma composition?If basaltic oceanic crust melts by subducting under basaltic oceanic crust, what would you expect to be the resulting magma composition?Distribution of Igneous Rocks in North AmericaSlide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Other aspects of Igneous IntrusionsPegmatites – Very coarse-grained textures Large crystals develop from late-stage crystallization of vaporLecture 9OutlineSlide 36Remember: Volcanic rocks are recognized by their textureRelationship of composition to volcanic rock typePyroclastic materialSlide 40Slide 41Slide 42Slide 43Slide 44Igneous rocksLect 8Questions to ponder•What are the 6 main igneous rock types? What controls how we classify them?•Know the texture and composition and how this relates to Bowen’s reaction series/•What are the types of plutonic rocks?•What are the types of plutonic intrusions?Igneous Rocks•“From Fire”•Crystallization of Magma/Lava•2 subcategories (with further subdivision)–Extrusive (Volcanic)•Lava at or very near the earth’s surface–Intrusive (Plutonic)•Magma at depth in earth’s crust•Silicate minerals dominate; some oxidesExtrusive (Volcanic)Intrusive (Plutonic)The Nature of Igneous Rocks•Form from Magma–Hot, partially molten mixture of solid liquid and gas–Mineral crystals form in the magma making a crystal “slush”–Gases - H2O, CO2, etc. - are dissolved in the magma–Magma is less dense than solid rockThe Nature of Igneous Rocks•Magma vs. Lava–Magma is molten rock beneath the surface•Magma solidifies to form intrusive (plutonic) igneous rocks–Lava is molten rock that has reached the surface•Lava solidifies to form extrusive (volcanic) igneous rocksIgneous Rocks –Texture•Texture – size, shape and arrangement of minerals•Igneous rocks > Interlocking crystals•Size of the crystals help us make the first division of Igneous Rocks•Crystal size determined by cooling rates of magmaRapid cooling and crystallizationSlow cooling and crystallizationSlow cooling – Intrusive (plutonic)•Large, visible interlocking crystals•Phane ros = “to see”•PHANERITIC texture*******Rapid cooling – Extrusive (volcanic)•Small, interlocking crystals•Crystals generally too small to see without a handlens•APHANITIC texture******Igneous Rocks – Composition•Composition = the mineralogy of the magma and hence, rocks•While texture allows us to separate Plutonic from Volcanic rocks, composition allows us to identify and name the rocks in each category•Composition based on Silica content and the relative abundance of Ferromag and Sialic mineralsRapid cooling and crystallizationSlow cooling and crystallizationUltramafic Komatite Peridotite(Greens)Mafic Basalt Gabbro(Darks)Intermediate Andesite Diorite(B & W, Grays)Felsic Rhyolite Granite(Pinks,WhitesLights)Composition(color)Volcanic Plutonic*******Other Special Textures•Vesicular texture – holes (Vesicles) in Volcanic rock left as contained gases exsolve from lava as a result of Pressure decreaseBasalts exhibiting classic vesicular texturePorphyritic Texture•Well formed crystals (phenocrysts)•Fine grained matrix (groundmass)–Aphanitic rocks•Complex cooling history–Initial stage of slow cooling•Large, well formed crystals form–Later stage of rapid cooling•Remaining magma crystallizes more rapidlyRocks with Porphyritic texture are called PorphyriesPhenocrystsA porphyry is generally a Volcanic (Extrusive) rockMagma is generated by the melting of rock.The type rock that is melted controls the composition of magma•Mantle materials are Ultramafic in composition•Continental crust is more Felsic (higher in silica, lower melting point)–Called “Granitic” in composition–Less dense than oceanic crust•Oceanic crust is more Mafic (Lower in silica and higher melting point)–Called “Basaltic” in composition–More dense than continental crustHow does the mixing of crust potentially control the magma composition?Ultramafic Komatite Peridotite(Greens)Mafic Basalt Gabbro(Darks)Intermediate Andesite Diorite(B & W, Grays)Felsic Rhyolite Granite(Pinks,WhitesLights)Composition(color)Volcanic PlutonicIf basaltic oceanic crust melts by subducting under granitic continental crust, what would you expect to be the resulting magma composition?INTERMEDIATE, but, various magmatic Differentiation processes could produce felsic productsIf basaltic oceanic crust melts by subducting under basaltic oceanic crust, what would you expect to be the resulting magma composition?•Perhaps Mafic, BUT, Magmatic differentiation can result in Intermediate material being produced.Distribution of Igneous Rocks in North AmericaRapid cooling and crystallizationSlow cooling and crystallizationIntrusive (plutonic) Igneous processes•Intrusions are classified by their size and shape•Large intrusions (plutons)•Batholiths – 100 km2 or greater•Stocks – Smaller than 100 km2 •Small intrusions•Dikes –discordant – Tabular shape–cuts across rock layers•Sills – concordant – Tabular shape–intrudes between rock layers•Laccoliths – Concordant – mushroom shapedDike cuts discordantly across rock layersDike cuts discordantly across rock layersConcordant sill intrudes between rock layersConcordant sill intrudes between rock layersOther aspects of Igneous Intrusions•Create rock fractures and upwarped rocks•Cause mineralizing fluids to move through surrounding rocksFractures filledWith minerals are calledVeinsPegmatites – Very coarse-grained texturesLarge crystals develop from late-stage crystallization of vaporCrystals at least 1 cm in diameterSome pegmatites may grow single crystals several meters in sizeLecture 9Volcanic Rocks and Extrusive ProcessesOutline•Volcanism–Volcanic