Magma formation, differentiation and Igneous ProcessesQuestionsPowerPoint PresentationIgneous RocksSlide 5Slide 6Slide 7Slide 8Slide 9Name change between Mineral composition and Magma/Rock compositionSlide 11Slide 12Slide 13Slide 14Magma Origins and DifferentiationSlide 16Crustal rocks can be melted to form magma in a variety of waysThe variety of Igneous Rocks?Magma Differentiation (1)Slide 20Magma Differentiation (2)Xenoliths – fragments of country rock (sometimes ultra mafic mantle)Slide 23Magma Differentiation (3)Slide 25Igneous Rocks –TextureSlide 27Slow cooling – Intrusive (plutonic)Slide 29Rapid cooling – Extrusive (volcanic)Slide 31Igneous Rocks – CompositionSlide 33Slide 34Slide 35How does the mixing of crust potentially control the magma composition?Magma is generated by the melting of rock. The type rock that is melted controls the composition of magmaIf 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?Slide 40Magma formation, differentiation and Igneous ProcessesLect 7Questions•What are Igneous rocks•How does magma form?•How does mixing crust lead to different rock types to form? •What are other processes of differentiation?Igneous RocksRock CycleTemperatureAnd PressureIgneous 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 rocksThe Nature of Magma•Composition varies widely–Oxygen plus major elements–Generally a silica (SiO2) melt–Silica and water content control viscosity •Viscosity (the ease of fluid flow)•High viscosity = “thicker” fluids (Honey)•Low viscosity = “thinner” fluids (Water)Magma Viscosity and silica•As magma cools, silica tetrahedron form links•Increasing linkages–Higher silica & lower temp•Linkages increase viscosityName change between Mineral composition and Magma/Rock composition•Magma that is high in Ferromag minerals is called MAFIC•Magma that is high in Sialic minerals is called FELSIC•Magma that is intermediate in composition is called INTERMEDIATE•Fortunately, the compositional terms between Magma and Rocks stays the sameBowen’sReactionSeries1250 C650 CMagma Viscosity increasingOrigin of Magmas•Solid rock is at equilibrium with its surroundings•Changes in the surroundings may cause solid rock magma–Raising T–Lowering P–Changing compositionMagma Origins and Differentiation•How and why do magmas form?•How can magma change composition?Origin of Magmas•Lowering Pressure–Mantle convection moves deep mantle rocks upwards. Less confining pressure near the surface•Raising Temperature–Hot mafic magma intrudes into the crust•Changing composition–Adding small amounts of water (lowers melting point)–Fractional Crystallization of magma–Partial melt of surrounding rocksCrustal rocks can be melted to form magma in a variety of ways1234The variety of Igneous Rocks?•If earth’s mantle is relatively uniform, how do we get such a variety of igneous rock types?DIFFERENTIATION!Magma Differentiation (1)•Fractional crystallization – high T mafic minerals crystallize first and settle out of magma. Magma becomes more Felsic over timeMagma Differentiation (2)•Partial Melt – Low T minerals in surrounding country rock melt into magma, making it more Felsic over time1200+ degrees CXenoliths – fragments of country rock (sometimes ultra mafic mantle)XenolithsMagma Differentiation (3)•Magma MixingProcesses of magma differentiationPartial meltIgneous 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 textureRapid cooling – Extrusive (volcanic)•Small, interlocking crystals•Crystals generally too small to see without a handlens•APHANITIC textureIgneous 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 mineralsName change between Mineral composition and Magma/Rock composition•Magma that is high in Ferromag minerals is called MAFIC•Magma that is high in Sialic minerals is called FELSIC•Magma that is intermediate in composition is called INTERMEDIATE•Fortunately, the compositional terms between Magma and Rocks stays the sameUltramafic Komatite Peridotite(Greens)Mafic Basalt Gabbro(Darks)Intermediate Andesite Diorite(B & W, Grays)Felsic Rhyolite Granite(Pinks,WhitesLights)Composition(color)Volcanic PlutonicRapid cooling and crystallizationSlow cooling and crystallizationHow 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 PlutonicMagma 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